| 1. |
- Joffrin, E., et al.
(författare)
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Overview of the JET preparation for deuterium-tritium operation with the ITER like-wall
- 2019
-
Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 59:11
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Forskningsöversikt (refereegranskat)abstract
- For the past several years, the JET scientific programme (Pamela et al 2007 Fusion Eng. Des. 82 590) has been engaged in a multi-campaign effort, including experiments in D, H and T, leading up to 2020 and the first experiments with 50%/50% D-T mixtures since 1997 and the first ever D-T plasmas with the ITER mix of plasma-facing component materials. For this purpose, a concerted physics and technology programme was launched with a view to prepare the D-T campaign (DTE2). This paper addresses the key elements developed by the JET programme directly contributing to the D-T preparation. This intense preparation includes the review of the physics basis for the D-T operational scenarios, including the fusion power predictions through first principle and integrated modelling, and the impact of isotopes in the operation and physics of D-T plasmas (thermal and particle transport, high confinement mode (H-mode) access, Be and W erosion, fuel recovery, etc). This effort also requires improving several aspects of plasma operation for DTE2, such as real time control schemes, heat load control, disruption avoidance and a mitigation system (including the installation of a new shattered pellet injector), novel ion cyclotron resonance heating schemes (such as the three-ions scheme), new diagnostics (neutron camera and spectrometer, active Alfven eigenmode antennas, neutral gauges, radiation hard imaging systems...) and the calibration of the JET neutron diagnostics at 14 MeV for accurate fusion power measurement. The active preparation of JET for the 2020 D-T campaign provides an incomparable source of information and a basis for the future D-T operation of ITER, and it is also foreseen that a large number of key physics issues will be addressed in support of burning plasmas.
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| 2. |
- Murari, A., et al.
(författare)
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A control oriented strategy of disruption prediction to avoid the configuration collapse of tokamak reactors
- 2024
-
Ingår i: Nature Communications. - 2041-1723 .- 2041-1723. ; 15:1
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Tidskriftsartikel (refereegranskat)abstract
- The objective of thermonuclear fusion consists of producing electricity from the coalescence of light nuclei in high temperature plasmas. The most promising route to fusion envisages the confinement of such plasmas with magnetic fields, whose most studied configuration is the tokamak. Disruptions are catastrophic collapses affecting all tokamak devices and one of the main potential showstoppers on the route to a commercial reactor. In this work we report how, deploying innovative analysis methods on thousands of JET experiments covering the isotopic compositions from hydrogen to full tritium and including the major D-T campaign, the nature of the various forms of collapse is investigated in all phases of the discharges. An original approach to proximity detection has been developed, which allows determining both the probability of and the time interval remaining before an incoming disruption, with adaptive, from scratch, real time compatible techniques. The results indicate that physics based prediction and control tools can be developed, to deploy realistic strategies of disruption avoidance and prevention, meeting the requirements of the next generation of devices.
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| 3. |
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| 4. |
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| 5. |
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| 6. |
- Marconi, A., et al.
(författare)
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ANDES, the high resolution spectrograph for the ELT : science case, baseline design and path to construction
- 2022
-
Ingår i: GROUND-BASED AND AIRBORNE INSTRUMENTATION FOR ASTRONOMY IX. - : SPIE - International Society for Optical Engineering. - 9781510653504 - 9781510653498
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Konferensbidrag (refereegranskat)abstract
- The first generation of ELT instruments includes an optical-infrared high resolution spectrograph, indicated as ELT-HIRES and recently christened ANDES (ArmazoNes high Dispersion Echelle Spectrograph). ANDES consists of three fibre-fed spectrographs (UBV, RIZ, YJH) providing a spectral resolution of similar to 100,000 with a minimum simultaneous wavelength coverage of 0.4-1.8 mu m with the goal of extending it to 0.35-2.4 mu m with the addition of a K band spectrograph. It operates both in seeing- and diffraction-limited conditions and the fibre-feeding allows several, interchangeable observing modes including a single conjugated adaptive optics module and a small diffraction-limited integral field unit in the NIR. Its modularity will ensure that ANDES can be placed entirely on the ELT Nasmyth platform, if enough mass and volume is available, or partly in the Coude room. ANDES has a wide range of groundbreaking science cases spanning nearly all areas of research in astrophysics and even fundamental physics. Among the top science cases there are the detection of biosignatures from exoplanet atmospheres, finding the fingerprints of the first generation of stars, tests on the stability of Nature's fundamental couplings, and the direct detection of the cosmic acceleration. The ANDES project is carried forward by a large international consortium, composed of 35 Institutes from 13 countries, forming a team of more than 200 scientists and engineers which represent the majority of the scientific and technical expertise in the field among ESO member states.
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| 7. |
- Stroth, U., et al.
(författare)
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Progress from ASDEX Upgrade experiments in preparing the physics basis of ITER operation and DEMO scenario development
- 2022
-
Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 62:4
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Tidskriftsartikel (refereegranskat)abstract
- An overview of recent results obtained at the tokamak ASDEX Upgrade (AUG) is given. A work flow for predictive profile modelling of AUG discharges was established which is able to reproduce experimental H-mode plasma profiles based on engineering parameters only. In the plasma center, theoretical predictions on plasma current redistribution by a dynamo effect were confirmed experimentally. For core transport, the stabilizing effect of fast ion distributions on turbulent transport is shown to be important to explain the core isotope effect and improves the description of hollow low-Z impurity profiles. The L-H power threshold of hydrogen plasmas is not affected by small helium admixtures and it increases continuously from the deuterium to the hydrogen level when the hydrogen concentration is raised from 0 to 100%. One focus of recent campaigns was the search for a fusion relevant integrated plasma scenario without large edge localised modes (ELMs). Results from six different ELM-free confinement regimes are compared with respect to reactor relevance: ELM suppression by magnetic perturbation coils could be attributed to toroidally asymmetric turbulent fluctuations in the vicinity of the separatrix. Stable improved confinement mode plasma phases with a detached inner divertor were obtained using a feedback control of the plasma β. The enhanced D α H-mode regime was extended to higher heating power by feedback controlled radiative cooling with argon. The quasi-coherent exhaust regime was developed into an integrated scenario at high heating power and energy confinement, with a detached divertor and without large ELMs. Small ELMs close to the separatrix lead to peeling-ballooning stability and quasi continuous power exhaust. Helium beam density fluctuation measurements confirm that transport close to the separatrix is important to achieve the different ELM-free regimes. Based on separatrix plasma parameters and interchange-drift-Alfvén turbulence, an analytic model was derived that reproduces the experimentally found important operational boundaries of the density limit and between L- and H-mode confinement. Feedback control for the X-point radiator (XPR) position was established as an important element for divertor detachment control. Stable and detached ELM-free phases with H-mode confinement quality were obtained when the XPR was moved 10 cm above the X-point. Investigations of the plasma in the future flexible snow-flake divertor of AUG by means of first SOLPS-ITER simulations with drifts activated predict beneficial detachment properties and the activation of an additional strike point by the drifts.
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| 8. |
- Meyer, H.F., et al.
(författare)
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Overview of physics studies on ASDEX Upgrade
- 2019
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 59:11
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Forskningsöversikt (refereegranskat)abstract
- The ASDEX Upgrade (AUG) programme, jointly run with the EUROfusion MST1 task force, continues to significantly enhance the physics base of ITER and DEMO. Here, the full tungsten wall is a key asset for extrapolating to future devices. The high overall heating power, flexible heating mix and comprehensive diagnostic set allows studies ranging from mimicking the scrape-off-layer and divertor conditions of ITER and DEMO at high density to fully non-inductive operation (q 95 = 5.5, ) at low density. Higher installed electron cyclotron resonance heating power 6 MW, new diagnostics and improved analysis techniques have further enhanced the capabilities of AUG. Stable high-density H-modes with MW m-1 with fully detached strike-points have been demonstrated. The ballooning instability close to the separatrix has been identified as a potential cause leading to the H-mode density limit and is also found to play an important role for the access to small edge-localized modes (ELMs). Density limit disruptions have been successfully avoided using a path-oriented approach to disruption handling and progress has been made in understanding the dissipation and avoidance of runaway electron beams. ELM suppression with resonant magnetic perturbations is now routinely achieved reaching transiently . This gives new insight into the field penetration physics, in particular with respect to plasma flows. Modelling agrees well with plasma response measurements and a helically localised ballooning structure observed prior to the ELM is evidence for the changed edge stability due to the magnetic perturbations. The impact of 3D perturbations on heat load patterns and fast-ion losses have been further elaborated. Progress has also been made in understanding the ELM cycle itself. Here, new fast measurements of and E r allow for inter ELM transport analysis confirming that E r is dominated by the diamagnetic term even for fast timescales. New analysis techniques allow detailed comparison of the ELM crash and are in good agreement with nonlinear MHD modelling. The observation of accelerated ions during the ELM crash can be seen as evidence for the reconnection during the ELM. As type-I ELMs (even mitigated) are likely not a viable operational regime in DEMO studies of 'natural' no ELM regimes have been extended. Stable I-modes up to have been characterised using -feedback. Core physics has been advanced by more detailed characterisation of the turbulence with new measurements such as the eddy tilt angle - measured for the first time - or the cross-phase angle of and fluctuations. These new data put strong constraints on gyro-kinetic turbulence modelling. In addition, carefully executed studies in different main species (H, D and He) and with different heating mixes highlight the importance of the collisional energy exchange for interpreting energy confinement. A new regime with a hollow profile now gives access to regimes mimicking aspects of burning plasma conditions and lead to nonlinear interactions of energetic particle modes despite the sub-Alfvénic beam energy. This will help to validate the fast-ion codes for predicting ITER and DEMO.
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| 9. |
- Deka, P. P., et al.
(författare)
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The MeerKAT Absorption Line Survey (MALS) Data Release. I. Stokes I Image Catalogs at 1-1.4 GHz
- 2024
-
Ingår i: Astrophysical Journal, Supplement Series. - 1538-4365 .- 0067-0049. ; 270:2
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Tidskriftsartikel (refereegranskat)abstract
- The MeerKAT Absorption Line Survey (MALS) has observed 391 telescope pointings at the L band (900-1670 MHz) at delta less than or similar to +20 degrees. We present radio continuum images and a catalog of 495,325 (240,321) radio sources detected at a signal-to-noise ratio (S/N) > 5 over an area of 2289 deg(2) (1132 deg(2)) at 1006 MHz (1381 MHz). Every MALS pointing contains a central bright radio source (S 1 GHz greater than or similar to 0.2 Jy). The median spatial resolution is 12 ''(8 ''). The median rms noise away from the pointing center is 25 mu Jy beam(-1) (22 mu Jy beam-1) and is within similar to 15% of the achievable theoretical sensitivity. The flux density scale ratio and astrometric accuracy deduced from multiply observed sources in MALS are <1% (8% scatter) and 1 '', respectively. Through comparisons with NVSS and FIRST at 1.4 GHz, we establish the catalog's accuracy in the flux density scale and astrometry to be better than 6% (15% scatter) and 0.'' 8, respectively. The median flux density offset is higher (9%) for an alternate beam model based on holographic measurements. The MALS radio source counts at 1.4 GHz are in agreement with literature. We estimate spectral indices (alpha) of a subset of 125,621 sources (S/N > 8), confirm the flattening of spectral indices with decreasing flux density, and identify 140 ultra-steep-spectrum (alpha < -1.3) sources as prospective high-z radio galaxies (z > 2). We have identified 1308 variable and 122 transient radio sources comprising primarily active galactic nuclei that demonstrate long-term (26 yr) variability in their observed flux densities. The MALS catalogs and images are publicly available at https://mals.iucaa.in.
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| 10. |
- Fynbo, J. P. U., et al.
(författare)
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Galaxy counterparts of metal-rich damped Ly alpha absorbers - I. The case of the z=2.35 DLA towards Q2222-0946
- 2010
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 408:4, s. 2128-2136
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Tidskriftsartikel (refereegranskat)abstract
- We have initiated a survey using the newly commissioned X-shooter spectrograph to target candidate relatively metal-rich damped Ly alpha absorbers (DLAs). Our rationale is that high-metallicity DLAs due to the luminosity-metallicity relation likely will have the most luminous galaxy counterparts. In addition, the spectral coverage of X-shooter allows us to search for not only Ly alpha emission, but also rest-frame optical emission lines. We have chosen DLAs where the strongest rest-frame optical lines ([O II], [O III], H beta and H alpha) fall in the near-infrared atmospheric transmission bands. In this first paper resulting from the survey, we report on the discovery of the galaxy counterpart of the z(abs) = 2.354 DLA towards the z = 2.926 quasar Q2222-0946. This DLA is amongst the most metal-rich z > 2 DLAs studied so far at comparable redshifts and there is evidence for substantial depletion of refractory elements on to dust grains. We measure metallicities from Zn II, Si II, Ni II, Mn II and Fe II of -0.46 +/- 0.07, -0.51 +/- 0.06, -0.85 +/- 0.06, -1.23 +/- 0.06 and -0.99 +/- 0.06, respectively. The galaxy is detected in the Ly alpha, [O III] lambda lambda 4959, 5007 and H alpha emission lines at an impact parameter of about 0.8 arcsec (6 kpc at z(abs) = 2.354). Based on the H alpha line, we infer a star formation rate of 10M(circle dot) yr(-1), which is a lower limit due to the possibility of slit loss. Compared to the recently determined H alpha luminosity function for z = 2.2 galaxies, the DLA-galaxy counterpart has a luminosity of L similar to 0.1L*(H alpha). The emission-line ratios are 4.0 (Ly alpha/H alpha) and 1.2 ([O III]/H alpha). In particular, the Ly alpha line shows clear evidence for resonant scattering effects, namely an asymmetric, redshifted (relative to the systemic redshift) component and a much weaker blueshifted component. The fact that the blueshifted component is relatively weak indicates the presence of a galactic wind. The properties of the galaxy counterpart of this DLA are consistent with the prediction that metal-rich DLAs are associated with the most luminous of the DLA-galaxy counterparts.
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| 11. |
- Zerbi, F. M., et al.
(författare)
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HIRES : The High Resolution Spectrograph for E-ELT
- 2014
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Ingår i: Ground-based and Airborne Instrumentation for Astronomy V. - : SPIE. - 9780819496157
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Konferensbidrag (refereegranskat)abstract
- The current instrumentation plan for the E-ELT foresees a High Resolution Spectrograph conventionally indicated as HIRES. Shaped on the study of extra-solar planet atmospheres, Pop-III stars and fundamental physical constants, HIRES is intended to embed observing modes at high-resolution (up to R=150000) and large spectral range (from the blue limit to the K band) useful for a large suite of science cases that can exclusively be tackled by the E-ELT. We present in this paper the solution for HIRES envisaged by the "HIRES initiative", the international collaboration established in 2013 to pursue a HIRES on E-ELT.
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| 12. |
- Fynbo, J. P. U., et al.
(författare)
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Galaxy counterparts of metal-rich damped Ly alpha absorbers - II. A solar-metallicity and dusty DLA at z(abs)=2.58
- 2011
-
Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 413:4, s. 2481-2488
-
Tidskriftsartikel (refereegranskat)abstract
- This is the second paper of a series reporting on the results from a survey conducted with the ESO VLT/X-shooter spectrograph. We target high-metallicity damped Lyman alpha absorbers (DLAs) with the aim of investigating the relation between galaxies detected in emission and those detected in absorption. Here, we report on the discovery of the galaxy counterpart of the z(abs) = 2.58 DLA on the line-of-sight to the z = 3.07 quasar SDSS J 091826.16+163609.0 (hereafter Q 0918+1636). The galaxy counterpart of the DLA is detected in the [O iii] lambda 5007 and [O ii] lambda lambda 3726, 3729 emission lines redshifted into the NIR at an impact parameter of 2.0 arcsec (16 kpc at z = 2.58). Ly alpha emission is not detected down to a 3 Sigma detection limit of 5 x 10-18 erg s-1 cm-2, which, compared to the strength of the oxygen lines, implies that Ly alpha emission from this galaxy is suppressed by more than an order of magnitude. The DLA has one of the highest metallicities measured so far at comparable redshifts. We find evidence for substantial depletion of refractory elements on to dust grains. Fitting the main metal line component of the DLA, which is located at z(abs) = 2.5832, we measure the metal abundances from Zn ii, S ii, Si ii, Cr ii, Mn ii, Fe ii and Ni ii to be -0.12 +/- 0.05, -0.26 +/- 0.05, -0.46 +/- 0.05, -0.88 +/- 0.05, -0.92 +/- 0.05, -1.03 +/- 0.05 and -0.78 +/- 0.05, respectively. In addition, we detect absorption in the Lyman and Werner bands of molecular hydrogen (H(2)), which represents the first detection of H(2) molecules with X-shooter. The background quasar Q 0918+1636 is amongst the reddest QSOs at redshifts 3.02 < z < 3.12 from the SDSS catalogue. Its UV to NIR spectrum is well fitted by a composite QSO spectrum reddened by SMC-/LMC-like extinction curves at z(abs) = 2.58 with a significant amount of extinction given by A(V) approximate to 0.2 mag. This supports previous claims that there may be more metal-rich DLAs missing from current samples due to dust reddening of the background QSOs. The fact that there is evidence for dust both in the central emitting regions of the galaxy (as evidenced by the lack of Ly alpha emission) and at an impact parameter of 16 kpc (as probed by the DLA) suggests that dust is widespread in this system.
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| 13. |
- Fynbo, J. P. U., et al.
(författare)
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Galaxy counterparts of metal-rich damped Lyman-alpha absorbers - II. A solar-metallicity and dusty DLA at z_abs=2.58
- 2010
-
Annan publikation (populärvet., debatt m.m.)abstract
- [Abridged]. Here, we report on the discovery of the galaxy counterpart of the z_abs=2.58 DLA on the line-of-sight to the z=3.07 quasar SDSS J091826.16+163609.0. The galaxy counterpart of the DLA is detected in the OIII 5007 and OII 3726,3729 emission lines redshifted into the NIR at an impact parameter of 16 kpc. Ly-alpha emission is not detected. The upper limit implies that Ly-alpha emission from this galaxy is suppressed by more than an order of magnitude. The DLA is amongst the most metal-rich DLAs studied so far at comparable redshifts. We find evidence for substantial depletion of refractory elements onto dust grains. Fitting the main metal line component of the DLA, which is located at z_abs=2.5832 and accounts for at least 85% of the total column density of low-ionisation species, we measure metal abundances from ZnII, SII, SiII, CrII, MnII, FeII and NiII of -0.12, -0.26, -0.46, -0.88, -0.92, -1.03 and -0.78, respectively. In addition, we detect absorption in the Lyman and Werner bands of hydrogen, which represents the first detection of H_2 molecules with X-shooter. The background quasar Q0918+1636 is amongst the reddest QSOs at redshifts 3.02<3.12 from the SDSS catalogue. Its UV to NIR spectrum is well fitted by a composite QSO spectrum reddened by SMC/LMC-like extinction curves at z_abs=2.58 with a significant amount of extinction given by A_V = 0.2 mag. This supports previous claims that there may be more metal-rich DLAs missing from current samples due to dust reddening of the background QSOs. The fact that there is evidence for dust both in the central emitting regions of the galaxy (as evidenced by the lack of Ly-alpha emission) and at an impact parameter of 16 kpc (as probed by the DLA) suggests that dust is widespread in this system.
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| 14. |
- Combes, F., et al.
(författare)
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PKS 1830-211: OH and HI at z = 0.89 and the first MeerKAT UHF spectrum
- 2021
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 648
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Tidskriftsartikel (refereegranskat)abstract
- The Large Survey Project (LSP) "MeerKAT Absorption Line Survey"(MALS) is a blind H I 21 cm and OH 18 cm absorption line survey in the L- and UHF-bands, primarily designed to better determine the occurrence of atomic and molecular gas in the circumgalactic and intergalactic medium, and its redshift evolution. Here we present the first results using the UHF band obtained towards the strongly lensed radio source PKS 1830-211, revealing the detection of absorption produced by the lensing galaxy. With merely 90 min of data acquired on-source for science verification and processed using the Automated Radio Telescope Imaging Pipeline (ARTIP), we detect in absorption the known H I 21 cm and OH 18 cm main lines at z = 0.89 at an unprecedented signal-to-noise ratio (4000 in the continuum, in each 6 km s-1 wide channel). For the first time we report the detection of OH satellite lines at z = 0.89, which until now have not been detected at z > 0.25. We decompose the OH lines into a thermal and a stimulated contribution, where the 1612 and 1720 MHz lines are conjugate. The total OH 1720 MHz emission line luminosity is 6100 L⊙. This is the most luminous known 1720 MHz maser line and is also among the most luminous of the OH main line megamasers. The absorption components of the different images of the background source sample different light paths in the lensing galaxy, and their weights in the total absorption spectrum are expected to vary in time on daily and monthly time scales. We compare our normalized spectra with those obtained more than 20 years ago, and find no variation. We interpret the absorption spectra with the help of a lens galaxy model derived from an N-body hydrodynamical simulation, with a morphology similar to its optical HST image. The resulting absorption lines depend mainly on the background continuum and the radial distribution of the gas surface density for each atomic and molecular species. We show that it is possible to reproduce the observations assuming a realistic spiral galaxy disk without invoking any central gas outflows. However, there are distinct and faint high-velocity features in the ALMA millimeter absorption spectra that most likely originate from high-velocity clouds or tidal features. These clouds may contribute to broaden the H I and OH spectra.
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| 15. |
- Emig, K.L., et al.
(författare)
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Discovery of Hydrogen Radio Recombination Lines at z = 0.89 toward PKS 1830-211
- 2023
-
Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 944:1
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Tidskriftsartikel (refereegranskat)abstract
- We report the detection of stimulated hydrogen radio recombination line (RRL) emission from ionized gas in a z = 0.89 galaxy using 580-1670 MHz observations from the MeerKAT Absorption Line Survey. The RRL emission originates in a galaxy that intercepts and strongly lenses the radio blazar PKS 1830−211 (z = 2.5). This is the second detection of RRLs outside of the local Universe and the first clearly associated with hydrogen. We detect effective H144α (and H163α) transitions at observed frequencies of 1156 (798) MHz by stacking 17 (27) RRLs with 21σ (14σ) significance. The RRL emission contains two main velocity components and is coincident in velocity with H i 21 cm and OH 18 cm absorption. We use the RRL spectral line energy distribution and a Bayesian analysis to constrain the density (n e ) and the volume-averaged path length (ℓ) of the ionized gas. We determine log ( n e ) = 2.0 − 0.7 + 1.0 cm−3 and log ( ℓ ) = − 0.7 − 1.1 + 1.1 pc toward the northeast (NE) lensed image, likely tracing the diffuse thermal phase of the ionized ISM in a thin disk. Toward the southwest (SW) lensed image, we determine log ( n e ) = 3.2 − 1.0 + 0.4 cm−3 and log ( ℓ ) = − 2.7 − 0.2 + 1.8 pc, tracing gas that is more reminiscent of H scii regions. We estimate a star formation (surface density) rate of ΣSFR ∼ 0.6 M ⊙ yr−1 kpc−2 or SFR ∼ 50 M ⊙ yr−1, consistent with a star-forming main-sequence galaxy of M ⋆ ∼ 1011 M ⊙. The discovery presented here opens up the possibility of studying ionized gas at high redshifts using RRL observations from current and future (e.g., SKA and ngVLA) radio facilities.
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| 16. |
- Lamalle, P. U., et al.
(författare)
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Expanding the operating space of ICRF on JET with a view to ITER
- 2006
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 46:2, s. 391-400
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Tidskriftsartikel (refereegranskat)abstract
- This paper reports on ITER-relevant ion cyclotron resonance frequency (ICRF) physics investigated on JET in 2003 and early 2004. Minority heating of helium three in hydrogen plasmas-(He-3)H-was systematically explored by varying the 3 He concentration and the toroidal phasing of the antenna arrays. The best heating performance (a maximum electron temperature of 6.2 keV with 5 MW of ICRF power) was obtained with a preferential wave launch in the direction of the plasma current. A clear experimental demonstration was made of the sharp and reproducible transition to the mode conversion heating regime when the 3 He concentration increased above similar to 2%. In the latter regime the best heating performance (a maximum electron temperature of 8 keV with 5 MW of ICRF power) was achieved with dipole array phasing, i.e. a symmetric antenna power spectrum. Minority heating of deuterium in hydrogen plasmas-(D)H-was also investigated but was found inaccessible because this scenario is too sensitive to impurity ions with Z/A = 1/2 such as C6+, small amounts of which directly lead into the mode conversion regime. Minority heating of up to 3% of tritium in deuterium plasmas was systematically investigated during the JET trace tritium experimental campaign (TTE). This required operating JET at its highest possible magnetic field (3.9 to 4 T) and the ICRF system at its lowest frequency (23 MHz). The interest of this scenario for ICRF heating at these low concentrations and its efficiency at boosting the suprathermal neutron yield were confirmed, and the measured neutron and gammay ray spectra permit interesting comparisons with advanced ICRF code simulations. Investigations of finite Larmor radius effects on the RF-induced high-energy tails during second harmonic (omega = 2 omega(c)) heating of a hydrogen minority in D plasmas clearly demonstrated a strong decrease in the RF diffusion coefficient at proton energies similar to 1 MeV in agreement with theoretical expectations. Fast wave heating and current drive experiments in deuterium plasmas showed effective direct electron heating with dipole phasing of the antennas, but only small changes of the central plasma current density were observed with the directive phasings, in particular at low single pass damping. New investigations of the heating efficiency of ICRF antennas confirmed its strong dependence on the parallel wavenumber spectrum. Advances in topics of a more technological nature are also summarized: ELM studies using fast RF measurements, the successful experimental demonstration of a new ELM-tolerant antenna matching scheme and technical enhancements planned on the JET ICRF system for 2006, they being equally strongly driven by the preparation for ITER.
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| 17. |
- Lamalle, P.U, et al.
(författare)
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Expanding the operating space of ICRF on JET with a view to ITER
- 2006
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Ingår i: Nucl. Fusion. ; 46, s. 391-
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Tidskriftsartikel (refereegranskat)abstract
- Mercury (Hg) has been used for millennia in many applications, primarily in artisanal mining and as an electrode in the chlor–alkali industry. It is anthropogenically emitted as a pollutant from coal fired power plants and naturally emitted, primarily from volcanoes. Its unique chemical characteristics enable global atmospheric transport and it is deposited after various processes, ultimately ending up in one of its final sinks, such as incorporated into deep sediment or bioaccumulated, primarily in the marine environment. All forms of Hg have been established as toxic, and there have been no noted biological benefits from the metal.Throughout time, there have been notable incidents of Hg intoxication documented, and the negative health effects have been documented to those chronically or acutely exposed. Today, exposure to Hg is largely diet or occupationally dependent, however, many are exposed to Hg from their amalgam fillings. This paper puts a tentative monetary value on Hg polluted food sources in the Arctic, where local, significant pollution sources are limited, and relates this to costs for strategies avoiding Hg pollution and to remediation costs of contaminated sites in Sweden and Japan. The case studies are compiled to help policy makers and the public to evaluate whether the benefits to the global environment from banning Hg and limiting its initial emission outweigh the benefits from its continued use or lack of control of Hg emissions. The cases we studied are relevant for point pollution sources globally and their remediation costs ranged between 2500 and 1.1 million US$ kg−1 Hg isolated from the biosphere. Therefore, regulations discontinuing mercury uses combined with extensive flue gas cleaning for all power plants and waste incinerators is cost effective.
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| 18. |
- Mantsinen, M. J., et al.
(författare)
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Localized bulk electron heating with ICRF mode conversion in the JET tokamak
- 2004
-
Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 44:1, s. 33-46
-
Tidskriftsartikel (refereegranskat)abstract
- Ion cyclotron resonance frequencies (ICRF) mode conversion has been developed for localized on-axis and off-axis bulk electron heating on the JET tokamak. The fast magnetosonic waves launched from the low-field side ICRF antennas are mode-converted to short-wavelength waves on the high-field side of the He-3 ion cyclotron resonance layer in D and He-4 plasmas and subsequently damped on the bulk electrons. The resulting electron power deposition, measured using ICRF power modulation, is narrow with a typical full-width at half-maximum of approximate to30 cm (i.e. about 30% of the minor radius) and the total deposited power to electrons comprises at least up to 80% of the applied ICRF power. The ICRF mode conversion power deposition has been kept constant using He-3 bleed throughout the ICRF phase with a typical duration of 4-6 s, i.e. 15-40 energy confinement times. Using waves propagating in the counter-current direction minimizes competing ion damping in the presence of co-injected deuterium beam ions.
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| 19. |
- Mayoral, M. L., et al.
(författare)
-
Hydrogen plasmas with ICRF inverted minority and mode conversion heating regimes in the JET tokamak
- 2006
-
Ingår i: Nuclear Fusion. - 0029-5515 .- 1741-4326. ; 46:7, s. S550-S563
-
Tidskriftsartikel (refereegranskat)abstract
- During the initial operation of the International Thermonuclear Experimental Reactor (ITER), it is envisaged that activation will be minimized by using hydrogen (H) plasmas where the reference ion cyclotron resonance frequency (ICRF) heating scenarios rely on minority species such as helium (He-3) or deuterium (D). This paper firstly describes experiments dedicated to the study of He-3 heating in H plasmas with a sequence of discharges in which 5 MW of ICRF power was reliably coupled and the He-3 concentration, controlled in real-time, was varied from below 1% up to 10%. The minority heating (MH) regime was observed at low concentrations (up to 2%). Energetic tails in the He-3 ion distributions were observed with effective temperatures up to 300 keV and bulk electron temperatures up to 6 keV. At around 2%, a sudden transition was reproducibly observed to the mode conversion regime, in which the ICRF fast wave couples to short wavelength modes, leading to efficient direct electron heating and bulk electron temperatures up to 8 keV. Secondly, experiments performed to study D minority ion heating in H plasmas are presented. This MH scheme proved much more difficult since modest quantities of carbon
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| 20. |
- Mayoral, M L, et al.
(författare)
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ICRF heating for the non-activated phase of ITER : From inverted minority to mode conversion regime
- 2005
-
Ingår i: Radio Frequency Power in Plasmas. ; , s. 122-129
-
Konferensbidrag (refereegranskat)abstract
- In the initial phase of ITER H plasmas will be used in order to avoid activating the machine. The reference ICRF heating scenarios rely on minority species such as Helium (3 He) or deuterium (D). These schemes' distinctive feature comes from the presence of the fast magnetosonic wave ion-ion hybrid resonance/cut-off pair, between the antennas and the minority cyclotron layer. In order to document these unusual heating schemes, ICRF experiments were carried out recently on JET. First, the use of He-3 ions in H plasmas was investigated with a sequence of discharges in which 5 MW of ICRF power was coupled to the plasma and the 3 He concentration was varied from below 1% up to 10%. The inverted minority heating regime was observed at low concentrations (up to similar to 2%). Energetic tails in the 3 He distribution were observed with effective temperatures up to 300 keV and central electron temperatures up to 6 keV. At around 2%, a sudden transition was reproducibly observed to the mode conversion regime, in which the ICRF fast wave couples to short wavelength modes, leading to efficient direct electron heating and central electron temperature up to 8 keV. All these experiments systematically used power modulation techniques to assess the radial profiles of the wave absorption by the electrons. Secondly, experiments to study the ICRF heating of D minority ions in H were performed. This heating scheme proved much more difficult since modest quantities of C6+ impurity, which has the same Z/A ratio than die D minority ions, led us directly into the mode conversion regime. This effect preventing any absorption by D ions at minority cyclotron layer, could make die (D)H scenario not suitable for the non-active phase of ITER.
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| 21. |
- Abolfathi, Bela, et al.
(författare)
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The Fourteenth Data Release of the Sloan Digital Sky Survey : First Spectroscopic Data from the Extended Baryon Oscillation Spectroscopic Survey and from the Second Phase of the Apache Point Observatory Galactic Evolution Experiment
- 2018
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Ingår i: Astrophysical Journal Supplement Series. - : IOP Publishing Ltd. - 0067-0049 .- 1538-4365. ; 235:2
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Tidskriftsartikel (refereegranskat)abstract
- The fourth generation of the Sloan Digital Sky Survey (SDSS-IV) has been in operation since 2014 July. This paper describes the second data release from this phase, and the 14th from SDSS overall (making this Data Release Fourteen or DR14). This release makes the data taken by SDSS-IV in its first two years of operation (2014-2016 July) public. Like all previous SDSS releases, DR14 is cumulative, including the most recent reductions and calibrations of all data taken by SDSS since the first phase began operations in 2000. New in DR14 is the first public release of data from the extended Baryon Oscillation Spectroscopic Survey; the first data from the second phase of the Apache Point Observatory (APO) Galactic Evolution Experiment (APOGEE-2), including stellar parameter estimates from an innovative data-driven machine-learning algorithm known as "The Cannon"; and almost twice as many data cubes from the Mapping Nearby Galaxies at APO (MaNGA) survey as were in the previous release (N = 2812 in total). This paper describes the location and format of the publicly available data from the SDSS-IV surveys. We provide references to the important technical papers describing how these data have been taken (both targeting and observation details) and processed for scientific use. The SDSS web site (www.sdss.org) has been updated for this release and provides links to data downloads, as well as tutorials and examples of data use. SDSS-IV is planning to continue to collect astronomical data until 2020 and will be followed by SDSS-V.
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| 22. |
- Combes, Françoise, et al.
(författare)
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PKS 1413+135: OH and H i at z = 0.247 with MeerKAT
- 2023
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 671
-
Tidskriftsartikel (refereegranskat)abstract
- The BL Lac object PKS 1413+135 was observed by the Large Survey Project MeerKAT Absorption Line Survey (MALS) in the L-band, at 1139 MHz and 12931379 MHz, targeting the HI and OH lines in absorption at z=0.24671. The radio continuum might come from the nucleus of the absorbing galaxy or from a background object at redshift lower than 0.5, as suggested by the absence of gravitational images. The HI absorption line is detected at a high signal-To-noise ratio, with a narrow central component, and with a red wing, confirming previous results. The OH 1720 MHz line is clearly detected in (maser) emission, peaking at a velocity shifted by-10 to-15 km s-1 with respect to the HI peak. The 1612 MHz line is lost due to radio frequency interference. The OH 1667 MHz main line is tentatively detected in absorption, but not the 1665 MHz line. Over 30 years a high variability is observed in optical depths, due to the rapid changes of the line of sight caused by the superluminal motions of the radio knots. The HI line has varied by 20% in depth, while the OH-1720 MHz depth has varied by a factor of ∼3. The position of the central velocity and the widths also varied. The absorbing galaxy is an early-Type spiral (maybe S0) seen edge-on, with a prominent dust lane, covering the whole disk. Given the measured mass concentration and the radio continuum size at centimeter wavelengths (100 mas corresponding to 400 pc at z=0.25), the width of the absorption lines from the nuclear regions are expected up to 250 km s-1. The narrowness of the observed lines (< 15 km s-1) suggests that the absorption comes from an outer gas ring, as frequently observed in S0 galaxies. The millimetric lines are even narrower (< 1 km s-1), which corresponds to the continuum size restricted to the core. The radio core is covered by individual 1 pc molecular clouds, whose column density is a few 1022 cm-2, which is compatible with the gas screen detected in X-rays.
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| 23. |
- Fynbo, J. P. U., et al.
(författare)
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On the two high-metallicity DLAs at z=2.412 and 2.583 towards Q 0918+1636
- 2013
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 436:1, s. 361-370
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Tidskriftsartikel (refereegranskat)abstract
- The quasar Q0918+1636 (z = 3.07) has two intervening high-metallicity Damped Lyman a Absorbers (DLAs) along the line of sight, at redshifts of z = 2.412 and 2.583. The z = 2.583 DLA is located at a large impact parameter of 16.2 kpc, and despite this large impact parameter it has a very high metallicity (consistent with solar), a substantial fraction of H-2 molecules and it is dusty as inferred from the reddened spectrum of the background QSO. The z = 2.412 DLA has a metallicity of [M/H] = -0.6 (based on Zn II and Si II). In this paper we present new observations of this interesting sightline consisting of deep multiband imaging and further VLT spectroscopy. By fitting stellar population synthesis models to the photometric Spectral Energy Distribution we constrain the physical properties of the z = 2.583 DLA galaxy, and we infer its morphology by fitting a Sersic model to its surface brightness profile. We find it to be a relatively massive (M-* approximate to 10(10) M-circle dot), strongly star-forming (SFR approximate to 30 M-circle dot yr(-1)), dusty (E(B - V) = 0.4) galaxy with a disc-like morphology. We detect strong emission lines from the z = 2.583 DLA ([O II] lambda 3727, [O III] lambda lambda 4960, 5007, H beta and H alpha, albeit at low signal-to-noise ratio except for the [O III] lambda 5007 line). The metallicity derived from the emission lines is consistent with the absorption metallicity (12 + log (O/H) = 8.8 +/- 0.2). We also detect [O III] lambda 5007 emission from the galaxy counterpart of the z = 2.412 DLA at a small impact parameter (<2 kpc). Overall our findings are consistent with the emerging picture that high-metallicity DLAs are associated with relatively luminous and massive galaxy counterparts, compared to typical DLAs.
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| 24. |
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| 25. |
- Noterdaeme, P., et al.
(författare)
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Discovery of a compact gas-rich damped Lyman-alpha galaxy at z = 2.2 : evidence of a starburst driven outflow
- 2012
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 540, s. A63-
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Tidskriftsartikel (refereegranskat)abstract
- We present the detection of Ly alpha, [OIII], and H alpha emission associated with an extremely strong damped Lyman-alpha (DLA) system (N(HI) = 10(22.10) cm(-2)) at z = 2.207 towards the quasar SDSS J113520.39-001053.56. This is the largest Hi column density ever measured along a quasi-stellar object (QSO) line of sight, though typical of those often found in DLAs associated to gamma-ray bursts (GRBs). This absorption system can also be classified as an ultra-strong Mg II system with W-r(lambda 2796) similar or equal to 3.6 angstrom. The mean metallicity of the gas ([Zn/H] = -1.1) and dust depletion factors ([Zn/Fe] = 0.72, [Zn/Cr] = 0.49) are consistent with (and only marginally larger than) the mean values found in the general QSO-DLA population. The [OIII]-H alpha emitting region has a very small impact parameter with respect to the QSO line of sight, b approximate to 0.1 '' (0.9 kpc proper distance), and is unresolved. From the H alpha line, we measure a significant star formation rate (SFR) approximate to 25 M-circle dot yr(-1) (uncorrected for dust). The shape of the Ly alpha line is double-peaked, which is the signature of a resonant scattering of Ly alpha photons, and the Ly alpha emission is spatially extended. More strikingly, the blue and red Ly alpha peaks arise from distinct regions extended over a few kpc on either side of the star-forming region. We propose that this is the consequence of a Ly alpha transfer in outflowing gas. The presence of starburst-driven outflows is also in agreement with the high SFR together with the small size and low mass of the galaxy (M-vir similar to 10(10) M-circle dot). By placing constraints on the stellar UV continuum luminosity of the galaxy, we estimate an age of at most a few 10(7) yr, again consistent with a recent starburst scenario. We interpret these data as the observation of a young, gas-rich, compact starburst galaxy, from which material is expelled through collimated winds powered by the vigorous star formation activity. We substantiate this picture by modelling the radiative transfer of Ly alpha photons in the galactic counterpart. Though our model (a spherical galaxy with bipolar outflowing jets) is a simplistic representation of the true gas distribution and velocity field, the agreement between the observed and simulated properties is particularly good (spectral shape and width of the Lyman-alpha emission, spatial configuration, escape fraction as well as absorption kinematics, HI column density, and dust reddening). Finally, we propose that selecting DLAs with very high Hi column densities may be an efficient way of detecting star-forming galaxies at small impact parameters from the background QSO lines of sight.
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| 26. |
- Ranjan, A., et al.
(författare)
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Molecular gas and star formation in an absorption-selected galaxy : Hitting the bull's eye at z similar or equal to 2.46
- 2018
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 618
-
Tidskriftsartikel (refereegranskat)abstract
- We present the detection and detailed analysis of a diffuse molecular cloud at z(abs) = 2.4636 towards the quasar SDSS J 1513+0352 (z(em) similar or equal to 2.68) observed with the X-shooter spectrograph at the Very Large Telescope. We measured very high column densities of atomic and molecular hydrogen with log N(H-I; H-2) similar or equal to 21.8; 21.3. This is the highest H-2 column density ever measured in an intervening damped Lyman-alpha system but we did not detect CO, implying log N(CO)/N(H-2) < -7.8, which could be due to a low metallicity of the cloud. From the metal absorption lines, we derived the metallicity to be Z similar or equal to 0.15 Z(circle dot) and determined the amount of dust by measuring the induced extinction of the background quasar light, A(V) similar or equal to 0.4. We simultaneously detected Lyman-alpha emission at the same redshift with a centroid located at a most probable impact parameter of only rho similar or equal to 1.4 kpc. We argue that the line of sight is therefore likely passing through the interstellar medium (ISM), as opposed to the circumgalactic medium (CGM), of a galaxy. The relation between the surface density of gas and that of star formation seems to follow the global empirical relation derived in the nearby Universe although our constraints on the star formation rate (SFR) and the galaxy extent remain too loose to be conclusive. We study the transition from atomic to molecular hydrogen using a theoretical description based on the microphysics of molecular hydrogen. We use the derived chemical properties of the cloud and physical conditions (T-k similar or equal to 90K and n similar or equal to 250 cm(3)) derived through the excitation of H-2 rotational levels and neutral carbon fine structure transitions to constrain the fundamental parameters that govern this transition. By comparing the theoretical and observed HI column densities, we are able to bring an independent constraint on the incident ultra-violet (UV) flux, which we find to be in agreement with that estimated from the observed SFR.
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| 27. |
- Salmi, A., et al.
(författare)
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JET experiments to assess the clamping of the fast ion energy distribution during ICRF heating due to finite Larmor radius effects
- 2006
-
Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 48:6, s. 717-726
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Tidskriftsartikel (refereegranskat)abstract
- Experiments have been performed on the JET tokamak with 2nd harmonic ion cyclotron resonance heating (ICRH) of hydrogen in deuterium plasmas to assess the role of finite Larmor radius (FLR) effects on the resonant ion distribution function. More specifically, the clamping of high-energy resonant particle distribution due to weak wave-particle interaction at high energy is studied. The distributions of ICRH heated hydrogen ions have been measured with a high-energy neutral particle analyser in the range of 0.29-1.1 MeV. By changing the electron density the energy E*, around which the wave-particle interaction becomes weak, is varied. The dependence of the ion distribution on E* is experimentally observed for a number of discharges and FLR effects are clearly seen to affect the high energy tail shape. Experiments have been analysed with the combination of ICRH modelling codes PION and FIDO, including FLR effects, and good agreement with measurements have been found.
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| 28. |
- Santala, M. I. K., et al.
(författare)
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Proton-triton nuclear reaction in ICRF heated plasmas in JET
- 2006
-
Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 48:8, s. 1233-1253
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Tidskriftsartikel (refereegranskat)abstract
- Fast protons can react with tritons in an endothermic nuclear reaction which can act as a source of neutrons in magnetically confined fusion plasmas. We have performed an experiment to systematically study this reaction in low tritium concentration (approximate to 1%) plasmas in the Joint European Torus. A linear dependence is found between excess neutron rate and tritium concentration when the DT fusion rate is low. We discuss the properties of the neutron emission, including anisotropy, from the proton-triton reaction in a fusion reactor environment and derive simple models for the calculation of the neutron yield from this reaction in terms of tritium density, fast ion temperature and fast ion energy content.
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| 29. |
- Hellsten, Torbjörn, et al.
(författare)
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Fast wave current drive in JET ITB-plasma
- 2005
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Ingår i: AIP Conference Proceedings. - : AIP. - 0094-243X. ; , s. 273-278
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Konferensbidrag (refereegranskat)abstract
- Fast wave current drive has been performed in JET plasmas with internal transport barriers, ITBs, and strongly reversed magnetic shear. Although the current drive efficiency of the power absorbed on the electrons is fairly high, only small effects are seen in the central current density. The main reasons are the parasitic absorption of RF power, the strongly inductive nature of the plasma and the interplay between the fast wave driven current and bootstrap current. The direct electron heating in the FWCD experiments is found to be strongly degraded compared to that with the dipole phasing.
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| 30. |
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| 31. |
- Mantsinen, M. J., et al.
(författare)
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Fast ion distributions driven by polychromatic ICRF waves on JET
- 2005
-
Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 47:9, s. 1439-1457
-
Tidskriftsartikel (refereegranskat)abstract
- Experiments have been carried out on the JET tokamak to investigate fast He-3 and hydrogen minority ion populations accelerated by ion cyclotron range of frequencies (ICRF) waves launched with multiple frequencies (i.e. up to four frequencies separated by up to approximate to 15%). This 'polychromatic' heating is compared with single-frequency, 'monochromatic', ICRF heating of reference discharges with similar power levels. Information on the fast ion populations is provided by two-dimensional gamma-ray emission tomography and the measurements are compared with numerical modelling. Polychromatic heating with resonances in the plasma centre (R-res approximate to R-0) and on the low magnetic-field side (LFS) (R-res > R-0) is found to produce predominantly high-energy standard trapped ions, while resonances on the high magnetic-field side (R-res < R-0) increase the fraction of high-energy passing ions. Monochromatic heating with a central resonance produces stronger gamma-ray emission with the maximum emission in the midplane close to, and on the LFS of, the resonance, in agreement with the calculated radial distribution of fast ion orbits. Both the fast ion tail temperature and energy content are found to be lower with polychromatic waves. Polychromatic ICRF heating has the advantage of producing smaller-amplitude and shorter-period sawteeth, consistent with a lower fast ion pressure inside the q = 1 surface, and higher ion to electron temperature ratios.
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| 32. |
- Eriksson, L-G, et al.
(författare)
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Destabilization of fast-ion-induced long sawteeth by localized current drive in the JET tokamak.
- 2004
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 92:23
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Tidskriftsartikel (refereegranskat)abstract
- In a tokamak fusion reactor the energetic alpha particles will transiently stabilize the magnetohydrodynamic activity causing sawtooth oscillations. The crash events terminating long sawtooth free periods can provide seed islands for neoclassical tearing modes [Phys. Rev. Lett. 88, 105001 (2002)]]. To shorten the sawtooth periods localized current drive near the q=1 surface is a possibility. This Letter provides the first experimental evidence for the effectiveness of this method in the different physics regime associated with fast-ion-induced long sawteeth on the JET tokamak.
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| 33. |
- Eriksson, L. G., et al.
(författare)
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On ion cyclotron current drive for sawtooth control
- 2006
-
Ingår i: Nuclear Fusion. - 0029-5515 .- 1741-4326. ; 46:10, s. S951-S964
-
Tidskriftsartikel (refereegranskat)abstract
- Experiments using ion cyclotron current drive (ICCD) to control sawteeth are presented. In particular, discharges demonstrating shortening of fast ion induced long sawteeth reported in (Eriksson et al 2004 Phys. Rev. Lett. 92 235004) by ICCD have been analysed in detail. Numerical simulations of the ICCD driven currents are shown to be consistent with the experimental observations. They support the hypothesis that an increase in the magnetic shear, due to the driven current, at the surface where the safety factor is unity was the critical factor for the shortening of the sawteeth. In view of the potential utility of ICCD, the mechanisms for the current drive have been further investigated experimentally. This includes the influence of the averaged energy of the resonating ions carrying the current and the spectrum of the launched waves. The results of these experiments are discussed in the light of theoretical considerations.
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| 34. |
- Konstantopoulou, Christina, et al.
(författare)
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Dust depletion of metals from local to distant galaxies : II. Cosmic dust-to-metal ratio and dust composition
- 2024
-
Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 681
-
Tidskriftsartikel (refereegranskat)abstract
- The evolution of cosmic dust content and the cycle between metals and dust in the interstellar medium (ISM) play a fundamental role in galaxy evolution. The chemical enrichment of the Universe can be traced through the evolution of the dust-to-metal ratio (DTM) and the dust-to-gas ratio (DTG) with metallicity. The physical processes through which dust is created and eventually destroyed remain to be elucidated. We use a novel method to determine mass estimates of the DTM, DTG, and dust composition in terms of the fraction of dust mass contributed by element X ( fMX ) based on our previous measurements of the depletion of metals in different environments (the Milky Way, the Magellanic Clouds, and damped Lyman-α absorbers (DLAs) towards quasars (QSOs) and towards gamma-ray bursts (GRBs)), which were calculated from the relative abundances of metals in the ISM through absorption-line spectroscopy column densities observed mainly from VLT/UVES and X-shooter, and HST/STIS. We also derive the dust extinction from the estimated dust depletion (AV,depl) for GRB-DLAs, the Magellanic Clouds, and the Milky Way, and compare it with the AV estimated from extinction (AV,ext). We find that the DTM and DTG ratios increase with metallicity and with the dust tracer [Zn/Fe]. This suggests that grain growth in the ISM is the dominant process of dust production, at least in the metallicity range (-2 ≤ [M/H]tot . 0.5) and redshift range (0.6 < z < 6.3) that we are studying. The increasing trend in the DTM and DTG with metallicity is in good agreement with a dust production and evolution hydrodynamical model. Our data suggest that the stellar dust yield is much lower (about 1%) than the metal yield and thus that the overall amount of dust in the warm neutral medium that is produced by stars is much lower than previously estimated. The global neutral gas metallicity is decreasing over cosmic time and is traced similarly by quasar-DLAs and GRB-DLAs. We find that, overall, AV,depl is lower than AV,ext for the Milky Way and in a few lines of sight for the Magellanic Clouds, a discrepancy that is likely related to the presence of carbonaceous dust associated with dense clumps of cold neutral gas. For the other environments studied here, we find good agreement overall between the AV,ext and AV,depl.We show that the main elements ( fMX > 1%) that contribute to the dust composition, by mass, are O, Fe, Si, Mg, C, S, Ni, and Al for all the environments, with Si, Mg, and C being equivalent contributors. There are nevertheless variations in the dust composition depending on the overall amount of dust. The abundances measured at low dust regimes in quasar- and GRB-DLAs suggest the presence of pyroxene and metallic iron in dust. These results give important information on the dust and metal content of galaxies across cosmic times, from the Milky Way up to z = 6.3.
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| 35. |
- Mantsinen, M. J., et al.
(författare)
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Bulk Ion Heating with ICRF Waves in Tokamaks
- 2015
-
Ingår i: RADIOFREQUENCY POWER IN PLASMAS. - : American Institute of Physics (AIP). - 9780735413368
-
Konferensbidrag (refereegranskat)abstract
- Heating with ICRF waves is a well-established method on present-day tokamaks and one of the heating systems foreseen for ITER. However, further work is still needed to test and optimize its performance in fusion devices with metallic high-Z plasma facing components (PFCs) in preparation of ITER and DEMO operation. This is of particular importance for the bulk ion heating capabilities of ICRF waves. Efficient bulk ion heating with the standard ITER ICRF scheme, i.e. the second harmonic heating of tritium with or without He-3 minority, was demonstrated in experiments carried out in deuterium-tritium plasmas on JET and TFTR and is confirmed by ICRF modelling. This paper focuses on recent experiments with He-3 minority heating for bulk ion heating on the ASDEX Upgrade (AUG) tokamak with ITER-relevant all-tungsten PFCs. An increase of 80% in the central ion temperature T-i from 3 to 5.5 keV was achieved when 3 MW of ICRF power tuned to the central He-3 ion cyclotron resonance was added to 4.5 MW of deuterium NBI. The radial gradient of the Ti profile reached locally values up to about 50 keV/m and the normalized logarithmic ion temperature gradients R/L-Ti of about 20, which are unusually large for AUG plasmas. The large changes in the Ti profiles were accompanied by significant changes in measured plasma toroidal rotation, plasma impurity profiles and MHD activity, which indicate concomitant changes in plasma properties with the application of ICRF waves. When the He-3 concentration was increased above the optimum range for bulk ion heating, a weaker peaking of the ion temperature profile was observed, in line with theoretical expectations.
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| 36. |
- Mantsinen, M. J., et al.
(författare)
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Modification of sawtooth oscillations with ICRF waves in the JET tokamak
- 2007
-
Ingår i: RADIO FREQUENCY POWER IN PLASMAS. - : AIP. - 9780735404441 ; , s. 35-42
-
Konferensbidrag (refereegranskat)abstract
- Methods of modifying sawtooth oscillations using waves in the ion cyclotron range of frequencies (ICRF) in the JET tokamak are presented. Examples of sawtooth stabilization by ICRF-accelerated high-energy ions are shown, including experiments with ICRF-acceleration of 4He-beam ions to simulate the effects of fusion born alpha particles. With high power ICRF heating in low-density plasmas, fast ion stabilization of sawteeth is lost and a new type of small-period and small-amplitude sawteeth appears. ICRF-induced radial pinch with toroidally asymmetric waves is found to be useful in affecting the radial profile of the ICRF-driven fast ion populations and thereby their influence on sawteeth. Ion cyclotron current drive (ICCD) applied close to the sawtooth inversion radius is effective in modifying the sawtooth period. The latest achievements include the successful application of ICCD to shorten the fast-ion-induced long-period sawteeth and thereby avoid triggering of neoclassical tearing modes (NTMs).
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| 37. |
- Nave, M. F. F., et al.
(författare)
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JET intrinsic rotation studies in plasmas with a high normalized beta and varying toroidal field ripple
- 2012
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 54:7, s. 074006-
-
Tidskriftsartikel (refereegranskat)abstract
- Understanding the origin of rotation in ion cyclotron resonance frequency (ICRF) heated plasmas is important for predictions for burning plasmas sustained by alpha particles, being characterized by a large population of fast ions and no external momentum input. The angular velocity of the plasma column has been measured in JET H-mode plasmas with pure ICRF heating both for the standard low toroidal magnetic ripple configuration, of about similar to 0.08% and, for increased ripple values up to 1.5% (Nave et al 2010 Phys. Rev. Lett. 105 105005). These new JET rotation data were compared with the multi-machine scaling of Rice et al (2007 Nucl. Fusion 47 1618) for the Alfven-Mach number and with the scaling for the velocity change from L-mode into H-mode. The JET data do not fit well any of these scalings that were derived for plasmas that are co-rotating with respect to the plasma current. With the standard low ripple configuration, JET plasmas with large ICRF heating power and normalized beta, beta(N) approximate to 1.3, have a very small co-current rotation, with Alfven-Mach numbers significantly below those given by the rotation scaling of Rice et al (2007 Nucl. Fusion 47 1618). In some cases the plasmas are actually counter-rotating. No significant difference between the H-mode and L-mode rotation is observed. Typically the H-mode velocities near the edge are lower than those in L-modes. With ripple values larger than the standard JET value, between 1% and 1.5%, H-mode plasmas were obtained where both the edge and the core counter-rotated.
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| 38. |
- Noterdaeme, J. M., et al.
(författare)
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Heating, current drive and energetic particle studies on JET in preparation of ITER operation
- 2003
-
Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 43:3, s. 202-209
-
Tidskriftsartikel (refereegranskat)abstract
- This paper summarizes the recent work on JET in the three areas of heating, current drive and energetic particles. The achievements have extended the possibilities of JET, have a direct connection to ITER operation and provide new and interesting physics. Toroidal rotation profiles of plasmas heated far off axis with little or no refuelling or momentum input are hollow with only small differences on whether the power deposition is located on the low field side or on the high field side. With LH current drive the magnetic shear was varied from slightly positive to negative. The improved coupling (through the use of plasma shaping and CD4) allowed up to 3.4 MW of PLH in internal transport barrier (ITB) plasmas with more than 15 MW of combined NBI and ICRF heating. The q-profile with negative magnetic shear and the ITB could be maintained for the duration of the high heating pulse (8 s). Fast ions have been produced in JET with ICRF to simulate alpha particles: by using third harmonic He-4 heating, beam injected He-4 at 120 kV were accelerated to energies above 2 MeV taking advantage of the unique capability of JET to use NBI with 4 He and to confine MeV class ions. ICRF heating was used to replicate the dynamics of alpha heating and the control of an equivalent Q = 10 `burn' was simulated.
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| 39. |
- Noterdaeme, J. M., et al.
(författare)
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Spatially resolved toroidal plasma rotation with ICRF on JET
- 2003
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 43:4, s. 274-289
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Tidskriftsartikel (refereegranskat)abstract
- Plasmas heated by ICRF only in the JET tokamak show distinct structures in the toroidal rotation profile, with regions where domega/dr > 0 when the minority cyclotron resonance layer is far off-axis. The rotation is dominantly co-current with a clear off-axis maximum. There is only a slight difference between a high-field side (HFS) or a low-field side position of this resonance layer: the off-axis maximum in the rotation profile is modestly higher for the HFS position. This is in contrast to the predictions of theories that rely mainly on the effects arising from ICRF-driven fast ions to account for ICRF-induced plasma rotation. The differences due to the direction of the antenna spectrum (co- or counter-) are small. A more central deposition of the ICRF power in L-mode and operation in H-mode both lead to more centrally peaked profiles, both in the co-direction. Strong MHD modes brake the rotation and lead to overall flat rotation profiles.
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