| 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
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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. |
- Abel, I, et al.
(författare)
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Overview of the JET results with the ITER-like wall
- 2013
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 53:10, s. 104002-
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Tidskriftsartikel (refereegranskat)abstract
- Following the completion in May 2011 of the shutdown for the installation of the beryllium wall and the tungsten divertor, the first set of JET campaigns have addressed the investigation of the retention properties and the development of operational scenarios with the new plasma-facing materials. The large reduction in the carbon content (more than a factor ten) led to a much lower Z(eff) (1.2-1.4) during L- and H-mode plasmas, and radiation during the burn-through phase of the plasma initiation with the consequence that breakdown failures are almost absent. Gas balance experiments have shown that the fuel retention rate with the new wall is substantially reduced with respect to the C wall. The re-establishment of the baseline H-mode and hybrid scenarios compatible with the new wall has required an optimization of the control of metallic impurity sources and heat loads. Stable type-I ELMy H-mode regimes with H-98,H-y2 close to 1 and beta(N) similar to 1.6 have been achieved using gas injection. ELM frequency is a key factor for the control of the metallic impurity accumulation. Pedestal temperatures tend to be lower with the new wall, leading to reduced confinement, but nitrogen seeding restores high pedestal temperatures and confinement. Compared with the carbon wall, major disruptions with the new wall show a lower radiated power and a slower current quench. The higher heat loads on Be wall plasma-facing components due to lower radiation made the routine use of massive gas injection for disruption mitigation essential.
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| 3. |
- Romanelli, F, et al.
(författare)
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Overview of the JET results
- 2011
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 51:9
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Tidskriftsartikel (refereegranskat)abstract
- Since the last IAEA Conference JET has been in operation for one year with a programmatic focus on the qualification of ITER operating scenarios, the consolidation of ITER design choices and preparation for plasma operation with the ITER-like wall presently being installed in JET. Good progress has been achieved, including stationary ELMy H-mode operation at 4.5 MA. The high confinement hybrid scenario has been extended to high triangularity, lower ρ*and to pulse lengths comparable to the resistive time. The steady-state scenario has also been extended to lower ρ*and ν*and optimized to simultaneously achieve, under stationary conditions, ITER-like values of all other relevant normalized parameters. A dedicated helium campaign has allowed key aspects of plasma control and H-mode operation for the ITER non-activated phase to be evaluated. Effective sawtooth control by fast ions has been demonstrated with3He minority ICRH, a scenario with negligible minority current drive. Edge localized mode (ELM) control studies using external n = 1 and n = 2 perturbation fields have found a resonance effect in ELM frequency for specific q95values. Complete ELM suppression has, however, not been observed, even with an edge Chirikov parameter larger than 1. Pellet ELM pacing has been demonstrated and the minimum pellet size needed to trigger an ELM has been estimated. For both natural and mitigated ELMs a broadening of the divertor ELM-wetted area with increasing ELM size has been found. In disruption studies with massive gas injection up to 50% of the thermal energy could be radiated before, and 20% during, the thermal quench. Halo currents could be reduced by 60% and, using argon/deuterium and neon/deuterium gas mixtures, runaway electron generation could be avoided. Most objectives of the ITER-like ICRH antenna have been demonstrated; matching with closely packed straps, ELM resilience, scattering matrix arc detection and operation at high power density (6.2 MW m-2) and antenna strap voltages (42 kV). Coupling measurements are in very good agreement with TOPICA modelling. © 2011 IAEA, Vienna.
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| 4. |
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- 2019
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Tidskriftsartikel (refereegranskat)
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| 5. |
- Coppin, K. E. K., et al.
(författare)
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Herschel-PACS observations of [O I]63 μm towards submillimetre galaxies at z~1
- 2012
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 427:1, s. 520-532
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Tidskriftsartikel (refereegranskat)abstract
- We present Herschel-PACS spectroscopy of the [O I]63 μm far-infrared cooling line from a sample of six unlensed and spectroscopically confirmed 870 μm selected submillimetre (submm) galaxies (SMGs) at 1.1
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| 6. |
- Geach, J.E., et al.
(författare)
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The SCUBA-2 Cosmology Legacy Survey: 850 μm maps, catalogues and number counts
- 2017
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 465:2, s. 1789-1806
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Tidskriftsartikel (refereegranskat)abstract
- We present a catalogue of similar to 3000 submillimetre sources detected (>= 3.5 sigma) at 850 mu m over similar to 5 deg(2) surveyed as part of the James Clerk Maxwell Telescope (JCMT) SCUBA-2 Cosmology Legacy Survey (S2CLS). This is the largest survey of its kind at 850 mu m, increasing the sample size of 850 mu m selected submillimetre galaxies by an order of magnitude. The wide 850 mu m survey component of S2CLS covers the extragalactic fields: UKIDSS-UDS, COSMOS, Akari-NEP, Extended Groth Strip, Lockman Hole North, SSA22 and GOODS-North. The average 1s depth of S2CLS is 1.2 mJy beam(-1), approaching the SCUBA-2 850 mu m confusion limit, which we determine to be sigma(c) approximate to 0.8 mJy beam(-1). We measure the 850 mu m number counts, reducing the Poisson errors on the differential counts to approximately 4 per cent at S-850 approximate to 3 mJy. With several independent fields, we investigate field-to-field variance, finding that the number counts on 0.5 degrees-1 degrees scales are generally within 50 per cent of the S2CLS mean for S-850 > 3 mJy, with scatter consistent with the Poisson and estimated cosmic variance uncertainties, although there is a marginal (2 sigma) density enhancement in GOODS-North. The observed counts are in reasonable agreement with recent phenomenological and semi-analytic models, although determining the shape of the faint-end slope (S-850 < 3 mJy) remains a key test. The large solid angle of S2CLS allows us to measure the bright-end counts: at S-850 > 10 mJy there are approximately 10 sources per square degree, and we detect the distinctive up-turn in the number counts indicative of the detection of local sources of 850 mu m emission
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| 7. |
- Geach, J.E., et al.
(författare)
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The SCUBA-2 Cosmology Legacy Survey: blank-field number counts of 450-mu m-selected galaxies and their contribution to the cosmic infrared background
- 2013
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 432:1, s. 53-61
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Tidskriftsartikel (refereegranskat)abstract
- The first deep blank-field 450 mu m map (1 sigma approximate to 1.3 mJy) from the Submillimetre Common-User Bolometer Array-2 SCUBA-2 Cosmology Legacy Survey (S2CLS), conducted with the James Clerk Maxwell Telescope (JCMT) is presented. Our map covers 140 arcmin(2) of the Cosmological Evolution Survey field, in the footprint of the Hubble Space Telescope (HST) Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey. Using 60 submillimetre galaxies detected at >= 3.75s, we evaluate the number counts of 450-mu m-selected galaxies with flux densities S-450 > 5 mJy. The 8 arcsec JCMT beam and high sensitivity of SCUBA-2 now make it possible to directly resolve a larger fraction of the cosmic infrared background (CIB, peaking at. similar to 200 mu m) into the individual galaxies responsible for its emission than has previously been possible at this wavelength. At S450 > 5 mJy, we resolve (7.4 +/- 0.7) x 10(-2) MJy sr(-1) of the CIB at 450 mu m (equivalent to 16 +/- 7 per cent of the absolute brightness measured by the Cosmic Background Explorer at this wavelength) into point sources. A further similar to 40 per cent of the CIB can be recovered through a statistical stack of 24 mu m emitters in this field, indicating that the majority (approximate to 60 per cent) of the CIB at 450 mu m is emitted by galaxies with S450 > 2 mJy. The average redshift of 450 mu m emitters identified with an optical/near-infrared counterpart is estimated to be = 1.3, implying that the galaxies in the sample are in the ultraluminous class (LIR approximate to 1.1 x 1012 L approximate to). If the galaxies contributing to the statistical stack lie at similar redshifts, then the majority of the CIB at 450 mu m is emitted by galaxies in the luminous infrared galaxy (LIRG) class with LIR > 3.6 x 1011 L-circle dot.
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| 8. |
- Curran, S.J., et al.
(författare)
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On the absence of molecular absorption in high-redshift millimetre-band searches
- 2011
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 416:3, s. 2143-2153
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Tidskriftsartikel (refereegranskat)abstract
- We have undertaken a search for millimetre-waveband absorption (through the CO and HCO(+) rotational transitions) in the host galaxies of reddened radio sources (z = 0.405-1.802). Despite the colour selection (optical-near-infrared colours of V - K greater than or similar to 5 in all but one source), no absorption was found in any of the eight quasars for which the background continuum flux was detected. On the basis of the previous (mostly intervening) H(2) and OH detections, the limits reached here and in some previous surveys should be deep enough to detect molecular absorption according to their V - K colours. However, our survey makes the assumption that the reddening is associated with dust close to the emission redshift of the quasar and that the narrow millimetre component of this emission is intercepted by the compact molecular cores. By using the known millimetre absorbers to define the colour depth and comparing this with the ultraviolet luminosities of the sources, we find that, even if these assumptions are valid, only 12 of the 40 objects (mainly from this work) are potentially detectable. This is assuming an excitation temperature of T(x) = 10 K at z = 0, with the number decreasing with increasing temperatures (to zero detectable at T(x) greater than or similar to 100 K).
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| 9. |
- Curran, S.J., et al.
(författare)
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Redshifted H I and OH absorption in radio galaxies and quasars
- 2011
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 413:2, s. 1165-1173
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Tidskriftsartikel (refereegranskat)abstract
- From a survey for the redshifted H i 21-cm and OH 18-cm absorption in the hosts of a sample of radio galaxies and quasars, we detect H i in three of the 10 and OH in none of the 14 sources for which useful data were obtained. As expected from our recent result, all of the 21-cm detections occur in sources with ultraviolet (UV) continuum luminosities of L(UV) 1023 W Hz-1. Our 21-cm detections in combination with those previously published give a total of eight (associated and intervening) H i-absorbing sources searched and undetected in OH. Using the detected 21-cm line strengths to normalize the limits, we find that only two of these eight sources may have been searched sufficiently deeply in OH, even though these are marginal.
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| 10. |
- Pétri, Jérôme A., et al.
(författare)
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Constraining the magnetic field geometry of the millisecond pulsar PSRJ0030+0451 from joint radio, thermal X-ray, and γ-ray emission
- 2023
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 680
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Tidskriftsartikel (refereegranskat)abstract
- Context. With the advent of multi-wavelength electromagnetic observations of neutron stars - spanning many decades in photon energies - from radio wavelengths up to X-rays and γ-rays, it has become possible to significantly constrain the geometry and the location of the associated emission regions. Aims. In this work, we use results from the modelling of thermal X-ray observations of PSR J0030+0451 from the Neutron Star Interior Composition Explorer (NICER) mission and phase-aligned radio and γ-ray pulse profiles to constrain the geometry of an off-centred dipole that is able to reproduce the light curves in these respective bands simultaneously. Methods. To this aim, we deduced a configuration with a simple dipole off-centred from the location of the centre of the thermal X-ray hot spots. We show that the geometry is compatible with independent constraints from radio and -ray pulsations only, leading to a fixed magnetic obliquity of α ≈ 75° and a line-of-sight inclination angle of ζ ≈ 54°. Results. We demonstrate that an off-centred dipole cannot be rejected by accounting for the thermal X-ray pulse profiles. Moreover, the crescent shape of one spot is interpreted as the consequence of a small-scale surface dipole on top of the large-scale off-centred dipole.
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