| 1. |
- 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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| 2. |
- 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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| 3. |
- Solano, E. R., et al.
(författare)
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Observation of Confined Current Ribbon in JET Plasmas
- 2010
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 104:18, s. 185003-
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Tidskriftsartikel (refereegranskat)abstract
- We report the identification of a localized current structure inside the JET plasma. It is a field-aligned closed helical ribbon, carrying current in the same direction as the background current profile (cocurrent), rotating toroidally with the ion velocity (corotating). It appears to be located at a flat spot in the plasma pressure profile, at the top of the pedestal. The structure appears spontaneously in low density, high rotation plasmas, and can last up to 1.4 s, a time comparable to a local resistive time. It considerably delays the appearance of the first edge localized mode.
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| 4. |
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| 5. |
- 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-
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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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| 6. |
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| 7. |
- Romanelli, M., et al.
(författare)
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JINTRAC: A system of codes for integrated simulation of Tokamak scenarios
- 2014
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Ingår i: Plasma and Fusion Research. - : Japan Society of Plasma Science and Nuclear Fusion Research. - 1880-6821. ; 9:SPECIALISSUE.2
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Tidskriftsartikel (refereegranskat)abstract
- Operation and exploitation of present and future Tokamak reactors require advanced scenario modeling in order to optimize engineering parameters in the design phase as well as physics performance during the exploitation phase. The simulation of Tokamak scenarios involves simultaneous modeling of different regions of the reactor, characterized by different physics and symmetries, in order to predict quantities such as particle and energy confinement, fusion yield, power deposited on wall, wall load from fast particles. JINTRAC is a system of 25 interfaced Tokamak-physics codes for the integrated simulation of all phases of a Tokamak scenario. JINTRAC predictions reflect the physics and assumptions implemented in each module and extensive comparison with experimental data is needed to allow validation of the models and improvement of Tokamak-physics understanding. © 2014 The Japan Society of Plasma Science and Nuclear Fusion Research.
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| 8. |
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| 9. |
- Blackwell-Whitehead, Richard, et al.
(författare)
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Infrared Mn I laboratory oscillator strengths for the study of late type stars and ultracool dwarfs
- 2011
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Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 525
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Tidskriftsartikel (refereegranskat)abstract
- Aims. The aim of our new laboratory measurements is to measure accurate absolute oscillator strengths for neutral manganese transitions in the infrared needed for the study of late-type stars and ultracool dwarfs. Methods. Branching fractions have been measured by high resolution Fourier transform spectroscopy and combined with radiative level lifetimes in the literature to yield oscillator strengths. Results. We present experimental oscillator strengths for 20 Mn I transitions in the wavelength range 3216 to 13 997 angstrom, 15 of which are in the infrared. The transitions at 12 899 angstrom and 12 975 angstrom are observed as strong features in the spectra of late-type stars and ultracool dwarfs. We have fitted our calculated spectra to the observed Mn I lines in spectra of late-type stars. Using the new experimentally measured Mn I log(gf) values together with existing data for Mn I hyperfine structure splitting factors we determined the manganese abundance to be log N(Mn) = -6.65 +/- 0.05 in the atmosphere of the Sun, log N(Mn) = 6.95 +/- 0.20 in the atmosphere of Arcturus, and log N(Mn) = -6.70 +/- 0.20 in the atmosphere of M 9.5 dwarf 2MASSW 0140026+270150.
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| 10. |
- Hellsten, Torbjörn, et al.
(författare)
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Observations of rotation in JET plasmas with electron heating by ion cyclotron resonance heating
- 2012
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 54:7, s. 074007-
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Tidskriftsartikel (refereegranskat)abstract
- The rotation of L-mode plasmas in the JET tokamak heated by waves in the ion cyclotron range of frequencies (ICRF) damped on electrons, is reported. The plasma in the core is found to rotate in the counter-current direction with a high shear and in the outer part of the plasma with an almost constant angular rotation. The core rotation is stronger in magnitude than observed for scenarios with dominating ion cyclotron absorption. Two scenarios are considered: the inverted mode conversion scenarios and heating at the second harmonic He-3 cyclotron resonance in H plasmas. In the latter case, electron absorption of the fast magnetosonic wave by transit time magnetic pumping and electron Landau damping (TTMP/ELD) is the dominating absorption mechanism. Inverted mode conversion is done in (He-3)-H plasmas where the mode converted waves are essentially absorbed by electron Landau damping. Similar rotation profiles are seen when heating at the second harmonic cyclotron frequency of He-3 and with mode conversion at high concentrations of He-3. The magnitude of the counter-rotation is found to decrease with an increasing plasma current. The correlation of the rotation with the electron temperature is better than with coupled power, indicating that for these types of discharges the dominating mechanism for the rotation is related to indirect effects of electron heat transport, rather than to direct effects of ICRF heating. There is no conclusive evidence that mode conversion in itself affects rotation for these discharges.
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