| 1. |
- Romanelli, F, et al.
(författare)
-
Overview of the JET results
- 2011
-
Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 51:9
-
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.
|
|
| 2. |
- Abel, I, et al.
(författare)
-
Overview of the JET results with the ITER-like wall
- 2013
-
Ingår i: Nuclear Fusion. - : IOP Publishing. - 1741-4326 .- 0029-5515. ; 53:10, s. 104002-
-
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.
|
|
| 3. |
- Kiptily, V. G., et al.
(författare)
-
Fusion Alpha-Particle Diagnostics for DT Experiments on the Joint European Torus
- 2014
-
Ingår i: FUSION REACTOR DIAGNOSTICS. - : AIP Publishing LLC. ; , s. 87-92
-
Konferensbidrag (refereegranskat)abstract
- JET equipped with ITER-like wall (a beryllium wall and a tungsten divertor) can provide auxiliary heating with power up to 35MW, producing a significant population of alpha-particles in DT operation. The direct measurements of alphas are very difficult and alpha-particle studies require a significant development of dedicated diagnostics. JET now has an excellent set of confined and lost fast particle diagnostics for measuring the alpha-particle source and its evolution in space and time, alpha-particle energy distribution, and alpha-particle losses. This paper describes how the above mentioned JET diagnostic systems could be used for alpha-particle measurements, and what options exist for keeping the essential alpha-particle diagnostics functioning well in the presence of intense DT neutron flux. Also, alpha-particle diagnostics for ITER are discussed.
|
|
| 4. |
|
|
| 5. |
- Kiptily, V. G., et al.
(författare)
-
Fast ions in mode conversion heating (He-3)-H plasmas in JET
- 2012
-
Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 54:7, s. 074010-
-
Tidskriftsartikel (refereegranskat)abstract
- Fast ions were analysed in experiments focusing on fundamental He-3 minority and mode conversion (MC) in the ion cyclotron resonance range of frequencies (ICRF) in H plasmas and on second harmonic heating of He-3 ions at 2.65 T mimicking D-T plasma heating in ITER at half its nominal toroidal magnetic field. Gamma-ray spectrometry, neutral particle analysers and fast-ion loss diagnostics provided information on the generation of fast-ion populations and on the distribution of ICRH power among the species in various heating scenarios and for a large range of He-3 concentrations. In the scenario with the fundamental He-3 minority and MC wave heating at B-T(0) = 3.41 T and f approximate to 32 MHz, fast He-3 ions accelerated by ICRH in the MeV energy range were detected in discharges with low He-3 concentration. In the experiments with a He-3 concentration scan it was found that at a He-3 concentration of approximate to 2.2% the He-3 ion losses disappeared while a population of energetic D ions gradually built up due to a redistribution of the ICRH power between species on reaching the first MC regime. Under those conditions the ICRF-heated D beam ions effectively absorbed the wave power at their Doppler shifted resonance, which was close to the plasma centre. In discharges with second harmonic heating of He-3 ions at B-T(0) = 2.65 T and f approximate to 52 MHz, the confined energetic He-3 ions were found in the MeV energy range. There is some evidence that the D ions were also accelerated by ICRF. This paper also demonstrates that the synergy of the various fast ion diagnostics allows making a broad picture of the physics of the redistribution of the absorbed ICRH power in complicated heating scenarios of JET.
|
|
| 6. |
- Perez, R. V., et al.
(författare)
-
Investigating fusion plasma instabilities in the Mega Amp Spherical Tokamak using mega electron volt proton emissions
- 2014
-
Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 85:11, s. 11D701-
-
Tidskriftsartikel (refereegranskat)abstract
- The proton detector (PD) measures 3 MeV proton yield distributions from deuterium-deuterium fusion reactions within the Mega Amp Spherical Tokamak (MAST). The PD's compact four-channel system of collimated and individually oriented silicon detectors probes different regions of the plasma, detecting protons (with gyro radii large enough to be unconfined) leaving the plasma on curved trajectories during neutral beam injection. From first PD data obtained during plasma operation in 2013, proton production rates (up to several hundred kHz and 1 ms time resolution) during sawtooth events were compared to the corresponding MAST neutron camera data. Fitted proton emission profiles in the poloidal plane demonstrate the capabilities of this new system.
|
|
| 7. |
- von Thun, C. Perez, et al.
(författare)
-
MeV-range fast ion losses induced by fishbones on JET
- 2010
-
Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 50:8, s. 084009-
-
Tidskriftsartikel (refereegranskat)abstract
- Energy and pitch angle resolved measurements of highly energetic (megaelectronvolt (MeV) range) suprathermal ions ejected from the plasma through interaction with fishbone oscillations are presented. The measurements are obtained with a 2D scintillator probe diagnostic installed on JET, which is designed to detect lost ions only above a certain energy threshold (E-min,E- D similar to 200 keV). In the case reported here the lost ions are identified as fast protons which had been accelerated to high energies by ICRF minority heating. The energy of the lost protons (similar to 0.5-4 MeV) is approximately one order of magnitude higher than the energy of the injected beam ions (maximum 130 keV) driving the fishbone. Losses arriving at the probe are enhanced by about a factor 10-20 with respect to MHD-quiescent levels, and are found to increase quadratically with the fishbone amplitude. Using a number of simplifying assumptions, numerical simulations have been performed which combine the HAGIS, MISHKA and SELFO codes (where the distribution function predicted by SELFO has been validated against neutral particle analyser measurements). The losses are found to originate from orbit stochastic diffusion of trapped protons near the plasma boundary or from counter-passing protons deep in the plasma core, which transit under the influence of the fishbone into an unconfined trapped orbit. The simulations show further that the losses are of non-resonant type. The simulated energy and pitch angle distribution of the losses, the temporal behaviour of the losses during a fishbone cycle and the scaling of the losses with the fishbone amplitude are compared with experiment. The simulation results are mostly in broad agreement with experiment, but some of the predictions could not be reconciled with experiment using this model.
|
|
| 8. |
- von Thun, C. Perez, et al.
(författare)
-
Numerical simulation of fast ion loss detector measurements for fishbones on JET
- 2011
-
Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 51:5, s. 053003-
-
Tidskriftsartikel (refereegranskat)abstract
- A synthetic diagnostic model for the simulation of energy and pitch angle resolved measurements of fast ion losses obtained by 2D scintillation-type detectors is presented and subsequently tested on a JET discharge with fishbones (previously documented in Perez von Thun et al 2010 Nucl. Fusion 50 084009). The simulated energy and pitch angle distributions at the detector are found to be in excellent agreement with the measurements. The simulations further suggest that nearly all the fast ion losses take place in the early growth phase of the fishbone cycle, and reach their maximum well ahead of the magnetic perturbation peak.
|
|
| 9. |
- Murari, A., et al.
(författare)
-
New developments in the diagnostics for the fusion products on JET in preparation for ITER, (invited)
- 2010
-
Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 81:10, s. 10E136-
-
Tidskriftsartikel (refereegranskat)abstract
- Notwithstanding the advances of the past decades, significant developments are still needed to satisfactorily diagnose "burning plasmas." D-T plasmas indeed require a series of additional measurements for the optimization and control of the configuration: the 14 MeV neutrons, the isotopic composition of the main plasma, the helium ash, and the redistribution and losses of the alpha particles. Moreover a burning plasma environment is in general much more hostile for diagnostics than purely deuterium plasmas. Therefore, in addition to the development and refinement of new measuring techniques, technological advances are also indispensable for the proper characterization of the next generation of devices. On JET an integrated program of diagnostic developments, for JET future and in preparation for ITER, has been pursued and many new results are now available. In the field of neutron detection, the neutron spectra are now routinely measured in the energy range of 1-18 MeV by a time of flight spectrometer and they have allowed studying the effects of rf heating on the fast ions. A new analysis method for the interpretation of the neutron cameras measurements has been refined and applied to the data of the last trace tritium campaign (TTE). With regard to technological upgrades, chemical vapor deposition diamond detectors have been qualified both as neutron counters and as neutron spectrometers, with a potential energy resolution of about one percent. The in situ calibration of the neutron diagnostics, in preparation for the operation with the ITER-like wall, is also promoting important technological developments. With regard to the fast particles, for the first time the temperature of the fast particle tails has been obtained with a new high purity Germanium detector measuring the gamma emission spectrum from the plasma. The effects of toroidal Alfven eigenmodes modes and various MHD instabilities on the confinement of the fast particles have been determined with a combination of gamma ray cameras, neutral particle analyzers, scintillator probe, and Faraday cups. From a more technological perspective, various neutron filters have been tested to allow measurement of the gamma ray emission also at high level of neutron yield.
|
|
