| 1. |
- Nabais, F., et al.
(författare)
-
Redistribution of ICRH fast ions in the presence of fishbones and Alfvén eigenmodes
- 2007
-
Ingår i: 34th EPS Conference on Plasma Physics 2007, EPS 2007 - Europhysics Conference Abstracts. - 9781622763344 ; , s. 607-610
-
Konferensbidrag (refereegranskat)abstract
- A set of experiments on fast ion redistribution was carried out in recent JET campaigns, in which the new fast ion loss detectors were used for the first time [1]. This paper reports on the experiments carried out with low density plasmas and high ICRH power, a scenario that allow large populations of highly energetic fast ions to be built up and a variety of instabilities to be destabilized. Fast ion losses were successfully measured and it could be confirmed they were effectively associated to MHD activity. Losses occurred at considerably high energies (of the order of few MeV) and two types of fast ions were identified by the gamma-ray diagnostics [2]: fast protons with an energetic tail in excess of 4.5 MeV due to ICRH tuned to a fundamental H-resonance in the centre of the plasmas and D-ions accelerated with second harmonic heating whose energies exceeded 0.5 MeV. Three types of losses were identified, one associated with sawtooth crashes, one associated with TAE and high frequency fishbones and a third group that seems to correlate with tornado modes. When tornado modes became unstable, a significant increase in the number of losses was measured and a change in both the energy and pitch angle of the lost ions was observed. In addition, it was also observed that the number of losses increased significantly with the ICRH power.
|
|
| 2. |
- Sandquist, P., et al.
(författare)
-
Bidirectional tornado modes on the joint european torus
- 2007
-
Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 14:12
-
Tidskriftsartikel (refereegranskat)abstract
- In discharges on the Joint European Torus [P. H. Rebut and B. E. Keen, Fusion Technol. 11, 13 (1987)] with safety factor q(0)< 1 and high-power ion cyclotron resonance heating (ICRH), monster sawtooth crashes are preceded by frequency sweeping tornado modes in the toroidal Alfven eigenmode frequency range. A suite of equilibrium and spectral magnetohydrodynamical codes is used for explaining the observed evolution of the tornado mode frequency and for identifying temporal evolution of the safety factor inside the q=1 radius just before sawtooth crashes. In some cases, the tornado modes are observed simultaneously with both positive and negative toroidal mode numbers. Hence, a free energy source other than the radial gradient of the energetic ion pressure exciting these modes is sought. The distribution function of the ICRH-accelerated ions is assessed with the SELFO code [J. Hedin , Nucl. Fusion 42, 527 (2002)] and energetic particle drive due to the velocity space anisotropy of ICRH-accelerated ions is considered analytically as the possible source for excitation of bidirectional tornado modes.
|
|
| 3. |
|
|
