Abstract Details
| status: | file name: | submitted: | by: |
|---|---|---|---|
| approved | reiman_presentation.pdf | 2019-02-22 13:27:57 | Allan Reiman |
Abstracts
Author: Allan H. Reiman
Requested Type: Pre-Selected Invited
Submitted: 2019-02-22 13:14:44
Co-authors: N. J. Fisch
Contact Info:
Princeton Plasma Physics Laboratory
Princeton University
Princeton, NJ 08544
USA
Abstract Text:
Currents driven by radio frequency waves in the interior of magnetic islands can stabilize deleterious tearing modes in tokamaks. We describe a previously unrecognized effect that can significantly facilitate that stabilization [1]. Present analyses of stabilization assume that the local power deposition and electron acceleration are unaffected by the presence of the island. This neglects the fact that the deposition is sensitive to the perturbation of the temperature, and that the deposition can significantly perturb the temperature in the island. (The temperature perturbation in the island also gives rise to an experimentally documented ohmic effect.) The nonlinear feedback on the power deposition in the island increases the temperature perturbation, and it can lead to a bifurcation of the solution to the steady-state heat diffusion equation, and a discontinuous jump in the steady-state temperature,. The combination of the nonlinearly enhanced temperature perturbation with the rf current drive sensitivity to the temperature leads to an rf current condensation effect, which can increase the efficiency of rf current drive stabilization and reduce its sensitivity to radial misalignment of the ray trajectories. Taking into account depletion of the wave energy, a third root of the steady-state diffusion equation is accessed above the bifurcation point [2]. There is a hysteresis effect, with stabilized islands on the third branch shrinking to smaller widths than would otherwise be achieved. The nonlinear threshold for the current condensation effect is in a regime that has been encountered in experiments, and will likely be encountered in ITER. The effect can potentially allow the stabilization of larger islands than would otherwise be possible, and could therefore have a significant impact on disruptivity. Work supported by DOE contract DEAC02-76CH03073. [1] A. Reiman and N. Fisch, Phys. Rev. Lett. 121, 225001 (2018). [2] E. Rodriguez, Sherwood Poster, this meeting.
Comments:
If not selected for an invited talk, place before the poster of E. Rodriguez.
