Conditions for seeing RF condensation in contemporary tokamaks
ORAL
Abstract
For RF (radio frequency) stabilization of magnetic islands, it is predicted that nonlinear effects associated with RF current condensation can significantly affect the profile of the power deposition and the profile of the RF driven current [1]. We have been investigating the conditions under which the effect is predicted to play a significant role in contemporary tokamaks. To investigate this, we use the OCCAMI code [2], which couples a ray tracing calculation with a solution of the nonlinear thermal diffusion equation in the magnetic island. We have used the code to perform scans investigating the strength of the effect as a function of various parameters in DIII-D, focusing particularly on the predicted effect of varying the parameters in shot 141060, one of a sequence of shots previously used to study RF stabilization of locked islands [3]. Top launch electron cyclotron current drive (ECCD) is of particular interest because of its high current drive efficiency [4]. For top launch ECCD, the nonlinear effects are most pronounced for parameters that make the EC current drive most efficient. That relation is broken by trapped particle effects for outside launch ECCD.
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Publication: [1] A.Reiman and N. Fisch, Phys. Rev. Lett. 121, 225001 (2018).<br>[2] R. Nies, A. Reiman, E. Rodriguez et al, Phys. Plasmas 27, 092503 (2020).<br>[3] F. Volpe, A. Hyatt, R. La Haye et al, Phys. Rev. Lett. 115, 175002 (2015).<br>[4] X. Chen, C. Petty, J. Lohr et al, Nucl. Fusion 62 (2022) 054001.
