Modelling of TAE mode excitation with an antenna in realistic X-point geometry

Modelling of TAE mode excitation with an antenna in realistic X-point geometry

Modelling of TAE mode excitation with an antenna in realistic X-point geometry 150 150 UKAEA Opendata
UKAEA-CCFE-PR(19)60

Modelling of TAE mode excitation with an antenna in realistic X-point geometry

Toroidal Alfven Eigenmode (TAE) excitation can be caused by fusion-born or Ion Cyclotron Resonance and neutral beam heating fast particles through wave-particle resonance. TAEs may affect fast particle confinement, reduce heating and current drive efficiency, cause damage to the first wall, and decrease overall plasma performance. Excitation of TAE modes with an external antenna has been very successful [1]. It was shown that TAEs, excited with an antenna, that are clearly visible in the limiter phase of the discharge disappear when the X-point forms, likely due to an increase in the damping rates. More detailed studies [2] show that the damping rates increase significantly with elongation and ellipticity. The aim of the present work is to investigate in detail the effect of the x-point geometry on the efficiency of the TAE excitation and the damping rate. The equilibrium from JET discharge #42870 during the X-point phase has been analysed with the CASTOR linear resistive MHD code including an antenna [3]. With the plasma boundary approaching the separatrix, the amplitude of the excited TAE mode is strongly reduced, in agreement with observations. Damping rates of 0.5 to 10% are found, consistent with previous results [1]. However, in the CASTOR code the x-point geometry can be only closely approximated. The JOREK-STARWALL nonlinear MHD code has been extended to include active coils [4]. This does allow the simulation of the excitation of TAE modes with an external antennas in full x-point geometry, including the scrape-off layer. The simulations of antenna excitation of TAE modes is challenging due to the low dissipation (i.e. resistivity, viscosity) that is required to avoid a strong damping. Results in a limiter plasma with the time evolution code JOREK are in good agreement with the steady state solution from CASTOR. Simulations of the JET case in x-point geometry will be compared to the linear MHD results to identify the cause for the absence of antenna excited TAE modes. References [1] A. Fasoli et al 2010 Plasma Phys. Control. Fusion 52 075015 [2] D. Testa et al 2001 Nucl. Fusion 41 809 [3] G.T.A. Huysmans et al Physics of Plasmas 2, 1605 (1995) [4] M. Hoelzl et al 2012 J. Phys.: Conf. Ser. 401 012010

Collection:
Journals
Journal:
Physics of Plasmas
Publisher:
AIP (American Institute of Physics)
Published date:
30/11/2021