Nonlinear simulations of core density collapses in Large Helical Device
POSTER
Abstract
The present analysis is dedicated to study the core density collapses (CDC) observed in Large Helical Device (LHD) induced by unstable ballooning modes at the plasma edge. Linear simulations using the FAR3d code find the destabilization of ballooning modes in the outer plasma region with n > 17 (n is the toroidal mode number). Nonlinear simulations find an inverse energy cascade from the saturating ballooning modes towards middle and low n modes as well as towards the thermal plasma. Plasma flux surface distortion during the ballooning mode saturation flatten the pressure gradients at the edge although enhanced at the inner plasma leading to the destabilization of low n modes at the plasma core. The simulation reproduces the inward propagation and the m=1 perturbation measured during the CDC. LHD performance deterioration could be caused by the magnetic surfaces distortion and wide stochastic magnetic field regions during ballooning modes and low n modes saturation.
*The authors would like to thank the LHD technical staff for their contributions in the operation and maintenance of LHD. This work was supported by the US DOE under Grant DE-FG02-04ER54742 and the Spanish National Research Project No. PID2022-137869OB-I00. Use has been made of Uranus, a supercomputed cluster located at the Universidad Carlos III de Madrid (Spain) and funded jointly by EU FEDER funds and by the Spanish Government via national Projects UNC313-4E-23612, ENE2009-12213-C03-03, ENE2012-33219, ENE2012-31753 and ENE2015-68265.
Publication: Special issue of IAEA FEC in Nuclear Fusion to be submitted
Presenters
-
Jacobo Varela Rodriguez