Stability analysis of TJ-II stellarator NBI driven Alfvén eigenmodes in ECRH and ECCD experiments

Abstract

In this paper, we analyze the impact of electron cyclotron resonance heating and electron

cyclotron current drive on the Alfvénic instabilities driven by neutral beam injection observed

in the TJ-II stellarator. An MHD stability analysis of driven Alfvén eigenmodes compatible

with the experimental plasma parameters is carried out in order to compare with the data

provided by magnetic coils, radiation monitors, and heavy ion beam probes. To this end, the

vacuum magnetic configuration modified by the different levels of plasma current, the thermal

plasma parameters and the fast ion pressure profiles generated by the co-injected neutral beam,

are entered in the FAR3d gyro-fluid code in order to follow the linear evolution of the

destabilized plasma equilibrium. Linear growth rates and radial location of the dominant

predicted modes coincident in frequency with the observed fluctuations are presented. Despite

the uncertainties related to the estimation of the rotational transform profile, the code

predictions agree within reasonable accuracy with the experimental results.