  The aim of the present study is to analyze the stability of the pressure
gradient driven modes (PM) and Alfven eigenmodes (AE) in the Large Helical
Device (LHD) plasma if the rotational transform profile is modified by the
current drive of the tangential neutral beam injectors (NBI). This study forms
a basic search for optimized operation scenarios with reduced mode activity.
The analysis is performed using the code FAR3d which solves the reduced MHD
equations describing the linear evolution of the poloidal flux and the toroidal
component of the vorticity in a full 3D system, coupled with equations for
density and parallel velocity moments of the energetic particle (EP) species,
including the effect of the acoustic modes. The Landau damping and resonant
destabilization effects are added via the closure relation. On-axis and
off-axis NBI current drive modifies the rotational transform which becomes
strongly distorted as the intensity of the neutral beam current drive (NBCD)
increases, leading to wider continuum gaps and modifying the magnetic shear.
The simulations with on-axis NBI injection show that a counter (ctr-) NBCD in
inward shifted and default configurations leads to a lower growth rate of the
PM, although strong n=1 and 2 AEs can be destabilized. For the outward shifted
configurations, a co-NBCD improves the AEs stability but the PM are further
destabilized if the co-NBCD intensity is 30 kA/T. If the NBI injection is
off-axis, the plasma stability is not significantly improved due to the further
destabilization of the AE and energetic particle modes (EPM) in the middle and
outer plasma region.
