Modeling of the beam excited fishbone mode in EAST

Many beam related instabilities have been observed in EAST. This paper reports on detailed calculations of beam driven fishbone and sawtooth instabilities using a general fishbone dispersion relation. The ideal fluid contribution and eigenfunction were calculated with the magnetohydrodynamic code NOVA, the kinetic contribution was evaluated with sample fast ion distributions in the guiding center code ORBIT, and the general inertial term was calculated using experimental data. The sawtooth branch was stabilized both by co-beam injection and balanced injection, but the stable domain for the sawtooth and fishbone modes is wider for balanced injection. The fishbone of the precessional branch is excited by both trapped and passing particles. To widen the stable domain, we propose a modulated balanced beam heating scenario for long pulse, high beta discharges in EAST, with the single beam pulse turn on time shorter than the plasma energy confinement time and longer than the beam ion slowing down time.