Co-counter asymmetry in fast wave heating and current drive and profile control in NSTX

In this paper, full-wave ICRF coupling models are applied to understand the difference in plasma response when antenna arrays are phased to drive currents co and counter to the plasma current. The source of this difference lies in the natural up-down asymmetry of the antenna's radiated power spectrum caused by Hall currents. When a poloidal field is applied, this up-down asymmetry acquires a toroidal component. The result is that plasma absorption (i.e., antenna loading) is shifted or skewed toward the co-current drive direction, independent of the direction of the magnetic field. When waves are launched to drive current counter to the plasma current, electron heating and current profiles are more peaked on axis, and this peaking becomes more pronounced at lower toroidal magnetic fields