  Alfv\'en cyclotron instabilities excited by velocity gradients of energetic
beam ions were investigated in MAST experiments with super-Alfv\'enic NBI over
a wide range of toroidal magnetic fields from ~0.34 T to ~0.585 T. In MAST
discharges with high magnetic field, a discrete spectrum of modes in the
sub-cyclotron frequency range is excited toroidally propagating counter to the
beam and plasma current (toroidal mode numbers n < 0).
