Drift-kink instability induced by beam ions in field-reversed configurations

The drift-kink instability in field-reversed configurations with a beam component is investigated by means of a three-dimensional particle simulation. The unstable mode with the toroidal mode number n=4 grows with the rate gamma similar to 0.1-1.0 omega(ci) for a strong beam current and deforms the plasma profile along the beam orbit in the vicinity of the field-null line. This mode is nonlinearly saturated as a result of the relaxation of current profile. Both the saturation level and the growth rate tend to increase as the ratio of the beam current to the plasma current I-b/I-p increases. It is also found that there is a threshold value of the beam velocity v(b)similar to v(Ti) (ion thermal velocity) for the excitation of the instability. (C) 1999 American Institute of Physics. [S1070-664X(99)00609-6].