E. Lazzaro et al., DENSITY SCALING OF THE THRESHOLD FOR LOCKED MODE-INSTABILITY IN THE PRESENCE OF TOROIDAL FIELD RIPPLE IN A TOKAMAK, Physics of plasmas, 4(11), 1997, pp. 4017-4022
The nonlinear excitation of magnetic islands in a tokamak by external
resonant magnetic perturbation is examined. The perturbation amplitude
threshold for the appearance of a locked mode is determined for a tok
amak with a rippled toroidal field. It is shown that the critical valu
e of the magnetic field is increased by the ripple induced damping of
toroidal rotation. Qualitative aspects of the experimentally observed
reduced scaling of the threshold density for mode locking, are predict
ed in the regime of low viscosity and dominant plasma inertial effects
. In such a case the scaling is shown to be close to n(i) similar to (
B) over tilde(r)(1/2) rather than n(i) similar to (B) over tilde(r)(3/
2) as predicted by the usual theory. (C) 1997 American Institute of Ph
ysics. [S1070-664X(97)03310-7].