THEORY OF ION BERNSTEIN WAVE-INDUCED SHEAR SUPPRESSION OF TURBULENCE

The theory of radio frequency induced ion Bernstein wave- (IBW) driven shear flow in the edge is examined, with the goal of application of s hear suppression of fluctuations. This work is motivated by the observ ed confinement improvement on IBW heated tokamaks [Phys. Fluids B 5, 2 41 (1993)], and by previous low-frequency work on RF-driven shear flow s [Phys. Rev. Lett. 67, 1535 (1991)]. It is found that the poloidal sh ear flow is driven electrostatically by both Reynolds stress and a dir ect ion momentum source, analogous to the concepts of helicity injecti on and electron momentum input in current drive, respectively. Flow dr ive by the former does not necessarily require momentum input to the p lasma to induce a shear flow. For IBW, the direct ion momentum can be represented by direct electron momentum input, and a charge separation induced stress that imparts little momentum to the plasma. The derive d E(r) profile due to IBW predominantly points inward, with little pos sibility of direction change, unlike low-frequency Alfvenic RF drive. The profile scale is set by the edge density gradient and electron dis sipation. Due to the electrostatic nature of ion Bernstein waves, the poloidal flow contribution dominates in E(r). Finally, the necessary e dge power absorbed for shear suppression on Princeton Beta Experiment- Modified (PBX-M) [9th Topical Conference on Radio Frequency Power in P lasmas, Charleston, SC, 1991 (American Institute of Physics, New York, 1991), p. 129] is estimated to be 100 kW distributed over 5 cm.