The second meeting of the RF Electric Field Shear Drive Team was held at MIT on May 13, 1998. The meeting was attended by A.~Bers, P.T.~Bonoli, M.Greenwald, I.Hutchinson, M.Porkolab, A.Ram, and J.Rice (MIT); B. LeBlanc (PPPL); L.Berry, E.F. Jaeger, and D.B. Batchelor (ORNL), and Lin-Liu (GA). Ben Carreras (ORNL), P.H. Diamond (UCSD), and C.K.Phillips (PPPL) were unable to attend. Topics that were presented and discussed at the meeting were:
The Oak Ridge group compared the predictions of three models for RF flow drive: compressible and incompressible fluid models and a kinetic model. Agreement between the models was found to depend on the wave type being considered with the agreement being best for electromagnetic (fast) waves. Large discrepancies were found when electrostatic (ion Bernstein) waves were considered. When compressibility was important (as with the IBW), the driven flow was found to be reduced significantly. Kinetic effects (including those from viscosity) were found to reduce the flow even further. A model calculation for Alcator C-Mod parameters indicated the mode converted IBW was the most promising candidate for RF flow drive with $\simeq 2.5~{\rm MW}$ of RF power needed to drive flows sufficient to stabilize turbulence. It was concluded that a fair amount of analysis still needed to be done in order to understand the differences between the predictions of the fluid and kinetic models in the electrostatic limit.
Ben LeBlanc (PPPL) presented further analysis of the poloidal rotation data obtained in TFTR with direct launch ion Bernstein waves. Measurements of rotation from impurity carbon were ``inverted'' to correspond to local values of the poloidal rotation velocity (previously only chord averaged rotation velocities had been presented). Based on IBW ray tracing calculations and the momentum equation, a poloidal rotation velocity was calculated and compared with experiment. The IBW power was found to be damped completely, just to the low field side (LFS) of the fifth cyclotron harmonic of tritium. The direction and order of magnitude of the predicted flow was in agreement with the experiment in the vicinity of this cyclotron layer. Measured rotation to the high field side of the tritium harmonic cyclotron layer could not be explained by the model unless about 20~\% of the IBW power was assumed to tunnel through the resonance layer. The reason(s) for this discrepancy will be studued in the future.
John~Rice (MIT) presented toroidal rotation mesurements from Alcator C-Mod, based on observations from shifted argon X-ray spectra. Toroidal rotation in the Co current direction was found in the presence of ICRF heating with no direct momentum input (opposite to the rotation in ohmic plasmas). Rotation velocities up to $1.3 \times 10^{7}~{\rm cm/s}$ were measured. The rotation velocity was found to peak at the magnetic axis, increase with increasing stored energy and decrease with increasing plasma current. Radial electric fields on the order of 300~V/cm were inferred at $r / a \simeq 0.3$.
The last presentation was by P.T~Bonoli (MIT) in which he described plans for Alcator C-Mod to perform RF induced internal transport barrier (ITB) experiments. This would be done in D-($^3$He)-(H) plasmas at $B_{0} \simeq 5.5 - 5.7~{\rm T}$. A combination of 4~{MW} of ICRF source power at 80~{MHz} would be used for central minority (H) heating and 4~{MW} of ICRF power at 60~{MHz} would be used to trigger an ITB via off-axis mode conversion electron heating in the presence of pellet fueling.
During discussion at the end of the meeting, attention centered on the whether the Strategic Simulation Initiative (SSI), within the office of Energy Research, could provide computational opportunities for solving problems related to rf shear drive, especially problems involving short wavelingth modes such as the IBW. Don Batchelor agreed to organize a conference call to discuss the possiblity of having a mini-conference at the New Orleans APS Meeting with talks on SSI related activities that could benefit researchers in the rf and rf shear drive community.