Alcator C-Mod Weekly Highlights June 16, 2008 FY2008 weeks of research operations: Target: 15 weeks Completed: 15.7 weeks Physics ------- Detailed analysis of A-coil ELM suppression experiments conducted during the last run campaign has been completed. The A-coils had no impact on ELM activity at higher q95. At q95~3.5 there may have been a suppression effect by the A-coil on ELMs, in particular when comparing situations with similar pedestal collisionality. It is speculated that the presence of the QC-mode at higher q95 may negate the effect of Chirikov parameters > 1. Post-campaign visual and photographic inspections of the lower divertor surfaces indicate that the boron coverage of the EF1 surface is asymmetric, with the surfaces near the A - C Ports having thicker boron layers. This asymmetry is possibly due to toroidally asymmetric net boron deposition during boronization. A method of evaluating MSE offsets, which relies on EFIT reconstructions during the ohmic phase of discharges is being developed. By using an EFIT reconstruction which has been modified to reproduce the sawtooth inversion radius observed on ECE signals, it is found that the timing of changes in sawtooth activity and the evolution of central safety factor subsequent to the application of lower hybrid current drive become well correlated. Also, the kinetic stored energy derived from these reconstructions is in better agreement with that evaluated directly from the density and temperature profiles. Operations ---------- We continued preparations for the machine inspection last week. Most diagnostics have been removed from the machine, and nearly all cabling and fibers have been either rolled back to the cell walls, or taken out of the cell completely. Only diagnostics and equipment required for the final few calibrations remain in the cell. The top of the cryostat has been completed cleared off and is being prepared for removal. The upper level of igloo blocks are also ready to be removed from the cell. ICRF Systems ------------ The J-Port antenna was removed from the vessel last week. It will be replaced with a new 4-strap antenna during the current up-to-air period. Simulations of the new antenna continue as we work to optimize the strip lines feeding the antenna straps. Lower Hybrid System ------------------- The lower hybrid launcher has been removed from the vessel. Calibrations will be performed to determine post-campaign phase and amplitude characteristics of the launcher for comparison with data taken before the start of the last campaign. Work continued on design and prototyping of the 2nd lower hybrid launcher. Simulations of disruption forces on the inconel 625 coupler design continued. A 4-way coupler prototype is leak-tight and ready to be annealed. Travel and Visitors ------------------- John Rice, Joe Snipes, Jerry Hughes, Ron Parker, and Miklos Porkolab attended the 35th EPS meeting in Crete. John gave an invited talk on "Spontaneous Rotation in C-Mod". Greg Wallace and Orso Meneghini are in Cadarache, France, until June 27th. They will be working with the Tore Supra Lower Hybrid group. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly