Alcator C-Mod Weekly Highlights June 23, 2008 FY2008 weeks of research operations: Target: 15 weeks Completed: 15.7 weeks Physics ------- Yijun Lin continues the analysis ICRF mode conversion data from the last run campaign. The toroidal flow scales with the ICRF power, and substantially exceeds the intrinsic rotation. The detailed physics is still under investigation. Operations ---------- The top and upper halves of the C-Mod igloo and cryostat have been removed, and work has begun on disassembly of the curved bus feeding the magnets. All ports and port extensions and liquid nitrogen cooling lines have been removed in preparation for removing the retaining cylinder. All diagnostic calibrations have been completed. With removal of the D and E-Port ICRF antennas last week all antennas have been removed from in-vessel. The antennas appear to be in very good condition, and are now in the rf lab undergoing a careful evaluation. ICRF Systems ------------ Simulations of a simplified model of the new 4-strap antenna show uniform fields and currents in the four straps. This model is being used as input to the detailed CAD model of the antenna which will in turn be input to the simulation as a final test of the design. We continued work on Intermediate Power Amplifier (IPA) upgrades. Lower Hybrid System ------------------- Fabrication of the 4th cart is proceeding. The cart chassis is complete and ready to be painted. Electronic components for the cart are being procured. We continued testing and debugging the new Coupler Protection System data acquisition and control boards. Diagnostics ----------- Steve Scott, PPPL, participated in the removal of the MSE diagnostic from the C-Mod torus, in preparation for the upcoming C-Mod machine inspection. Robert Granetz has been investigating damage to the in-vessel x-ray tomography signal cables, much of which occurred on a single discharge that had a large population of relativistic runaway electrons and terminated in a disruption. However, some degradation to the cables had occurred more than a month earlier during a series of apparently benign discharges. The role of runaway electrons is being investigated in the process. Travel and Visitors ------------------- Gerrit Kramer visited the PSFC this week to investigate a long-standing problem with the swept-frequency reflectometer, namely excessive loss of signal somewhere along the waveguide/antenna system which effectively precluded its use to measure density fluctuations during the FY08 campaign. A careful inspection revealed the presence of tiny titanium droplets on the surface of the plasma-facing reflectometer antennas and in the in-vessel waveguides which created a rough surface that impeded the propagation of the microwaves. The waveguides will be replaced and refurbishment/redesign options for the antenna horns are being considered. David Mikkelsen, PPPL, visited MIT to work with Alex Ince-Cushman on shot selection for a study of density peaking in H-mode plasmas. He also advised Brock Bose on his GYRO simulations. After the EPS meeting, Miklos Porkolab attended the satellite meeting: EFTSOMP2008- Workshop on E fields, Turbulence and Self Organisation in Magnetized Plasma, June 16-17, Hersonissos, Greece, where he presented an invited talk: Turbulence studies in ohmic plasmas in the Alcator C-Mod tokamak with PCI and GPI diagnostics. Greg Wallace and Orso Meneghini continued their work with the Tore Supra Lower Hybrid group in Cadarache, France, last week. Greg has learned much about the Tore Supra launcher system, and Orso has been working on a TOPLHA simulation of the Tore Supra multi-junction launcher. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly