Alcator C-Mod Weekly Highlights January 19, 2010 FY2010 weeks of research operations Base Target: tbd Base Completed: 1.7 weeks ARRA Target: 5 weeks ARRA Completed: 5.0 weeks Plasma Shots: 807 Operations ---------- Routine maintenance of C-Mod systems continued last week. Refurbishment and upgrades were performed on liquid nitrogen systems, the cell water cooling unit, C-Mod gas system, and vessel heater and thermocouple electronics. Work also continued on the lower hybrid launcher and protection and control systems. A brief up-to-argon was conducted on Tuesday afternoon to clean one of the wide angle view windows, remove a re-entrant tube that limited the view of the HIREX_SR diagnostic, and to improve diagnostic access at C-Hor. A leak-check was done on Wednesday, followed by a vessel bake that extended through the weekend. Lower Hybrid System ------------------- Several test waveguide/window assemblies were taken to our e-beam welding vendor last week and welded, nominally using the same settings used for welding the launcher components. Coatings on the window similar in appearance and rf performance to those found on the launcher were obtained. Discussions with the vendor indicated that an error was made in the e-beam focus setting after the earlier successful welds of the prototype and first column launcher splitter were made. We have found that ultrasonic cleaning of the test pieces in water results in rf performance at the level of uncoated windows. Several more tests, including operation at high power, will be required to qualify this cleaning process for use on the actual launcher. ICRF Systems ------------ Bill Beck visited our vendor last week to inspect components that will make up the five high power vacuum feedthroughs for the new advanced ICRF antenna. The components are within tolerance and fit together properly. The vendor is proceeding with preparations for brazing the first feedthrough. In preparation for the resumption of tokamak operations, all the FMIT transmitters have been tested into a dummy load. We also successfully tested FMIT#1 (D antenna) at relatively high frequency amplitude modulation (~500 kHz) in preparation for exciting TAEs with ICRF AM modulation and for beat frequency experiments. Analysis from experiments investigating ICRF heated, high density discharges indicates that inner wall fueling with an active cryopump can avoid the antennas' so-called neutral pressure limit up to ~0.5 times the Greenwald density. The magnetic configuration had little impact on the density obtained for a given neutral pressure. For densities above ~0.5 times the Greenwald density, MARFEs are common and lead to high neutral pressure. Alternator ---------- The alternator was brought up to full speed last Friday. Extensive checks of the drive motor transformer and power inverter indicated proper operation, and no overheating of the transformer windings was detected. Travel and Visits ----------------- David Brower, Weixing Ding, and Will Bergersen, all from UCLA, visited last week as part of the C-Mod/UCLA collaboration on polarimetry. Their extensive experience with the polarimeter system on the Madison Symmetric Torus was of great help in identifying sources of vibration-induced phase noise on the C-Mod Polarimeter single chord mock-up. Randy Wilson, PPPL, visited last week to discuss the MIT/PPPL collaboration and to help with work on the lower hybrid launcher. He also had discussions with other C-Mod scientists in preparation for the upcoming PAC meeting. Ken Liao, UT-FRC, visited last week and participated in beam-into-gas experiments to quantify the performance of the diagnostic neutral beam. Perry Phillips, UT-FRC, traveled to MIT last week to prepare the FRCECE system for the rest of the campaign. The detector for channel 29 was replaced, and the attenuators in the intermediate frequency boxes were optimized to improve signal levels. The FRCECE is now ready for plasma operation. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly