Alcator C-Mod Weekly Highlights July, 3, 2006 FY2006 weeks of research operations: Planned: 14 weeks Completed: 14.4 weeks Operations ---------- Last week was a scheduled maintenance period at Alcator C-Mod. No plasma operations were scheduled. Scheduled routine maintenance was carried out on the MIT Alternator, including cleaning of the heat exchangers which resulted in reduction of the oil drain operating temperatures of the flywheel seals by 15 degrees. The phase-reference selector switch assembly in the EF3 power supply was replaced. This switch was exhibiting an intermittent problem with one of 14 cam-operated contacts. The faulty contact could create a spurious type one fault (loss of sync voltage) and generate a circuit breaker trip signal during operation. The repair was completed and off-line tests simulating power supply operation were successful. A small leak at one of the HIREX (High Resolution X-ray Diagnostic) beryllium windows was repaired by replacing the window following a helium backfill of the vessel. The tokamak was then pumped down and successfully leak-checked. Plasma operations are scheduled to resume this week. ICRF System ------------ The J-port transmission line was reconfigured from 50MHz to 70MHz, and the 50MHz stub was removed from the dummy load. A high-voltage arc in the FMIT#4 crowbar cabinet during transmitter tuning resulted in some minor damage, which has been repaired. The crowbar was tested successfully and returned to service. Re-tuning of the FMIT#3 and #4 transmitters from 50MHz to 70MHz is now complete. Lower Hybrid System -------------------- Conditioning of klystrons to higher voltage continued last week. Eleven klystrons have operated up to 45kV for short pulses. The #6 klystron exhibited excessive body current at elevated beam voltage, and is slated to be replaced with a spare tube. Preparations for new klystron drive calibrations at increased voltage and power are underway. Diagnostics ----------- The final tests of the Wall Actuated Scanning Probe (WASP) using the 1-J magnet have been completed. This 4-electrode scanning Langmuir-Mach probe is designed as an upgrade to the existing single-electrode Inner Wall Scanning Probe (ISP) in C-Mod, providing unique information on parallel and perpendicular flows, fluctuation spectra and plasma profiles in the high-field side scrape-off layer. The goals of the test in the 1-J magnet were to evaluate the durability of the probe by cycling it a large number of times, verify that the probe moved as expected with all wires and final bushing materials in place and to revisit the electro-mechanical drive capabilities of the probe. The tests were successful on all three points. We successfully cycled the probe a total of 400 times. The probe motion was not significantly affected by the wires and they easily survived the test as well. The return spring on the probe functioned well, bringing it back to the wall under no-drive conditions. The probe also demonstrated the capability of turning around quickly without bouncing off the limit springs. This means we can control the plunge depth of the probe without greatly increasing its dwell time in the plasma. We conclude that the WASP should be ready for installation in its current configuration during the next manned access up-to-air. Travel and Visitors ------------------- Sasha Pigarov (UCSD) visited with B. LaBombard on Tuesday to discuss the modeling of cross-field transport and scrape-off layer plasma flows in C-Mod using the UEDGE code for lower-null, near-balanced double null and upper-null discharges. A set of seven different EFIT reconstructions were identified, having SSEP parameters spanning from -5 mm to +5 mm. These will allow some basic tests to be performed of the computational meshes that are generated for UEDGE. Sasha also met with Bob Granetz and Aaron Bader to discuss our planned measurements of dust motion in the SOL. Sasha told us that he expects us to find toroidal velocities of dust particles in the range of 100 m/s, and also that there could be dust moving perpendicularly away from the wall (rebounding from collisions with the wall). Sasha is also very interested in measurements on the distribution of dust in the pumping duct, which could be made at the beginning of the next manned access. Stewart Zweben (PPPL) was at C-Mod this week to discuss the the new GPI divertor telescope, which is being designed by Bob Ellis of PPPL. He also is continuing analysis of the limiter vs. divertor plasma comparison from GPI data taken earlier in this run. Paul Bonoli attended the SciDAC 2006 Conference in Denver, CO on June 25-29, 2006, representing the RF SciDAC Project along with Drs. Fred Jaeger and Don Batchelor. The RF SCiDAC Project received an Invited Poster at this meeting that was presented by Dr. Fred Jaeger entitled "Quasilinear Evolution of non-thermal ion distributions in ion cyclotron resonance heating". The poster presentation will also appear as a publication in the journal Plasma Physics and Controlled Fusion. This meeting was sponsored by the Office of Science and consisted of Oral and Poster Presentations on high performance computing research in physics, engineering, and bio-medical research. Bruce Lipschultz attended both the ITPA Coordinating Committee meeting (June 26-27) and the IEA coordinating meetings for Large tokamaks and Poloidal divertors (June 28-29). These meetings were both held in Cadarache France organized by the CEA. Bruce attended the ITPA CC meeting as co-chair of the ITPA SOL/ divertor group. Discussion centered around the future of ITPA as ITER gets going. The EU point of view was that ITPA should be come part of the IT. Other partners and the leaders of the ITPA groups argued for a broader mission. Drs. Ikeda and Holtkamp attended the meeting. Holtkamp pointed toward the independence of ITPA as being very positive in that ITPA could point out to IT when there were problems or issues that needed to be addressed. Bruce also attended the IEA coordinating meeting. The central issue discussed there was whether to replace all the implementing agreements and bilateral agreements with one 'fusion' implementing agreement that would cover all activities from engineering to physics to databases as the machines come and go. There was general support for this. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly