Alcator C-Mod Weekly Highlights March 13, 2000 Alcator C-Mod is now undergoing ECDC conditioning of the vessel wall. ECDC will be in operation more or less 24 hours a day over the next two weeks as we prepare for plasma startup. Work continues on the RF and DNB systems, and diagnostic installation. Engineering: ----------- ECDC was begun last Tuesday. Cleanup of the vessel surfaces has been going well, with our primary interest being the the reduction of water and hydrogen in the machine. The light from the ECDC has also been useful for testing and aligning new TV views of the antennas. The alternator came back online this week. It was brought up to half speed on Wednesday, vibration levels were checked, and all systems were checked for proper operation. New signals monitoring the exciter supply have been added to the CAMAC system. The diborane system has been moved from under the diagnostic stand to the cell entry vestibule. This change gives much better access to the diborane cabinet while also freeing up valuable real estate near the machine. Re-routing of control cables, gas lines, and vents was required. DNB --- All filament and arc supply gate and voltage regulator boards were tested and adjusted as required for proper regulation in dummy loads. Gate block circuits were added to all filament supplies to block gates if the setpoint is below a couple of volts; all were tested successfully. Smoothing capacitors were tested on filament 2 supply with marked improvement in ripple. We will be adding these capacitors to each of the four filament supplies. The filament cables and connectors were inspected, and problems identified by testing with 100A at 10V. The filaments were characterized and documented. Parallel cables were added for the longest straight run of filament cabling, to reduce the voltage drop, and the tests were repeated. The data are being analyzed to evaluate the improvement. ICRF: ----- We completed modifying the resonant loops on D and E-port to move the feed point to a high voltage point. This required shortening the 36" probe section to 17.3" and 12.5" for D and E-port, respectively. Impedance measurements indicate that loop lengths correspond to 80.1 MHz and 80.3 MHz for D and E-port, respectively. During the disassembly process, E-port feedthru #3 (numbered from top of the port down) was found to have a loose center conductor connection. It had arc damage and required a rebuild. We made measurements so that a single piece could be made to eliminate this assembly problem. Transmitter tuning and testing is being repeated due to identification of a calibration error in the diagnostics used in tuning the transmitters. We have requested RF engineering support from PPPL and expect C. Brunkhorst to visit this week. Physics: -------- The TCI interferometer is back in operation. Changes have been made to the plasma arm to allow measurements to be made somewhat farther out in major radius. The radial coverage has also been reduced to increase the radial resolution on the outer channels. These changes also allowed nearly 3 meters of optical pathlength together with several large mirrors and mounts to be removed from the plasma and reference arms which should improve alignment stability. The new visible TV view of the E-port antenna is operational. Gerd Schilling continued work on the C-Mod collaboration Field Work Proposal, and prepared the C-Mod contribution to the US - Japan RF Workshop to be held at PPPL March 14-16. Visitors and Travel -------------------- Bruce Lipschultz traveled to JET to participate in US-JET collaboration discussions held March 7-9. He was part of a group representing the different US laboratories as well as particular physics areas. Bruce collected from US labs proposals for work on edge physics for JET for 2001-2002. The meeting was very helpful for understanding the JET program and their plans. The JET task force leades expressed strong interest in a number of US proposals including those from MIT. Bruce also spent part of 3/9 and 3/10 discussing a number of physics issues with the JET edge/divertor group. These discussions centered around similarities between C-Mod and JET in the area of wall-recycling. He brought back some typical JET data for comparison with C-Mod results. He also gave 2 presentations - SOL transport and wall recycling, and Mo impurity sources and their effect on the core plasma.