Alcator C-Mod Weekly Highlights May 24, 2004 Invessel work began on Thursday last week with radiation measurements, visual inspections, photographic documentation, and collection of dust samples. Removal and crating of the RFX diagnostic neutral beam was completed, and the DNB has been shipped to Italy. Progress continued on lower hybrid, ICRF, diagnostic, magnet power, and alternator systems last week. Operations ---------- On Monday Alcator C-Mod was backfilled with nitrogen. A 2-1/8" flange suspected of being the source of a very small, hard to find leak was removed and blanked off. The vessel was then pumped down, and a leakcheck on Tuesday confirmed that the leak had been fixed. On Tuesday and Wednesday the machine was brought up-to-air several times and then pumped back down to neutralize heavy boron hydrides. After being left up-to-air overnight on Wednesday, the first invessel work began on Thursday morning. A radiation survey showed relatively high count rates at three limiter locations, the j-port antenna Faraday shield, and at both of the CXRS shutter locations. Lead shielding was placed over these locations, except for the Faraday shield, and the count rate was reduced to near background levels. The Faraday shield will be removed from the vessel early this week. Following this process, a vacuum cleaner fitted with a 1 um filter was used to remove virtually all the visible dust from the vessel. Visual inspections of the PFCs and diagnostics proceeded on Thursday and Friday. Lower Hybrid System ------------------- We successfully concluded high power testing of the rwg this week. The rwg and fwg were subsequently mated without an rf gasket and alignment measurements were taken. The units were then assembled with the rf gasket in place and high power testing was begun of the assembly. Four waveguides have been successfully tested so far with input power of 100 kW and 0.5 s pulses. Testing will continue this week. Updates to control software drivers needed for the phase and amplitude control system have been installed and are performing correctly after an extensive amount of work with the vendor. Simulations performed using a lookup table in real-time to counter act the non-linear effects of the IQ detector have been very successful. A very accurate lookup table can be used at a very small expense in computation time. ICRF Systems ------------ We have removed transmission line hardware up to the vacuum feedthroughs on the j-port antenna. The j-port horizontal flange will be removed and modified to increase high voltage standoff capability. Diagnostic Neutral Beam and Related Diagnostics ----------------------------------------------- Over the past week-and-a-half the RFX short-pulse DNB has been disassembled, removed from the C-Mod cell, crated up, and shipped to the RFX lab in Italy. A new long-pulse beam from Russia will arrive in the autumn to replace it. For MSE an easier method to calibrate the orientation of the transmission axis of a linear polarizer has been developed that is expected to be accurate to 0.03 degrees. Collimated light from an LED is passed through a horizontally-mounted polarizing cube beamsplitter and then through the polarizer mounted on a precision rotating stage. The transmission axis is determined by measuring the apparent direction of the transmission axis as the cube is rotated a few degrees about the vertical direction, with repeat measurements taken with the cube rotated 180 degrees. The intersection of the two trend lines determines the actual orientation of the transmission axis. Measurements of the linear polarizer that will be used in the upcoming in-vessel MSE calibration are in agreement with previous measurements based on a vertically-oriented Brewster window, which was accurate to about 0.1 degrees. Invessel inspection of the MSE optics has determined that all MSE glass optical elements are in good condition. This inspection confirms that steps taken during the last up-to-air to disruption-harden the MSE optics were successful. The plasma-facing MSE lens was found to be coated with an as-yet undetermined material. The in-vessel MSE calibration will be performed both prior to and after cleaning this lens so that the calibration can be used for both the previous run campaign and the upcoming run campaign. Power Systems and MIT Alternator -------------------------------- We continued to prepare for modifications to the power supply gate drive boards last week. Components were ordered, and our machine shop made modifications to the mounting hardware. We also continued maintenance on alternator systems including oil lift pumps, oil filtration, and helium gas coolers. Travel and Visits ----------------- Miklos Porkolab attended the JET 25th Year anniversary celebrations in Culham, England, on May 20th. Miklos as well as Dave Baldwin, General Atomics, represented the US at the celebration. Among the many dignitaries from Europe, European Commissioner for Research, Phillipe Busquin gave the opening speech and talked about the future of JET and ITER. Other historical presentations on JET were given by Drs. D. Palumbo, F. Waelbroek, P. H. Rebut, and F. Troyon. Martin Greenwald gave the physics seminar at the University of California, San Diego last week entitled "Core and Edge Transport in Alcator C-Mod - Connections Across the Separatrix." Steve Scott, PPPL, discussed the needs of experimentalists for comprehensive plasma simulations at the steering committee workshop for the Fusion Simulation Project held last week in Boulder, CO.