Alcator Weekly Highlights August 4, 2003 Alcator C-Mod continues a period of maintenance. Work proceeded last week on preparations for the alternator inspection, high power testing of lower hybrid components, and work on ICRF systems. Physics ------- Stewart Zweben, PPPL, was at MIT this week to continue analyzing data from the "Edge Minority Heating" experiment in June. First results from TRANSP runs done by Catherine Fiore suggest a significant fraction of minority ion tail loss for the inner edge resonance location. First analysis of the fast GPI diode data show an apparent reduction in edge light fluctuations during edge RF; however, this effect may be due to profile changes rather than electric field changes, since the frequency spectrum does not change significantly with RF. Operations ---------- Alcator C-Mod is now at room temperature and the vessel heaters have been turned off. Maintenance work on the cryostat and LN2 cooling system will begin this week. Preparations for the alternator inspection which will begin early this week have continued. The 2 MW drive motor has been removed from the drive train. Instrumentation and electrical connections have also been removed. Vendor equipment needed for the inspection has arrived on-site. Lower Hybrid Project -------------------- At MIT, the first high power tests of the lower hybrid rear waveguide assembly (RWG) were conducted successfully last week. From 35 to 60 kW of power for up to 250 ms was delivered to several of the coupler channels. The tests were limited by arcs in the waveguide delivering power to the RWG from the cell. We are investigating the cause of these arcs. This waveguide run is temporary and was set up for these tests only; it will not be used when the system is installed onto C-Mod. Nevell Greenough, PPPL, spent last week at MIT working with Monty Grimes to complete the RWG testing. A decision has been made by PPPL and MIT to remove the ceramic window bricks from the titanium couplers based on the results received from a series of prototype coupler braze tests performed by our vendor over the past month. A new set of test brazes will be performed on prototype couplers that will have the ceramic windows removed using a braze removal process being developed by another of our vendors. In parallel, a purchase order will be awarded to have 150 new ceramic bricks fabricated and metalized to facilitate re-brazing with new ceramic bricks if the old bricks are not usable. This new scope will reduce the risk of failed braze attempts on the four couplers and also remove and replace several ceramic windows that cracked during the initial brazing process. MIT and PPPL worked together to analyze the mechanical stresses in the titanium couplers and ceramic windows induced during the braze process. There is some concern that the ceramic windows will crack when they are removed from the couplers. This issue also relates to the cracks seen in some of the ceramic windows. MIT will continue this analysis work and try to identify the source of the cracking. Low power testing of the forward stacked waveguide assembly (FWG) was completed at PPPL this week with very good results from 91 of the 96 waveguides (losses less than 0.4 db). Five channels have losses greater than 0.5 db and will be reworked to reduce these losses to an acceptable level. To investigate the value of hand polishing discolored blotches on the copper plating, PPPL will disassemble one FWG stack and hand polish five adjacent plates at one end of the stack. After polishing, the plates will be reassembled into the stack and re-tested at low power to determine the effect of polishing on losses. The polishing fixture was delivered from the local machine shop this week to support this effort. A decision will be made next week on whether to polish all the plates or to start final assembly of the FWG. ICRF Systems ------------ A driver grid capacitor and some associated interlock instrumentation have been repaired on the FMIT #2 transmitter. Testing and tuning of the driver is planned for this week ICRF related hi-yard equipment has been inspected as part of routine maintenance of these systems. Travel and Visits ----------------- Miklos Porkolab and Martin Greenwald traveled to Gaithersburg, Md to attend a meeting of the Fusion Energy Sciences Advisory Committee on Thursday and Friday of last week.