Alcator C-Mod Weekly Highlights July 28, 2003 Alcator C-Mod has completed it's experimental campaigns for fiscal year 2003, and is currently in a maintenance period. The tokamak is in a standby mode. Data analysis and modeling of results from the campaign is continuing. The regular Quarterly Review of the C-Mod Program was held by video-conference on Monday, July 21, with participation from MIT, PPPL, U. Texas, and DoE OFES. Presentations are available at http://www.psfc.mit.edu/cmod/sciprogram/Q_rev_Jul03/ Physics ------- Analysis of locked mode data with Ip=1 MA, BT=5.4 T indicates that the range of densities at which the mode appears is reduced from 1.7e20/m^3 with adverse (i.e. destabilizing) applied 2/1 field to less than 4e19/m^3 with stabilizing applied field. The factor of >4 in the accessible density indicates that we are able to compensate the intrinsic error very well in the "best" case. As previously noted, the C-Mod experiments appear to contradict earlier size scalings for the threshold error field for mode locking which predicted B_lock ~ R^(-9/5) by a factor>10. The threshold density inferred from 1MA, 5.4T C-Mod discharges is about a factor of 2 above predictions of dimensionally constrained scalings based on single-machine fits of DIII-D and JET data. Diagnostics ------------ The two color interferometer CO2 detector (10 channel) is being refurbished and its window replaced with coated optics to improve throughput. ICRF System ------------ FMIT#2 was disassembled and the problem with the driver was identified as a failed screen by-pass capacitor (a kapton sheet between two plates). The kapton sheet was replaced and the tube was successfully hi-potted before reassembly. A control reporting problem with the driver filament air flow has been investigated and a fix will be implemented shortly. Measurements of the D-port resonant loops showed that the high voltage point was off from the expected location. A new configuration has been identified and could be tested in the next campaign. Lower Hybrid Project -------------------- Testing has begun on the rear waveguide system . Tests have been completed on 6 out of 48 waveguides. We are able to run up to 500msec pulses at a power level of 60kW+ and for about 100-200msec at 100kW before transmission line arcing occurs in the long run from the klystrons to the C-Mod setup area. There have been no problems in the rear waveguide so far. Travel and Visitors ------------------- Stew Zweben(PPPL) was at C-Mod 7/21-7/25 to work on analysis of data from the summer run. He reviewed GPI data with Jim Terry, discussed TRANSP runs of MP330 ("Edge Minority Heating for H-mode Control") with Catherine Fiore and Steve Wukitch, and worked on a code to infer velocity fields from the PSI camera data. The camera is being returned to PPPL, and will be reinstalled at C-Mod for the next campaign. Doug Loesser(PPPL) and Bob Childs (MIT) were at Omley Industries in Oregon 7/24-25 for discussions on progress in rebrazing the Lower Hybrid coupler ceramic windows. Nevell Greenough spent the week at MIT reassembling the Lower Hybrid rear waveguide for power testing. Tom Fredian and Joshua Stillerman attended the 4th IAEA Technical Meeting on Control, Data Acquisition and Remote Participation for Fusion Research, held at General Atomics in San Diego. Tom Fredian presented a paper: "Migration of Alcator C-Mod Computer Infrastructure to Linux." Tom Fredian and Joshua Stillerman also attended the 3rd MDSplus users group meeting, also held at General Atomics. Fredian chaired the meeting. There were approximately 40 attendees from the US, Europe, Japan and South Korea. A detailed discussion of "Long Pulse / Continuous extensions to MDSplus" was included in this meeting. Bruce Lipschultz co-chaired the ITPA meeting on SOL/divertor physics held in St. Petersburg Russia the week of July 14, following EPS. A number of studies on ELM cross-field transport were presented. They indicate that although the power delivered to the wall in an ELM may not be a concern, that the potential for sputtering of the wall was significant. A similar concern for the wall also came up with regard to disruption power deposition. JET either has poor energy accounting or a substantial fraction of the disruption energy is going to the wall (primarily during the current quench). The topic of the wall/blanket tile material was thus a hotly discussed topic. There is a concern that a Be wall tile will be melted during disruptions with the damaged surfaces leading to problems during 'normal' operation.