Alcator C-Mod Weekly Highlights March 24, 2008 FY2008 weeks of research operations: Target: 15 weeks Completed: 9.7 weeks Operations ---------- Research operations continued at Alcator C-Mod last week. Two run days were scheduled, but a vacuum leak curtailed operation on Wednesday. A total of 30 plasma discharges were produced with a reliability of 56%. The successfully completed run on Tuesday supported an experiment of the Transport and Rotation studies groups. Following the tokamak plasma operations on Wednesday, an experiment using the boronization system and the Surface Science Station (S^3) was carried out to characterize discharge parameters and deposition profiles using a mixture of 20% diborane (B2D6) and 80% helium, for comparison with our standard 10% diborane 90% helium mixture. Thursday and Friday were scheduled maintenance days, with the primary focus of returning the FMIT#3 ICRF transmitter to service. Electron cyclotron discharge cleaning (ECDC) has been carried out over the last few days to ameliorate the effects of Wednesday's vacuum incident and associated disruptions. Plasma operations are planned to continue this week. Operation Details ----------------- The run on Tuesday was dedicated to MP#519, "Main ion rotation and temperature measurements in helium plasmas". Spectroscopic measurements of the HeII line at 468.6 nm, enhanced by charge exchange with the diagnostic neutral beam, were employed to determine temperature and velocity profiles in the edge and pedestal region of helium majority plasmas. Data were obtained in both L-mode H-mode discharges, with the best signal to noise obtained in stationary L-mode plasmas. Spectra were obtained for four spatial locations viewing the beam toroidally and poloidally during shot-to-shot scans of plasma density and ICRF power. Run Planning ------------- A meeting of the C-Mod Experimental Program Committee was held on Monday, March 24, to discuss plans for the remainder of the FY08 experimental campaign. Priorities for the remaining five-plus weeks of operation, including program milestones and completion of student theses, were discussed. A tentative timetable was established for frequency changes of the FMIT#3&4 ICRF transmitters to 50 MHz and 70 MHz. We do not presently envision carrying out any reversed field experiments this year. Lower Hybrid ------------ Initial analysis of MSE data obtained during LHCD experiments on March 20 indicates changes in the measured pitch angle of up to 25% during the LH pulse. Radial profiles of the pitch angle during LHCD relative to the preceding ohmic phase clearly show the dependence on LH phasing. ICRF Systems ------------- FMIT transmitters #1 and 2 (D- and E-port antennas) operated successfully during plasma experiments last week. The J-port antenna system remained unavailable due to the loss of the FMIT#3 final power amplifier (FPA) tube. On Thursday we began the process of replacing this tube with one from FMIT#1, in order to restore full power to the J-port antenna. A spare with a lower power rating will be placed in FMIT#1, which is considered less crucial for near-term experiments than the frequency tunable J-port system. Diagnostics ----------- The new dual laser FIR lasers for the polarimeter diagnostic was set up and successfully brought online by the vendor's engineers on Monday. Design of the PLC system for control of this diagnostic has begun. Travel and Visitors -------------------- Martin Greenwald, Igor Bespamyatnov, Istvan Cziegler, Eric Edlund, Darin Ernst, Catherine Fiore, Jerry Hughes, Alex Ince-Cushman, Brian LaBombard, Liang Lin, Ken Marr, Rachael McDermott, Miklos Porkolab, John Rice, Bill Rowan, Steve Scott, Noah Smick, and Joe Snipes participated in the 21st US Transport Task Force Workshop in Boulder, CO last week. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly