Alcator C-Mod Weekly Highlights July 20, 2009 FY2009 weeks of research operations Target: TBD Completed: 1.2 weeks Discharges: 220 Operations ----------- Plasma operations continued on Alcator C-Mod last week. A total of 93 discharges were produced during four days of plasma operation, with startup reliability of 80%. The runs continued the ICRF commissioning process, and also supported two miniproposals, in the Boundary and ICRF topical science areas. Machine cleanliness continued to improve, and the H/(H+D) ratio was reduced to the 10-20% range during Friday's run. Commissioning of the D- and E-port antennas continued on Tuesday, with each being conditioned up to ~1MW, and overlapping of the two rf pulses accomplished, keeping the total power at 1MW. The disruptivity was increased during the second pulse, as was density evolution (outgassing) associated with the ICRF. The H/D ratios were typically above 10%, too high for efficient minority heating. The runs on Wednesday and Thursday were devoted to MP#557, "Commissioning of new divertor heat flux diagnostics". The goal of this experiment was to test and optimize the performance of the new set of diagnostics, including surface and bulk thermocouples, tile calorimeters, and a new IR camera, which have been installed to diagnose the heat flux to the lower divertor and limiters. These diagnostic systems are expected to contribute to the proposed FY2010 USDoE Joint Facilities Milestone "Conduct experiments on major fusion facilities to improve understanding of the heat transport in the tokamak scrape-off layer (SOL) plasma, strengthening the basis for projecting divertor conditions in ITER". The scanning probes were also conditioned during these discharges. Plasmas with a controlled outer divertor strike point were developed, allowing the heat flux to be delivered to a specified constant location during the shot. On Wednesday the strike point was positioned at three different sensor locations, with data obtained simultaneously on the IR camera and surface thermocouples, as well as the tile calorimeters and Langmuir probes. On Thursday these results were extended by carrying out a fine-scale scan of plasma density from 0.8 to 1.3e20/m^3 with a fixed strike-point location. As the density was raised and the divertor transitioned from sheath-limited to high-recycling, there was a noticeable decrease in energy arriving on the divertor (reduced tile delta-T there) and increase in energy arriving on the GH and AB outboard limiters. Quantitative analysis of these data is in progress. Optimization of the IR camera diagnostic was also carried out, including installation of a plasma light filter for the higher density shots. Long time exposures were recorded to facilitate cross-calibration with respect to the tile temperatures measured by the tile thermocouples. Line-outs of the raw IR level across the divertor target showed smooth decays on both sides of the peak heat flux location. The peak often displayed a double maximum feature; this phenomenon is being investigated. Friday's run supported MP#558 "Characterization of RF sheaths during ICRF". This experiment began characterization of RF sheaths in low single pass regimes with the recently installed Katsumata and B-dot probes adjacent to the A-B limiter. Density and current scans were carried out in a standard LSN discharge at 5.4T. Staircase RF waveforms at power levels of 0.5, 0.9, and 1.3MW were employed for both D- and E-port antennas. The B-dot amplitude was highest with D antenna for 0.8 MA - 1.2 MA and the floating potential also responded most strongly to D antenna over the same current range. At 0.6 MA, the B-dot and Katsumata probes respond to both D and E antennas. Current scans were completed at densities (nebar) of 8e19 and 1.2e20/m^3. Further experiments, including scans of toroidal field and observations in He majority plasmas are planned. Plasma operations are planned to continue this week. Physics -------- C-Mod researchers submitted abstracts for 31 contributed posters, 12 contributed orals in the C-Mod session, 3 contributed orals in the ITER support session, and 7 invited/tutorial presentations for the upcoming APS meeting in Atlanta. In addition, Prof. Miklos Porkolab will be giving the Maxwell prize talk. ICRF Systems ------------ The D and E antennas have been operated to ~1.3 MW independently for short pulses, and were used in support of the experiment on Friday. The coaxial transmission network for the J-port antenna is being readied for operation. Both J-port transmitters have now been operated to ~2 MW into dummy load. For FMIT#3, a new tuning procedure was evaluated and found to be efficient. The driver output was matched to 50 ohm load. We then used only the FPA input load and tune to match the Driver to the final. Lower Hybrid System ------------------- Testing of analog fiber modules for the Transmitter Protection System (TPS) was begun, and initial results are satisfactory. Work continued on the Coupler Protection System (CPS) Upgrade. DNB System ---------- Repair of the arc source is proceeding. Diagnostic Systems ------------------- A scan of the vertical position of the H-port ECE diagnostics was carried out during the runs on Tuesday and Wednesday. This both confirmed the vertical alignment of the system and showed that far off axis measurements are feasible, which may be useful for future studies of non-thermal emission with LHCD. The core Thomson scattering diagnostic is now operating with both available laser sources, allowing 60 measurements per second. The FRCECE electron cyclotron emission diagnostic has been calibrated and made operational and is now available for experiments. Travel and Visitors -------------------- Bruce Lipschultz traveled to Cadarache, France, for a 2 day meeting (July 15-16) of the ITPA Coordinating committee. As chairman of the SOL/Divertor committee he presented a summary of work occurring over the past year and plans for the coming year. The information presented included both aspects of research done and development of R&D plans to address ITER high priority needs. Martin Greenwald traveled to PPPL for the kick-off meeting of the FSP (Fusion Simulation Program). The annual meeting of the US Plasma Facing Components community was hosted by MIT PSFC (Dennis Whyte) from July 8-10. The 35 attendants presented their research highlights from the last year and discussed PFC research directions and priorities. Perry Phillips (U. Texas) visited MIT last week to work on the FRCECE diagnostic system. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly