Alcator C-Mod Weekly Highlights October 18, 2010 FY2011 weeks of research operations Target: 15 weeks Completed: 0.65 weeks Plasma Shots: 78 Operations ----------- Plasma operations resumed at Alcator C-Mod last week. A fresh boronization was carried out on Tuesday night, and three run days (Wed.-Fri.) were scheduled and completed. All three experiments contributed to the thesis research of graduate students working at Alcator C-Mod. A total of 78 plasma discharges were produced with a startup reliability of over 90%. Runs supported research in the Transport and ICRF Physics areas. Plasma operations are planned to continue this week. Conference ----------- C-Mod was well-represented at the 23rd IAEA Fusion Energy Conference in Daejeon, Korea. Participants affiliated with C-Mod included Earl Marmar, John Rice, Yijun Lin, Greg Wallace, Syunichi Shiraiwa, Dennis Whyte, Chuck Kessel (PPPL) , Randy Wilson (PPPL), Val Izzo (UCSD), Miklos Porkolab, Bob Granetz, Peter Catto, Wendell Horton (U.Tx.), Orso Meneghini, and Alberto Loarte (ITER). Presentations and papers may be found on the web at www.psfc.mit.edu/research/alcator/pubs/iaea Miklos Porkolab served as chair of the International Program Committee for the Meeting. Physics ------- The final report on the 2010 Joint Research Target milestone was submitted to the US DoE Office of Fusion Energy Sciences on October 8. The primary goal of the milestone was to "Conduct experiments on major fusion facilities to improve understanding of the heat transport in the tokamak scrape- off layer (SOL) plasma..." Coordinated experiments were carried out on Alcator C-Mod, DIII-D, and NSTX, and a number of important results were obtained. All high level goals of the milestone were met. The 207-page document can be found at http://www.science.energy.gov/ofes/ProgramTargets/FY2010_JRT_Q4report_final.pdf A number of C-Mod presentations at the upcoming APS-DPP meeting are related to this research, including two invited talks (LaBombard, Loarte) and three contributed talks/posters. This research motivated the build-up of a diagnostic infrastructure on C-Mod that will continue to yield valuable results well beyond the time period of the milestone. Operations Details ------------------ Wednesday's run primarily supported MP#572 "Detailed scan of low collisionality H-Modes". This was the first day of operation following a three-week maintenance interval, and the day began with a sequence of power system tests to verify operation of these systems. Several plasma shots were then devoted to refining the density calibration of the Thomson Scattering diagnostic using ECE cut-offs (MP#296), verifying diagnostic alignments, and conditioning the ICRF antennas. The objective of MP#572 is to use the correlation reflectometry system to study the density fluctuations inside the pedestal of low collisionality H-Modes. The peakedness of the density profile has been found to depend on collisionality, with lower collisionality correlating with more peaked profiles. The increased density peakedness inside the pedestal is necessary for O-mode reflectometry cutoff localization. A target shot with a steady EDA H-mode and satisfactory density peaking was established by the end of the day, but more runtime will be required to complete the experiment. Thursday's run was dedicated to MP#598 "Impurity Transport Studies in L and H-Mode Plasmas Using the Modified HIREX Sr. Spectrometer". The spatially resolving HIREX_SR soft xray diagnostic was configured to observe emission from Ca, which was injected (in the form of CaF2) by the laser blow-off (LBO) technique. Impurity transport was documented under a variety of plasma conditions, including an L-mode power scan, low-collisionality H-modes at low plasma current, and I-modes. These data are being analyzed. On Friday we carried out the first day of dedicated experiments in support of MP#606 "Measurements of Mode Converted Waves in D-H Plasmas with Phase Contrast Imaging". This phase of the experiment was carried out with a low hydrogen fraction H/(H+D)~.05. The goal is to have measurements in steady RF heated plasmas, with optimum parameters for PCI. Each ICRF antenna was operated separately at different power levels to see the minority tail effects on wave damping. Three ICRF frequencies (78, 80, and 80.5MHz) were employed, and the phasing of the four-strap J-port antenna (78MHz) was varied from heating to co- and counter-current drive orientation. The majority of the experiment was carried out using upper-null equilibria to avoid H-mode transitions. The toroidal field was adjusted to 5.6T to position the mode-conversion layer appropriately in the field of view of the PCI diagnostic. These data are being analyzed, and a second day of operation, at higher minority concentration, is planned. ICRF Systems ------------ The ICRF system was operated in support of operations last week for the first time since installation of the new solid state amplifiers in FMIT#1 and #2 (which feed the D- and E-port antennas, respectively). The new amplifiers operated well up to 1 MW total output but appeared to cause a transmitter blanking at high power (>1.5 MW). The cause of this effect is being investigated. A faulty instrumentation cable which initially inhibited operation of FMIT#2 was identified and repaired. FMIT#2 was then operated up to 2.1 MW into L-mode, with pulse width limited by the blanking issue mentioned above. On Wednesday, reconditioning of the J-port antenna following boronization was compromised by having used a boronization recipe that called for boronizing the antenna straps. During the previous campaign, we found that boronizing the straps was unnecessary and had developed a recipe that only coated the limiters and protection tiles and minimized the antenna recovery time to just a few discharges. During Friday's run, the FMIT#3 stub tuner required adjustment; the stub tuner will be examined during the maintenance day. Lower Hybrid System -------------------- Two new klystrons, purchased under ARRA funding, arrived at MIT on Tuesday, and have passed initial inspections for physical condition, vacuum, filament continuity, isolation, and HV standoff. Testing of the high power "Magic Tee" multijunction setup proceeded last week. Diagnostic Neutral Beam Systems ------------------------------- The DNB operated successfully in support of plasma experiments last week. Travel and Visitors ------------------- The MIT Energy Initiative External Advisory Board, chaired by former Secretary of State George Schultz, visited the PSFC for a briefing on fusion energy and a tour of the C-Mod experiment. The board consists primarily of leaders from industry and academia, as well as former government officials. A contingent of C-Mod physicists (listed above) attended the IAEA Fusion Energy Conference in Daejeon, Korea, last week. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly