Alcator C-Mod Weekly Highlights May 14, 2007 FY2007 weeks of research operations: tentative target: 15 weeks Completed: 3.45 weeks Operations ---------- Plasma operations continued at Alcator C-Mod last week. Two run days were scheduled and completed in support of Miniproposals in the operations and edge/divertor topics. A total of 49 plasma discharges were produced with a startup reliability of 75%. Plasma operation is planned to continue this week. Operation Details ------------------ On Wednesday we carried out the first boronization of the current campaign, employing a new technique for localizing the ECDC flux and boron deposition using a vertical field in addition to the standard toroidal field (MP#470). The quartz microbalances (QMBs) and probes on the surface science station (S^3) were used to monitor and diagnose the deposition of the boron film. The boronization was carried out over a period of about five hours, most of which was spent with the ECDC resonance held at a single location while the S^3 position and orientation were scanned to study the deposition profile. The operating pressure was also reduced by about a factor of three relative to our previous boronization process, as this was found to improve the axisymmetry of the discharge as well as the radial localization. The basic conclusion of the s3 radial scan is that the local boron deposition rate is mostly strongly linked to plasma flux as diagnosed with the probe. The deposition measured by the QMBs was peaked about 10cm outside the EC resonance, consistent with the estimated location of the upper hybrid resonance. The peak rate on the QMB oriented perpendicular to the field was 8nm per 3 minutes, which, taking into account the field pitch angle, corresponds to a rate of ~20nm/hour for horizontal surfaces. A restricted radial scan of the resonance location from the inner wall to R=65 cm (well inboard of the RF antennas) was performed for about 45 minutes. Plasma operation on Thursday was principally devoted to evaluation of the fresh boronization carried out on Wednesday. In another departure from the standard boronization process, no additional ECDC was carried out prior to the start of the run. A steady EDA H-mode was obtained on the first shot of the day, with a total of 1.5MW of ICRF heating. Molybdenum levels were reduced by an order of magnitude from pre-boronization levels. Coating of unshuttered lenses and windows was reduced relative to previous boronizations, and the D- and E-port ICRF antennas did not seem to require significant reconditioning, implying that the application of the vertical field and restricted resonance scan was successful in avoiding unwanted film deposition at large R. However, after the first few shots the molybdenum levels and radiated power fraction began to increase, and the H-mode behavior degraded. It seems clear that the total boron thickness was not sufficient for sustained high performance operation. It also appears that the location covered did not include all of the important surfaces. The run on Friday supported MP#480 "Topology effect on SOL total flow vector", from the Divertor and Edge Physics group. These experiments are designed to explore the role of scrape-off layer flows in the transport of the edge plasma, and employ an array of scanning probes including the newly-installed Wall-Actuated Scanning Probe (WASP). A series of ohmic discharges including Lower and Upper single null and near Double null configurations, at a range of densities were investigated. Direct measurements of the flows and determination of the fluctuation-induced transport fluxes were obtained. Program Planning ----------------- The C-Mod Experimental Program Committee met on Monday to review miniproposals for near-term experiments. Eight MP's were approved. ICRF Systems ------------- The addition of SF6 in the ferrite tuners allowed larger voltages, up to ~30 kV, and power, up to 1 MW, to be applied but one tuner has continued to arc at higher voltages. We plan to test into vacuum conditions to investigate the arc location and are investigating placement of some pre-matching to reduce RF fields in the tuning network. We have successfully implemented a new gate board in FMIT#1, and will soon replace the remaining gate boards in the other transmitters. Lower Hybrid System -------------------- The lower hybrid system was not required for plasma operations last week. Maintenance activities included inspection of the waveguide system and cleaning of spare circulators. Test fixtures for a new optical waveguide arc detector system have been fabricated and are being installed. Long Pulse Diagnostic Neutral Beam System ------------------------------------------ The DNB was operated into C-Mod plasmas last week during both Thursday and Friday's runs for 1.4 s pulse lengths at 50kV with modulation. Some beam over-current faulting was evident on Thursday at beam currents of approx. five amps, but the condition causing the spurious faults was repaired prior to Friday's run. Beam currents on Friday were in excess of six amperes. Travel and Visitors -------------------- Paul Bonoli, Yijun Lin, Alex Parisot, Andrea Schmidt, Greg Wallace, Randy Wilson (PPPL), John Wright, and Steve Wukitch attended and presented recent results at the 17th Topical Conference on Radiofrequency Power in Plasmas in Clearwater Florida. Paul Bonoli, Yijun Lin and Steve Wukitch also attended the first USBPO Plasma-Wave Interactions Workshop following the Topical Conference. Jerry Hughes participated in the ITPA Pedestal topical group meeting in Garching from May 7-10, as well as joint sessions with the Divertor/SOL Topical Group. Bruce Lipschultz was also in Garching to participate in the Divertor/SOL group meeting. In addition, Dennis Whyte and Amanda Hubbard participated in these meetings from MIT using remote conferencing tools. Martin Greenwald, Joe Snipes, and John Rice participated in meetings of the ITPA topical groups on confinement, databases, modeling and transport in Lausanne, Switzerland, May 7-10. Rice chaired the Rotation Working Group session on May 8. Catherine Fiore attended a workshop sponsored by the APS Committee on the Status of Women in Physics entitled "Gender Equity: Strengthening the Physics Enterprise in Universities and National Laboratories" which was held at the American Center for Physics in College Park, MD. The attendees included physics department chairs from 50 top research universities as well as national laboratory directors or designates from 17 National Labs. The workshop, which was jointly funded by DOE and NSF was also attended by a number of deputy and associate directors from the Office of Science at DOE as well as NSF division and program directors. Catherine served on the steering committee for this workshop. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly