Alcator C-Mod Weekly Highlights May 10, 2010 FY2010 weeks of research operations Base Target: 13 weeks Base Completed: 9.7 weeks ARRA Target: 5 weeks ARRA Completed: 5.0 weeks Plasma Shots: 1630 DOE Visit --------- Last Tuesday, Dr. Bill Brinkman, Director of the DOE Office of Science, and Ms. Abby Benson, Assistant Director of the MIT Washington Office, visited MIT. At the PSFC, they met with Earl Marmar and Martin Greenwald, and were given a tour of the C-Mod facility. ITER Divertor Gas Injection --------------------------- Last August, MP#563 "Toroidal asymmetry of impurity seeding in support of ITER divertor gas injection requirements" was run on C-Mod. This experimental program was proposed by Richard Pitts, ITER Org, to help define the number of toroidal gas injection locations required for ITER. Significant, systematic, toroidal asymmetries in nitrogen were seen as gas was puffed from five toroidally spaced divertor capillary locations. Asymmetries were observed in NV radiation, the AXUV diodes responses looking clockwise and counter-clockwise toroidally, and in neutral pressures as measured by in-vessel Penning gauges. The ITER baseline design has been modified to increase the number of gas box locations from one to four, in large part because of results obtained during these experiments. This work was done in close collaboration with Brian LaBombard, Bruce Lipschultz, Matt Reinke, and Jim Terry. Physics ------- We have continued the 1D finite-difference time-domain numerical study of scattering of rf waves in the presence of LH driven density fluctuations at wavelengths planned for the new reflectometer. A localized density perturbation was allowed to propagate in the plasma, and both up-shifted and down-shifted signals were analyzed. Previously observed phenomena in a COMSOL finite element simulation can be partly explained by 1) adopting a wave-matching condition and 2) modifying the dispersion relation of the probe beam. However, it was also observed that, depending on the fluctuation wavenumber profile, the position where maximum response occurs can be shifted. Further analysis and comparison with COMSOL is planned. Data analysis from FY08 lower-hybrid discharges shows an effect on the Lyman alpha mid-plane spectrometer. The radial peak of the Lyman alpha emissivity shifts farther into the scrape-off-layer (SOL) away from the last closed flux surface with the application of lower hybrid power. This effect scales with density and applied Lower-Hybrid power, which may indicate lower hybrid power loss into the SOL. It is important to note that the spectrometer does not view the field lines directly connected to the lower-hybrid launcher. Analysis will continue looking specifically for time-dependent effects during discharges with rapid 100% modulation of the lower hybrid power. Operations ---------- In-vessel work continued last week. The stainless steel upper divertor cryopump gas shields that were deformed during the last run period are being replaced with Inconel 625 for added strength. Refurbishment of the in-vessel flux loops began last week with removal of the wall modules and heat shields required to gain access to the loops. New TZM tiles are being delivered by our machine shop for cleaning, baking, and installation. MDSplus ------- The MDSplus Data Management System has been submitted to MIT's Technology Licensing Office so that it can be formally licensed for open source distribution. A BSD open source license has been requested. Lower Hybrid System ------------------- All external work on the lower hybrid launcher has been completed and final preparations are being made for installation in the vacuum vessel port. Our vendor has begun high power testing of three of our new klystrons. ICRF Systems ------------ All five (four plus a spare) vacuum feedthroughs procured for the new Advanced ICRF Antenna have been successfully tested at high power. Diagnostics ----------- Work continued last week on the control, AC power, signal feedthrough panels, optical mounts, and gas system for the polarimeter. Setup and alignment of the optical components for the single chord system has begun. Travel and Remote Participation ------------------------------- Miklos Porkolab was in Vienna, Austria all last week for a meeting of the IAEA International Program Committee. He is the Chair of the committee. Igor Bespamyatnov and Ken Liao, UT-FRC, were at MIT last week working on the WideView CXRS optical systems. Steve Wukitch was in California last week visiting our vendor for ICRF tubes and klystrons. Earl Marmar participated remotely by teleconference in the 25th Executive Committee Meeting of the IEA Implementing Agreement for Cooperation among Large Tokamak Facilities, which was held in Aix-en-Provence, France, on Sunday, May 9. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly