Alcator C-Mod Weekly Highlights May 9th, 2011 FY2011 weeks of research operations Target: 15 weeks Completed: 14.5 weeks Plasma Shots: 1706 Physics ------- Andrea Schmidt successfully defended her thesis last week on May 3rd. Her thesis, submitted to the MIT Physics Department, is entitled "Measurements and Modeling of Lower Hybrid Driven Fast Electrons on Alcator C-Mod". An experiment in which lower hybrid (LH) power is square-wave modulated on a time scale much faster than the current relaxation time and does not significantly alter the poloidal magnetic field inside the plasma, and thus allows for realistic modeling and consistent plasma conditions for different n|| spectra. Inverted hard x-ray profiles show clear changes in LH-driven fast electron location with differing n||. Inverted hard x-ray profiles show clear changes in LH-driven fast electron location with differing n||. Boxcar binning of hard x-rays during LH power modulation allows for 1 ms time resolution, which is sufficient to resolve the build-up, steady-state, and slowing-down of fast electrons. Ray-tracing/Fokker-Planck modeling in combination with a synthetic hard x-ray diagnostic shows quantitative agreement with the x-ray data for high n|| cases. The time histories of hollow x-ray profiles have been used to measure off-axis fast electron transport in the outer half of the plasma, which is found to be small on a slowing down time scale. DoE Quarterly Review -------------------- The C-Mod DoE Quarterly review (FY2011, Q2) was held on Thursday, May 5. The review was carried out by videoconference with participants from MIT, FES (Germantown and San Diego), PPPL and U. Texas. Presentation viewgraphs from the review are linked at http://www.psfc.mit.edu/research/alcator/pubs/Q_Reviews/Q-rev_May_2011/q-rev_may_2011.pdf DoE Early Career Research Program --------------------------------- The DOE Office of Science announced last week its selections for five-year awards under the Office's Early Career Research Program. One of these awards went to Professor Anne White, in the MIT Department of Nuclear Science and Engineering. Her application is titled "Electron Temperature Fluctuation Measurements and Transport Model Validation at Alcator C‐Mod". The 65 awardees, encompassing all research areas supported by the Office of Science, were selected from a pool of about 1,150 university- and national laboratory-based applicants. Selection was based on peer review by outside scientific experts. More details on the program can be found at http://www.science.energy.gov/news/in-the-news/2011/05-06-11/ Operations ---------- Work continued invessel on diagnostic calibrations and preparations to the vessel walls for installation of the new ARRA funded rotated antenna. ICRF Systems ------------ The new ARRA funded rotated antenna is undergoing a test fit-up. We have found some locations where rf breakdown could be an issue. Modifications to the internal side plates that are mounted between the current straps are being considered to improve the rf breakdown capabilities of the antenna. Some antenna components will have edges radius-ed to a greater degree. Sample plating tests are continuing to qualify vendor procedures prior to production plating. Lower Hybrid System ------------------- Work continued on testing of a fast ferrite waveguide tuner based on garnet. Further measurements for different sizes and magnetic configurations were taken last week to determine the best arrangement. The new prototype is now ready for high power testing, planned to begin this week. A boroscope inspection of the LH launcher was completed. 62 of the 64 windows are in good condition. Window 7D has what appears to be a copper coating on the plasma side of the window. Window 16B has what appears to be a stainless steel blob of metal across the mid-plane of the window on the plasma side. These windows may require cleaning before pumpdown. A calibration of the LH launcher radial position was performed. The new calibration is in good agreement with the calibration performed last year. Work continued on debugging problems with the voltage controlled phase shifters and attenuators for the low power microwave control system. A comparison of current and former calibration shots shows significantly more noise in the current calibrations. Tests are being performed to isolate the source of the noise in the system. Diagnostics ----------- Representatives from one of the vendors being considered to supply Nd:YAG lasers for a planned upgrade of the Thomson scattering diagnostic, visited with Jerry Hughes to discuss their proposal. Travel and Visitors ------------------- Prof. Brian Worth from University of Tennessee visited to discuss numerical modeling of plasma-surface interaction. In particular, modeling and diagnosis of tungsten/molybdenum nano-tendrils was discussed, including recent C-Mod experiments that successfully developed fuzz in the divertor. Prof. Worth is one of the principal investigators of the PSI Science Center The PSFC participated in the campus wide open house held in celebration of MIT's 150th anniversary on Saturday, April 30th by hosting 4 tours of Alcator C-Mod and 3 demonstrations by Mr Magnet (Paul Thomas). Of the 20000 people on campus, approximately 400 made their way to the PSFC to learn about plasmas and magnets. The hour long tours of C-Mod, run by graduate students Goeff Olnyk and Bob Mumgaard, were attended by 130 people from the surrounding communities. In preparation for an upcoming ITER STAC meeting, the US STAC members requested a briefing via teleconference from several US scientists familiar with certain critical issues on ITER. This included C-Mod scientists Steve Wukitch and Robert Granetz, who updated the US STAC members on ICRF hardware and disruption mitigation requirements respectively. The 2011 International Sherwood Fusion Theory Conference was held May 2-4 in Austin, TX. In attendance from MIT were Peter Catto, Bruno Coppi, Antoine Cerfon, Darin Ernst, Jeff Freidberg, Matt Landreman, Bo Li, P. Rebusco, Jesus Ramos, Linda Sugiyama, Anne White, and T. Zhou. Dr. Matt Landreman gave an invited talk on “Neoclassical flow, Current, and Electric Field in a Quasi-Isodynamic Stellerator”. Experimental investigation of the I-mode, disruption mitigation, edge pedestal studies, and core turbulent transport are active areas of the Alcator C-Mod research program and theoretical work on these areas was the focus of many presentations at the Sherwood conference. Posters directly related to C-Mod experiments included those by B. Coppi and T. Zhou on the I-mode regarding the connection between the Heavy Particle Mode and the observed Weakly Coherent Mode, X. R. Fu (UT Austin) on turbulent impurity transport in C-Mod and A. E. White on the gyrokinetic simulation-based design of the new Correlation ECE system on C-Mod. Many Sherwood presentations focused on theory and models of intrinsic rotation in tokamaks, including those by Felix Parra and Michael Barnes (Oxford, UK), whose work on gyrokinetic theory and simulation of momentum transport was highlighted in the Review Talk “The History and Present Status of Gyrokinetic Theory” given by John Krommes (PPPL). All abstracts, the program and the invited talks from the conference will be available online at the 2011 Sherwood Conference website http://ptolemy.ph.utexas.edu/ _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly