Alcator C-Mod Weekly Highlights April 23, 2012 FY2012 weeks of research operations Target: 17 Completed: 5.6 Plasma Shots: 753 Research -------- A comprehensive set of edge fluctuation measurements has been obtained across many L-H transitions and H-L back-transitions featuring steady high-power ICRH above 3 MW. An initial interpretation of the transitions focuses on their apparent dithering nature and its possible indication of limit-cycle interactions between microturbulence and zonal flows. The gas puff imaging system captured these transitions and data is being analyzed to determine the presence of zonal flows. Operations ---------- The vessel has been undergoing a 120 C bake since Thursday, 4/12. On Wednesday, 4/18, Electron Cyclotron Discharge Cleaning in deuterium was begun to prepare the vessel walls for operation. The alternator was successfully brought up to full speed last Friday in preparation for plasma operation. Cycle tests of the data system were successfully completed last week. Final inspections of the magnet power supplies are underway. ICRF Systems ------------ All four FMIT transmitters have been successfully tested into a dummy load and are ready for plasma operation. All rf transmission lines are leak tight and filled with SF6. The E-Port FFT tuners have been reinstalled in the C-Mod cell, and the FFT control and cooling systems are back on-line. Lower Hybrid Systems -------------------- Calibrations for the lower hybrid transmitters have been verified in preparation for plasma operation. Checks of the Collector Over Temperature System (COTS) are underway with pulse lengths of over 1.5 s. Lower hybrid pulse lengths without COTS were limited administratively to 0.5 s. Diagnostics ----------- The initial fourteen fast TCI demodulator boards were completed last week and installed in the TCI rack in the cell. The TCI CAMAC crates and associated old demodulators were removed. The new CPCI system will be capable of a 5 MHz data rate for each of the ten TCI chords. An additional ten demodulator boards will be available soon for high resolution differential measurements (dNL/dr). The 3-chord Polarimeter has been aligned and is ready for plasma operation. Additional acoustic and magnetic shielding has been added to this diagnostic to help reduce vibration induced noise on the polarimeter signals. Remote Participation, Travel, and Visitors ------------------------------------------ Yijun Lin was at the Institute of Plasma Physics of the Chinese Academy of Sciences (ASIPP) from April 9 to April 20 helping to bring up the power of the ICRF system on the EAST tokamak and also discussing with ASIPP scientists future collaboration. Paul Bonoli, Amanda Hubbard, Greg Wallace, and Chuck Kessel (PPPL), attended the Eighth ITPA Integrated Operations Scenario Topical Group Meeting held at CIEMAT, in Madrid, Spain from April 16-19. Amanda gave a presentation on "Status and Plans for Research on Alcator C-Mod in Support of ITER H-mode Scenarios". Greg gave a talk on "C-Mod LHCD Progress and Plans", and Paul presented "Future work on Joint Modeling Activity JA-7". Chuck gave two talks; one on "Ramp up modelling (JA-1)", and another on "Modelling of flat top discharges from IOS-1.1". George McKee (GA), visited last week and gave the PSFC seminar on "Long-wavelength turbulence investigations in DIII-D". While here he had discussions with Darin Ernst, Anne White, Matt Reinke, Jim Terry, John Rice, Miklos Porkolab, and Martin Greenwald. UCLA graduate student Jon Hillesheim visited the PSFC last week and met with Seung-Gyou Baek, Michael Barnes, Arturo Dominguez, Darin Ernst, Jerry Hughes, Cornwall Lau, Yunxing Ma, Felix Parra-Diaz, and Anne White to discuss Doppler reflectometry, Correlation ECE, GS2 and GYRO turbulence simulations and comparisons with experiment. Jon gave a talk at the Turbulence Simulation Group Meeting on Thursday 4/19 on "Observation of a critical gradient threshold for electron temperature fluctuations in low torque DIII-D plasmas". Jon's experimental thesis work at DIII-D has revealed a critical gradient threshold for long wavelength electron temperature fluctuations, which increase substantially above a threshold in a/LTe. The increase in normalized temperature fluctuation level is concurrent with increased electron heat flux and transport stiffness. At high 1/LTe, measurements are consistent with gradTe-driven trapped electron mode turbulence. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly