Alcator C-Mod Weekly Highlights December 21, 2009 FY2010 weeks of research operations Base Target: tbd Base Completed: 1.7 weeks ARRA Target: 5 weeks ARRA Completed: 5.0 weeks Plasma Shots: 807 Operations ----------- Plasma operations continued at Alcator C-Mod last week. Four run days were scheduled and three were completed. The start of Thursday's run was delayed for an hour while a spurious fault indication in the OH1 power supply was investigated and cleared. A fault indication in a 4160V AC power transformer associated with the drive system of the MIT alternator resulted in cancellation of Friday's experiment. A total of 80 plasma discharges were produced with a startup reliability of over 85%. The runs supported experiments from the Transport Physics and MHD topical areas. This week begins a scheduled maintenance interval at Alcator C-Mod. No plasma operations are plannned. Operation Details ----------------- Experiments on Tuesday and Wednesday were devoted to MP#571 "Further investigation of turbulence and transport in low density ohmic plasmas to resolve the mystery of electron transport". Previous experiments had established a contradiction between gyrokinetic code predictions and the experimentally inferred values of electron and ion thermal diffusivity in the low density "neo-Alcator" regime. These results were reported at the November APS meeting by L. Lin (see http://www.psfc.mit.edu/research/alcator/pubs/APS/APS2009/2009_APS_CMOD_Lin_v3.pdf ) Last week's experiments were aimed at verifying and extending the previous experimental results by obtaining improved profile measurements for the electron density and ion temperature, extending the turbulence measurements, and extending the parameter range, particularly at the lowest densities. Density scans were completed at three toroidal fields (2.6, 3.9, and 5.2 tesla) and a range of currents from 0.4 to 1.0MA. The last part of the run on Wednesday was devoted to a series of discharges used for calibration of the Thomson scattering density measurements using cut-off of the electron cyclotron emission (MP#296). This same-day calibration is intended to improve the accuracy of the density profile, which is crucial for comparison with the code predictions relating to TEM mode transport. Thursday's experiment was devoted to MP#590 "Reinforcing Characterization of Driven Alfven Eigenmodes". The purpose of this run is to reproduce the conditions at which a resonance had been detected using the Active MHD (AMHD) Spectroscopy antenna in swept frequency mode, and to try to observe the same resonance in the absence of AMHD antenna current variations. The mode structure is of particular interest, since recent data have indicated n=0 modes, identified as Global Alfven Eigenmodes (GAEs). Previous studies on C-Mod have primarily involved Toroidal Alfven Eigenmodes (TAEs) with 4 < n < 13. The experiments concentrated on excitation of stable modes by operating the antenna at a fixed frequency f~850 kHz while varying the density and toroidal field. Synchronous detection analysis of Thursday's run shows several features of resonances, though spectrogram and trace analysis of magnetics probe signals do not always reinforce this picture. These data are being analyzed, and further experiments are planned. ICRF Systems ------------ The ICRF system was operated successfully in support of C-Mod experiments last week. Lower Hybrid System -------------------- Assembly of the Lower Hybrid launcher, including RF and Langmuir probes, thermocouples, and the reflectometer system, has been completed. The launcher assembly has been installed in the vacuum test stand for leak checking and initial bakeout. Fit-up work for the LH jungle gym required prior to transport of the launcher to the cell has been completed. Work continued on installation of the waveguide runs between klystrons and jungle gym. Supports were fabricated and installed. Travel and Visitors ------------------- Martin Greenwald traveled to PPPL for a meeting of the Fusion Simulation Program (FSP) management team. Stewart Zweben (PPPL) was at MIT last week to help take GPI data using the new Phantom 710 camera viewing the outer midplane. Many good shots were obtained at the camera's maximum frame rate of 380,000 frames/sec, both for low density and density-limited Ohmic discharges. The motion of individual blobs across the SOL could be tracked clearly, and blob birth inside the separatrix could be seen near the density limit. Bruce Lipschultz and Brian LaBombard attended the ITPA SOL/DIV meeting in San Diego (chaired by Lipschultz). Brian subsequently participated in a meeting of the international program committee for the 19th Conference on Plasma-Surface Interactions, which will be held in San Diego, May 2010. He also met with Rajesh Maingi (NSTX) and Tony Leonard (GA) to discuss plans for the FY2010 joint facility experiments on boundary layer heat transport. Earl Marmar attended the 8th IEA Large Tokamak Workshop on Implementation of the ITPA Coordinated Research Recommendations, a joint workshop of the IEA Large Tokamak, Poloidal Divertor and TEXTOR Implementing Agreements. The meeting was held at the KSTAR Research Center, in Daejeon, Korea, on December 15 and 16. The agenda included reports of 2009 ITPA joint experiments, plans for joint experiments in 2010, and status and plans for the world's major tokamaks. The workshop concluded with executive committee meetings of the Large Tokamak and Poloidal Divertor IEA Agreements, including discussions of the near term plans to combine these two agreements, and the completion of formal procedures to add Korea as a member of the Poloidal Divertor Agreement. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly