Alcator C-Mod Weekly Highlights May 21, 2007 FY2007 weeks of research operations: tentative target: 15 weeks Completed: 4.16 weeks Operations ---------- Plasma operations continued at Alcator C-Mod last week. Three run days were completed. A total of 62 plasma discharges were produced with a startup reliability of 78%. Plasma operation is planned to continue this week. Operation Details ------------------ A fresh boronization was carried out on Monday evening utilizing the new technique including both vertical and toroidal field to improve localization of the boron ionic deposition. The range of sweep of the ECDC resonance was extended to cover radii from near the inner wall to near the outboard limiters. Vacuum conditioning of the J-port ICRF antenna was carried out on Tuesday. The experiment on Wednesday supported MP#482 "CXRS diagnostic development", and was aimed at developing methods of background subtraction in order to improve the reliability of temperature, density and velocity measurements using active charge exchange spectroscopy, particularly in the H-mode pedestal region. Steady EDA H-modes were produced with a range of target densities. The outer gap was also dynamically varied to scan the pedestal across the field of view of the diagnostics. The main part of Thursday's run was devoted to MP#487 "Effect of plasma configuration on edge turbulence". The purpose of this experiment is to characterize the broadband edge turbulence spectrum of L-mode and H-mode plasmas in different magnetic configurations (LSN, USN, DN). Dynamic scans of the outer gap were performed during the L-mode phase of discharges in each of the three configurations. Radial structure of the turbulence was documented in each case. EDA H-mode plasmas were produced with a long pre-transition observation period as well as a period covering the L-H transition and extending for ~0.1 sec into the EDA QC-mode phase. Finally, a dynamic scan from lower to upper single null (SSEP scan) was performed to study the direct and immediate response to configuration variation. The pedestal and SOL turbulence was found to respond more to the SSEP scan than internal modes, as expected. Comparisons of mid-plane turbulence data with data from probe and X-point diagnostics are being analyzed. Friday's experiment (MP#479) was designed to study the role of magnetic shear in setting the pressure gradients near the last closed flux surface (LCFS) in ohmic L-mode discharges. The shear was varied by systematically reducing the inner gap in such a way as to change from a double null to an inner-wall limited plasma, while keeping the shape of the internal surfaces nearly constant. The inner gap was scanned in 2mm steps. In limited discharges the spacing between the LCFS and the separatrix was systematically varied up to DSEP=12mm. Data were obtained with the scanning probes as well as with the edge Thomson scattering diagnostic, providing measurements inside the LCFS and in the SOL. ICRF Systems ------------- Following successful testing, the fast ferrite tuners (FFT) were removed from the E-port antenna transmission line and the unit which had experienced arcing at higher powers was opened for inspection. No obvious defects were found. We plan to use vacuum conditioning to test the maximum voltage capability of the FFT network. Lower Hybrid System -------------------- Repairs to the high voltage power supply modules have been completed, and the HVPS was tested up to 45kV. Testing is planned to continue this week. Long Pulse Diagnostic Neutral Beam System ------------------------------------------ All DNB systems are operational near full parameters. The DNB was operated into C-Mod plasmas last week for all three run days. The DNB operated for 1.4 second pulse lengths at 50kV with modulation. Beam currents have been approximately six amperes. A spare lanthenum hexaboride cathode has been assembled using material from a new vendor. The emission properties have not yet been tested. Travel and Visitors -------------------- Paul Bonoli and Martin Greenwald participated in the US Department of Energy's Fusion Simulation Workshop that was held in Rockville, MD from May 16-18, 2007. Bruce Lipschultz chaired, attended and presented a talk (D retention in C-Mod) at the SOL/divertor meeting in Garching Germany, May 7-10. He also attended and presented a talk at the EU Special Working Group on High-Z meeting in Garching May 10-11. He then traveled to Culham laboratories, UK for collaborative work with Steve Lisgo on C-Mod modelling, discussions with the engineers working on tungsten tiles for the ITER-like wall, discussions with Glenn Counsell and Steve Lisgo on MAST - C-Mod collaborations (including ITPA Joint Experiment DSOL-5), and discussions with Neil Conway on CXRS measurements. The Culham visit lasted from May 14-16. Joe Snipes met in Lausanne on May 14-15, with Ambrogio Fasoli, Duccio Testa, and Alex Klein to discuss our MIT/JET/CRPP collaboration on Energetic Particle-Wave Interactions and Alfven Eigenmodes on JET. David Brower of UCLA visited the Alcator C-Mod group on Friday, May 11th. He spent time with Jim Irby, Earl Marmar, Darin Ernst, Miklos Porkolab, Amanda Hubbard, and Catherine Fiore. He presented the weekly seminar, and his talk was entitled, "MAGNETIC FLUCTUATION-INDUCED PARTICLE TRANSPORT AND FLOW GENERATION." _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly