Alcator C-Mod Weekly Highlights April 2, 2012 FY2012 weeks of research operations Target: 17 weeks Completed: 5.6 weeks Plasma Shots: 753 Operations ----------- Alcator C-Mod is presently up-to-air for planned maintenance and upgrades. Refurbishment of the ARRA-funded Field Aligned ICRF Antenna continued. The lower hybrid launcher windows have been cleaned. In-vessel diagnostic installations are proceeding. Physics ------- A report detailing the first results from the new C-Mod fast ion loss detector (FILD) diagnostic was given during the Science Meeting on March 26 by David Pace (now at GA). The FILD measures the pitch angle and energy of ICRH-accelerated ions that reach its position on the wall near the outer midplane. A rich variety of loss behavior has been observed, including dependencies on individual antennas that change with plasma current and shape, and synchronization with the sawtooth cycle. ICRF System ----------- Re-assembly of the ARRA-funded field aligned antenna is nearly complete. All the Faraday screen assemblies and front and side protection tiles have been installed. The current and voltage probes have been connected, and the thermocouples have been refurbished and installed. FFT#1 has been re-assembled and is being prepared for installation. Trouble-shooting of a gas leak detected during pre-assembly inspection is in progress. Alan Binus and Steve Wukitch visited with our vendor on Friday to witness pulse testing of a solid-state fast opening switch that could replace our ignitron based high voltage protection system crowbar. This new system has significant advantages: it modernizes the HV protection, eliminates the mercury filled ignitron, allows re-application of HV within a C-Mod discharge, and improves tube protection by reducing potential for off normal events. This development work was primarily funded through an SBIR Phase II contract. Lower Hybrid System ------------------- Progress on the LH controls upgrade continues. The control computer was run for a 5s pulse in real time feed-forward operation with no missed cycles using a 721x201 look up table (0.5 deg and 0.1 dB precision) for the phase shifter and attenuator. The design of the LH3 launcher 8-way splitter assembly was tested with two independent FEM simulations. The simulations confirm that good plasma-launcher coupling is obtained over a wide range of N_parallel and plasma density profiles, indicating that the design is satisfactory. The model has been integrated into the LH3 mechanical design. Our TPS upgrade SBIR vendor visited the PSFC on Wednesday to discuss performance of the TPS upgrade and future improvements. A modification to the TPS firmware was made to extend the upper limit for the collector heat capacity from 20 to 40 kJ/K. Development of a more sophisticated analytic calculation of the collector temperature is in progress to determine if the observed lag in downstream coolant temperature measurements can be simulated. Diagnostics ----------- An upgrade of the core CXRS/fast ion diagnostic has been completed. The upgrade consisted of moving the 6-axis translation stage from the detector to the spectrometer. With the spectrometer mounted on translation stages and the camera fixed, optical alignment is greatly simplified when accessories such as the blocking bar and the soon-to-be-added CXRS/BES calibration unit are added. Travel and Visitors -------------------- Dr. Cheng Yang from the Institute of Plasma Physics (IPP) of the Chinese Academy of Sciences arrived at the Plasma Science and Fusion center on March 22, 2012. He will be a visiting scientist here for the next six months and will be working with Paul Bonoli, Ron Parker, John Wright, Greg Wallace, and Syun'ichi Shiraiwa. They will be conducting simulations of lower hybrid current drive (LHCD) in the IPP EAST Tokamak using a variety of simulation codes including LSC, GENRAY-CQL3D, and the TORLH and LHEAF codes. They will also apply integrated simulation capabilities such as the Integrated Plasma Simulator (IPS) to the EAST LHCD experiments if time permits. Anne White visited DIII-D March 26-30, and met with scientists from GA, UCLA and UCSD to discuss data analysis plans for ongoing JRT 2012 experiments and turbulence-transport experiments that are planned for C-Mod and DIII-D. While at DIII-D, Anne worked with Max Austin (UT-Austin) on data analysis for the ITPA joint experiment: investigating the TS-ECE discrepancy. Both C-Mod and DIII-D have completed experiments to investigate the discrepancy seen at TFTR and JET between Thomson Scattering and ECE measurements of temperature in high temperature plasmas (Te > 5-7 keV). The TS-ECE discrepancy (which remains unexplained) is a concern for ITER where temperatures will be ~ 20 keV. Evan Davis, an MIT graduate student, was at LLNL last week working with X. Xu to run BOUT++ simulations of C-Mod. In particular, they are running higher fidelity linear and nonlinear simulations than were obtained in Summer of 2011, and they are also incorporating the measured radial electric field into the simulations. Earl Marmar visited GA Tuesday through Thursday last week; he participated in DIII-D Program Advisory Committee as a member of the committee. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly