Alcator C-Mod Weekly Highlights February 28, 2011 FY2011 weeks of research operations Target: 15 weeks Completed: 12.2 weeks Plasma Shots: 1447 Operations ----------- Last week was a scheduled maintenance week at Alcator C-Mod. No plasma operation was scheduled. The C-Mod Program Advisory Committee will be meeting at MIT on Wednesday through Friday of this week, which is also scheduled for maintenance. A TF bus connection in the power room that was observed to be operating at above-normal temperature during high-field operation has been disassembled and is in the process of being re-plated. It will be ready for reassembly early this week. A new set of Belleville washers has been ordered to replace the old ones when the bus connection is reassembled. All other washers will be replaced when all the bus connections are reconfigured for normal field operation. The tokamak cryogenic system is in standby mode and the magnets are being allowed to warm up during the maintenance interval. The torus remains under high vacuum. Diagnostic windows which can be isolated behind gate valves are being cleaned. Physics ------- Recent analysis of ICRF heated discharges finds examples of increased sawtooth periods during co-current (+90 degree) phasing of the J-port antenna compared to counter-current (-90 degree) phasing. This effect may be consistent with the partial stabilization of sawteeth during co-current ICRF injection. In addition to a longer period and larger amplitude, the co-current ICRF sawteeth appear to produce an environment in which coherent modes of both lower (250 kHz) and higher frequency (700 kHz) are excited. These modes are presently unidentified, though the higher frequency band exhibits characteristics similar to the sawtooth-induced reversed shear Alfven eigenmodes (RSAE) previously studied on Alcator C-Mod. Other interesting features of the co-current phasing include reduced neutron rates (even though the temperature is slightly higher) and a more peaked ICRF tail ion radial profile. Analysis of the existing data set continues, and new experimental proposals are being planned. ICRF Systems ------------ The arc damage to the FMIT#3 transmitter output cavity has been repaired. The transmitter has been tested successfully at 2MW into a dummy load and is ready for operation. Modifications to the breakdown test cavity have been completed and it is being re-assembled. We plan to test copper and tungsten samples in support of an SBIR project. Fabrication of the ARRA-funded rotated antenna continued last week. Quality control issues with our vendor regarding the Faraday screen rods have been addressed, and we are awaiting a revised schedule on the second set of rods. The back center plate machining is complete and the process of cleaning and polishing the surfaces in preparation for copper plating has begun. The Z plate fabrication is expected to be completed this week. The plating test of the brazed components has been completed successfully, and the first bellows tube is expected to arrive this week. Our vendor has completed the back plate manufacturing fixture and expects to begin machining these large components this week. Fourteen of 18 TZM tiles have been EDM cut from stock, and the radius tool and programming have been successfully tested. Lower Hybrid System -------------------- The LH system was operated at high power to test a prototype waveguide stub tuning assembly. Progress continues this week on the fourth klystron cart. New electrical box locations for the fourth cart were chosen and obstructions with existing equipment were assessed. Parts were fabricated for the fourth cart Collector Over-Temperature System Resistance Temperature Detector (COTS/RTD) instrumentation cabinet, and wiring was started on this project. Low power phase shifters and attenuators for the control system have been tested. The combined phase shifter/attenuator package is able to produce accuracies of < 1 deg and < 0.5 dB across a range of 360 deg and 20 dB. TPS upgrade interface boards were populated and tested. Diagnostics ----------- The WideView CXRS diagnostic is being upgraded for measurement of fully stripped helium profiles in the core of C-Mod. The new application will support light impurity transport studies and will assist in establishing the initial conditions for D(He3) heating and flow drive. The initial results were obtained during C-Mod operation on Feb. 7. Modifications to the entrance slit curvature on the spectrometer were warranted to improve spectral shape measurements, and have been completed. The diagnostic has been recalibrated in preparation for the next series of experiments. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly