Alcator C-Mod Weekly Highlights September 20, 2010 FY2010 weeks of research operations Base Target: 13 weeks Base Completed: 16.0 weeks ARRA Target: 5 weeks ARRA Completed: 5.0 weeks Plasma Shots: 2599 Operations ----------- Last week was the first week of Cell and Power Room activity since plasma operation stopped on 9/10. We expect for C-Mod to remain under vacuum until plasma operations resume in early October. One of the Cell closed loop chillers has been repaired restoring backup capability to the primary system. Servicing of the alternator hot gas blower system was begun last week. The unit has been removed and sent out-of-house for this work. The C-Mod heater and thermocouple system is also being serviced. Upgrades to the alternator PLC system continued last week along with discussions on upgrades of the engineering data acquisition system to CPCI. ICRF Systems ------------ We continued developing the antenna strap manufacturing process. We have completed several practice cuts that evaluate the wire EDM capability to cut the complicated antenna geometry and are satisfied with the capability. We also completed a set of test cuts to assess the process to cut the radius on the straps. We have found a manufacturing technique to reduce the process from 5-axis to 3-axis, and to eliminate much of the previously anticipated hand work. We plan to cut the first full size stainless strap soon. We have also worked to complete the back plate design, and we have coordinated with the MHD group to prevent pockets for the B poloidal coils from interfering with strap pockets and studs. The disruption analysis looks acceptable, and we are continuing to refine the model. RF modeling of the strap connection to the strip line has been completed, and the design has been accepted. Installation of the new solid state, 10 kW amplifiers (TOMCO) is progressing well. The old IPA has been removed from FMIT#2 and the TOMCO has been installed with the RF connections and power connections completed. The remaining work is to complete the control system and begin testing. FMIT#1's old IPA will be removed starting next week. The ICRF arc experiment has been restarted. FMIT#4 has been re-plumbed and the transmitter control and data acquisition have been modified to allow RF operation without the FPA. Initial power experiments have been started, but further refinement of the test set up need to be completed. These experiments are being performed to develop a better understanding of breakdown events in ICRF antennas as part of a graduate student thesis. Steve Wukitch traveled to the vendor's site in Backnang-Waldrems, Germany, for a preliminary design review of the new fast ferrite tuners. The principal issue identified during the review is related to thermal loads during 5 second pulses which may limit the ferrite tuner performance at high power. Data analysis we are performing of the prototype that has been in service on C-Mod should provide a benchmark for the simulations and a direct measure of both the power and thermal limits. These new FFT systems are being purchased under ARRA funding. The delivery of the high power tetrodes from our vendor has been rescheduled due to delays in manufacturing of the pyrolytic graphite grids. The process has been re-qualified, and the tubes are now expected at the end of October and November. These tubes will be purchased under ARRA funding. We met with another of our our vendors to discuss progress on designs and plans for upgrading one transmitter power supply. The vendor has a phase II SBIR contract to replace our ignitron based crowbar with a fast opening switch, install switching power supplies for the screen and grid, and provide design and coordination for upgrading the high voltage supply. Lower Hybrid System -------------------- Low power directional couplers have been specified and their procurement begun. These new couplers will directly monitor drive power to the klystrons and allow us to better understand the driver/klystron power chain. Diagnostics ----------- Initial results from the C-Mod Polarimeter indicate approximately 10% discrepencies in the level of Faraday rotation compared to simulated results from EFIT and separate density measurements. This is within the error bars of the polarimeter system as currently configured. We anticipate significant improvements following implementation of planned modifications to enhance the stability of the FIR lasers. First results for the density profile measurements from the LH-SOL reflectometer have been attained. Ramp up scenarios and changes due to ICRF/LH can be clearly seen; interesting new physics may be revealed upon further analysis. Comparisons with Thomson scattering and the LH Langmuir probes for all three waveguide runs (top,middle, and bottom) look reasonable. All the results for the reflectometer have been attained under the differential phase mode. The full phase channels should be up and running sometime during the next campaign. Plans include fully calibrating the phase of the waveguide runs, motorizing the waveguide switches so that we can get results from the top, middle and bottom horns during the same shot, and designing and installing the waveguides to the ICRF SOL reflectometer. Travel and Visitors ------------------- On Tuesday, Sept 14, Earl Marmar gave a tour of C-Mod to three visiting Professors from Shanghai Jiao Tong University. Their visit was coordinated through the MIT Energy Initiative (MITEI). John Rice attended the EU/US TTF meeting in Cordoba Spain Sept. 6-10 and gave a talk on C-Mod rotation results in I-mode. John Wright, Haruhiko Kohno, Jungpyo Lee, and Paul Bonoli attended the annual workshop of the SciDAC Center for Simulation of Wave-Plasma Interactions that was held at Princeton Plasma Physics Laboratory on September 14-16, 2010. The titles of their talks were: "A numerical analysis of the RF wave propagation under the sheath boundary condition in the ion cyclotron range of frequencies" (H. Kohno) "Some Progress on Edge Coupling Simulations in the Lower Hybrid Range of Frequencies" (P. T. Bonoli) "Improvements to wave codes" (J. C. Wright) "Theoretical Studies of Toroidal Rotation Induced by Lower Hybrid Wave Fields" (J. P. Lee) _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly