Alcator C-Mod Weekly Highlights March 8, 2010 FY2010 weeks of research operations Base Target: 13 weeks Base Completed: 6.6 weeks ARRA Target: 5 weeks ARRA Completed: 5.0 weeks Plasma Shots: 1289 Operations ----------- Plasma operations continued at Alcator C-Mod last week. Four run days were scheduled and three were completed. Experiments supported research in the Boundary and Transport topical science areas, and the Diagnostic Development activity. A total of 84 plasma discharges were produced with a reliability of 89%. Boronizations were performed on Tuesday and Wednesday nights. A leak in the alternator standby seal-oil pressure regulator prevented operation on Thursday. The regulator, which had been recently refurbished as part of our regular preventive maintenance procedures, was repaired by the vendor and re-installed on Thursday afternoon. Research operations are planned to continue this week. Program Planning ---------------- A meeting of the Experimental Program Committee was held on Monday 3/1. Plans for the remainder of the current campaign were discussed. We expect to operate for four more weeks before a planned manned-access vent. We will conclude this run period with 1-2 weeks with the J-port antenna at 70 MHz, primarily to study ITB discharges. MPs #595a, 599, 600 and 602 were approved. Operation Details ----------------- Two experiments were conducted on Tuesday. The first portion of the run was devoted to MP#593 "Vertical Equilibrium Shifts for triggering ELMs". Using the same technique as was employed in previous experiments with EDA H-modes, we attempted to trigger or pace ELMs in ELM-free H-modes and I-mode targets. We did not carry out a boronization prior to this experiment. We began with a 1MA EDA H-mode similar to those used in the previous run, with 200Hz modulation of the vertical position. We observed synchronized D-alpha spikes which were qualitatively similar to the earlier results, though with less contrast. As we lowered the target density the H-modes became less EDA-like and more transient. Under these conditions, we observed D-alpha spikes with exponential tails, correlated with sudden drops in the edge Te; these events were correlated with upward plasma motion (away from the X-point). Molybdenum radiation was high in these discharges, and stationary conditions were not obtained. We then attempted to apply the vertical modulation technique to upper single null I-mode discharges, but the radiated power fraction was too high and no sustainable I-mode temperature pedestal was achieved at either 1.2 or 1.35MA. We were able to demonstrate stable operation with 100Hz vertical modulation of up to 6mm in these discharges, but no ELM-like behavior was observed. The final two hours of Tuesday's run was devoted to additional work on MP#502, "HIREX_SR calibration", in preparation for scheduled experiments later in the week. Vignetting measurements were completed on the H-like spectrometer system. Work remains to be done on the He-like system. The run on Wednesday was devoted to MP#591 "Boundary Layer Heat Transport Experiments in H-mode Plasmas". These experiments contribute to the FY2010 OFES Joint Facility Milestone to investigate boundary layer transport and heat flux "footprints". The primary goals of Wednesday's experiment were to record heat flux footprints from the IR camera system in stationary EDA H-modes with 1 MA of plasma current under fixed and swept strike point conditions, and to compare footprints in lower single null versus near double null discharges (1 MA conditions). Good progress was made towards these goals. Steady EDA H-modes were obtained with RF power between 0.5 and 4.8MW, and an L-mode shot with Prf~0.3MW was also produced for comparison. The run on Friday was devoted to MP#598 "Impurity Transport Studies in L and H-Mode Plasmas Using the Modified HIREX_SR Spectrometer". The purpose of this run was to characterize H-mode impurity confinement through scans in Ip, Pin, and density. The major goal of this miniproposal is to change the parameters thought to drive turbulent transport by variations in R/Ln. This experiment comprises part of the thesis research of an MIT graduate student. Impurities (CaF2) were introduced using the Laser Blow-Off (LBO) technique. A limited range of conditions were successfully obtained, including data for EDA H-modes at 0.4, 0.6, and 0.8MA plasma currents. Stationary EDA operation at higher current was not obtained. ICRF Systems ------------ The driver on FMIT#2 (E-port antenna) suffered a short (~4 Ohms to ground) on the screen grid circuit during operation on Friday. The cause is believed to be a shorted bypass capacitor. The driver amplifier will need to be disassembled for repair. In order to test manufacturing feasibility, a half size current strap for the new four-strap antenna was successfully wire EDM'ed from a block of stainless steel. A second feedthrough was also delivered from our vendor. Lower Hybrid System -------------------- We successfully cleaned the lower hybrid launcher windows last week using a mild acid etch followed by seven rinse cycles in distilled water and ethanol. Borescope inspections of approximately twenty of the windows thus far indicated they are in excellent condition. Low power rf tests indicated 15 of the 16 splitters were now preforming as designed. One splitter has acceptable but somewhat higher reflection coefficient and relative phase-shift between output ports than expected. We are investigating the cause of this effect. Testing of the new Coupler Protection System (CPS) continued last week. All expected fault conditions have been simulated and the system performed as designed. All channels have been tested. Work also continued on the new RF probe data system and electronics. Testing procedures are being developed and tried out. Travel and Visitors ------------------- David Mikkelsen (PPPL) spent the week at MIT to work with the C-Mod group on GYRO simulations (to study density peaking, impurity transport, momentum transport, and ITB formation), and to plan a particle transport experiment in C-Mod. Prof. Rob Goldston (PPPL) visited the PSFC and gave a seminar entitled: "The fastest path to fusion electricity: a fusion pilot plant". He also had discussions regarding collaborations and edge physics with a number of scientists and engineers, including Amanda Hubbard, Dennis Whyte, Brian LaBombard, Jim Terry, Jeff Freidberg, Joe Minervini and Leslie Bromberg. Manfred Bitter, Ken Hill and Luis Aparicio-Delgado, all from PPPL, were at MIT from Mar.1-5 to operate the x-ray fluctuation spectrometer. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly