Alcator C-Mod Weekly Highlights April 10, 2006 FY2006 weeks of research operations: Planned: 14 weeks Completed: 6.9 weeks Operations ---------- Plasma operations continued at Alcator C-Mod last week. Four run days were scheduled and completed. A total of 81 plasma discharges were produced, with a reliability of about 80%. Research operations supported miniproposals from the Divertor/Edge, Lower Hybrid, and Transport topics. Additional run time was devoted to ICRF conditioning activities. The first full (overnight) boronization of the year was carried out on Thursday night. Plasma operations are planned to continue this week. Run Summaries ------------- Wednesday's experiment supported MP#430 "Localization of boronization effect". Boronization was carried out between shots using ten minutes of ECDC with 20% B2D6 + 80% He, with the location of the resonance sweep varied. Good 1MA EDA discharges were obtained on the first plasma following each boronization for a range of resonance locations. The best performance of the day reached 200kJ with P_rf=3MW, after a boronization with the resonance scanned from R=0.7 to 0.8m. During the run some difficulty was noted in controlling the diborane pressure, which complicates quantitative analysis of the results. Late in the day the piezo valve on the diborane system failed; the valve was successfully replaced on Thursday, prior to the scheduled overnight boronization. Thursday's run was devoted to MP#418 "Lower Hybrid Coupling Studies". The first portion of the run was aimed at verifying proper operation of the coupler protection system (CPS) before increasing the power and RF pulse length. Good progress was made on the CPS during this run. The focus of the run was then changed to further study coupling. Preliminary analysis of LH reflection coefficient data obtained earlier indicated that a small ~0.5 mm vacuum gap may be present. On Thursday, more coupling data were obtained at a position of about 1 mm behind the LH limiter, about 2 mm further in than had been explored previously. Moving the launcher closer to the plasma reduced the reflection coefficient as expected. More detailed analysis is needed to compare these data to previous results and theory. Part of Friday's run was dedicated to MP#448 "Comparison of Small ELM regimes on C-Mod, MAST and NSTX ", a Joint Experiment proposed through the ITPA. Rajesh Maingi (ORNL) served as co-Session Leader via a remote connection from PPPL, along with Amanda Hubbard at C-Mod. Hendrick Meyer (UKAEA) also participated remotely. The goals of the experiment were to establish a matched shape (except for aspect ratio) and a set of non-dimensional parameters which will be employed by all three machines, and to begin scans of beta and nu*. The shape match was obtained with q95=5.5 (Bt=5.4T, Ip=0.7MA); pedestal collisionality was ~1, as desired, with some range obtained during scans of input power and target density. Pedestal beta was limited by available power, rather than by MHD activity; RF power levels up to 3.7MW were used during these studies. EDA H-mode performance was generally good, with H89~2 and H98y~1. At the highest power and lowest density there were indications of small ELMs. These discharges will be analyzed further, and will provide target parameters for next week's scheduled NSTX experiment on this topic. Diagnostic Neutral Beam Systems ------------------------------- One of the old-design high voltage inverters, which had been diagnosed as the source of high frequency artifacts on the beam voltage, failed during testing and has removed from the system. There are presently six (out of eight) operating inverters installed in the beam high voltage system. Electrostatic shields for the new inverter gate drive boards are ready for installation, and a prototype front panel has been successfully fitted. Lower Hybrid System -------------------- Copper bus and G10 parts have been machined for the klystron test stand. The parts will form a high current, high frequency bus structure that will pulse a transformer to generate high voltage to a klystron under test. ICRF System ----------- The quarter-wave transformer installed in the FMIT#1 (D-port) transmission line/matching system was successful in reducing the voltage at the stub tuner and phase shifter by ~25%. The D-port antenna was conditioned up to 1.5MW for 1 sec pulses during Tuesday's run. Initial results indicate Multipactor and RF Glow conditioning of the J-port antenna on Monday improved the operation of this antenna. On Tuesday the antenna successfully coupled 2.5MW (steady) and up to 3MW for short periods. However, the performance of the J-port antenna following boronization later in the week continued to be limited. Travel, Visitors, and Meetings ------------------------------ Stewart Zweben was at MIT last week to help prepare for a possible 1/2 day run of MP429, "SOL turbulence in limiter plasmas". The PSI-5 camera gain was increased to its maximum in order to minimize the amount of gas puff needed to get good imaging data. He also worked on an analysis code for the fast diode detectors. Martin Greenwald, Kirill Zhurovich, John Rice and Darin Ernst presented papers at the Transport Task Force Meeting in Myrtle Beach, SC last week. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly