Alcator C-Mod Weekly Highlights Feb. 7, 2005 FY 2005 weeks of research operation planned: 17 weeks, completed: 0 weeks. Alcator C-Mod has completed pre-operations testing and begun startup and conditioning. Conditioning runs are planned to continue this week. Operations ---------- On Monday, Jan 31, the high temperature bakeout was completed and we began testing and checkout of run-time systems. The shot cycle and data acquisition system was tested, and some issues related to computer software and operating system upgrades since last year's operation were identified and addressed. In addition, the new digital plasma control system (DPCS) was used for the first time to test the gas fueling system; all of the piezo-valves used to inject gas into the torus were successfully tested under DPCS control. Some difficulties with the gas system instrumentation were identified; these were remedied later in the week. Power systems tests in preparation for plasma operation were carried out Monday through Friday. These tests began with a detailed checkout of the alternator systems lasting through Wednesday. This was the first operation of the MIT alternator, which provides the 13.8kV AC prime power for the C-Mod magnet systems, since installation of the new neutral grounding system during the maintenance period. On Wednesday the alternator readiness checklist was completed and we began individual testing of each of the power supplies and magnet systems. During this testing sequence, which is primarily conducted under PLC control, we also identified and corrected some difficulties with magnetic diagnostic signals, and continued to monitor the inputs, outputs and open-loop response of the digital control system. Additional issues with the shot cycle and data acquisition system continued to be addressed. The power system testing was completed on Friday, using DPCS for waveform control of two magnet systems. Upon completion of the power system tests, we began initial plasma operation under control of the new digital plasma control system (MP#399). As anticipated, obtaining plasma startup with the new system required some tuning of the field programming to account for differences in gains and offsets relative to the old hybrid analog/digital hardware. In addition, it was determined that the main Rogowski coil used to measure the plasma current was malfunctioning, and this signal had to be replaced with an alternate. After six attempts, short-duration (<150 msec) plasmas with currents of 150kA and 500kA were obtained. We expect to continue plasma conditioning operation this week. In order to facilitate ongoing work on the Lower Hybrid and ICRF systems during this testing and startup period, we are operating C-Mod on a split shift, with maintenance and prep work carried out in the cell and power room from 5:00 AM to noon and tokamak operations from noon to 7:00 PM. Meetings -------- The C-Mod Program Advisory Committee (PAC) met on Wednesday through Friday last week. PAC members in attendance were Vincent Chan (GA, chair), Rich Groebner (GA), Dale Meade (PPPL), John Sarff (U. Wisc.), Yuichi Takase (U. Tokyo), George Tynan (UCSD), Mike Ulrickson (Sandia), Dennis Whyte (U. Wisc.), and Rostom Dagazian (OFES, ex officio). John Willis (OFES) also participated by remote access on the first day. Presentations on the C-Mod Program results and plans were made by Earl Marmar, Amanda Hubbard, Steve Wolfe, Paul Bonoli, Martin Greenwald, Steve Wukitch, Randy Wilson, Bruce Lipschultz, Bob Granetz, Steve Scott, and Jim Irby. Vugraphs from the meeting are available at http://www.psfc.mit.edu/cmod/sciprogram/CMod_PAC_2005.htm . The first FY05 quarterly review was completed on Friday. Discussions were carried out among E. Marmar, J. Irby and R. Dagazian, including details of scheduling for the FY05 campaign, and a brief review of the quarterly milestones for the FY05 C-Mod science target. The milestone for the first quarter was completed ahead of schedule, on December 21, 2004. For details, see: http://www.psfc.mit.edu/cmod/sciprogram/FY05_level1_targets/ Physics ------- The expected temperature collapse associated with the planned disruption mitigation high pressure gas-jet injection experiments has been modeled in two ways in NIMROD. Either, the temperature profile is altered as an initial condition, or a cold front is allowed to propagate inward as a function of time. In both cases, instabilities arise that alter the magnetic topology. In the latter case, a large stochastic region forms that propagates inward ahead of the cold front. Initial results from a laboratory setup for a proposed diagnostic to detect particulates in the edge region, and behind the outboard divertor of C-Mod were presented at the weekly staff meeting. Currently detection of particulates is limited to those greater 40 microns in size, due to electronic noise. The pumpdown curves (pressure vs. time) at the beginning of each campaign (after all vacuum leaks fixed but before wall conditioning) since 1995 have been compared. The pressure achieved after 100 minutes of pumping had steadily increased from 1994 to 2003, increasing from about 4e-5 Torr to 4e-3 Torr. The most recent pumpdown, after BN tile removal and wall scrubbing, reached 2e-5 Torr after 100 minutes of pumping, a dramatic reduction. ICRF Systems ------------ Repair and testing of the crowbar circuit for transmitter #1 was completed, and tuning into dummy load has begun. Crowbar triggers for transmitters #3 and #4 have been successfully tested. Lower Hybrid System ------------------- The forward and rear waveguide assemblies were joined together last Saturday and all bolts and turnbuckles were torqued to final specifications. Early this week all twelve input guides to the rwg will be tested with the network analyzer to generate a baseline for the launcher assembly. Following these measurements, we will be ready to complete the waveguide runs from the klystrons to the rwg with sections of flexible waveguide. Diode detectors for most of the directional couplers and probes for the cart and launcher ends were put into place. Klystron testing is continuing. One circulator was found to produce fault indications from the transmitter protection system (TPS) and has been replaced with an older unit. This is not expected to impact the schedule for commissioning the lower hybrid system. Arrangements are being made to return the faulty circulator to the vendor for repair. Control power service was installed for the CPS rack. Cable and fiber optic installation is proceeding. Travel and Visitors -------------------- Dale Meade, Randy Wilson, Rich Hawryluk, Ed Synakowski, and Gerd Schilling (PPPL) were at C-Mod for the PAC meeting last week. Dale served on the PAC, and Randy presented the C-Mod talk on Lower Hybrid progress, status and plans. Steve Scott presented a talk on the progress and status of the MSE diagnostic. Ed Synakowski also held discussions with C-Mod physicists regarding planned experiments. Stewart Zweben (PPPL) brought the Princeton Scientific Instruments PSI-5 camera up to C-Mod last week, and helped to set it up and test it. He also worked on a collimated gas nozzle design for GPI, looked at the cross-correlation between inner and outer edge fast diode turbulence signals, and made audio sound files of the C-Mod fast diode signals in order to listen for higher-order correlations (none were apparent). _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly