Alcator C-Mod Weekly Highlights Jan 2, 2001 Alcator C-Mod was warmed up last week in preparation for in-vessel work scheduled to begin this week. Work on ICRF and Lower Hybrid equipment, the glow discharge system, and new tiles and septum for the J-port antenna also continued. Physics -------- Data obtained from the fast scanning magnetic and Langmuir probes during EDA discharges have been carefully analyzed over the past few weeks. A strong (~ 5 G at LCFS) magnetic component of the Quasi-Coherent (QC) mode in the 100 - 150 kHz frequency range was found in EDA H-mode together with local density fluctuations of (delta n)/n ~ 30% that were sufficiently in phase with the electric field fluctuations to drive substantial particle transport. Thus, the QC mode appears to be responsible for the increased edge particle transport found in EDA H-mode. A letter is being prepared for submission to Plasma Physics and Controlled Fusion entitled "Quasi-Coherent Signature of Enhanced D alpha H-modes in Alcator C-Mod", by J. Snipes, B. LaBombard, M. Greenwald, I.H. Hutchinson, J. Irby, Y. Lin, A. Mazurenko, and M. Porkolab. General Engineering ------------------- Alcator C-Mod has been warming up since 12/22 and is now warm enough to shut down the GN2 vaporizer and vessel heaters, both necessary operations required before in-vessel work can begin. Glow discharge cleaning in helium will be run overnight to break down any remaining heavy boron hydrides and will, along with multiple backfills with moist room air, make the vessel safe for entry. Work continued on a new board layout and upgraded design for our ratiomatic vacuum gauge controllers. A prototype controller was tested successfully during the last week of the run campaign. These controllers provide an analog output proportional to the log of the pressure over the several decade pressure range needed during C-Mod operation. A modification to the glow discharge system has been made to allow arc detection trip points to float with a programmed offset relative to the electrode voltages. As adjustments to electrode current are made, or electrode voltages change during conditioning, the trip points now automatically adjust to these changing conditions. ICRF System ----------- Preparations for the invessel work on the J-port antenna continues. The new boron nitride tiles, septum, and RF probes are in various stages of detailed design or fabrication. An internal review of proposed changes to the antenna was held on 12/22/00, and a decision was made to proceed with the up-to-air to implement them. Work continued on the new demodulator design. The design incorporates modern, more easily obtainable limiter and mixer components, that will provide more operational reliability and range. Prototype testing of the design is progressing. The new demodulator is part of an ongoing upgrade of the ICRF control system. Repairs have been made to the phase shifter that limited the J-port antenna power level during 70 MHz operation. Lower Hybrid System ------------------- The first Lower Hybrid control chassis from National Instruments arrived last week. We have begun to set up the hardware and bring up networking capability so that testing can begin. This system will be used for fast control of the lower hybrid RF phase and amplitude. It will control the power reaching the launcher from the twelve klystron sources. Work is also progressing on new analog fiber optic link circuitry. Breadboarding of some Lower Hybrid protection circuits was also started last week. DNB System ---------- A small change to the DNB beamline vacuum system is being made so that DNB testing can continue during the up-to-air. Visitors and Travel ------------------- Tom Fredian visited NIFS in Toki, Japan to install MDSplus on the CHS experiment. Tom together with Jeff Schachter from General Atomics installed MDSplus and MDSplus related utilities such as ReviewPlus and provided training on the use of the software. Several people from PPPL visited MIT over the last couple of weeks as part of our collaboration. Joel Hosea visited on 12/18-19 to join in the ICRF group discussions on modifications to the PPPL J-port antenna. Stewart Zweben came 12/19-21 to participate in the experiments and obtain additional edge turbulence images under different plasma conditions. The weekly diagnostic neutral beam meeting was held on 12/18, with Norton Bretz and Gerrit Kramer attending via videoconference and Gerd Schilling attending in person. Yuri Rokhman and David Terry attended Labview software programming courses from 12/18/00 to 12/22/00 at National Instruments in Woburn, MA.