Alcator C-Mod Weekly Highlights December 6, 1999 The maintenance period continued on Alcator C-Mod last week. The major focus of effort continues to be the DNB installation. Invessel work was also begun, and work on RF, power, and alternator systems continued. Engineering: ------------ A great deal of work was done last week preparing to run the DNB power systems for the first time. This major DNB project milestone was completed on schedule. Work done during the last few days included checkout of the PLC control program, and a checkout and debug of all the control circuitry, first operation of the crowbar protection circuit, hi-pots of equipment with and without the modulator tube installed, and a hi-pot of the modulator tube itself. Preparations are now being made to power up the beamline, our next major DNB milestone. We also continued work on the RF systems. Work on the transmitter water systems is moving along very quickly. A plan has been formulated for maintenance and upgrades to some RF instrumentation circuitry. The first manned entry into the vessel occurred last Monday. After careful checks for diborane and activation, the vessel was entered and a several day long period of documentation was carried out. Our main interest was in investigating the j-port antenna which, as reported last week, exhibited density and power limits above which a large influx of impurities was generated. Initial findings included indications of significant arcing between protection tiles and at high voltage locations around the current straps. A meeting will be held next week at MIT with MIT and PPPL personnel to discuss these problems and make plans to fix them. We have also continued boron nitride tile development in case some of the tiles can be usefully replaced with non-conductive material. Physics: -------- It has been noted that the perpendicular propagation speed of the density fluctuations in EDA H-mode (~-1 km/s) is far less than both the estimated diamagnetic velocity (~12 km/s) and the magnetic fluctuation velocity (-10 to -50 km/s). A possible interpretation is that the density fluctuations propagate at the bulk ion velocity which is close to zero in the lab frame because of viscosity, whereas the magnetic fluctuations propagate at the ExB or even electron (diamagnetic) velocity. A great deal of time was dedicated last week to preparation for the Ideas Forum to be held at MIT on Dec 7 and 8. Meetings were held to discuss all the major topics including Pedestal Transport & Stability, Core Transport, ICRF Current & Flow Drive, High Performance Operation, and Divertor & Edge Studies. Information on the Ideas Forum, including instructions for remote participation, is available on the Web at http://www.psfc.mit.edu/cmod/forum2000/forum2000.html . Travel and Visitors: -------------------- Dr. Y. Nakamura is visiting from JAERI for a period of 4 weeks. He is collaborating with R. Granetz on TSC modeling of VDE stability, analysis of C-Mod VDE data, and planning experiments on neutral point operations to mitigate disruption effects. Miklos Porkolab participated in a review at the Institute for Plasma Research at the University of Maryland.