Alcator C-Mod Weekly Highlights April 18, 2000 Operations: ----------- Last week was a maintenance week at Alcator C-Mod. No plasma runs were scheduled. During testing last Friday, a stainless steel shutter used to protect a mirror during discharge cleaning became detached and had to be removed from the vessel. A brief up-to-helium vent was carried out, following which the machine was pumped back down and ECDC in deuterium carried out over the weekend. Vacuum conditions appeared to be acceptable as of Monday. Plasma operations are scheduled to resume this week. Physics and Diagnostic Systems ------------------------------ An absolute calibration of the Michelson interferometer was carried out over two days. The measured sensitivity vs frequency proved very stable, when compared to measurements over a year ago. All of the other ECE diagnostics (GPC, GPC2, radiometers) are cross-calibrated to this instrument during plasma operation. We have now installed a total of six TV cameras viewing the plasma and in-vessel hardware. When the data acquistion is fully operational, we will be digitizing the images from all six cameras. The views include a wide angle view inside the vessel, a view of the J port antenna, a view of the D port antenna, a view of the E port antenna, and two nearly indentical, tangential views of the divertor region. Presently the E port antenna is being viewed by the LANL-supplied fast-framing, gated, visible camera. The digitized frames from the cameras are also being compressed and made available on the WEB, allowing after-shot access by operators, diagnosticians, and any other interested parties. The site for these images is http://www.psfc.mit.edu/cmod/PlasmaVideo/imagedir.plx which can also be reached by clicking on the "Plasma Videos from Recent Shots" line in the C-Mod "Experimental Operations" page of the PSFC WEB-site. ICRF Systems: ------------- The C-Mod ICRF transmitters #2, #3 and #4 have been retuned to provide 2 MW output power each into a dummy load. Control logic issues that are common to all four transmitters have been discovered and still need to be fixed before operation is resumed. Diagnostic Neutral Beam ----------------------- Progress on the DNB continued. Paralleling the filament cables was finished. The additional cabling reduced the total resistance by approx. 10 milliohms, adding another volt at 100 A. A new, isolated current measurement system was installed to improve the measurement of the accelerator current. The vacuum instrumentation was fixed, with 2 new ion gauges and a replacement gauge controller installed, and a new monitor for the RGA connected. The sticky source gas valve was replaced with a new valve. Travel and Visitors -------------------- Bill Dorland visited the PSFC for 2 days. The main activity was working with Martin Greenwald and Howard Yuh on the adaptation of the gyrokinetic stability code (GS2) to use MDSplus data structures. A standard gs2 tree was agreed on and built. We expect to have the I/O modules and a GUI for setting control values and entering data within a month or two. Bill also delivered a seminar which discussed the difference between gyrokinetic and gyrofluid simulations of ITG turbulence. Chris Brunkhorst came to MIT for the week to help with the transmitter retuning. Norton Bretz came on 4/14 and will stay over the weekend working on MSE software. Matthias Groth visited MIT last week and presented a seminar on 'Measurements and modeling of helium and neon enrichment in the JET divertor'. He also spent considerable time in discussions with C-Mod staff regarding similarities and differences between C-Mod and JET results in this area. Models of compression and enrichment were also discussed. David Winslow (UT-FRC) and Keith Carter (UT-FRC) visited the PSFC to work on the Texas probe system and attend the EPC meeting. Alignment of the probe drive, installation of the vacuum system, and installation of the PLC electronics were completed.