Alcator C-Mod Weekly Highlights July 28, 1997 Last week was a maintenance week on Alcator C-Mod; no runs were scheduled. Next week will also be a maintenance week. Maintenance work on the RF system continues. The leaking E-port H-probe on the external 6" coax line has been removed and repair work is underway; this line, which is not connected to the C-Mod vacuum system, is normally pressurized with SF6 during RF operation. Work on the PLC for transmitters #3 and #4 is progressing. Preliminary design work has begun on tuned arc detectors. Dr. Cynthia Phillips from PPPL was visiting last week and worked with Paul Bonoli on ICRF modeling. Cross-calibrations between TORIC, METS, and CARDS on comparisons with second harmonic tritium data on TFTR were done. TORIC performed well, especially relative to the old FISIC code, which failed badly on this case. This result taken together with C-Mod benchmark tests that have been done indicate the the code is robust enough for incorporation into TRANSP. The interface will be done as part of the collaboration; a meeting will be held in August to further discuss details of the interface. A problem in TORIC related to the toroidal broadening of the Z-function (an option) was identified and corrected. The comparisons between TORIC and TFTR second harmonic tritium heating data indicate that TORIC may be overestimating the direct electron damping of the fast wave in this case. Further comparisons with C-Mod data would be useful in verifying the electron damping model in TORIC. Preliminary simulations of the shear Alfven wave heating regime in C-Mod were done with the METS code and TORIC [f=40 MHz and B_t=8.0 T]. Initial results were encouraging but further theoretical and numerical studies are needed to assess the potential for transport barrier formation using this technique. A series of fast wave current drive simulations were run as support documentation for the existing fast wave current drive mini-proposal. The results indicate that preheating of the plasma with the 80 MHz system in D(H) provides a target plasma in which the phased rf waves at 40 MHz will damp more efficiently on electrons. The mini-proposal will be revised accordingly. Preparation of the DNB power supplies continued with power and control wiring. Remaining aspects of the low capacitance transmission line design, fabrication, and installation await the results of the consultation on truss loading. Development of the new control system for the DNB continued with documentation of requirements for the vacuum system control interface. Draft designs for the beam aperture that will facilitate MSE and BES spatial resolution requirements were completed and are ready for heatload simulations. New support structures for the DNB accelerator were completed and all of the vacuum system backing line components were in place ready for final assembly. Matt Sampsell, a UT-FRC graduate student, completed tests of the prototype BES spectrometer and returned to Austin. Working with Ron Bravenec and Don Patterson who participated remotely from Austin, he remedied CAMAC problems and measured an acceptable dark noise in the system. It is now ready for test observations of plasma light when operation begins again. Ricky Maqueda from Los Alamos visited C-MOD to work on the IR imaging system. The re-entrant periscope was disassembled, the damage on it assessed and modifications to its design to avoid future damage are being considered. A review of the alternator fault and plans for repair was held on July 25th at MIT. Dave O'Neill from PPPL, Rostom Dagazian and Stan Staten from DOE, and Joe Minervini from MIT were on the review panel. Presentations describing the MIT alternator, the most likely fault scenarios, and the repair plans were given. Generally, the panel felt we were moving in the proper manner toward repair of the rotor. Dr. K. Kondo (University of Tokyo) finished his two week visit to C-Mod last week. While he was here he studied the locations of the Mo generation in the divertor. Two conclusions from this study are: 1) The Mo source at the divertor plates in L-mode plasmas is small and increases in H-mode plasmas, and 2) at the outer divertor plate, the peak in the Mo source is located slightly higher than the strike point as determined from EFIT. Bob Granetz was in San Diego last week at a US/ITER disruption workshop. Recent results on this topic from the US fusion program were discussed, and further tasks which could be worked on during the next year were identified. Dr. Granetz presented data from our massive D2 killer pellet run, in which we found that quickly raising the density from 1-2e20 m-3 to 1.6e21 m-3 leads to a thermal quench disruption in which the current quench is not accelerated at all compared to naturally occurring disruptions. Josh Stillerman made two presentations on the MDSplus data acquisition system and on support for remote collaborations at the IAEA Workshop on Data Acquisition and Management for Fusion Research held in Garching, Germany, last week.