Alcator C-Mod Weekly Highlights June 8, 2001 Alcator C-Mod was in operation four days this week. Very good progress was made conditioning both the machine and the ICRF antennas. Up to 3.7 MW of ICRF power was coupled into the plasma, though heating efficiency was low because the hydrogen fraction was still high. However, conditioning of the machine and antennas is now sufficient for boronization to take place early next week. Physics ------- Time has been devoted during two runs for ASDEX shape development. This experiment will produce equivalently shaped plasmas on C-Mod as on ASDEX Upgrade and attempt to match dimensionless parameters v*, rho* and beta near the edge of the plasma (the H-mode pedestal region), both at the L-H transition and in the fully developed H-mode. We can now generate plasmas needed for the ASDEX/C-Mod scaling studies. Bill Dorland from the University of Maryland visited for a day and a half to help bring up the parallel version of the gyrokinetic stability code, gs2, on our newly built Beowulf cluster. We expect the cluster to achieve computational rates of over 20 Gflops. ICRF Systems ------------ All calibration factors have now been obtained for the J-Port antenna needed to operate with [0,pi,0,pi] phasing. The maximum injected power thus far from the antenna is ~1.7 MW for ~50 ms. This power level was limited only by the antenna conditioning time and will improve with operation time and boronization. The new optical monitoring diagnostics of the J-port strip lines detected signal when the D and E-Port antennas were active. Comparisons with the voltage data indicate the induced voltage from D and E-Port antennas are low when the light signal is detected and high when no light is observed. This result suggests that the low induced voltage is sufficient to initiate multipactoring. The induced voltage from D and E-Port antennas will decrease as the H/D ratio decreases and absorption improves. D and E-Port antenna conditioning has improved greatly during the week. Approximately 1.25 MW was obtained from each antenna, or about 2.5 MW total. The density rise associated with the RF pulse has been greatly reduced as the conditioning improved. By the end of the run on Friday, several discharges obtained ~3.7 MW of coupled power from the D, E, and J-Port antennas for approximately 100 ms, and some plasma heating was observed. The heating efficiency will improve as the H/D ratio is reduced with machine conditioning and boronization. On the first application of high voltage on Wednesday, the FMIT#4 transmitter crowbarred. Upon disassembly, one of the by-pass capacitors on the driver cavity was found to have arced. The capacitor was replaced and the transmitter was brought back into operation into plasmas on Friday. Lower Hybrid MIE Project ------------------------ We continue to work on the serial fiber optic link and the realtime software and hardware needed for phase and amplitude control of the klystrons. Details of the C-Mod cell layout of the LHCD launcher and associated equipment are being resolved through close communication between PPPL and C-Mod personnel. C-Mod and PPPL are also coordinating the mapping of klystrons to waveguide components and developing a convention for signal names. The wiring of transmitter HV control sub-chassis, and Transmitter Protection System chassis is proceeding. DNB --- The DNB was baked for three days at a higher temperature than previously in an effort to further reduce water contamination of the beam. We will not know the benefits of the bake until several days of beam operation have been completed. Diagnostics ----------- Larry Guttadora continues to check out the reflectometer upgrade circuits at PPPL before returning them to MIT. The filter tuning for the BES diagnostic was re-calibrated and the filter passband was measured using a spectrometer. This passband measurements will greatly simplify future calibrations. Inner Divertor -------------- A stainless steel C-Plate has been received from the vendor and is undergoing fitup tests in our divertor mock-up. Tiles, tile support plates, and ribs are all interlocking very tightly as intended. The expected 0.020" gap between tiles, and the fish-scale high points are well within spec. Delivery of the inconel C-Plates needed for the girdle are well into final production and should begin arriving in-house over the next few days. The Backing-plates, being produced by another vendor, have been delayed by a week. Difficulties programming the machining of the upper surface of the plate were solved by a visit by MIT personnel early in the week. Power Systems ------------- A problem with the EF2U power supply during the run on Tuesday was traced to a failure in the power supply's auxiliary step-start contactor. The contactor was replaced with a spare unit. We are investigating why the contactor failed. Travel and Visits ----------------- Justin Burruss, from General Atomics in San Diego, visited Tom Fredian and Josh Stillerman last week to discuss MDSplus and to demonstrate some relational database applications he has developed (both web and IDL based) which could be useful for viewing the C-Mod databases. Ron Parker and Jim Irby visited PPPL to serve on the FIRE Pre-Conceptual Design Review Committee from July 5-7. Very good progress has been made on magnet, divertor, PFCs, vessel, and fueling systems.