Alcator C-Mod Weekly Highlights May 5, 2003 Plasma operation continued at Alcator C-Mod last week, with four run days scheduled and completed. The principal activities were machine conditioning, re-comissioning of the ICRF system, and diagnostic calibration. A total of 80 plasma discharges were produced with startup reliability of over 90%. Plasma operations are scheduled to continue this week. Operations ---------- All tokamak systems continued to perform well last week. Overall engineering reliability was ~90% for the week. Discharges with upper null and inner-wall limted equilibria were run in order to condition all the plasma contact surfaces. The H/D ratio continues to decrease as the vessel conditioning proceeds, and reached the ~10% level in some discharges on Friday. Brief H-modes were produced with ICRF heating in Lower Single Null discharges during Friday's run, indicating that the proton fraction is low enough for minority heating. We are continuing a regimen of baking at 60C and electron cyclotron discharge cleaning (ECDC) in deuterium during off-operating hours. Physics ------- Mode conversion electron heating was observed during ICRF conditioning discharges early in the week, while the H/D ratio was in the ~30-40% range. Clear break-in-slope signatures were obtained on the high resolution FRECE radiometer signals, which can be analyzed to determine the power deposition profile and compare with theoretical predictions. The Active MHD Spectroscopy system was operational for all runs last week, concentrating on the TAE frequency range around 500kHz. Responses were seen in both limited and diverted equilibria. These results are being analyzed. A portion of Friday's run was used to cross-calibrate the Thomson Scattering density signal to the cut-off of the second harmonic ECE. For this calibration, the density is ramped up during the shot and the toroidal field is decreased to between 4 and 3.5 tesla. The resulting cutoff of the ECE emission is a precise measure of the local density, which can be used to determine the absolute calibration of the TS signal. Analysis of core toroidal rotation data from the HIREX system taken during the locked mode shots observed in run 1030425 indicates that the rotation in these ohmic L-mode shots slows from ~2e4 m/sec in the counter-current direction to essentially zero as the locked mode appears. ICRF Systems ------------ The D- and E-port antennas have been conditioned to >1.5MW each at ~20 kV and the J-port four-strap antenna was conditioned to ~2.5 MW for short pulses, into L-mode plasmas Further conditioning is required for H-mode operation which results in higher maximum voltages. On Friday a high voltage fault in the screen crowbar unit prevented operation of FMIT#4. The SCR's were replaced and the screen crowbar was successfully wire tested. High voltage was then successfully applied to the transmitter. Further dummy load tests will be used to verify operation status. Diagnostic Neutral Beam System ------------------------------- The beam continues to operate with very good performance. It has been firing into C-Mod plasmas every run day with very few faults. Typical parameters are 49 kV, 4A beam current. BES and MSE diagnostics are being brought on-line. Lower Hybrid Project -------------------- We continue to bring up the phase and amplitude control system for the klystrons. A representative from the vendor providing some of the control software will be here this week to help develop the routines that communicate with our MDS-Plus software. Other programming issues will also be addressed. Mock-ups of the waveguide runs that will connect the klystrons to the launcher have been built up in the cell in preparation for placing the order for the waveguide. Travel and Visitors ---------------------- Paul Bonoli attended the International Sherwood Fusion Theory Conference in Corpus Christi, Texas. He presented a poster titled "A Comparison of Different Models for Lower Hybrid Current Drive". Co-authors on the paper were Miklos Porkolab and John Wright from MIT and Bob Harvey from CompX. Doug Loesser, Joe Frangipani, and Dave Miller were at MIT this week to disassemble the LH launcher for C-Mod vacuum preparation. Martin Greenwald visited Dartmouth College to deliver the weekly physics colloquium and to confer with Barrett Rogers on edge turbulence and the density limit.