Alcator C-Mod Weekly Highlights December 23, 2002 The maintenance period continued on Alcator C-Mod last week. Invessel work on diagnostic systems, ICRF antennas, and wall tiles proceeded. Work on the LH MIE Project and the ICRF transmitters continued. Operations ---------- All three antennas have been disassembled and are being carefully inspected. J-Port antenna tiles that fractured during the last run campaign have been redesigned. A prototype will be fabricated and tested on our vibration test stand. The upper cryostat cover has been removed and an inspection of all instrumentation cables is underway. Improved insulation and chafe protection is being added to the lower TF arm instrumentation. Inspections of the vertical TF arm instrumentation is also proceeding. Physics ------- C-Mod program milestone 71.0 was completed in November, 2002: 71.0 Measure current density profile with MSE. An MSE system, operated in conjunction with the DNB, is being installed and the system will undergo evaluation. The MSE diagnostic on C-Mod has successfully measured the current density profile over the entire minor radius at densities relevant for the planned lower hybrid program. Field pitch angles are determined with error bars of 0.1-0.3 degrees, even near the plasma center, at line-average densities up to 1e20 m-3. The error bars are determined from shot-to-shot scatter and from the standard deviation during a single-shot beam pulse. Changes in the current density profile that occur with the onset of sawteeth have been observed. MSE has also documented that ICRF heating during the early current ramp does indeed affect the current profile. Pitch angle profiles at even higher densities, up to 2e20 m-3, have been measured over the outer half of the plasma radius with good accuracy. The signal-to-background ratio becomes an important issue at higher densities, but improved analysis methods are being developed to better filter out the background, and a background emission monitoring system will be incorporated into the present MSE system to better characterize the plasma emission. Lower Hybrid Project -------------------- Work continues on the HVPS crowbar. Preventative maintenance on the klystron vac-ion pumps has been completed. Installation of the fast body current sensors continues. Design and testing of the serial-fiber-optic-link (SFOL) is nearly complete. The Low Power Microwave rack SFOL receiver chassis assembly including wiring is complete. The Low Power Microwave rack SFOL transmitter chassis assembly is near completion, and the parts have arrived to finish the I/Q detector wiring inside the chassis. ICRF ---- The S-parameters for the D, E, and J-Port antennas have been measured and compared with previous measurements. No substantial differences were found. An rf model is being developed to evaluate the best position and design for new voltage and current probes on the D and E-Port antennas. The FMIT4 FPA was reassembled, tuned to 70 MHz, and tested successfully for 4 second long pulses at 1.6 MW into the General Atomics dummy load. Tests will also be run at 78 MHz. Diagnostic Neutral Beam ----------------------- Conditioning continued this week as the beam performance continued to improve. Full length beam shots at currents of approximately four amps were obtained. The background pressure showed slow increase during beam operation indicating that the beam source is still outgassing. Travel and Visits ----------------- Martin Greenwald traveled to PPPL for the NCSX PAC meeting and to consult with Doug McCune on TRANSP implementations. Mark May from LLNL visited C-Mod from December 9th to 12th and presented his visible spectrometer for toroidal rotation measurements at the weekly meeting. He plans to measure rotation in the outer half of the plasma (r/a > 0.5) from the Doppler shift of visible M1 lines and charge exchange lines populated through interaction with the neutral beam. He discussed the proposed diagnostic and measurements with John Rice, Jim Terry, Bruce Lipschultz, and William Rowan (U Texas).