Alcator C-Mod Weekly Highlights October 13, 2003 Alcator C-Mod resumed plasma operation last week. Work continued on Lower Hybrid and ICRF systems and diagnostics. Operations ---------- After extensive consultation with GE, the MIT alternator was brought back into operation on Wednesday and C-Mod power tests were begun. By Thursday afternoon all supplies and support systems had been tested and one plasma discharge was produced. On Friday, plasma cleanup continued, with the first full length plasmas of the campaign. Following successful vacuum conditioning, plasma conditioning of the D- and E-Port ICRF antennas was also begun. Diagnostic Neutral Beam ----------------------- We have continued to prepare the beam for plasma operation. Conditioning of the beam has resulted in reliably obtained peak beam currents of over 4 A, at voltages of 48 kV. ICRF Systems ------------ Both FMIT#3 and #4 (J-Port antenna transmitters) have been tested at 50 MHz to greater than 1.5 MW for 500 ms into a dummy load. The mechanical measurements of the cavities were taken for future reference and for inclusion in the cavity models. The tuning of the J-Port antenna, with the new external matching components needed for 50 MHz operation, has been found to be a very sensitive operation. This effect has caused some faulting of the J-Port antenna during plasma operation. We are addressing this issue. Lower Hybrid Systems -------------------- A design review was held at PPPL on 10/10 for the brazing of new ceramic windows into the Lower Hybrid coupler. Attending from MIT were Bob Childs, Jim Irby, Ron Parker, Rui Vieira, and Steve Wukitch. Attending from PPPL were Larry Dudek (chairman), Bob Ellis, Joel Hosea, Steve Jurczynski, Jay Kung, George Labik, Doug Loesser, Steve Raftopoulos, Gerd Schilling, Skip Schoen, and Randy Wilson. The review went extremely well, with comprehensive discussions of the relevant technical issues. We have agreed to begin preparing the couplers for brazing, including a modification to the coupler wall at each end to reduce the tensile force on the ceramic. Two of the three-window prototypes using the Gapasil brazing compound have been taken to MIT for additional tests. We continue to test the two reconditioned klystrons and prepare them for operation. NSTX X-Ray Spectrometer ----------------------- The NSTX X-Ray Spectrometer was installed and operated on C-Mod during the last run period. The X-Ray spectrometer is now operational again at C-Mod with several improvements. The spectrometer has been equipped with a new spherically bent quartz crystal, and a new 2D position sensitive detector with a spatial resolution of 0.1 mm will be installed this week. Due to these changes, the spectral resolution will be increased by a factor of 2 and the uncertainty for the ion temperature measurement will be reduced by a factor of 4 (from presently 600 eV to 150 eV). Brass plates with rectangular apertures were installed at the entrance and exit ports of the crystal housing to reduce the hard X-rays and bremsstrahlung background. A support for additional lead shielding of the detector has been fabricated and was installed last weekend. Travel and Visits ----------------- Marco Valisa is visiting from RFX, and has been able to run the beam and become familiar with day-to-day beam operation. Matt Sampsell and Bill Rowan, UT-FRC, assisted Marco in acquiring and analyzing the initial beam spectral measurements which will be used to determine the beam divergence and the acceleration voltage which produces the optimum component mix for the diagnostics. Stewart Zweben, PPPL, was at C-Mod last week to work on analysis of edge minority heating and edge turbulence experiments. Alan Lynn, UT-FRC, was at MIT last week to reassemble the FRCECE diagnostic. He returned it to operation in time for the first plasma shots on 10/9. Joe Snipes attended the IAEA Technical Meeting on Energetic Particles from 10/6 to 10/9 at General Atomics in San Diego where he presented a talk on Active and Passive MHD Spectroscopy on Alcator C-Mod. Paul Bonoli also traveled to General Atomics last week where he attended an ITPA meeting of the Steady-State and Energetic Particles Group. Jim Irby was at PPPL from 10/7 to 10/9 to serve on the NCSX Preliminary Design Review committee. Along with Bob Childs, Ron Parker, Rui Vieira, and Steve Wukitch, he also attended the Lower Hybrid Coupler Brazing Review on 10/10.