Alcator C-Mod Weekly Highlights June 7, 2004 The first plasma of Alcator C-Mod was included as one of the signature events noted in the timeline of Charles Vest's Presidency at MIT. It shares the 1993 page with the Nobel Prize to Phil Sharp, Houseman's identification of the Huntington's disease gene, Widnal's appointment as US Air Force Secretary, need-blind admissions, and the visit of Carlos Salinas (president of Mexico) to speak at Commencement. A link to the timeline can be found at http://web.mit.edu/timeline/93.html Last week we continued invessel work, development of the lower hybrid system, and general maintenance of ICRF and power equipment. Operations ---------- We continued work on the TF converters with upgrades to the driver boards. The 480/4160 transformer in the power room has been disconnected and moved out of the way in preparation for the new DNB transformer. A new conduit from the power room to the control room UPS has been run. This run will provide a backup power source for the UPS. We continued maintenance on the alternator systems. The cooling water valves, the 4160 V breakers, and the 13.8 kV switchgear are being checked and refurbished. We also continued invessel documentation and MSE calibrations. The fixturing for the MSE linearly polarized light source has been installed, and measurements of polarization fraction and direction have been done for channels at the edge and at the mid-radius. As expected, the instrument has excellent linearity on its optical axis, but degrades somewhat towards the plasma edge. Stray polarization of plasma emission was found to be about 3%, and background reflection from the RF antennas was found to be negligible. Magnetic fields applied to the PEM's had an insignificant effect. Work continues on calibrating the remainder of the MSE channels. The bolometer box and associated cabling have been removed from the vessel and are being setup in the lab for testing and eventual upgrades. ICRF Systems ------------ With the J-Port antenna removed from the machine, discharge tracking and melting of stainless steel surfaces behind the back plate on straps 1 and 4 have been observed. We are evaluating how a voltage could be developing between the antenna back plate and the vessel wall, while investigating a number of approaches to improve the contact between the vessel and the antenna structure. CPI has confirmed the first new 4CM25000KG (2274) tube is ready for shipment. These 2 MW, CW tubes are used by both MIT and PPPL in the transmitter final amplifier stage. Since NSTX is currently in operation, and may require a spare tube, we have agreed to let the first tube go to PPPL. The next three tubes are expected to ship 6/14, 7/13, and 8/14 to MIT, in time for the beginning of our next run campaign. A development project has begun with Kurt Slenes of TPL, Inc., Albuquerque, NM, to provide high dielectric constant material for external RF DC breaks. The proposed material, with a dielectric constant of 40, will replace the kapton (dielectric constant of 3.5) in the PPPL designed DC breaks. This change is aimed at reducing the RF leakage associated with the present breaks. New digital panel meters have been installed to better indicate transmitter tuning element positions. This upgrade should make tuning the transmitter much easier and more reliable. The low resolution position indicating potentiometers will be replaced this week. All transmitter cabinets were opened, thoroughly cleaned, and inspected. Several long lead time components, primarily high voltage semiconductors, were identified as candidates to be added to our backup list. A search for a vendor or alternate component is underway. Lower Hybrid Project -------------------- A set of twelve copper plated alumina windows arrived in-house from our vendor last week. These windows will be subjected to braze tests, including production of a 3-window prototype. Following a positive evaluation of the braze, the vendor will produce the first 100 production windows to be used in the couplers. New solenoid power supplies are being installed on the klystron carts. One new supply is currently installed. The other two supplies have been tested and will be installed this week. We continue to analyze the discharge observed on the outside of rwg during high power testing. A simulation model has been developed of the rwg guide and is being run with various boundary conditions and guide gap widths. A mechanical model of the guide has also been developed to be used in designing alternate clamping schemes. Work continues on the klystron filament voltage and current monitor board. The voltage to frequency converters are operating properly and at the correct frequencies. An oscillation occurs on turn-on when the power monitor IC switches on and off over a small input voltage range. This issue should be easily resolved with a programming change. LH heater chassis wiring is complete and ready for testing. Calibrations of the lower hybrid SFOL boards that link the IQ detectors to the control system are in progress. Diagnostics ----------- A set of buffer amplifiers is being added to the TCI system to help with alignment and general monitoring of the system during operation. Upgrades to the TCI amplifier box, its power supply and front panel, and all associated cable runs are being implemented. A complete documentation package detailing the two years of operation of the short pulse RFX DNB on C-Mod is being prepared for use by the RFX group. This package should be of great use to the beam operators in Italy. We continued work on the PC board layout for the prototype Thomson scattering integrators. Work on the CPCI interface to the integrators also continued. Progress was made last week on the new Active MHD control interface. Travel and Visits ----------------- Martha Redi, PPPL, was at MIT on June 4th to continue her discussions with John Rice and others about the analysis of off-axis ICRF-induced ITB experiments and her EPS 2004 manuscript. Kent McCormick of IPP-Garching visited MIT and spoke with a number of scientists about the HDH-mode on W7-AS. He also gave an informal seminar on the W7-AS HDH-mode results in comparison with EDA H-mode and other steady ELM-free regimes on other machines. Naoko Ashikawa, a member of the LHD wall conditioning group, NIFS, visited last week. She discussed boronization, glow discharge cleaning, and ECDC with Earl Marmar, Jim Irby, and John Rice.