Alcator C-Mod Weekly Highlights July 6, 2004 FY 2004 weeks of operation planned: 18 weeks, completed: 18.9 weeks. We are currently up-to-air with the primary goal of installing the lower hybrid launcher. In addition, a large number of invessel activities are ongoing in support of ICRF and diagnostic systems. Maintenance and upgrades to diagnostic and power systems are also in progress. Operations ---------- We continued invessel work last week. After careful inspection and cleanup, the D-Port antenna current straps and Faraday shield were re-installed invessel. The boron nitride tiles on all three antennas will be replaced with molybdenum tiles for the next run period. This change will allow a direct comparison of performance using these two materials. Boron nitride on the MHD antennas will also be removed and the lower hybrid launcher will be installed with molybdenum protection tiles. We continue to remove, clean, and refurbish molybdenum wall tiles. ICRF Systems ------------ We continued to investigate the tuning of the FMIT #3 and #4 transmitters during 50 MHz operation. We now believe that differences in the positioning and composition of the ferrites used to damp high frequency oscillations result in the behavior seen. 50 MHz notch filters have arrived which should aid in the tuning at 50 MHz by eliminating any ambiguity about which frequency component is being monitored during tuning. Lower Hybrid Project -------------------- Tests of the amplitude and phase control timing board have been successfully completed, and this board is now considered ready for operation. Problems with the serial fiber optic link boards have been tracked down to damaged CPLDs (complex programmable logic device). The CPLDs will be replaced once a method to better protect them has been developed. We continued prototype testing of the lower hybrid vacuum windows last week. Some surface cracks in the alumina windows were observed in the latest 3-window sample. Another 3-window sample braze will be made this week with a change in the coupler wall thickness to reduce stress on the windows. Thirty-eight out of 48 waveguides of the rwg/fwg assembly have been power tested successfully to 100 kW for 0.5 s. One of the outer guides appears to be limited in power level by a discharge developing in the rwg. We will continue testing guides until all guides have been tested, and will then return to any problem guides for more evaluation. Diagnostics ----------- The in-vessel calibration of the Motional Stark Effect (MSE) diagnostic on Alcator is about 90% complete. Last week we completed the calibration of the system still in its configuration from the end of the last run campaign, including a coating on the plasma-facing first lens. Following the as-found calibration, a blackish coating was easily removed from the lens with distilled water, which is consistent with the coating being a boron compound. This step increased the lens transmission by at least a factor of two. We were not able to further clean the surface, and a new lens was installed, and re-calibration was begun. We have completed the major part of this process. There is little difference in the response to linearly polarized light between the coated-lens and new/clean-lens configuration. The error terms involving cos(2 theta) and cos(4 theta) are changed less than 10%, and the polarization fraction improves only by about 5%. Installation of the Active MHD amplifier, DC power supply and CAMAC rack AC power distribution system is underway. The construction of a low voltage MHD DC power supply for tuning purposes is also underway. We continued the refurbishment of the bolometer array and associated electronics last week. Work also continued on upgrades to the TCI electronics. Power Systems ------------- We continued to procure spare parts needed for the next run period. All spare fuse inventories except for the EF3 power supply are now up to adequate levels. Spare EF3 fuses will be in-house before the next run period. The maintenance on the alternator contactor panel is complete. All the needle bearings were replaced on the contactor solenoid assembly. All contactor auxiliary contacts were also burnished to remove oxidation. The 2000 HP alternator drive motor lift pumps have been serviced. The interior surfaces of the 2000 HP motor brush box, and also the brush rigging were cleaned and repainted with an insulating paint. New brushes were installed where needed. The brush rigging and armature windings were hi-potted successfully to greater than 1 GOhm to ground. A contract to upgrade the alternator river water supply cooling system has been awarded. This upgrade will provide a backup water cooling supply for the alternator and will greatly reduce operational down time if problems occur in the primary system. We are also working with GE to develop improvements to the stator neutral grounding system. Fault currents could be reduced substantially with carefully considered modifications to this system. A review process will be required before any changes are implemented. Travel and Visits ----------------- Bruce Lipschultz attended the ITPA Coordinating Committee meeting in Shanghai to give a report on progress of the work of the ITPA Topical group on SOL and Divertor phyiscs. He then went to the ASIPP in Hefei to see the HT-7 tokamak as well as learn about the status of the EAST tokamak. Bruce also visited the Southwestern Institute of Plasma Physics (SWIPP) in Chengdu. The EPS meeting in London, England was well attended by C-Mod scientists. Those attending included Nils Basse, Catherine Fiore, Amanda Hubbard, Ian Hutchinson, Alex Parisot, Miklos Porkolab, Joe Snipes, Martha Redi, and Gerd Schilling. Presentations made included: Fiore --- "Internal Transport Barrier Production and Control in Alcator C-Mod" (invited talk) Basse --- "Turbulence in Alcator C-Mod and Wendelstein 7-AS plasmas during controlled confinement transitions" (poster) Hubbard --- "Dependence of the L-H Threshold on Magnetic Configuration and Relation to Scrape-off-layer Flows" (talk) Hutchinson --- "Potential and Frictional Drag on a Floating Sphere in a Flowing Plasma" (poster) and "Spin Stability of Dust in a Flowing Plasma" (talk) Parisot --- "Initial results from phased ICRF operations on Alcator C-Mod" (poster) Redi --- "Benchmarking nonlinear turbulence simulations on Alcator-C-Mod" (poster) Schilling --- "Assessment of ICRF Antenna Performance in Alcator C-Mod" (poster) Snipes --- "Fast Particle Driven Alfv=E9n Eigenmodes in Alcator C-Mod" (poster)