Alcator C-Mod Weekly Highlights February 7, 2003 We continue to work invessel on diagnostics and instrumentation. Work on ICRF, Lower Hybrid MIE, and power systems proceeded. Physics ------- Matt Sampsell, UTexas, presented BES measurements of the quasi-coherent mode at the weekly C-Mod Physics Meetings. In discharges with highly collisional edges and central parameters with ne ~ 1.8 10^20 m^-3, Te ~ 2.5 keV, and Btor ~ 5.3 T, the peak relative fluctuation amplitude was found to be ~ 26% (ņe/ne). Three poloidally-spaced views at Rmid ~ 89 cm were used to obtain a poloidal wave number for the mode of ~ 2 cm^-1 and poloidal velocity of ~ 3 km/s. Radially-spaced channels located the mode in the steep gradient region, less than 1 cm inside of the separatrix, with a FWHM ~ 5 mm. Improvements to the BES spatial resolution were proposed for future experiments. David Mikkelsen, PPPL, spent the week at MIT refining estimates of the ion temperature profile in C-Mod plasmas. These estimates are based on solutions to an ion power balance equation using measured electron density and temperature, and DD neutron emission. Many sources of uncertainty are being included in order to derive a range of plausible values for R/L_Ti in several C-Mod plasmas, some heated purely ohmicly, and others also by ICRF. Operations ---------- Invessel work this week included installation of the new f-port probe cables. These cables were damaged during the last campaign when an open shunt connection forced currents generated during disruptions to find ground through the cables. The shunt connections are now being refurbished also. The first of the field control coils was completed and tested this week. The new control coil power supply was used to drive 3 kA of current through the coil. Instrumentation for the new supply including both PLC and CAMAC hardware and software was operated successfully. Winding of the second of the eight coils has also been completed. A new LN2 feedline to the ECE diagnostics lab has been completed and is now operational. This line will greatly ease maintenance of the LN2 cooled ECE detectors during C-Mod operations. ICRF Systems ------------ We continue to use the rf simulation code to model the fast ferrite tuners. We are looking at both waveguide and strip line structures. The antenna modifications have made good progress. The E-port flange has been installed on the machine after vacuum testing the individual feedthroughs. D-port flange has been removed for inspection and refurbishment of the feedthroughs. The new center conductors for the D and E-port feedthroughs have arrived from the vendor. The bushings for the center conductors have also been completed. The J-Port horizontal flange has been removed and modifications (additional 1/4-20 taps and copper plating) are expected to be completed early next week. Lower Hybrid MIE Project ------------------------ At MIT, the HVPS crowbar passed all tests prior to application of high voltage. We are now working through the fault detection system with high voltage applied. Arc detectors are now being tested and installed on the carts. Three detectors did not meet specification, but more than enough spares were available to populate the carts. Our first high power circulator was shipped by the vendor last week. The remaining circulators will be delivered by early summer. Detailed specifications are being developed for the waveguide flanges. A vendor for the waveguide and flanges will be determined within the next few days. At PPPL, the LHCD launcher is continuing to progress well. All components have now been ordered except thermocouples needed to monitor temperature throughout the launcher structure. The vacuum shroud and forward waveguide assembly have been welded and leak checked. Minor welding warpage has been corrected for exact fitup of the port extension to the waveguide. The radial motion device has been reassembled and tested. The forward waveguide/shroud assembly will be joined to the port extension and radial motion device on the RF Test Facility vacuum test stand in the coming weeks, and vacuum integrity and motion will be checked. The instrumentation patch panel is being fabricated, and its cabling is >50% completed. The rear waveguide is expected in house 2/13, the standard loops will be delivered 2/10, and the remaining components (high power phase shifters) are on schedule for delivery in February as well. Diagnostic Neutral Beam ----------------------- An intermittent inverter protection fault was tracked down and fixed this week. This fault has on occasion caused shortened beam pulses. A faulty IGBT was the cause of this problem. Travel and Visits ----------------- Bruce Lipschultz traveled to San Diego to attend the DIII-D Advisory Committee meeting, February 4-6. The committee reviewed the DIII-D group's presentations for their 5-year plan.