Alcator C-Mod Weekly Highlights August 9, 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 in-vessel activities are ongoing in support of ICRF and diagnostic systems. Maintenance and upgrades to diagnostic and power systems are also in progress. Physics ------- The double magnetic probe and Phase Contrast Imaging (PCI) diagnostics took data simultaneously during the run of 1040416 in EDA H-mode with a JFT-2M-like plasma shape. Both diagnostics measured a double quasi-coherent mode (QCM) with frequencies of about 65 kHz and 130 kHz throughout the EDA H-mode. This run day was the first time such harmonics of the QCM have been observed. The measured poloidal wave number k_theta, just above the outboard mid-plane, as measured by the double magnetic probe, was about 1/cm for the lower frequency mode and 2/cm for the higher frequency mode. The PCI measured radial wavenumbers of about 2.5/cm and 5/cm for the two frequencies at the top and bottom of the plasma. Calculations, assuming a field-aligned perturbation, of the radial wavenumber at the top and bottom of the plasma at the last closed flux surface based on the magnetic measurements indicate that the radial wavenumber should be roughly 4/cm there for the higher frequency mode. This wavenumber is somewhat smaller than the 5/cm measured by the PCI, and we are working to understand this difference. The lower frequency mode was also visible on toroidally separated pick-up coils on the outboard limiter, apparently because of the lower poloidal wavenumber. The resulting toroidal mode numbers ranged from 4 < n < 14, which is also somewhat lower than the typical n numbers for QCMs with normally shaped plasmas. The PCI also shows a broader radial k spectrum at the top than at the bottom of the plasma for these QCMs. Operations ---------- We continued the PC to PLC interface software upgrade last week. New PCs with the software upgrade have been moved into the control room where live control tests of the CRYO system will begin this week. We began to re-install the inner wall tile modules last week following an extensive cleanup and vacuum bake campaign. Ninety-six of 120 modules are now back in-vessel. Refurbishment of the scanning inner wall probe has been completed. Lower Hybrid System ------------------- One PPPL coupler and two 3-window braze test samples have been copper plated. These components were baked over the weekend to clean them and verify the surfaces were properly plated. Brazing of these components is scheduled for later this week. Worked continued on the microwave probes last week. Positioning pins, housings, installation tooling, and tests fixtures are being fabricated. A recently reconditioned klystron is being returned to the company for repair. The problem has been tracked down to an improperly fabricated filament/cathode assembly supplied by the vendor. This problem affects at least two of our spare klystrons. New assemblies will be procured and repairs will be made by the vendor under warranty. We continue to develop the phase and amplitude control system. Links to MDSplus continue to be developed. Vector modulators are being tested and made operational as part of the control loop. Components have been fabricated in our shop to allow better alignment to be maintained between the forward and rear waveguide assemblies. A re-evaluation of the rf gasket that electrically joins these components is being pursued. Some reduction in the gasket spring constant may be required to ensure good rf contact. Diagnostics ----------- We continued the two-color interferometer upgrade last week. New cabling, buffer amplifiers, and alignment fixtures are being fabricated and installed. Travel and Visits ----------------- Dr. Sang Gon Lee is visiting from the Korean Basic Sciences Institute (KBSI), as part of a collaboration on x-ray spectroscopy with John Rice, Alex Ince-Cushman and Manfred Bitter (PPPL). He will spend two weeks at the PSFC, and is helping to set-up a crystal spectrometer on loan from KBSI which is aimed at pedestal/edge measurements of ion temperature and rotation profiles using highly charged neon ions. Dr. Myoung Chul Kyum and Dr. Charles J. Ju also from Korea Basic Science Institute met with Tom Fredian, Josh Stillerman, and Steve Wolfe last week to discuss MDSplus, data grids, and general data system, database, and plasma control issues for k-star.