Alcator C-Mod Weekly Highlights October 12, 2004 FY 2005 weeks of operation planned: 14 weeks, completed: 0 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 ------- Characterization of the transition from L- to EDA H-mode in C-Mod plasmas is being carried out using the recently upgraded PCI diagnostic. The number of channels has been increased from 12 to 32, and the sampling rate from 1 to 10 MHz. This expansion of diagnostic capability has been used to study broadband turbulence, in addition to the analysis of the QC-mode associated with EDA H-mode. Changes in broadband turbulence averaged over all wavenumbers at the transition from L- to EDA H-mode can be interpreted as being due to modifications of the Doppler rotation of the bulk plasma. Cross diagnostic correlations using additional fluctuation measurements of D-alpha light and the poloidal magnetic field show separate features in two different frequency ranges at the transition. Operations ---------- We have completed clean-up and re-assembly of the tungsten brush tiles. Following documentation of the tiles, a 500 C bake, and a welding operation to secure the retaining pins, the tiles will be ready to install in-vessel. Lower Hybrid System ------------------- The #3 PPPL coupler was brazed last Friday. Over the weekend we determined that at least two of the channels have voids and will need to be repaired. At planned, we are continuing to prepare the #4 PPPL coupler for brazing. As contingencies, the #3 MIT coupler, which is not yet brazed, or the #5 PPPL spare, which is brazed and leak-tight but requires final machining, could be used in place of #3 PPPL. Design of the protection limiters for the lower hybrid coupler is nearly complete. Simulation of disruption forces for both the limiter and the launcher grill indicate the design is acceptable. Plans for the launcher Langmuir probe array include six probes installed between the grills, with two each at the three poloidal locations. These probes will be used to monitor plasma density at the mouths of the couplers, one of the critical factors affecting wave-coupling through the scrape-off layer. Redesign work on the CPS (Coupler Protection System) continued last week. Changes are being made to improve the system flexibility. RF drive input to the klystrons can now be inhibited to individual klystrons as well as all klystrons together. ICRF System ----------- Two of three new 2 MW FPA tubes are now in-house and have successfully passed hi-pot tests. With delivery and a successful hi-pot of the third tube, we will have the full complement of four sources for operation, plus 2 high-power spares. We continued to work on fabrication of the rf bypass capacitor arrays for the J-Port antenna. Work also continued on repackaging of the FMIT crowbar trigger circuits. Long Pulse DNB -------------- We are preparing for installation of the new diagnostic neutral beam with particular emphasis on installation of the power services. Cable for the 5 kV service has been ordered. A vendor has been given the contract for installing this new service. Another vendor will verify settings, calibrations, and coordination for this new system. Conduit and cabling for control of the 5 kV breaker has been completed. The cable tray run for the 5 kV service has been laid out. Wiring from the 5 kV load side limit amp to the 4160/480 transformer has been completed. The final 100 A, 600 V disconnect has been installed in the cell. Work has continued on the hardwired control system for the new DNB AC power system. The master control drawing has been completed and is ready to be reviewed. Drawings for the auxiliary control stations are being produced. Diagnostics ----------- Bill Rowan, UT-FRC, is developing a Monte Carlo technique to analyze the error in the CXRS measurements of ion temperature and rotation. Initially, the analysis was used to determine the error of a line profile consisting of a single Gaussian. The error analysis technique was then modified to use a better representation for the signal-to-noise ratio and is now being applied to the actual line profile used in the CXRS analysis. Ron Bravenec, UT-FRC, began a two week visit to C-Mod to continue the BES fiber upgrade. During his last visit, he acquired and polished the fibers. During this visit, he will complete ferruling of the spectrometer end of the fibers. In this upgrade, the fibers that were previously in use were combined into a tightly packed configuration to obtain higher spatial resolution in the edge region. The newly acquired fibers will replace these in the coarse spatial array. We continued development of limiting amplifiers for the polarimeter prototype last week. Proper operation of the input filter was verified. Design of the rf drivers for the Bragg cells also continued. Travel and Visits ----------------- Catalin Teodorescu, University of Maryland, visited Jim Irby on 9/30 to discuss two-color-interferometry and plans for a new interferometer for the MCX experiment. Pablo Acedo, Carlos III University, Madrid, was at MIT on 10/7 and 10/8 discussing interferometry on the TJ-II Stellarator and interferometry and polarimetry on C-Mod with Jim Irby and Rick Murray. Joe Snipes visited with Nikolai Gorelenkov at PPPL 10/4 to 10/6 to learn to use the Nova-K code. Dexter Beals and Bob Granetz spent last week in Novosibirsk, Russia at the Budker Institute of Nuclear Physics participating in the successful operation, testing, and characterization of new long pulse DNB. They also discussed the installation schedule. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly