Alcator C-Mod Weekly Highlights August 28, 2006 FY2006 weeks of research operations: JOULE target: 14 weeks Completed: 16.7 weeks Operations ---------- Work continued in-vessel last week. All lower outer divertor modules have been removed from the machine and are being prepared for a careful inspection. Approximately half of the upper vessel protection hardware has been removed in preparation for installation of the cryopump. The alternator and flywheel lube oil heat exchangers have been cleaned. One heat exchanger spool piece has been sent out for repair following the discovery of localized corrosion. A vendor has been chosen to upgrade the piping supplying water cooling to the alternator lube oil coolers with stainless steel hardware. Lower Hybrid System ------------------- Faults in the lower hybrid high voltage power supply stopped testing of the klystrons last week. Discussions about the fault are ongoing with the vendor who supplied the power supply, and replacement components have been ordered. Work continued on the coupler protection system upgrade. The design of the FPGA programs and also the chassis communication scheme required for multiple chassis of fault/data acquisition boards are being developed. ICRF Systems ------------ Work on the fast ferrite real-time tuner system continued. Instrumentation needed to monitor the power supplies that drive the tuners is being debugged. Data acquisition and control hardware and software is being developed and tested. The J-Port antenna has been removed from in-vessel and is being carefully inspected as we try to determine the reason for problems encountered during the last run campaign. The #4 rf vacuum feedthrough shows some damage that may have contributed to the observed performance limits. Diagnostics ----------- Stewart Zweben, PPPL, has been analyzing a BOUT simulation by Maxim Umansky of LLNL for comparison with edge turbulence data in C-Mod. Steve Scott has completed a detailed analysis of recent spectrum measurements of the diagnostic neutral beam (DNB). The beam was fired into the C-Mod torus with a 1 mTorr helium backfill. Spectra were taken along two viewing sight-lines of the Motional Stark Effect (MSE) diagnostic, at two values of toroidal magnetic field (2.0 and 5.4 Tesla), and at two values of applied vertical field. The purpose of these measurements was to document the behavior of a spectral feature on the blue side of the unshifted H-alpha wavelength that would be emitted by charge exchange neutrals from ripple trapped fast ions. Howard Yuh of Nova Photonics, Inc. has conjectured that emission associated with this mechanism impairs the measurement of magnetic field line pitch angles by the MSE diagnostic. The observed dependence of the blue spectral feature on MSE channel number and on pitch angle are in good agreement with numerically simulated spectra computed from Yuh’s model. The magnitude of the blue feature is also in good (30-50%) agreement with the simulated spectra. These results are compelling evidence that this effect is the cause of long-standing MSE calibration anomalies when the DNB is injected into a gas-filled torus. The DNB will be rotated approximately 7 degrees toroidally during the present maintenance period to eliminate the source of the polluting fast ions. Leonid Dorf from the LANL P-24 Plasma Physics group and Jim Terry worked at Alcator C-Mod for a week between 8/17 and 8/23 to troubleshoot and upgrade the infrared spectrometer diagnostic installed at A-Top port. Installation of a new hard drive was required followed by re-installation of all data acquisition and control software. Alignment and calibration of the IR spectrometer was then begun. A new optical system setup uses a 75 mm focal length, 1.5" diameter BaF2 infrared lens to focus the beam from the existing IR Periscope, which views the lower divertor region, onto the entrance slit of the spectrometer. A hot molybdenum tile installed inside the machine in the field of view of the periscope optics was used to provide a thermal source. A Ne lamp emitting in the visible range was installed along the optical axis of the system, outside the machine, to assist with alignment. By comparing the signals received by the detector and the IR camera it was determined that the signal from the plasma will not be sufficient to be measured by the spectrometer's Hammamatsu IR detector array. The detector will be tried without the spectrometer, to determine the maximum IR signal level from the periscope, experimentally. Visitors and Travel ------------------- Mark May, LLNL, visited last week and had discussions with Alex Graff, John Rice, Jim Terry and Bruce Lipschultz on upgrades to the Visible Doppler Spectrometer as well as the best application for this diagnostic during the next run campaign. Leonid Dorf, LANL, visited MIT from 8/17 to 8/23. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly