Alcator C-Mod Weekly Highlights May 16th, 2011 FY2011 weeks of research operations Target: 15 weeks Completed: 14.5 weeks Plasma Shots: 1706 Operations ---------- In-vessel work last week included removal of several diagnostic and wall components for inspection and calibration or preparation for upgrades. The MSE and CXRS calibrations continued. We continued routine maintenance work on the magnet supplies and commutation switches. A full inspection of the thyristor transformers, the interphase transformers, the circulating current reactors, all cable assemblies and bus connections located inside and outside of the cabinets is underway, as is testing of all the convertor, crowbar and bypass cabinet gate drives. Routine maintenance of the alternator continued. ICRF Systems ------------ Work continued on the new ARRA funded rotated antenna. Two of the four straps have been polished and are being prepared for plating. E-beam welding of the rf feedthrough test samples is underway. Modifications to the sideplates to increase the rf voltage standoff capability are being done in our shop. The FMIT#4 driver stage has been reconfigured to allow rf breakdown experiments to continue during the up-to-air period. This work is part of an MIT graduate student thesis. Lower Hybrid System ------------------- High power tests of an updated lower hybrid fast ferrite tuner prototype were conducted this week. The FFT behavior as a function of external applied magnetic field was as expected based on low power tests, however the phase through the FFT drifted during high power (50+ kW) tests. Breakdown occurred at 75 kW along a thin piece of Teflon in the test waveguide. A new prototype without the Teflon is under construction for testing next week. Tests of the LH "Mod Box" phase shifters and attenuators continue. Calibration shots with good signal to noise ratio have been obtained using serial fiber optic links to set the phase shifter and attenuator control voltages. Diagnostics ----------- To assess the reproducibility of the MSE diagnostic over long time periods under benign conditions (no plasma; no vacuum), over a period of ~60 hours the MSE diagnostic was illuminated with linearly polarized light whose direction was varied with a rotational stage. Over this time period, the RMS deviation in measured angle was only 0.009 degrees, and the coefficients of two fit-error terms [the MSE measured angle varies linearly with incident polarization angle, with small cos (2 theta) and cos (4 theta) error terms] were reproducible to better than 0.004 degrees. So under these benign conditions, MSE’s reproducibility far surpasses the design goal of 0.1 – 0.2 degrees. In separate in-vessel calibration activities, it was demonstrated that the effects of swapping one avalanche photodiode detector and swapping one bandpass filter for another have negligible effects ( < 0.03 degrees) on the polarization angles measured by MSE. The design of the shutter for the new in-vessel, before/after shot MSE calibration system has been completed and quotes are being solicited for machining. Travel and Visitors ------------------- Plans are underway to upgrade the Thomson scattering diagnostic to use two 50Hz lasers. The new lasers will increase the reliability of this crucial diagnostic. A representative from a vendor being considered to supply these lasers visited with Jerry Hughes to discuss a proposal. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly