Alcator C-Mod Weekly Highlights December 31, 2012 FY2013 weeks of research operations Target: tbd Completed: 0.53 weeks Plasma Shots: 61 Research -------- As part of the LLNL/PPPL/MIT collaboration, core molybdenum impurity content was estimated in molybdenum dominated plasmas using two techniques: total radiated power and VUV atomic line emission. Estimates of relative molybdenum content in ICRH heated plasmas with monopole vs. dipole operation from both techniques were shown to roughly agree during 100ms steady state conditions. Core molybdenum content was estimated to increase by only 5-25% during steady state periods of monopole vs. dipole ICRH operation. Operations ---------- Monday and Tuesday of last week were MIT holidays. The remainder of the week was used to continue work on routine maintenance of engineering systems. Maintenance was completed on the alternator drive motor control system and the alternator seal oil system. In-vessel calibrations continued. Advanced Outer Divertor (AOD) ----------------------------- Updates on EF1 heat shield and floor tile drawings, and changes to drawings specifying tile locations are in process. Work on the radiation shield specifications and power control procedures continued. Procurement is underway for Inconel sheet material needed to fabricate the sheet shunt prototypes. Analysis of the sheet shunt configuration continues, as does work on the AOD COMSOL disruption analysis model. Sample tungsten bar material supplied by one of our vendors is in-house, and a plan for qualifying this material for use as tiles in the AOD is being developed. ICRF Systems ------------ Work continued on preparing the FMIT#3 and #4 transmitters for operation at 53 MHz. All metering issues have been resolved. Lower Hybrid Systems -------------------- A new ferrite test component has been baked and installed in the lh fft tuner waveguide. The fft will be tested at high power using SF6 or N2 to pressurize the waveguide. Tests will begin as soon as a leak at one of the waveguide flanges is sealed. Work continued on the high level System on a Chip (SOC) boards needed for advanced lh control system functionality. These boards will be capable of direct interaction with our MDS+ data acquisition servers. Diagnostic Systems ------------------ The MSE automated robotic calibration system has been installed in-vessel. The system performed the post-campaign calibration of all the MSE channels without human intervention; a task which traditionally requires multiple days of manned access. The system has completed additional automated scans while operated remotely from off-site. The MSE inter-shot calibration system, installed in FY11 and operated successfully over the previous campaign, is designed to calibrate the MSE diagnostic in-vacuum immediately after a plasma discharge. In order to better quantify the applicability of this new system, it was operated simultaneously with the automated in-vessel calibration system while heat was applied to various MSE optical elements, causing stress-induced birefringence. The two calibration systems were used at all MSE channels, at multiple polarization angles, throughout the heating and cooling of the optical components. The time-resolved diagnostic response inferred from the inter-shot system will be compared to the diagnostic calibration determined by the more established in-vessel calibration method to determine how accurately the inter-shot calibration system tracks the induced polarization calibration drift. The conclusions of this test will be propagated to the MSE error estimates in the magnetic reconstructions for the previous campaign. The shoelace antenna has been removed from the vessel and is undergoing an inspection. This system has been operated successfully over the past two run campaigns after its initial installation in August 2011. However, two rungs of the antenna's molybdenum windings were damaged during a series of high-power I-mode discharges late in the FY2012 run campaign. Local heat deposition from ICRF-driven energetic minority ions is thought to be responsible for melt damage, which resulted in two rungs developing open circuits. Plans are being developed for re-stringing the antenna, with the possible option of removing two or more of the rungs located near the outer midplane. In addition, the antenna's winding pitch may be changed from 14 degrees to 10 degrees. This change would allow the antenna to couple to a higher range in q95 (between 3 and 5) and thus enable the A-port scanning probe system to be used to interrogate the structure of driven modes, which have been found to map magnetically to the antenna windings. An interference has been discovered between the polarimeter shutter bellows and the vessel wall that may explain erratic behavior of the shutter during the last run campaign. The shutter is being removed for a more careful evaluation and probable modification. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly