Alcator C-Mod Weekly Highlights January 22, 2007 Physics ------- Paul Bonoli (MIT), John Wright (MIT) and Bob Harvey (CompX) have worked very closely over the past few months with Professor Ron Parker (MIT) and graduate students Andrea Schmidt and John Liptac to model and analyze LHCD experiments on Alcator C-Mod. They used the bounce averaged Fokker Planck code CQL3D combined with the ray tracing code GENRAY to compute the self-consistent evolution of the non-thermal electron tail during LHCD. The predicted electron distribution functions were then used in a synthetic diagnostic code to compute the hard X-ray emission. These results were compared with experimental measurements of hard X-ray spectra. Bonoli, Wright, and Harvey implemented CQL3D-GENRAY on the PSFC computing cluster MARSHALL, where the simulations were performed. They also worked with Schmidt to set up cases for analysis and investigate convergence problems between the Fokker Planck code and ray tracing related to proper choice of the velocity space grids in the Fokker Planck code. Detailed modeling of these experiments showed good agreement between the predicted and measured integrated current (ohmic plus LH) for a 1 MA discharge (shot #1060728014) and an 0.53 MA discharge (shot #1060728011). The measured hard X-ray spectra were found to be broader (spatially) than the predicted spectra from the synthetic diagnostic in the CQL3D-GENRAY model. This discrepancy suggests that spatial diffusion of the fast tail electrons may be an important effect. The next phase of this modeling activity will be to implement ad-hoc models for the fast electron diffusivity and study the effects on the driven current profile and electron distribution function. This analysis should serve as a basis to define future experiments for measuring the confinement time of fast electrons during LHCD in C-Mod. In general, the detailed comparisons between synthetic and actual hard X-ray diagnostics is serving as an important validation of the models employed in CQL3D-GENRAY in the LHRF regime. This modeling work was featured in an invited talk by Professor Parker at the 48th Annual Meeting of the Plasma Physics Division of the American Physical Society in Philadelphia, PA on Oct. 30 - Nov. 3, 2006. On Friday, January 19th, an Experimental Program Committee meeting was held to review the results of the task group prioritization activities, revise the run-time allocations, and develop a preliminary outline plan for the 2007 Experimental Campaign. Operations ---------- On Wednesday of last week the explosive fuses for the alternator were successfully tested by a representative of the fuse vendor as part of our standard preventative maintenance program. These protection devices are now ready for operation. These fuses can completely isolate the alternator from its load if a fault condition is detected. Work continued last week on the shutter system and retro-reflectors for the polarimeter. An electro-forming technique is being developed for the retro-reflectors. We also continued work on the bolometer components. Our liquid nitrogen vendor has repaired hairline cracks in the liquid nitrogen vacuum feed-line from the 19,000 gallon tank. Work continued on the new liquid nitrogen manifolds for the diagnostic labs and the cell. Preparations have been made for installation of the exhaust lines from the cyropump to the liquid nitrogen sump. Cryopump -------- Installation of the upper chamber cryopump was begun early last week and is now approximately 75% complete. The 1" diameter Inconel tube that makes up the primary pumping surface has been successfully welded and leak checked, as have most of the liquid nitrogen lines. Installation will continue this week. Lower Hybrid System ------------------- A second high power, long pulse circulator was brought back into full power operation last week. We will continue refurbishment and conditioning of the remaining circulators this week. Work continued on the Field Programmable Gate Array programming for the Coupler Protection System upgrade. ICRF Systems ------------ The control and protection system for the #2 Fast Ferrite Tuner (FFT) magnet power supply has been programmed and successfully tested. Work is proceeding on the #1 magnet power supply system. The E-Port horizontal extension is now installed and leak tight and ready for installation of the E-Port antenna as soon as the cryopump installation is complete. Travel and Visits ----------------- Last week Stewart Zweben, PPPL, was at MIT to help Jim Terry with the installation of the new divertor GPI view. The final optical alignment was done and the in-vessel bellows was successfully leak checked. He brought the new PPPL Phantom 7.3 fast camera to C-Mod and began to test its operation. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly