Alcator C-Mod Weekly Highlights June 2, 2008 FY2008 weeks of research operations: Target: 15 weeks Completed: 15.7 weeks PSI Conference -------------- Alcator C-Mod was well represented at the the 18th International Conference on Plasma Surface Interactions in Controlled Fusion Devices, held in Toledo, Spain, May 26-30. An invited talk was given by Bruce Lipschultz on "Hydrogenic retention in a high-Z plasma facing component tokamak Alcator C-Mod". Co-authors included D.G. Whyte, J. Irby, B. LaBombard, and G.W. Wright. Contributed orals included "On the consequences of neutron and plasma induced damage for fuel retention in the bulk of plasma facing materials", D.G. Whyte "Observations and Interpretation of the Spatial Structure of Edge Turbulence at the Outboard Midplane and High-Shear Region of Alcator C-Mod", J.L. Terry, S.J. Zweben, B. LaBombard, I. Cziegler, O. Grulke, R.H. Cohen, D.D. Ryutov, M. Umansky, T. Stoltzfus-Dueck, J. Krommes, D. Stotler. Posters presented were "H-mode edge profile modification and density control with pumping and magnetic balance regulation in Alcator C-Mod", J.W. Hughes, A.E. Hubbard, B. LaBombard, B. Lipschultz, R. McDermott, M.L. Reinke, J.L. Terry, D.G. Whyte "Relationship between Edge Gradients and Plasma Flows in Alcator C-Mod", B. LaBombard, N. Smick, A. Graf, K. Marr, R. McDermott, M. Reinke, M. Greenwald, J.W. Hughes, B. Lipschultz, J.L. Terry, D.G. Whyte "ICRF Specific Impurity Sources and Plasma Sheaths in Alcator C-Mod", S.J. Wukitch, B. Labombard, Y. Lin, B. Lipschultz, E. Marmar, M. Reinke, D. Whyte, and the Alcator C-Mod Team (presented by Bruce Lipschultz). Operations ---------- On Monday, shutdown and removal of equipment from the cell in preparation for the machine inspection was begun. The transmission line and matching components for all three ICRF antennas have been removed along with the E-Port Fast-Ferrite-Tuner prototype. Waveguide is being removed from the lower hybrid system and preparations are being made for phase and position calibrations of the launcher. Many diagnostic and C-Mod systems have been shut down and made safe for machine entry including the Two Color Interferometer, neutron and x-ray detectors, diborane system, glow discharge system, electron cyclotron discharge system, TV cameras, cyropump feed lines and control system, non-axisymmetric correction coils, and Thomson Scattering. The top of the machine is almost clear of equipment, and the igloo covers will be removed soon. Alcator C-Mod was brought up-to-air last Friday after approximately 24 hours of glow discharge cleaning in helium. Glow discharge cleaning reduces the levels of volatile boron compounds indicated by our monitors following the up-to-air. Diagnostics ----------- Perry Phillips, UT-FRC, has begun the design of a new enclosure for FRCECE with improved magnetic shielding and capacity for an additional RF mixer. The new mixer will be added to the FRCECE system to extend its electron temperature measurement capability to lower toroidal fields. Stray magnetic fields have been identified as the source of mixer failures in the past, and the new enclosure will reduce this effect. A prototype position feedback system for the polarimeter diagnostic was tested successfully during the last week of C-Mod operation. This system was able to reduce transverse vibration levels from a beam returned from the inner wall retro-reflectors by a factor 2 to 4 with a less than 3 ms response time. It also successfully compensated for long term shot-to-shot thermal drifts of the alignment. On 5/23 the vessel was backfilled with hydrogen and a successful calibration of the Thomson Scatterining system was conducted on 5/24. ICRF Systems ------------ Work continued on the design of the new 4-strap antenna. Simulations of the design are being performed, and a vendor is being chosen for the vacuum feedthroughs. Work continued on improvements to the documentation of the FMIT crowbar and hi-yard drawings. Lower Hybrid System ------------------- We continue to develop brazing and welding techniques for fabrication of the 4-way splitters and vacuum windows needed for the new launcher. An alumina window has been successfully brazed into a diffusion brazed stainless steel/copper/stainless steel waveguide laminate. The cover of the 4-way splitter prototype has been successfully ebeam welded onto the splitter body. A braze joint near the rf output window of our #117 klystron was identified as the source of the vacuum leak that required its return to the vendor last week. The vendor expects to seal the leak and attempt re-conditioning of the klystron over the next two weeks. Travel and Visitors ------------------- Bruce Lipschultz, Dennis Whyte, Brian LaBombard, and Jim Terry attended the 18th International Conference on Plasma Surface Interactions in Controlled Fusion Devices, held in Toledo, Spain, May 26-30. Pat MacGibbon was in California last week working with our vendor on the evaluation of the #117 klystron. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly