Alcator C-Mod Weekly Highlights October 27, 2008 FY2009 weeks of research operations: Target: TBD Completed: 0 weeks Physics ------- An ion trajectory tracing code is being developed at Purdue University by Jean Paul Allain and Jeffrey Brooks in collaboration with Dennis Whyte and Roman Ochoukov at MIT. The code self-consistently solves for ion trajectories in the sheath along the outer divertor plate of Alcator C-Mod. The primary goal is to develop a model that simulates the net erosion/deposition profile that is seen along the outer divertor of C-Mod. C-Mod data including electron temperature, edge density, grazing angles along the outer divertor plate from the EFIT reconstruction, and boron ion fluxes from spectroscopic views are used as input to the code. B3+ ions have been identified as the dominant sputtering species, even though their plasma ion fraction is < 1%. The current computation model has no means to account for ICRF effects on the sheath, and an analytic expression for the ICRF enhancement of the sheath that can be added to the model is being developed. On C-Mod a new mode of operation, the enhanced L-mode, has been discovered. This mode can persist for many energy confinement times and is characterized by an edge QC-like mode observed by magnetics and PCI between 100-150 kHz, H-mode energy confinement, L-mode particle confinement, increased co-current toroidal rotation, and increased edge poloidal rotation in the electron diamagnetic direction. Significant levels of edge Er shear have been observed in this mode without initiating the formation of a density pedestal. Operations ---------- We continued soldering of feltmetal to the TF vertical legs last week. Five of twenty legs are now complete. The fixturing needed to plate the TF core fingers is being fabricated. This equipment will be tested on a mock-up of the TF core before being used on the actual core. We also continued installation of the new heaters on the inner wall. Lower Hybrid System ------------------- High power tests of the copper plated 4-way splitter are indicating acceptable losses. Tests have been run at up to 259 kW for 0.5 s without faults in the splitter or the transformer. ICRF Systems ------------ The 10 kW solid-state Intermediate Power Amplifier (IPA) has been run into a dummy load successfully at full power using a temporary control box. Work is now underway to complete the control system interconnections, and run the IPA as part of the transmitter control system including cavity tuning. Diagnostics ----------- Jim Terry and Matt Reinke have been working with Peter Beirsdorfer, LLNL, to deploy a VUV/SXR flat-field imaging spectrometer on C-Mod for FY09. Its specialized grating covers a wide spectral range (1-5 nm or 5-20 nm) intended for low-Z and high-Z impurity monitoring. The instrument will eventually allow spatially resolved spectra to be collected. A metal (TZM) retro-reflector has been supplied by our vendor for use in the polarimeter diagnostic. Initial optical tests indicate good performance over a 10 m optical path-length. Survivability of the metal retro-reflector mounted on the C-Mod vessel inner wall is expected to be much better than the glass components tested during previous C-Mod campaigns because of TZM's much higher heat capacity, thermal conductivity, and improved sputtering characteristics. Travel and Visits ----------------- Jim Myra of Lodestar Research Corporation visited the PSFC to give a seminar on "Edge turbulence, blobs and interaction with sheared flows". While here he had extensive discussions with C-Mod staff on several topics, including plasma edge turbulence, RF-induced sheath physics and RF flow drive. Roman Ochoukov visited Purdue University last week to discuss the ion tracing codes being developed there in collaboration with Jean Paul Allain and Jeffrey Brooks. Paul Bonoli, Amanda Hubbard, Randy Wilson, Bob Granetz, and Steve Wukitch attended the ITPA meetings in Lausanne, Switzerland from Oct 20 to 22. Paul, Amanda, and Randy, attended the first meeting of the new Integrated Operational Scenarios group. Paul gave two talks: "Recent Progress on Advanced ICRF Simulations for ITER and Alcator C-Mod" and "Comparison of LHCD Predictions for Alcator C-Mod and ITER Using the LSC and CQL3D Codes". Bob Granetz attended the MHD group meeting, and Steve Wukitch attended the Energetic Particle group meeting. Jerry Hughes attended the ITPA Pedestal Topical Group meeting, and John Rice attended the Transport Topical Group meeting, both in Milan, Italy from Oct 20 to 22. The Pedestal meeting was a forum for personnel from C-Mod, DIII-D, NSTX, MAST, JET, ASDEX-Upgrade, JT-60U and TEXTOR to discuss ITER-relevant questions. Also, in a joint session with the Transport and Confinement Topical Group, they discussed efforts needed to project H-mode accessibility to ITER (i.e. L-H transition thresholds). Among the tasks needed is a careful compilation of data for L-H threshold experiments from multiple machines; an effort which will be organized by Jerry Hughes. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly