Alcator C-Mod Weekly Highlights June 21, 2005 FY2005 weeks of research operations Planned: 17 weeks Completed: 9.4 weeks FESAC Facilities Panel Meeting ------------------------------ A Facilities Panel Meeting involving Alcator C-Mod, DIII-D, and NSTX was held at NRL last week. Earl Marmar, Amanda Hubbard, Martin Greenwald, and Bruce Lipschultz delivered presentations on C-Mod. The presentations along with other information may be found at http://www.psfc.mit.edu/research/alcator/pubs/Fesac/index.htm Operations ---------- Alcator C-Mod was boronized on Monday evening. On Tuesday,MP 415, Rotation and H-mode Thresholds for LSN and USN at different Ip and ne produced very interesting new data on L to H transitions. On Wednesday, MP 404a, Parametric Dependence of Moderate n Alfvén Eigenmode Damping Rates was successfully run. On Thursday morning a high temperature interlock caused us to suspend operations to repair a lubrication oil heat exchanger. This work proceeded into the weekend, followed by a successful full systems test. Alcator C-Mod resumed plasma operation on Monday morning. Physics ------- Last Tuesday, the H-mode power threshold as a function of plasma current for LSN discharges with nl around 0.9e20 /m^2 was partially mapped out. For 1.0 MA plasmas, H-mode was achieved with only 240 kW of ICRF power, for 0.8 MA, with 470 kW. H-modes were not obtained at 0.6 MA with up to 880 kW of RF power. All of these values are considerably lower than found previously, possibly due to the recent boronization, but emphasising the variability of results in this area. The 0.6 MA L-mode target plasmas had a stronger counter-current rotation, and subsequent higher H-mode power threshold, consistent with earlier speculation. On Wednesday the dependence of the Alfven eigenmode damping rate on plasma parameters was investigated. The plasma elongation was scanned from 1.15 to 1.65, and the active MHD frequency was swept 100 kHz above and below the TAE frequency as calculated with the Digital Plasma Control System (DPCS) in real-time. The real-time calculation agreed with the EFIT determined calculation within ± 10% and often with much better agreement. Weak TAE resonances were found. A detailed analysis of the resonances remains to be done to determine how the damping rate scales with elongation and/or edge shear. Lower Hybrid ------------ We continued simulation work on the water loads to be used on the rear waveguide section of the launcher. The loads will replace what is currently a shorting plate covering the waveguide. Designs for 3-window and 24-window stainless steel prototypes have been sent out for fabrication. The design of the full 24-window stainless steel coupler has been completed and a vendor selected with delivery expected early to mid August. FEA results continue to be very promising for this design. ICRF Systems ------------ Progress continues on the detailed design of the new 4-strap antenna. A problem with a low power RF driver limited use of the J-Port antenna last week. The driver has been replaced, and the system should be available for the runs this week. Travel and Visits ----------------- Traveling to NRL for the Facilities Panel Meeting were Earl Marmar, Bruce Lipschultz, Martin Greenwald, Amanda Hubbard, Bob Granetz, Ron Parker, Miklos Porkolab, Paul Bonoli, Steve Wukitch, and Steve Scott (PPPL). Jim Zaks and Dexter Beals visited Ceramics-to-Metal Seals Inc. to discuss the fabrication of replacement ceramic cathode assemblies for the lower hybrid klystrons. Refurbishment of more klystrons will add to the number of spares available for the 3 MW system and also help prepare for the eventual upgrade to a 4 MW source power system. Perry Phillips, UT-FRC, visited last week and installed the new local oscillator in the FRC-ECE. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly