Alcator C-Mod Weekly Highlights February 14, 2011 FY2011 weeks of research operations Target: 15 weeks Completed: 11.3 weeks Plasma Shots: 1350 Operations ----------- Plasma operations continued at Alcator C-Mod last week. One run day was scheduled and completed. The experiment supported research in the Lower Hybrid Physics area. A total of 27 plasma discharges were produced with a reliability of 84%. The remainder of last week was devoted to scheduled maintenance. The principal activity was reconfiguration of the bus work and power systems for operation with reversed toroidal field and plasma current. Plasma operations are planned to continue this week. Run Planning ------------ A meeting of the Experimental Program Committee was held on Wednesday, Feb 9. Priorities for the remainder of the present campaign were discussed, and the operation plan for the next three calendar weeks was finalized. Eight mini-proposals were reviewed and approved. Operation Details ----------------- Monday's run was devoted to MP#641, " LHCD density limit in H and He discharges". The goal was to determine if a density limit for LHCD exists in H and He, and if so at what density. The density limit for diverted D discharges occurs at line averaged densities 0.8-1.0e20 m-3. The density limit in H was found to be at a slightly higher density than for D (0.9-1.1e20 m-3), but non-thermal electron emission drops to the same level as in D above 1.2e20 m-3. The density limit in He occurs at the same line averaged density as for H, however non-thermal electron emission falls less steeply above the density limit in He as compared to H or D. Limited discharges in D, H, and He do not exhibit a density limit across the range of line averaged densities scanned (up to 1.6e20 m-3). ICRF Systems ------------ Progress continued on fabrication of the ARRA-funded rotated four-strap ICRF antenna. The back plates fabrication drawings from our vendor have been reviewed, and we will visit their facility this week. The back center plate and Z plate are being machined in our machine shop and are nearing completion. The strip line shields have been sent to a vendor for fabrication. Issues involving translation of our solid model drawing files by the vendor are being resolved. We have successfully plated a stainless steel strap that had undergone the bead blasting surface treatment that will be used to remove the residue resulting from the EDM process. We have also tested the stripping and re-plating process and have successfully plated an inconel drop with detailed RF contact surfaces. The TZM molybdenum tiles are being rough cut from stock in preparation for in-house EDM machining. The port flange has been polished and passed our vacuum shop acceptance tests. The 45 degree coaxial elbows, part of the external coaxial network, have been received. The coaxial lines for the current and voltage probes and the SMA feedthroughs for these probes have been ordered. Bending of the TZM rods for the Faraday screen at our vendor is pending an inspection report on their ability to meet our specified tolerances and inspection of a sample rod. We have received the zirconium washers and are awaiting the zirconium tubes to complete the Faraday rod fastening system. Lower Hybrid System -------------------- The LH system was required for Monday's run on the LHCD density limit in He and H discharges. The system performed nominally with the alternative main ion species. Progress continues on the 4th klystron cart and transmitter protection system upgrades. Diagnostics ----------- The wide view CXRS was reconfigured for measurement of helium spectra for Monday's run. Ambient and CX spectra were acquired for helium fueled plasmas and for the trace helium in hydrogen fueled plasmas following the changeover to H. Results from this run demonstrate the ability to measure the spectra to trace levels of helium. Initial assessment of the data indicate that the analysis will produce helium density and temperature. Travel and Visitors ------------------- Paul Bonoli and Martin Greenwald attended a Planning Workshop for the Fusion Simulation Project that was held at General Atomics on February 8-11, 2011. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly