Alcator C-Mod Weekly Highlights April 19th, 2011 FY2011 weeks of research operations Target: 15 weeks Completed: 14.5 weeks Plasma Shots: 1706 Operations ---------- C-Mod was vented to air on Thursday of last week after one day of glow discharge cleaning to reduce the levels of heavy boron compounds on he vessel walls. On Friday, following several pump-down and up-to-air cycles to reduce the boron levels still more, the diborane monitors no longer indicated any diborane at the parts-per-billion level. The vessel was then left vented, and the first radiation level survey was conducted. Preparations are being made for vessel manned entry. Maintenance of major C-Mod engineering systems has begun including the magnet power supplies and breaker systems, and the alternator. ICRF Systems ------------ We have secured the J-Port antenna transmission line and have tagged out D and E antennas in preparation for vessel entry and dummy load repair. The SOL reflectometer wr90 waveguide run over the A and B ports has been removed to allow crane access at B port. The back plates for the new rotated ARRA funded antenna are being inspected by our vendor, and they have sent pictures of the back plate with additional side plates fitting into place on the back plate. We accepted delivery of one of the two remaining top/bottom plates. We have started EDM fabrication of another long strip line. We have sent the final set of Faraday rods out for polishing to remove minor tooling marks. Our vendor is preparing to plate a set of trial tubes to qualify the process for plating the inside of the bellows tube assemblies. We have also prepared a set of plates and strip line covers for plating. A teleconference with our vendor to discuss the progress of the FFT fabrication was held last week. Lower Hybrid System ------------------- Progress on the 4th klystron cart continues. The CAD model of the cart was upgraded to give the filament power supply vendor accurate space constraints for their system. New digitizer mounts were designed and are awaiting fabrication. Preparations were made to test the low power phase shifter and attenuator (possible replacement for the vector modulators) as an integrated part of the klystron control loop. Bench tests for the components were favorable, and a "live" test of the components controlling an actual klystron will show the real performance that can be expected if a decision is made to replace the vector modulators. A shielded box for the phase shifter/attenuator has been designed and is being fabricated. Travel and Visitors ------------------- Amanda Hubbard and Paul Bonoli attended the 6th Meeting of the ITPA Topical Group on Integrated Operation Scenarios (IOS) that was held at JET, Culham, UK, 11th to 14th, April 2011. Amanda gave an overview talk on recent research on Alcator C-Mod in support of ITER Scenarios and also gave a talk on recent progress and 2011 plans for the Joint Experimental Activity IOS-5.3: "Assessment of lower hybrid current drive at high density for extrapolation to ITER advanced scenarios". Paul gave a talk in which he reported on the status of the Joint Modeling Activity on Steady State Exploration (IOS-JA7). The C-Mod RF Group's contribution to the IOS 5.2 joint experiment on maintaining ICRH coupling in the expected ITER regime was presented by Marie-Line Mayoral (JET) at the ITPA IOS meeting in Culham. The scrape off layer density profile and ICRF loading were characterized under a variety of conditions including gaps as large as 12 cm. Except in the cases with large gap, the loading is more dependent on the SOL density profile than the evanescent length and independent of additional gas puffing. Impurity seeding with N2 and Ne improved antenna resilience to arcing without modification of the SOL density profile. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly