Alcator C-Mod Weekly Highlights March 05, 2012 FY2012 weeks of research operations Target: 17 Completed: 5.6 Plasma Shots: 753 Operations ---------- Alcator C-Mod has begun an up-to-air period which will last several weeks. A glow discharge was run for several hours in helium last week to help reduce volatile products produced during boronization and prepare the vessel for entry. The warm-up of the machine, which began on 2/24, is now complete, and the machine is ready to be brought up to air. During the up-to-air, we will modify the connections between the vacuum feedthrough and the current straps of the ARRA-funded advanced ICRF antenna. The new connections have been designed to be more robust and can be more reliably installed. A leak in the polarimeter shutter on the inner wall will be repaired, and modifications to several diagnostics will be made. The lower hybrid limiter configuration will also be modified. Installation of the new RFQ accelerator will begin. The accelerator will be used for between-shot surface analysis. ICRF Systems ------------ Our vendor is ready to start testing of the first ARRA-funded FFT pair as soon as a shipment of cables we have sent arrives at their site. One of our engineers is preparing to visit the vendor site to witness the tests. Our electronics shop continues to fabricate control components for the new FFTs. The repair to FFT#2 is nearing completion. The ferrite loaded strip line has been reassembled and the cooling lines were successfully leak checked. Series arcing on the transition from strip line to coax is a design issue that is being investigated. Different transition configurations are being modeled to eliminate this fault. Two ignitrons for the FMIT#3 transmitter crowbar have arrived and will be installed before operation resumes. Diagnostics ----------- The new intensified CID camera system from LLNL was fielded in the cell last week for tests of the data acquisition system. It was successfully triggered and data was stored in the spectroscopy tree. This system will be used to observe the spatial profile of molybdenum and boron sputtering and redeposition on the GH limiter. During the vent, the imaging system fiber bundle and final optics will be installed in the GH limiter viewing periscope at K-port. The camera will be relocated near K-port, and the system will be available for the duration of the experimental campaign. This diagnostic is being developed by Alexander Tronchin-James and Vlad Soukhanovskii as part of a collaboration with LLNL. A new paper in Review of Scientific Instruments on "Surface thermocouples for measurement of pulsed heat flux in the divertor of the Alcator C-Mod tokamak" by D. Brunner and B. LaBombard has been published can be found at http://link.aip.org/link/?RSI/83/033501 The paper discusses a novel set of thermocouple sensors that have been developed to measure heat fluxes arriving at divertor surfaces in Alcator C-Mod. These sensors operate in direct contact with the divertor plasma, which deposits heat fluxes in excess of 10 MW/m^2 over a 1 s pulse. Thermoelectric EMF signals are produced across a non-standard bimetallic junction: a 50 um thick 74% tungsten-26% rhenium ribbon embedded in a 6.35 mm diameter molybdenum cylinder. The unique coaxial geometry of the sensor combined with its single-point electrical ground contact minimizes interference from the plasma/magnetic environment. Incident heat fluxes are inferred from surface temperature evolution via a 1D thermal heat transport model. For an incident heat flux of 10 MW/m^2, surface temperatures rise 1000 C/s, corresponding to a heat flux flowing along the local magnetic field of 200 MW/m^2. Separate calorimeter sensors are used to independently confirm the derived heat fluxes by comparing total energies deposited during a plasma pulse. Langmuir probes in close proximity to the surface thermocouples are used to test plasma-sheath heat transmission theory, and to identify potential sources of discrepancies among physical models. Remote Participation, Travel, and Visitors ------------------------------------------ Martin Greenwald, Amanda Hubbard, Earl Marmar, and Miklos Porkolab attended the FESAC meeting in Bethesda, Maryland on Feb 28th and 29th. Martin is the FEASAC Chair, and Amanda is a Committee member. Both Prof. Porkolab and Dr. Marmar made public comments to FESAC concerning plans in the proposed FY13 FES budget. Dr. Marmar's comments can be found at http://fire.pppl.gov/FESAC_Marmar_Comment.pdf Greg Wallace and Ron Parker attended the KSTAR Workshop held in Muju Resort, Korea on February 22-24, 2012. The meeting was useful for identifying areas for potential expansion of collaborative activities between the PSFC and KSTAR beyond the ongoing collaboration in the area of lower hybrid coupler design and simulation. David Mikkelsen visited the C-Mod group to discuss turbulence simulations of an Ohmic rotation-reversal discharge and of ITB plasmas with off-axis ICRH, to discuss work-flow design for the data analysis server, and install the GACODE suite on the data analysis server. Robert Granetz was at the Institute for Plasma Research (IPR) in Ahmedabad, India last week for a meeting on Indo-US collaboration in fusion, and to discuss startup issues and magnetics instrumentation on the rebuilt SST-1 superconducting tokamak. At the Indo-US meeting, scientists working on ICRF and LH expressed keen interest in coming to C-Mod to perform experiments and observe operations. Field errors are a major concern for the SST-1 due to finite assembly tolerances. Methods for measuring, and possibly correcting, the field errors were discussed in detail. SST-1 is scheduled to begin operations later this summer, and would greatly benefit from collaborations with C-Mod. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly