Alcator C-Mod Weekly Highlights February 14, 2003 Work continued on ICRF components, the Lower Hybrid MIE Project, and fabrication of the new control coils. Results from gas conductance and flow experiments from the last run campaign are discussed. Physics ------- Analysis of gas conductance and flow data obtained from a series of dedicated experiments performed during the 1020725 run day (MP#313, "Instrumented Divertor Leakage Experiments") has been performed. In these experiments, a known deuterium gas flow rate was injected through capillary tubes located at a variety of points in the vacuum vessel where neutral pressures and/or gas flow (inferred via D-alpha emission) are also recorded (open ports, closed ports, under the C-divertor flap, and over the C and D-divertor flap). The idea was to run a reference discharge with no capillary puffs and record the pressures, and then repeat discharges with known capillary gas throughput at a variety of locations and measure the neutral pressures again (focusing on their change). From this data, the effective gas conductance was quantified (i.e., relationship between gas throughput and pressure difference). By puffing gas and recording pressure changes without plasma, the vacuum conductance was also measured. Conductances measured with and without plasma were used to constrain numerical modeling of neutral transport and to provide guidance for optimizing a cryopump located in the upper chamber. Analysis indicates a strong plasma plugging effect at locations where the divertor structure is opened for diagnostics access (the so-called "open-port" locations), as evidenced by a factor of ~4 reduction in the local gas conductance with plasma present. The effect is most dramatic for locations in the upper chamber region where there is no neutral baffle structure; a factor of ~5 reduction in the local gas conductance is found there. Gas conductance through an open divertor flap is measured to be a factor of ~3 lower than that which has been commonly assumed using the area of the open flap. The conductance through the flap is found to be similar with or without plasma present, indicating that there is no "plasma plugging" effect occurring at this location. The gas flow rate through a flap that is adjacent to an "open-port" location is found to be a factor of 2 lower than at a location distant from open ports. The latter result suggests that significant toroidal variations in the pressures exist under the lower divertor modules. A preliminary draft report can be found at: www.psfc.mit.edu/people/labombard/gas_cond_n_flow_meas.pdf Operations ---------- We continued with fabrication and installation of the new control coils. Four of the eight coils are now complete, and one has been installed on the igloo. Layout of the patch panel needed to connect the coils to the power supply has been completed and procurement of parts begun. ICRF Systems ------------ Work continued on the fabrication, copper plating, and installation of upgrade components for the antennas needed to improve voltage handling capability. Detailing of the BN tile modification drawings has been completed and machining on the new tiles will begin next week. Work on the control system upgrades continued. Diagnostic Neutral Beam ----------------------- Modifications to the java code that operates the beam are being made. The current software requires a manual START input from the operator at the control console before each C-Mod shot. This function will be automated before the next run campaign. Lower Hybrid MIE Project ------------------------ At MIT, the HVPS crowbar system is now operational with high voltage applied. The dummy load for the HVPS is being brought back into operation in preparation for tests of the HVPS and crowbar next week. We have received the first high power circulator from the vendor. A mounting frame is being fabricated to secure the circulator to the cart. Work continues on PLC control software, and the fast phase and amplitude control systems. Fiber optic terminations from the network lines to the transmitter data acquisition chassis have been completed. The fiber optic network lines have been successfully tested. At PPPL, removal of excess braze material from the air side of the ceramic windows for the LH coupler has been completed. Careful but tedious manual scraping and very fine sandblasting were successful in cleaning the ceramic surface. A far smaller amount of material remains to be removed from the vacuum side, and, following a vacuum leak check, the metal surfaces will then be copper plated. The remaining assembly work is also progressing well. A check on the delivery of outstanding procurements together with the in-house progress indicate completion by the end of March. Travel and Visits ----------------- Amanda Hubbard was at PPPL for a meeting of the FESAC Fusion Development Path Panel this week. Martha Redi, PPPL, visited MIT this week to work with Catherine Fiore and Paul Bonoli on analysis of the off-axis RF ITB for gyrokinetic drift mode instabilities. New results discussed were comparative simulations with the GYRO code and GS2, use of the GKV viewer for nonlinear simulations, and eigenfunction plots of instabilities in the ITG, TEM and ETG range of frequencies. Work is progressing on preparations for the spring meetings and journal publications.