Alcator C-Mod Weekly Highlights Sept. 19, 2005 FY2005 weeks of research operations Planned: 17 weeks Completed: 18.4 weeks Operations ---------- Alcator C-Mod was brought up-to-argon last Monday after warming up to room temperature over the previous twelve days. The HEPAir blower was then used to purge clean room air though the vessel, and particulate, diborane, and oxygen levels were monitored for twelve hours to ensure the vessel was safe for manned entry. On Wednesday, the first manned entry was made, and documentation and cleanup was begun. In addition to the usual post-campaign assessments, we are carefully evaluating and removing titanium dust from the vessel. Preventative maintenance of the alternator systems continued last week. New filters for the lube oil system have been installed and an inspection of the heat exchangers has begun. Upgrades continued to the engineering PLC control system. Physics Research ---------------- Gas-jet disruption mitigation on C-Mod has been simulated (Mohammad Bakhtiari, Dennis Whyte, U. of Wisconsin) by using a new numerical gas flow model that provides the time history of the gas delivery rate and pressure into the plasma volume. The gas delivery is used as input to solve the evolution of the plasma ionization and thermal balance with the KPRAD codes, thus removing any adjustable parameters in the simulation except the particle mixing in the plasma. Using the assumption of strong MHD mixing, the simulation matches the measured timing of the plasma termination and the current quench rate to within ~25% for three gas species: Helium, Neon and Argon. The experimental data is found to be highly reproducible when simply organized by gas species. These results indirectly validate the robustness of the MHD mixing, which will be assessed in detail using NIMROD, and generally encourage the predictability of designing benign plasma terminations with the proper choice of gas species and their delivery rate. ICRF Systems ------------ Repair of the #3 transmitter power supply continued last week with replacement of diodes and snubbers where required. Preparations are being made to test the diode stack as soon as all the new components have been installed. We began to address intermittent faults on the #1 transmitter high voltage control system last week. Grounding issues with some of the instrumentation and faulted capacitors in the Ross bottle trigger circuitry are currently being investigated as possible causes. Work continued on the repair of the fast ferrite tuner (FFT) power supply. The FFT system has been moved from the power room to the rf lab following MIT's renovation of the rf lab space. Floor loading of the lab is now adequate for the FFT hardware. Work also continued on the fabrication of the new J-Port antenna septa, which are required when the antenna Faraday screen has been removed. The molybdenum components are back in-house following initial machining using a water jet cutter, and final machining is ongoing in our machine shop. Lower Hybrid System ------------------- New anodes designed to improve the plating inside the stainless steel coupler guides were fabricated last week. Tests will be conducted this week by a plating vendor using the new anode configuration. We have procured an eddy current meter that will allow us to make accurate measurements of the plating thickness inside the coupler waveguides at the window locations. Numerous samples with known plating thicknesses were checked with the new instrument to verify proper operation. Cross calibrations with our XRF instrument were also made. Several braze tests were accomplished over the weekend, to examine wetting of various plated and un-plated stainless surfaces, using both cusil and a possible alternative, Lithobraze 720. The latter is cusil with 0.3% lithium added, which may improve wetting of un-plated stainless steel. We continued work on detector diode calibrations of forward and reflected power. A system to generate arcs in a test waveguide is being developed so that arc protection instrumentation can be tested. Work on a 3rd harmonic arc detector continued. This system depends on the non-linear nature of the arcs to produce an unambiguous indication if arcs occur in the lower hybrid system. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly