Alcator C-Mod Weekly Highlights March 28, 2005 FY2005 weeks of research operations Planned: 17 weeks Completed: 2.5 weeks Operations ---------- Last week was a scheduled maintenance period at Alcator C-Mod. No plasma operation was planned. Routine maintenance activities were carried out on the alternator system, cryogenics, vacuum, power systems, and control systems during the week. Instrumentation associated with a new control scheme for the non-axisymmetric field coils (A-coil) was installed. On Thursday and Friday a series of test pulses, including gas puffing, were performed to verify proper operation of a the data acquisition routines for pressure and RGA (residual gas analyzer) data before and after shots. This information is required for planned upcoming experiments. Plasma operations are scheduled to resume this week. Long Pulse Diagnostic Neutral Beam System ----------------------------------------- The beam installation is complete, and testing of all systems has been completed. Many final details need to be addressed, but the beam is ready for operation. Four members of the Russian team departed at the beginning of the week, leaving the principal engineer and physicist to finish beam conditioning and tuning. The beam was run at voltages up to 50 kV and beam currents of ~6 Amperes. The beam has been operated both with modulation and without modulation, and the longest unmodulated pulses have been ~ 0.5s. Further conditioning is required in order to run longer pulses. Mass flow controllers were installed in the anode and cathode hydrogen gas supply lines. Testing showed improvements in the beam current control during long pulse length shots. Early testing with the mass flow controllers revealed that increased flow was required in the anode gas valve. The valve was removed and a restriction orifice in the valve was changed to a slightly larger orifice. The valve was re-installed on the source, the source was leak checked, and re-evacuated. The gas flow was greatly improved to the anode, but the source needed to be re-conditioned after coming up to atmospheric pressure. Conditioning required a few days of vacuum pumping and beam conditioning shots, but the beam performance was back up to 6A, 50 kV as of mid-day Saturday. The vacuum hardware required for a new duct to connect the beam to the C-Mod vacuum vessel has arrived, and machining is in progress. Work continues on the interlock electronics required to allow the beam to fire into the vacuum vessel. Due to the higher available power and the longer shot capability in the new beam, additional interlocks on plasma conditions will be combined to give a "permissive" signal to the beam high voltage control electronics. The final two members of the Russian team departed on Sunday morning. Ten members of the beam installation team from Budker institute were working at Alcator C-Mod for the past month. Lower Hybrid System ------------------- Drive leg calibrations have now been completed for all twelve klystrons, and we are ready to drive all 96 coupler waveguides into vacuum and plasma. The installation of the rear launcher probes is complete, and the 48 probe attenuators have arrived and are being installed. The circulator for a klystron on cart 3 had to be removed due to excessive reflected power. The circulator was replaced with an older unit, and the vendor is being consulted. We received and successfully tested high power dummy loads for the launcher input switched load assemblies now being designed. The switches are on order and are expected next month. When completed, the new assemblies will allow switching each of the twelve transmitters from the dummy load to the launcher without requiring cell access. Calibration work associated with the CPS (Coupler Protection System) was carried out, but the work was hampered by data acquisition system difficulties. Temporary replacement digitizers have been installed and the CPS work is proceeding. ICRF System ------------ Maintenance was performed on the FMIT#4 crowbar trigger circuits. The unit was successfully tested and the transmitter is back in service. Pressure transducer signals for the J-port antenna system have been re-routed and connected. Diagnostics ----------- Work continued on the installation of the SiLi X-Ray detector. This system will allow simultaneous monitoring of Mo, Ti, Fe, and other high-Z impurities with time resolution as high at 50 ms. The new firewire based video camera software and hardware were tested during the week and optical filters added as required. The optical table for the polarimeter/interferometer prototype is nearly complete, and the polarimeter section of the diagnostic has been successfully operated in the lab. Travel and Visitors --------------------- Randy Wilson was at MIT for the week (a maintenance week), working with the C-Mod engineers on further preparations for higher power, longer pulse operation of the Lower Hybrid system. Dr. Nakanishi from NIFS visited Tom Fredian and Josh Stillerman for two weeks. Dr. Nakanishi explored data mining techniques to enable scientists to rapidly search for waveforms with matching characteristics. His approach is based on correlation of low frequency components in the power spectrum. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly