Alcator C-Mod Weekly Highlights February 12, 2007 FY2007 weeks of research operations: tentative target: 15 weeks Completed: 0 weeks Physics ------- High frequency steady TAEs in the frequency range from 600 kHz to 1.2 MHz have often been observed in H minority ICRF heated Enhanced D-alpha H-modes on C-Mod. This frequency range corresponds to the TAE frequency around q=1 so these appear to be modes excited in the core. Since they were not previously observed in lower density L-modes or in ELM-free H-modes, and since the time history of the frequency tracked that of the quasi-coherent mode in EDA H-mode, it seemed that there might be some form of coupling between the edge QCM and the core TAEs. Recently, however, similar TAEs with the same toroidal mode spectrum in the range of 6 < n < 10 have been observed in nearly the same frequency range during a series of ICRF heated ELM-free H-modes at low density with reversed field. It was also noted that the modes stabilize when the ICRF power level is dropped to between 2.5 and 1.3 MW, indicating that a substantial drive is necessary to excite these modes. So, while there may still be coupling of a radially broad core TAE with an edge QCM in cases in which both modes are present, it is clear that the TAEs can be excited and persist throughout much of the ELM-free H-mode phase without a QCM present. Operations ---------- A dry nitrogen gas purge of the Alcator C-Mod cryostat was begun last Thursday. This process is required to reduce the water vapor in the cryostat to below 200 ppm at which point we can introduce liquid nitrogen to the sump for cooling the magnets. The HEAT system, thermocouple scanners, ECDC, vacuum, and other systems required for bake and wall conditioning are being brought back on-line. Cryopump -------- Installation of upper divertor protection hardware, gas baffles, in-vessel feedlines, and vacuum feedthroughs is proceeding. Development of PLC control software for the cryopump continued last week as did fabrication of the liquid nitrogen and liquid helium transfer lines and control hardware. Lower Hybrid System ------------------- Work continued last week on the new high power water loads. Assembly of the first load is complete, and it has been installed and is ready for high power tests. Low power tests of the load confirmed the simulation results indicating a very low reflection coefficient. Work also continued on the coupler protection system upgrade hardware and software. On Wednesday of last week a teleconference was held between MIT and PPPL to discuss the 2nd lower hybrid launcher and the hardware needed to feed it. The division of responsiblities for this upgrade was discussed. ICRF Systems ------------ All work has been completed on the control and protection system for the fast ferrite tuner (FFT). The Intermediate Power Amplifier (IPA) drive electronics for the #3 and #4 transmitters is being upgraded to provide more power to this stage. This change should make high power operation of the J-Port antenna more robust. The D- and E-Port antenna installation is complete. Work on the J-Port antenna has begun. Long Pulse Diagnostic Neutral Beam ---------------------------------- We continue to checkout and bring back on-line the DNB power systems. An upgrade to the gas system is nearly complete, after which we will be ready to test filament, arc, and accel supplies. Diagnostics ----------- Work continued on the fabrication, assembly, installation, calibration, and alignment of many in-vessel diagnostics including bolometry, Charge Exchange Recombination, Beam Emission Spectroscopy, Motional Stark Effect, polarimetry, halo Rogowskis, and probes. Travel and Visits ----------------- David Mikkelsen, PPPL, was at MIT all last week discussing experimental plans for the upcoming C-Mod campaign and collecting experimental data for turbulence simulations. The first data set obtained for analysis is a high power EDA H-mode, and GYRO simulations of its ohmic phase have begun. Several C-Mod scientists participated in the First Workshop on Diagnostic Development for Burning Plasmas, sponsored by the US-BPO Diagnostics Topical Group, at GA Feb. 6-8. Jim Terry, who is a Deputy Leader of this group, was one of the organizers of the meeting. He presented a talk at GA on ITER Issue Cards and also led a discussion on these issues. Amanda Hubbard and Steve Scott, who have been involved in USIPO Tasks on ECE and MSE diagnostics participated remotely from MIT, as did Miklos Porkolab, Joe Snipes, Jerry Hughes and Liang Lin. Charles Skinner visited MIT last Friday and was the PSFC seminar speaker during which he discussed dust measurements on NSTX. He also met with Catherine Fiore, Earl Marmar, Bruce Lipschultz, Dennis Whyte, Bob Granetz, Aaron Bader, and Steve Scott. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly