Alcator C-Mod Weekly Highlights November 1, 2004 FY 2005 weeks of research operation planned: 14 weeks, completed: 0 weeks. We are currently up-to-air with the primary goal of installing the lower hybrid launcher. In addition, a large number of in-vessel activities are ongoing in support of ICRF and diagnostic systems. Maintenance and upgrades to diagnostic and power systems are also in progress. Physics ------- Darin Ernst, Martin Greenwald, Ian Hutchinson, Earl Marmar, Miklos Porkolab, John Rice, Jim Terry, and John Wright are attending the IAEA Fusion Energy Conference this week in Vilamoura, Portugal. Alcator C-Mod papers and posters to be presented at the conference can be found at http://www.psfc.mit.edu/cmod/sciprogram/iaea/index.html Joe Snipes has been working with Nikolai Gorelenkov of PPPL to learn how to use the Nova-K code to model Alfven eigenmode stability in C-Mod ICRF heated discharges. The stability part of the code is a fully kinetic treatment with a distribution in pitch angle, a Maxwellian velocity distribution, and a radial distribution of the fast ion beta profile from TRANSP calculations. The experiments showed that for central or outboard resonances out to R_res/R_axis = 1.1, Alfven cascades and TAEs were unstable, whereas for inboard resonance heating at R_res/R_axis = 0.9 no Alfven cascades were observed and only a weak downward sweeping frequency mode was observed. To attempt to model this effect, the Alfven eigenmode stability was calculated for the central resonance case leaving everything fixed but varying the ICRF resonance position in the distribution function of the fast ions from R_res/R_axis = 0.8 to 1.14. A slightly reversed shear q profile was chosen with q_0 = 2.8 and q_min = 2.7 at r/a = 0.4. Two n=2 modes were found and their growth rates were the largest when the resonance was just to the outboard side. The growth rate fell off rapidly on the inboard side becoming stable for the lower frequency mode at 311 kHz by R_res/R_axis = 0.9 as in the experiment. The other mode at 385 kHz was also nearly stable by that resonance position. The mode frequency in the experiment was 360 kHz, just in between these two unstable modes, suggesting that a slight modification to the assumed q profile would be required to fit the frequency precisely. There was qualitative agreement between the experiment and the calculations in that the inboard resonance was stable or nearly stable to the calculated eigenmodes. Operations ---------- A review was held on October 26 at MIT to consider proposed changes to the alternator stator neutral grounding system. John Lacenere, PPPL, Bill Cary, General Atomics, and Steve Fairfax, MTechnology, served on the committee. We greatly appreciate their very useful input into this issue. Modifications have been made to the engineering display board in the C-Mod control room to allow a large video display screen to be installed. This screen will be used to display plasma videos and important physics and engineering data during the next run campaign. Work continued upgrading the TORVAC PC to PLC interface software. ICRF System ----------- Work continued on the crowbar trigger circuitry. One FFT (fast ferrite tuner) is ready for low power tests. Completion of the second tuner is awaiting delivery of a pressure control component. The rf bypass capacitors are ready to be welded onto the antenna side plates and installed in-vessel. This installation will complete all planned work on the J-Port antenna during this up-to-air period. Lower Hybrid System ------------------- Work continued on development of repair techniques for the #3 PPPL coupler. The #4 PPPL coupler and windows are now ready for brazing, pending good results from a final 3-window braze test now in our furnace. Assembly of the fwg/rwg (forward/rear waveguide) launcher components continued last week. We expect to complete assembly this week. The lower hybrid limiter is approximately 50% complete. We expect to finish this major in-vessel component within the next one to two weeks. Fabrication of the Coupler Protection System continues. Inter-chassis wiring has begun. The optical interface card has been ordered. We continued work on the filament V-f and f-V system. One rack chassis containing the receiver board, filament variacs, and the new digital panel meters is nearly complete. Filament transmitter boards have been calibrated, mounted, and connected in the high potential area on all twelve klystrons. Long Pulse DNB -------------- Working with one of one of our contractors, we have specified IOC (instantaneous over current) protection for the 5 kV circuit for the DNB, and price and delivery for new components is being determined. Another contractor is in-house installing the cable tray and 5 kV cable. Conduit and 120 VAC wiring for testing the 5 kV limit amp have been installed. Control wiring and status indication for the 5 kV breaker and limit amp are also being installed. The transformer support structure in the cell on the top of the DNB support stand has been modified to allow transverse mounting of the DNB transformer tank at the South end of the stand. This change was required due to the increased height of the new long pulse DNB. Diagnostics ----------- Ron Bravenec and Bill Rowan, UT-FRC, worked with Ed Fitzgerald to complete the design for integration of the new BES ferrule into the existing MSE/BES image dissector. Machining will start next week. Bill Rowan and Bob Granetz completed repairs to the CXRS shutter. Bill has also continued development of his Monte Carlo error analysis software for CXRS data. A reliable error estimate can now be assigned to the results of a non-linear parametric fit to the line blend observed. Travel and Visits ----------------- Monty Grimes, Bob Childs and Dexter Beals traveled to SLAC and to our klystron rebuild vendor Oct 20 through Oct 22. They received a good overview of the steps that SLAC uses to process their klystrons. They met with our vendor to review the rebuild process. Several changes to the process and materials used to rebuild the LH klystrons will be incorporated into the next tube rebuild. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly