Alcator C-Mod Weekly Highlights March 27, 2006 FY2006 weeks of research operations: Planned: 14 weeks Completed: 5.9 weeks Operations ---------- Plasma operations continued at Alcator C-Mod last week. Four run days were scheduled and 2.75 days were completed. Repair of a capacitor bank and an alternator oil-pump motor contactor limited operation on Tuesday and Wednesday. Operations on Tuesday and Thursday were devoted to ICRF conditioning activities (MP#355), and the run on Friday was in support of MP#409, "SOL Phase Space studies". A total of 63 plasma discharges were produced with a reliability of 70%. Plasma operations are planned to continue this week. Physics ------- A report was presented at the weekly Science Meeting on the preliminary analysis of the ECE response to Toroidal Alfven Eigenmodes (TAEs) excited by an external antenna. A possible plasma response was observed through cross-correlation of the ECE signal with a monitor of the antenna. Signals were very small and additional work is needed to eliminate the possible cross-talk in the digitizers. Friday's run (MP#409, "SOL Phase Space") successfully obtained data in matched upper and lower single null discharges for a range of densities 1 < nebar < 3e20/m3 at 1.1MA plasma current. Data were obtained from scanning probes, fast diode signals and core (HIREX) rotation monitors. Preliminary assessment of the results indicates that, at 1.1 MA, core rotation in LSN is the same as USN for the same density discharge. In both cases, the rotation is seen to be a strong function of density. The parallel flows near the separatrix are also of similar magnitude in USN and LSN, although they are different farther out into the SOL. Flows on the inner wall still reverse (roughly) in LSN compared to USN. Flows near the separatrix at the outer midplane also exhibit a strong dependence on nebar (decreasing with density), which may relate to the observations of core rotation. Further analysis will compare the separatrix/core plasma flow values directly. Diagnostics ----------- Precision measurements of the gain ratio at 44 vs 40 kHz for the new MSE avalanche photodiodes confirm that the gain ratio has negligible dependence on intensity: as the intensity changes a factor of twenty, the gain ratio changes less than a factor of 7 x 10^-5, corresponding to a change in pitch angle of only 0.005 degrees. This result indicates that when avalanche photodiode detectors (APDs) are used, MSE calibration data can be applied accurately to pitch-angle measurements over a large dynamic range in intensity. The first measurements of plasma light with the new APD detector confirm that its sensitivity is ~30 times greater than the photomultiplier tube it replaces. Long Pulse Diagnostic Neutral Beam System ------------------------------------------ The high voltage transformer was successfully assembled, tested, and re-installed in the cell last week. Following a hi-pot, the transformer was successfully brought back into operation, and the DNB high voltage system was operated up to 40kV output with the original inverter control boards. One of the new high voltage inverter control boards has been tested at low power and found to have very good performance with clean operation at 20 kHz with IGBT turn-on rise times of less than 700 ns. Final component values for the board have been selected and the remainder of the boards are being fully populated. Final mechanical design of an electrostatic shield for the switching electronics is underway. Lower Hybrid System ------------------- Work on the Coupler Protection System (CPS) continued. Trip levels on the reflected power signals were set, and firmware to mask the turn-on transient for 40usec after the HVPS is energized has been added to the CPLD program in the interlock circuitry. ICRF Systems ------------ Conditioning of the ICRF antennas continued this week with two run days devoted to this task. The D-port dipole antenna conditioned quickly to 1.2 MW and eventually up to 1.4 MW. The E-port antenna (FMIT#2) is operating up to 1.4 MW reliably and required little conditioning to reach this level of performance. A fault in the FMIT#2 crowbar unit interrupted further conditioning of E-port on Thursday. This has been repaired and the system should be available for operations this week. Conditioning of the four-strap J-port antenna is proceeding more slowly, partially due to failed retries after an initial arc indication. The effective J antenna fault level for the reflected to forward power ratio appears lower than the nominal 25%, and the reason for this discrepancy is being investigated. Travel and Visitors -------------------- Justin Burruss from General Atomics visited last week to port the TRANSP run preparation tools used at the PSFC from the OpenVMS operating system to linux. This should enable users to prepare and submit TRANSP runs from the C-Mod linux workstations and to use the more friendly FusionGrid authentication procedures. TRANSP run submission was one of the few remaining operations still running on our OpenVMS systems. This work should bring us closer to retiring all C-Mod OpenVMS systems. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly