Alcator C-Mod Weekly Highlights April 3, 2006 FY2006 weeks of research operations: Planned: 14 weeks Completed: 6.2 weeks Operations ---------- Plasma operations continued at Alcator C-Mod last week. Three run days were scheduled and completed. A total of 66 plasma discharges were produced, with a reliability of about 75%. Ten hours of research run time was dedicated to two experiments involving boronization and wall conditioning: MP#430 "Localization of boronization effect" and MP#446 "Intra-shot diborane injection". Additional run time was devoted to conditioning of the ICRF antennas under MP#355. Plasma operations are planned to contine this week. Physics -------- Intra-shot boronization (MP#446) was attempted for the first time on C-Mod last week. The primary objectives of the run were to see how much diborane we could inject into the plasma without causing disruptions, and to judge if the diborane affected performance positively. The 20% B2D6 + 80% He bottle was used to fuel the plasma through the boronization manifold at the top of the vessel. We puffed up to 27.5 Torr-l of the helium-diborane mix into the vessel during the discharge. This amount of gas nearly doubled the density following the H-Mode and caused the plasma to disrupt during rampdown. Approximately 2 monolayers of boron would have been deposited on the vessel walls, assuming a uniform deposition over 10 m2 of surface at this fueling rate. The quality of the H-Modes, the carbon III levels, stored energy, and radiation, among other indicators, did not show significant change following several discharges with diborane puffing. The first between-shot boronization of the current campaign was carried out on Friday, as part of the run in support of MP#430 "Localization of boronization effect." A 20 minute ECDC boronization was performed with the resonance location swept from 0.50 to 0.92 m, using the 20% diborane mix. The following discharge exhibited a steady EDA H-mode with 1MW of ICRF power. The rest of the MP requires steady 3MW ICRF pulses, and will be scheduled for a future run day. Diagnostic Neutral Beam Systems ------------------------------- The DNB high voltage system testing has been completed with operation at voltages up to the design value of 50 kV. The DNB was operated in test mode early in the week for long pulses of 1.2 seconds at beam ion currents of 6.5 to 7 amperes (also the design value). The DNB was then operated into C-Mod plasmas. The DNB long pulse interlock chassis was retested after replacement of three fiber optic receivers. The interlock CPLD responds correctly to the beam trigger and correctly terminates the high voltage permissive 100ms after the high voltage on signal is received. Several of the interlock inputs require modification before the interlock can be made operational. The new high voltage inverter driver boards have been populated and will be tested this week. A prototype electrostatic shield for the driver boards has been fabricated and is ready for test fitting. Lower Hybrid System -------------------- Modifications were made to the twelve LH coupler protection system reflected and forward power interlock circuits to allow a gated mask of faults. The CPLD program was modified to gate the faults only during the RF gate. This prevents the turn on/off of HV from causing noise induced nuisance fault trips. Testing of the intermediate directional couplers using a mismatched section of waveguide inserted between the high power switch and the dummy load was begun. This section of waveguide provides a calibrated reflected power level with which to test and set the interlocks. Installation of high-pass filters at the input of the intermediate reflected power diodes has been determined to filter out noise associated with ICRF operation. Travel, Visitors, and Meetings ------------------------------ Igor Bespamyatnov, a graduate student from the University of Texas, Austin, Fusion Research Center, continued his visit to MIT. He has been completing his analysis of CXRS data from the last campaign. Ian Hutchinson participated in the video conference meeting of the National Research Council's Plasma Science Committee on Friday, March 31. David Johnson, Team Leader for the US ITER Diagnostics effort, visited the PSFC on Monday. He presented a seminar "Getting started on US ITER Diagnostics", and met with a number of C-Mod scientists, including Earl Marmar, Steve Scott, Jim Terry, Martin Greenwald, Amanda Hubbard, Ian Hutchinson, and Bob Granetz. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly