Alcator C-Mod Weekly Highlights Jan 30, 2012 FY2012 weeks of research operations Target: 17 weeks Completed: 2.3 weeks Plasma Shots: 393 Operations ----------- Plasma operations continued at Alcator C-Mod last week. Three run days were scheduled and two were completed. A total of 62 plasma discharges were produced with a reliability of over 90%. Runs supported experiments in the ICRF Physics and Lower Hybrid Physics tasks. The first boronization of the 2012 experimental campaign was carried out on Monday night. After boronization, the H/D levels were reduced to < 5% during ICRF-heated H-mode discharges, and EDA H-modes were readily obtained with ~1MW of ICRF heating. Run time was lost on Tuesday morning due to a problem with the air switch (13.8kV breaker). The switch was repaired and returned to service by 15:30, and two hours of plasma operation were completed; the remainder of the scheduled experiment was completed on Wednesday. On Friday two hours of run time were lost due to a vacuum problem and data system issues. A scheduled maintenance day was held on Thursday to continue commissioning of the new Thomson scattering lasers and calibration of the LH system. Plasma operations are planned to continue this week. Quarterly Review ---------------- The DoE quarterly review for FY2012, Q1 was held by video-conference last Monday. FES participants included Jim Van Dam, Steve Eckstrand, John Mandrekas and Mark Foster. PPPL and U.Texas also participated remotely. Viewgraphs from the review presentations can be found at http://www.psfc.mit.edu/research/alcator/pubs/Q_Reviews/Q-rev_Jan_2012/Q-rev_Jan-2012.pdf Operation details ----------------- Experiments on Tuesday and Wednesday were devoted to MP#669, "Rotated Antenna Commissioning and Initial Characterization". Boronization recovery on Tuesday was very rapid for the field-aligned J-port antenna, requiring only two shots to obtain fault-free operation at the 1MW level. The D- and E-port dipole antennas required five and two discharges, respectively, to achieve clean 1MW operation after the boronization. We investigated the plasma response and power compatibility of each of the antennas into H-mode discharges. The core Mo XXXII brightness was significantly lower for the field-aligned J-port antenna than with either the D- or E-port antennas. With all antennas operating simultaneously we successfully coupled up to 3.5 MW into H-mode plasmas, but experienced faulting at higher power. We investigated core Mo response in H-mode for each antenna at the 1MW level with plasma currents between 800kA and 1.1MA, but were unable to obtain H-modes at this power for Ip=500kA. On Friday we carried out MP#605, "LH2 Lower hybrid Launcher Checkout and Conditioning". The goal of the run was to increase the LH power to the plasma. We succeeded in coupling up to 750kW for up to 0.5 sec. Both upper and lower single null target plasmas were employed. Most discharges were at 700kA, with some 500kA operation later in the day. The loop voltage transiently decreased to ~0.2V in the 500kA discharges. ICRF System ----------- Spurious low readings on the DC1 reflected power monitor were investigated and repaired. A meeting was held to discuss fabrication of a second rotated (field-aligned) antenna. Several items were identified as requiring immediate action: identifying a vendor to bend the molybdenum rods, ordering the inconel material for four straps, ordering resistive washers, and reviewing detail drawings of bellows tubes and flanges. The Mo rods and resistive washers are long lead time items required for the Faraday screen. Lower Hybrid System ------------------- The LH system was calibrated at 50 kV klystron beam voltage. Klystron 3 is limited to 177 kW due to increasing body current at higher powers. The 50 kV calibration allowed for operation into plasma at higher power levels. Up to 750 kW of net power was delivered to the plasma during operations on Friday. Work continues on making high time resolution collector coolant temperature measurements with downstream thermocouples. Faster time response thermocouples were ordered and will be tested this week. The downstream thermocouple measurement is necessary to verify the heat capacity used in the transmitter protection system (TPS) collector over temperature subsystem (COTS) calculation. Diagnostic Neutral Beam System ------------------------------- A temporary transformer was installed to vary the 3rd grid voltage. That grid's function is to prevent electrons from getting into the HV acceleration grids. Early in the week we increased the 3rd grid voltage by 5%, 10%, and 15%, and verified that the preset voltage level was sufficient to suppress any electron contribution to the beam current. The temporary transformer has now been removed. Diagnostics ----------- Maintenance days on Monday and Thursday were used to investigate the low Thomson scattering signals observed during plasma discharges over previous run days. It was determined on Monday that the polarization angle of the beams from the newly commissioned upgrade lasers was not consistent with vendor specifications, and therefore was not optimal for use in the existing Thomson scattering geometry. In order to rotate the polarization, we installed a half-wave plate in the beam line of one laser prior to Friday's run, and this change resulted in a tenfold increase in scattered light. The polarization of the second laser will be modified in a similar fashion. Travel and Visitors -------------------- Randy Wilson of PPPL visited C-Mod on Friday to participate in the LH run. Dr. Yang Ren, PPPL, visited C-Mod last week to discuss collaborations as part of the 2012 Joint Research Target. During his visit, Dr. Ren spoke with Will Bergerson, Felix Parra-Diaz, Darin Ernst, Catherine Fiore, Martin Greenwald, Nathan Howard, Cale Kasten, John Rice, Naoto Tsujii, Anne White and other C-Mod-team members about diagnostics, data analysis, and turbulence modeling. Dr. Ren also gave a talk at the PSFC/C-Mod turbulence group meeting on "Experimental Study of Parametric Dependence of Electron-gyro Scale Turbulence on NSTX". Dr. Michael Roberts, former Division Director at DoE's Office of Fusion Energy Sciences, visited MIT where he had discussions with Earl Marmar concerning C-Mod and ITER. He also toured the Alcator control room. Dr. Roberts is currently Director of RobertsInternational, LLC, and chairs the International ITER Council's Export Control Working Group. The PSFC hosted a visit by Tim Kaine, former Governor of Virginia and current candidate for U.S. Senate. Gov. Kaine was taken on a tour of the C-Mod facility. Kaine has a longstanding interest in energy and environmental issues. The C-Mod EF2 upgrade team met with the vendor's team to discuss their progress and plans for completion of the first three tasks. Documentation was presented and reviewed to determine how many boards are to be provided for the system. Both teams will work on a block diagram and signal list for all of the signals and equipment they are responsible for so that we can be sure that these responsibilities are well defined and agreed upon. The teams also spent several hours after the meeting to take measurements and photos of the existing power room equipment. Approximately 50% of the work to complete Tasks 1-3 is done, and the vendor estimates that another 6 weeks will be required for completion. Eight more of the Cosine intercept boards for the upgrade fabrication were received last week. Arturo Dominguez traveled to PPPL on Friday, 1/20/2012, to work with Gerrit Kramer on the reflectometry collaboration using the FWR2D code (Elfresco). _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly