Alcator C-Mod Weekly Highlights July 9, 2012 FY2012 weeks of research operations Target: 18 weeks Completed: 9.3 weeks Plasma Shots: 1450 Operations ----------- Plasma operations continued at Alcator C-Mod last week. Three run days were scheduled and completed. A total of 57 plasma discharges were produced with a reliability of 72%. A clean vent (backfill with argon) was performed on Monday in order to install a replacement gate valve for the A-port Scanning Probe system. Runs on Tuesday and Thursday were devoted to continued machine cleanup and conditioning, following the vacuum incident reported last week. A short (one hour) boronization was carried out on Thursday night in order to reduce the hydrogen fraction to a level consistent with efficient minority ICRF heating. The run on Friday was in support of research in the Transport Physics topical area. Plasma operations are planned to continue this week. Program Planning ---------------- A meeting of the Experimental Program Committee (EPC) was held on 7/2. We reviewed the status of the machine and plans for the week, then priorities for the balance of the campaign. A table that shows the current state of run priorities and allocations is being updated and circulated weekly. Four new experimental proposals were reviewed and approved. Physics ------- Operation Details ----------------- The run on Friday was devoted to MP#689 "Validation of gyrokinetic transport models across the ITG/TEM boundary in L-mode and I-mode plasmas". The motivation for this experiment was to study changes in core turbulence and transport across the ITG/TEM boundary in RF heated plasmas. We wish to investigate how well turbulent-transport models can simultaneously match impurity particle transport and heat transport in ITG and TEM dominant plasmas. This is the second day of a dedicated OFES 2012 Joint Research Target validation experiment, and was devoted to gathering key fluctuation/transport data not obtained on day1, including the use of Laser Blow Off (LBO) for measurements of impurity transport , and CECE and fast TCI measurements of Te and ne fluctuations. A five step run plan was successfully completed. Data were obtained with LBO, CECE, reflectometer and FTCI in discharges that were matched extremely well (ne, Te, rotation, WMHD, neutron rates, etc.) to the target discharges in TEM and ITG dominated regimes from the previous run day in February. A series of shots with increasing density at low power in ITG-dominated L-mode was also obtained in order to study hollowing of the rotation profiles and associated changes in transport and fluctuations. An intermediate power ITG L-mode case was also obtained to document LBO data as part of an RF power scan. In addition, we carried out small Bt scans in order to vary the location of the CECE fluctuation data in both a high power TEM case and a low power ITG case. ICRF Systems ------------ The ICRF systems were run in support of experiments and were also utilized to recondition the tokamak following a vacuum incident that resulted in significant increase in the hydrogen to deuterium ratio. During reconditioning, some nitrogen seeded L-mode discharges were heated with up to 3.2 MW of power from the Field-Aligned J-port antenna, corresponding to 9.6 MW/m2 power density; this represents the highest power coupled through this antenna so far. These experiments have further refined our estimates of the maximum sustainable voltage for this antenna, which is ~45 kV. For short pulses (<100 ms), the antenna has reached 48-50 kV. In preparation for the second Field-Aligned antenna, boron carbide resistive washers have been successfully coated with copper by CVD. The copper coating passed a "tape" pull test and is now being evaluated for surface contact resistance. The washers used in the first field-aligned antenna are uncoated, and the resistance of the washer-Faraday rod system is dominated by surface resistance between the rod-washer and washer-ground. Lower Hybrid System ------------------- The apparent body current trips in Klystron#10 were determined to be due to an instrumental fault caused by improper grounding of a thermocouple. This klystron is now back in service at nominal performance. Modeling work in support of an advanced real-time control system for the LH-3 coupler is in progress. A model of the low power system has been generated based on calibration data, and we now have a state-space model suitable for design of a Multiple-Input-Multiple-Output (MIMO) controller. Travel and Visitors -------------------- The 39th EPS meeting was held in Stockholm, Sweden with C-Mod contributions from Miklos Porkolab (invited), Ron Parker (poster), Yungxin Ma (poster), Steve Wukitch (poster) and Luis Delgado-Aparicio (oral contribution). Christel Fenzi from Tore Supra is visiting from July 5-13 to assist with Hirex-Sr, and is learning earning more about the system in anticipation of implementation of a similar x-ray crystal diagnostic at Tore-Supra. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly