Alcator C-Mod Weekly Highlights February 16, 2010 FY2010 weeks of research operations Base Target: 13 weeks Base Completed: 4.3 weeks ARRA Target: 5 weeks ARRA Completed: 5.0 weeks Plasma Shots: 1040 Operations ----------- Plasma operations continued at Alcator C-Mod last week. Four run days were scheduled. Experiments supported research in the Transport, ICRF Physics, and Boundary/Edge topical science areas. A total of 70 plasma discharges were produced with a reliability of about 75%. The experiments on Wednesday and Thursday featured operation at a toroidal field of ~8 tesla; this marked the first operation at this field during the current experimental campaign. Boronizations were performed on Monday and Thursday nights. Research operations are planned to continue this week. Operation Details ------------------- Tuesday's experiment in support of MP#593 continued attempts to trigger edge-localized modes on C-Mod by rapidly displacing the plasma equilibrium in the vertical direction, a technique that has been demonstrated on TCV, ASDEX Upgrade, JET and NSTX. Prior to the experiment, new modeling was performed with the Alcasim control system simulator, in order to identify vertical modulation parameters that retained vertical control at plasma currents higher than the 0.8MA demonstrated in a previous experiment. We then successfully applied the modulation algorithm to H-mode plasmas at up to 1MA. We identified what appear to be small, minimally perturbative ELMs, preferentially triggered by both the upward and downward excursions of the plasma centroid. Initial attempts to pace these events by varying the triggering frequency from 25 to 200Hz were also successful. The runs on Wednesday and Thursday were dedicated to MP#597 "ICRF Mode Conversion Flow Drive at 8T". The goal of these experiments was to explore MCFD at 8T, using all available ICRF power at f~80MHz, in order to test the parametric scaling of this effect observed at lower field with f~50MHz. The on-axis toroidal field was varied in a narrow range (7.8 to 8.0T) in order to tune the mode conversion localization, while the density, plasma current, and He^3 concentration were scanned over wider ranges. Up to 4.8MW of ICRF power was coupled to the plasmas. The observed toroidal rotation, up to about 80km/sec, was in the range expected for the intrinsic rotation (Rice scaling) in these L-mode discharges. However, the rotation with the J-port four-strap antenna operated with -90 degree phasing was lower than that with +90 degree phasing by about a factor of two with similar power and change of stored energy, while the rotation with dipole phasing was intermediate between the two. The sensitivity to antenna phasing suggests a portion of the rotation is due to RF flow drive, although the effect is considerably weaker than at the lower field and frequency. It is noteworthy that all of these 8T L-mode discharges featured quite high temperatures, with Te0 up to 9keV. Data from these experiment, including PCI observations of the mode converted waves, are being analyzed. Friday's experiment was dedicated to MP#591 "Boundary Layer Heat Transport Experiments in H-mode Plasmas". This MP supports the 2010 OFES Joint Facilities Milestone to investigate boundary layer transport and heat flux "footprints". This run was our first aimed at systematically recording heat-flux footprint profiles with the new IR camera system, using the suite of IR camera support software that has been developed to provide preliminary analysis of IR data between shots. This first in a series of experiments envisioned under this MP targeted high power ICRF-heated EDA H-mode plasmas with pedestal parameters non-dimensionally matching a dataset recently documented by DIII-D (MP-2010-62-02). The IR camera stabilization programs, needed to account for vibrations in the camera periscope mounting system, worked well. IR calibration parameters were evaluated on each shot by comparing tile temperatures as measured by thermocouples with IR emissivity after the temperatures had equilibrated, at ~30 sec after the discharge. Surface temperatures during the discharge reached up to ~1100 C, and the profiles followed the strike point location during sweeps. Stationary EDA discharges were obtained at slightly higher q95(~4) than the original target. The RF power was scanned between 1 and 4MW, providing a range of pedestal parameters that included shots which essentially overlayed the scaled profiles from the recent DIII-D experiments. Detailed analysis of the heat flux data from these experiments is underway. Program Planning ---------------- The C-Mod Experimental Program Committee (EPC) met on Monday 2/8 to review experimental proposals and to discuss run plans for the rest of FY10. Topical group and thrust leaders are preparing updated lists of priority runs based on the current facility schedule. DNB Systems ----------- At the C-Mod science meeting on Monday, Igor Bespamyatnov (UT-FRC) presented a description of the ALCBEAM code that has been developed to simulate the Diagnostic Neutral Beam, both to characterize beam performance and to help with CXRS analysis. ICRF Systems ------------ A new version of the amplitude modulator for the ICRF transmitter waveform with a 1 MHz bandwidth has been developed and is being readied for additional experiments. The first feedthrough for the new rotated 4-strap antenna was successfully leak checked at the vendor. The feedthrough passed visual inspection and we will proceed with manufacturing the other feedthroughs. ARRA Activities ---------------- A purchase order using ARRA funds has been issued for the new fast ferrite tuners. The raw FFT power supplies, also purchased under ARRA funding, have been delivered. Lower Hybrid System -------------------- Last Wednesday a review of the proposed cleanup procedure for the lower hybrid launcher vacuum windows was held at MIT with video-conference participation from PPPL and GA. Earl Marmar gave a welcome and introduction. Jim Irby presented the charge to the review panel, and Rui Vieira presented a description of the launcher, and the work done to develop a cleanup procedure. Participants from PPPL were Rich Hawryluk, Randy Wilson, Charles Gentile, and Larry Dudek, and from GA were Peter Petersen and Kurt Holtrop. Ron Ballinger and Martin Greenwald served as internal reviewers, and Catherine Fiore also participated in her capacity as the PSFC safety officer. The proposed cleaning process involving an etch of the window surfaces with dilute HCl was considered appropiate. A document listing reviewer comments and recommendations, along with C-Mod responses, has been distributed for comment. Work last week on the new launcher primarily involved preparations for the cleanup process. A lifting fixture has been designed and is now being fabricated. A fume hood to surround the launcher and support equipment is also being fabricated. Travel and Visitors ------------------- On Friday 2010/02/12 Robert Granetz participated via remote conferencing in a DIII-D run studying disruption runaways. This is a research topic that is the subject of ITPA MDC-16, involving experiments on a number of tokamaks worldwide, including C-Mod and DIII-D. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly