Alcator C-Mod Weekly Highlights March 28, 2011 FY2011 weeks of research operations Target: 15 weeks Completed: 13.7 weeks Plasma Shots: 1630 Operations ----------- Plasma operations continued last week at Alcator C-Mod. Two research run days (Wednesday and Friday) were scheduled and completed. The runs supported Miniproposals in the ICRF and Transport areas. A total of 67 plasma discharges were produced with a reliability of 98%. All operations last week were carried out with "normal" field and current direction, i.e. I parallel to B and ion grad-B drift toward the lower divertor. A fresh boronization was carried out on Thursday. Plasma operations are planned to continue this week. Run Planning ------------- On Monday, Mar 21, a meeting of the C-Mod Experimental Program Committee was held to consider Miniproposals for upcoming experiments and to establish plans for the remainder of the current operating period. Three miniproposals were considered and approved. Two of these were scheduled for run time. A schedule for the remaining days of operation was decided upon. Operation Details ----------------- Following completion of the reconfiguration of the bus work for normal field direction, power tests were carried out on Monday. After individual tests of all power systems, two plasma discharges were produced to verify overall system readiness for operation. The run on Wednesday was devoted to MP#624 "Measurements of Mode Converted Waves in D-He3 plasmas with Phase Contrast Imaging". This MP comprises part of the thesis research of an MIT graduate student. For these experiments the J-port four-strap antenna system was operated with f=50MHz, and the D-He3 mode conversion regime was employed, with toroidal fields near 5.1T. Most of the day was spent with high He3 concentration of approximately 25%. Fluctuation intensities measured with the PCI diagnostic were lower than expected, and lower than observed in previous experiments at B~8T and f=78MHz. During this experiment, the CXRS system was used to provide an independent measure of the He3 concentration. The relative concentrations determined by the two methods (PCI and CXRS) were observed to disagree as the helium puff was reduced later in the run. The final few shots were carried out with He4 majority plasmas in order to facilitate an absolute calibration of the CXRS measurement. These data are being analyzed. On Friday we carried out MP#636 "Study of ELMy H-mode toroidal field scan". This experiment contributes to the 2011 OFES Joint Facilities Research Target on Pedestal Physics. Phil Snyder (GA) served as co-session leader for this experiment using remote participation tools. The run also had the participation of ITPA collaborators Tom Osborne (GA), Marc Beurskens (CCFE) and Lorenzo Frassinetti (KTH-Stockholm), who were on-site at MIT. The purpose of this run was to expand the C-Mod data set in ELMy H-mode to reduced values of magnetic field. On-axis fundamental D(H) heating with J-port at 50MHz was used at B=3.5T. These data were needed to complete a comparison of C-Mod results to the predictions of the EPED model for pedestal width, and to provide information about whether pedestal width shows any scaling with normalized gyroradius. The main goals of this experiment were accomplished. We began by reproducing a low-elongation, high lower triangularity ELMy H-mode case studied in an earlier experiment, using 80MHz ICRF from D and E-port for central heating at 5.5T. We then reduced the field to 3.5T and used the 50MHz heating for the remainder of the run. We easily obtained ELMy H-mode at the lower field. Then we spent the remainder of the day varying power and density at Ip of 700kA, 560kA, and 440kA. ELMs were obtained at all three currents, with QCM activity more prevalent at the lower currents. Pedestal profile data suitable for EPED analysis and stability calculations were obtained. Additionally, we obtained Gas Puff Imaging data showing ELM precursors and filament propagation, as well as SOL and pedestal reflectometry. For the last three shots on Friday, the Diagnostic Neutral Beam was operated in deuterium. These data are being analyzed to evaluate the neutral flux into the plasma, for comparison with MSE and CXRS data. ICRF Systems ------------ The J-port antenna system continued to operate at 50MHz in support of last week's experiments. The first two current straps (#1 and #4) for the ARRA-funded rotated four-strap antenna have been successfully brazed. The first two braze joints have been visually inspected; polishing of the braze areas will be performed before sending the straps to be plated. The TZM side tiles are also being polished to remove machining marks to reduce field enhancement from surface irregularities. We have received the remaining three bellows tubes and they are ready to be plated as well. Two more top and bottom plates have arrived and the final two are under inspection at the vendor. The remaining coaxial cables and ceramic tubes for the Faraday screen fastener assembly have arrived. Only one machining operation remains to be done on the 34 Faraday rods prior to TiC coating. Lower Hybrid System -------------------- The Lower Hybrid System was not required for plasma operation last week. Pat MacGibbon and Dave Terry took part in the design review for the new filament power supply system at the vendor's site. Work continued on the Collector Over-temperature/Resistive Temperature Detector system (COTS/RTD) for the fourth klystron cart. Travel and Visitors ------------------- Last week Stewart Zweben (PPPL) was at MIT to discuss GPI data and analysis, and to give a talk at our weekly turbulence group meeting, "Search for Edge Zonal Flow in NSTX and C-Mod". He also discussed plans for modification of GPI hardware with Jim Terry. Visitors Tom Osborne (GA), Marc Beurskens (CCFE) and Lorenzo Frassinetti (KTH) collaborated on analysis of pedestal data in ELMy H-mode, and participated in Friday's experiment. Data from prior C-Mod experiments were examined as potential contributions to PEP-2, an ITPA joint experiment among C-Mod, JET, DIII-D and ASDEX Upgrade. As a part of this visit, a number of analysis tools developed for ELM and pedestal analysis on JET and DIII-D are being imported for use on C-Mod data. Martin Greenwald traveled to PPPL for a meeting of the Fusion Simulation Project (FSP) planning team, then to Washington DC where he presented a briefing to the NRC Plasma Science Committee. Amanda Hubbard visited Univ. Wisconsin at Madison on Monday, and gave a seminar on "Separation of energy and particle transport barriers in the I-Mode regime in Alcator C-Mod". She saw and discussed research on several U.W. plasma experiments in different departments, and had discussions on future collaborations regarding I-mode models. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly