Alcator C-Mod Weekly Highlights September 21, 2009 FY2009 weeks of research operations Target: 9 weeks Completed: 8.2 weeks Discharges: 1071 Operations ----------- Plasma operations continued on Alcator C-Mod last week. Five run days were scheduled. A fresh boronization was performed on Wednesday night. Experiments supported research in the Transport and MHD topical science areas. A total of 120 plasma discharges were produced with a reliability of 85%. Plasma operations are planned to continue this week. Operations Details ------------------ Monday's run was used to access ELMy H-mode across a range of plasma current, in order to provide a test of the EPED1 model developed by Phil Snyder (GA). The EPED1 model provides a testable prediction for pedestal height and width in an H-mode edge limited by MHD peeling-ballooning modes. In order to hasten access to ELMy H-mode, the equilibrium known as the "JFT2-M shape" was used. ELMy and EDA H-modes were obtained over a range of 500 to 900kA, providing pedestal data to which EPED1 predictions will be compared. Both Snyder and Rich Groebner participated in the experiment remotely from General Atomics. Tuesday's experiment was in support of MP579 "Characterization and optimization of I-mode". The main focus for the day was the characterization of H-mode avoidance and I-mode on q95, Ip, B toroidal. A planned density scan was not started due to time limitations. Preliminary analysis shows that the H-mode avoidance was most sensitive to q95, rather than B or Ip; however the available range in B is limited due to concentration on a single ICRF heating scenario. The upper cryopump was used successfully to maintain very steady density nebar~1.2e20 m-3 during RF power steps. The best I-mode performance on this day was at q95~4 with Wth~150 kJ and H98~1, which was held steady and ELM-free for the length of the RF pulse. The pedestal had a Te ~ 650 eV. Strong coherent oscillations, previously associated with I-mode, were seen on edge reflectometry. Wednesday's experiment was devoted to MP#566b "Study of the RSAE tunneling efficiency during the current ramp". Eric Edlund (PPPL) visited MIT to serve as session leader. The purpose of these experiments is to study the influence of the plasma edge on the relative amplitude of the edge and core fluctuations from reversed shear Alfvén eigenmodes (RSAEs) measured by the Mirnov coils and PCI, respectively. The experiments are intended to provide data for comparison of the observed dependence of the magnetic signature of the RSAE mode on the edge q with calculations of the near-edge amplitudes calculated by the NOVA code, and to motivate extension of the NOVA calculations to include more realistic (non-fixed) boundary conditions. Simultaneous observations of RSAEs using the phase contrast imaging (PCI) and external magnetics were made over a series of discharges with ICRF injected during the current ramp. The edge q was varied by changing the plasma current at fixed Bt and equilibrium shape. RSAE modes were observed during the current ramp on both diagnostics over a relatively small range of current (700 to 850kA). In addition, RSAE modes associated with sawtooth activity were observed during the flattop at 0.84 < Ip < 1.12MA using the PCI diagnostic, but not at lower current. As in previous experiments, these flattop RSAEs were not observed on the Mirnov loops, although TAE modes appeared on both diagnostics for a much wide range of current. These data are being analyzed. On Thursday and Friday we carried out MP#571 "Further Investigation of Turbulence and Transport in Low Density Ohmic Plasmas to Resolve the Mystery of Electron Transport". Liang Lin (UCLA) visited MIT to serve as Session Leader for these experiments. This Miniproposal aims to extend previous work which indicated a discrepancy between experimental observations of turbulence and transport and gyrokinetic simulations using the GYRO code in the low-density "linear ohmic" transport regime. Last week's experiments on C-Mod covered a range of current (0.4< Ip < 0.8MA) and field (2.6 < Bt< 5.2T) at constant q95~4, followed by a range of current (0.4 < Ip < 1MA) at fixed Bt=5.2T . At each condition the density was scanned from the linear regime up to the transition to the "saturated ohmic" regime. Data are being analyzed and results are expected to be reported in Dr. Liang's Invited talk at the upcoming APS DPP Meeting. ICRF Systems ------------ All antennas and transmitters were run successfully in support of physics operations last week. We have continued to analyze and refine the tilted 4-strap antenna design. The manufacturing drawings for the feedthroughs have been approved. Purchase orders for material for the Inconel straps and other components are being prepared. Lower Hybrid System ------------------- All transformers have been machined to the proper length so that the WR-187 waveguides will mate to the C-Port vacuum flange, and the transformers will mate to the 4-way splitters. We expect the in-vacuum WR-187 waveguides and flanges to be available from our vendor soon. Tests of the induction heating procedure to braze the waveguides to the flanges have been successfully completed. The lower hybrid launcher support box/bellows system has been assembled with its drive screw and will be tested this week. Assembly of the rear waveguide components has started, and fabrication of the launcher support cart has been completed. Travel and Visitors -------------------- Martin Greenwald spent the week at PPPL for a meeting of the FSP (Fusion Simulation Program) management team, culminating in presentations at the first PAC meeting. Earl Marmar served as a member of the PAC at the meeting on Thursday and Friday. David Mikkelsen worked with researchers at MIT on GYRO turbulence simulations of momentum transport in C-Mod plasmas and to further develop ideas for an experimental study of hydrogen isotope transport. Eric Edlund (PPPL) visited MIT on Tuesday-Friday. He served as Session Leader for the experiment on Wednesday. Liang Lin (UCLA) visited MIT on Thursday-Friday and served as Session Leader for the experiments on those days. He also met with Peng Xu and Jim Irby to discuss the MIT polarimeter system as part of the UCLA/MIT collaboration. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly