Alcator C-Mod Weekly Highlights September 14, 2009 FY2009 weeks of research operations Target: 9 weeks Completed: 7.2 weeks Discharges: 951 Operations ----------- Plasma operations continued on Alcator C-Mod last week. Three run days were scheduled and completed. A fresh boronization was performed on Thursday night. Experiments supported research in the Transport, Boundary, Operations, and ITER H-mode Scenarios topics. A total of 72 plasma discharges were produced with a reliability of 85%. Plasma operations are planned to continue this week. Operations Details ------------------ Two experiments were carried out on Wednesday. The first supported MP#565 "Measurement of in-out asymmetry in boron density". The goal was to directly infer the ratio of B^(+4) density at the high- and low-field sides of the plasma, for comparison with a theoretical model of poloidal asymmetry. The experiments were carried out in He plasmas in order to minimize charge-exchange recombination light from B^(+5). Data were obtained in L- and H-modes at three different values of plasma current and at least two different densities at each current. The second experiment on Wednesday, MP#569 "Demonstrating Stable EDA H-mode with Significant Impurity Seeding" was designed to establish operational techniques for creating steady EDA H-mode plasmas seeded with enough non-intrinsic impurities to produce an additional 1 to 2 MW of radiated power. These techniques will be employed in support of part of MP#564 "Power requirements for high confinement H-modes and the role of radiated power spatial distribution" from the ITER H-mode Scenarios task. Impurity seeding was successfully applied introducing neon, nitrogen, and a xenon-deuterium mixture through the main chamber piezo valves. The most favorable results were obtained with the impurity puff started prior to the ICRF turn-on and the L- to H-mode transition. The plenum pressure was adjusted so that the initial rise in Prad did not result in radiative collapse of the ohmic target. The cryopump was employed to control recycling in these experiments, but indications were that the pump was not necessary. Thursday's experiment was the third in the series of run days devoted to MP#570 "Boundary layer heat transport experiments in L-mode plasmas", which supports the FY10 OFES Joint Milestone "... measure the divertor heat flux profiles and plasma characteristics in the tokamak scrape-off layer in multiple devices to investigate the underlying thermal transport processes..." This day concentrated on measurements of the heat-flux footprint at reduced field (4 tesla), with plasma currents of 800kA and 400kA (q95~3 and 6, respectively). The density was scanned from nebar~0.7 to 2.8e20/m^3 at 800kA, and from 0.5 to 1.8e20/m^3 at the lower current; the divertor was fully detached at the highest densities. On Friday, we carried out MP#577 "ITER-like discharge ramp-up studies". This experiment built on the development work carried out on Sept. 3, and investigated the effects of ICRF heating, in both L- and H-modes, during the current ramp. The experiment was carried out following a fresh boronization to minimize impurity influx. Early x-point formation was improved, with diversion obtained as early as 70msec. Ramp-up to q95~3 was accomplished by 0.5sec, followed by a flattop of > 0.5sec. All shots employed ICRF heating at the 3MW power level in the flattop. ICRF power was introduced beginning at ~0.1sec (following divertor formation), with a variety of power levels and staircase waveforms. The data are being analyzed and compared with simulations. Program Planning ---------------- A meeting of the Experimental Program Committee was held on Tuesday, Sept 8. Six experimental proposals were reviewed and approved (MPs 566b, 575a, 577a, 578, 579, 580. See http://www.psfc.mit.edu/research/alcator/program/cmod_runs.php?miniproposals for details.) Campaign status and short-term plans were also discussed. ICRF Systems ------------ All antennas and transmitters were run successfully in support of physics operations last week. Measures taken to improve system reliability have been successful. Lower Hybrid System ------------------- Assembly of the lower hybrid launcher has begun, with work started on the support stand and slide, bellows and vacuum flanges, and radial drive components. The sixteen 4-way splitters are being stacked into an assembly to check fit-up and verify dimensions. The transformers that match the splitters to the waveguide are being prepared for brazing and welding operations. Preparations are being made for leak-checks and a vacuum bake of the final assembly. Major items still in production by our vendors include the sixteen waveguides needed to feed the in-vacuum transformers, and the ex-vacuum rear waveguide components that feed power to the launcher. Travel and Visitors -------------------- Last week, Paul Bonoli, John Wright, Steve Richardson, and Jungpyo Lee attended the annual Workshop of the SciDAC Center for the Simulation of Wave-Plasma Interactions. The workshop was held at Oak Ridge National Laboratory from September 9-11, 2009. For about one and half days, the workshop focused on summarizing Center accomplishments from the past year. During the last full day of the workshop detailed discussions occurred on future directions for the Center. Syun'ichi Shiraiwa and Orso Meneghini visited GA this week to present their work on full wave RF modeling and discuss collaboration with GA colleagues in coupling it to a Fokker-Planck code and the RF-particle following code ORBIT RF. Chuck Kessel (PPPL) visited MIT on Friday to serve as Session Leader for his experiment MP#577. Peter Beiersdorfer was at MIT on Friday to install the grating for the LLNL flat-field spectrometer and discuss proper focusing of the instrument with Matt Reinke and others. Installation is planned for before the end of the FY09 campaign. Results from the McPherson showing a density sensitivity of a boron-like Fe line pair that is routinely observed in C-Mod plasmas were discussed. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly