Alcator C-Mod Weekly Highlights July 5, 2011 FY2011 weeks of research operations Target: 15 weeks Completed: 14.5 weeks Plasma Shots: 1706 Physics ------- Two papers documenting important physics results from Alcator C-Mod have been published recently in Nuclear Fusion: "Power requirements for superior H-mode confinement on Alcator C-Mod: experiments in support of ITER", by J. Hughes et al. Power requirements for maintaining sufficiently high confinement (i.e. normalized energy confinement time H_98 >= 1) in H-mode and its relation to H-mode threshold power scaling, Pth, are of critical importance to ITER. In order to better characterize these power requirements, recent experiments on the Alcator C-Mod tokamak have investigated H-mode properties, including the edge pedestal and global confinement, over a range of input powers near and above Pth. In addition, we have examined the compatibility of impurity seeding with high performance operation, and the influence of plasma radiation and its spatial distribution on performance. Find this paper at http://iopscience.iop.org/0029-5515/51/8/083007 "Observations of core toroidal rotation reversals in Alcator C-Mod ohmic L-mode plasmas", by J.E. Rice et al. Direction reversals of intrinsic toroidal rotation have been observed in Alcator C-Mod Ohmic L-mode plasmas following modest electron density or toroidal magnetic field ramps. The reversal process occurs in the plasma interior, inside of the q = 3/2 surface. For low density plasmas, the rotation is in the co-current direction, and can reverse to the counter-current direction following an increase in the electron density above a certain threshold. Reversals from the co- to counter-current direction are correlated with a sharp decrease in density fluctuations with kR >= 2 cm-1 and with frequencies above 70 kHz. The density at which the rotation reverses increases linearly with plasma current, and decreases with increasing magnetic field. There is a strong correlation between the reversal density and the density at which the global ohmic L-mode energy confinement changes from the linear to the saturated regime. Find this paper at http://iopscience.iop.org/0029-5515/51/8/083005 Amanda Hubbard gave an invited talk at the EPS Conference on Plasma Physics in Strasbourg, France on "Separation of energy and particle transport barriers in the I-mode regime on Alcator C-Mod and ASDEX Upgrade". John Wright, Miklos Porkolab, Greg Wallace, Luis Delgado-Aparicio, PPPL, and Stewart Zweben, PPPL, presented talks and posters on C-Mod results. All these presentations can be found at http://www.psfc.mit.edu/research/alcator/pubs/eps/eps2011/eps_2011.html Operations ---------- In-vessel work last week included installation of fast response thermocouples on the GH full limiter and the AB split limiter. Assembly was then completed on both limiters and mounting hardware was tightened to specification. ICRF Systems ------------ The current straps for the new ARRA-funded rotated antenna are at our vendor for plating. In addition, the back plates, back center plate, U-mounting blocks, and antenna boxes are ready for plating. A fit-up of the 2nd antenna box indicated several of the Faraday rods were out of tolerance. This issue is being resolved. A 3rd set of rods have been machined and are being prepared for fit-up into the 3rd box. All shims for the antenna boxes have been fabricated and successfully fit-up. Steve Wukitch and Alan Binus in a teleconference with our vendor last week verified that the production phase of the ARRA-funded Fast Ferrite Tuners is well underway. The next critical step is brazing of the center conductor. Another teleconference will be held following the brazing to assess the braze results and refine the delivery schedule. Lower Hybrid System ------------------- Ethernet prototype boards needed for the Transmitter Protection System (TPS) have been successfully tested. Wiring lists for the TPS cart current monitors and directional couplers have been developed. We continue to work with the vendor to review progress on the new filament power supplies. Diagnostics ----------- The window for the new CECE diagnostic is being modeled for both optical and mechanical performance. In-vessel mirrors have been designed and are being procured. We continued fabrication of the 3-chord polarimeter with procurement of new mounts, beam-splitters, detectors, and lenses. The focal length of prototype TPX lenses have been measured and fabrication techniques discussed with the vendor. Travel and Visitors ------------------- Dr. Ranjana Gangradey, from the Institute for Plasma Research, Bhat, India, visited C-Mod last Thursday and Friday. She had discussions with Bob Granetz, Martin Greenwald, Ian Hutchinson, Brian LaBombard, and Jim Irby about the SST-1 superconducting tokamak, pellet injectors, cryogenic systems, and plasma fueling. Following the IAEA-TM meeting in San Francisco, Martin Greenwald spent two days in Berkeley at a meeting of the Fusion Simulation Planning Group. Amanda Hubbard, Greg Wallace, John Wright, Miklos Porkolab, Luis Delgado-Aparicio, PPPL, and Stewart Zweben, PPPL were at the European Physical Society Conference on Plasma Physics in Strasbourg, France last week. Dennis Whyte presented an invited talk "Recent results from Alcator C-Mod" at the SOFE meeting held in Chicago, Illinois. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly