Alcator C-Mod Weekly Highlights April 25th, 2011 FY2011 weeks of research operations Target: 15 weeks Completed: 14.5 weeks Plasma Shots: 1706 Physics ------- Three recently published journal articles documenting Alcator C-Mod physics results are now available on-line: 1) "ICRF mode conversion flow drive on Alcator C-Mod", by Y. Lin, J.E. Rice, S.J. Wukitch, M.L. Reinke, M.J. Greenwald, A.E. Hubbard, E.S. Marmar, Y. Podpaly, M. Porkolab, N. Tsujii and the Alcator C-Mod team: http://stacks.iop.org/0029-5515/51/063002 This paper documents a detailed study of ion cyclotron range of frequency (ICRF) mode conversion (MC) flow drive on the Alcator C-Mod tokamak including its dependence on plasma and RF parameters. 2) "High confinement/high radiated power H-mode experiments in Alcator C-Mod and consequences for International Thermonuclear Experimental Reactor (ITER) Q[sub DT] = 10 operation," by A. Loarte, J. W. Hughes, M. L. Reinke, J. L. Terry, B. LaBombard, D. Brunner, M. Greenwald, B. Lipschultz, Y. Ma, S. Wukitch, and S. Wolfe, Physics of Plasmas (Vol.18, Issue 5): http://link.aip.org/link/?PHP/18/056105 Experiments in Alcator C-Mod in (Enhanced D-alpha) EDA H-modes with extrinsic impurity seeding (N2, Ne, and Ar) have demonstrated a direct correlation between plasma energy confinement and edge power flow, achieving values of H98 ≥ 1 for edge power flows only marginally exceeding the scaled power for access to H-mode confinement in these conditions 3) "Scaling of the power exhaust channel in Alcator C-Mod," by B. LaBombard, J. L. Terry, J. W. Hughes, D. Brunner, J. Payne, M. L. Reinke, I. Cziegler, R. Granetz, M. Greenwald, I. H. Hutchinson, J. Irby, Y. Lin, B. Lipschultz, Y. Ma, E. S. Marmar, W. L. Rowan, N. Tsujii, G. Wallace, D. G. Whyte, S. Wolfe, S. Wukitch, G. Wurden, and Alcator C-Mod Team, 22 April 2011, in Physics of Plasmas (Vol.18, Issue 5): http://link.aip.org/link/?PHP/18/056104 Parametric dependences of the heat flux footprint on the outer divertor target plate are explored in EDA H-mode and ohmic L-mode plasmas over a wide range of parameters with attached plasma conditions Operations ---------- Work continued invessel on diagnostic calibrations. Routine maintenance continued on C-Mod power systems. The alternator limit amp work continued. The G-Horizontal port extension is being replaced with a new wider extension that will allow for easier invessel entry. ICRF Systems ------------ Inspection of the J antenna found some arc damage at the bridge section on the center two straps. The antenna model will be used to examine if the voltage is higher at this location for the center two straps compared to the two outer straps. Plans for the spacing in the bridge region of the new ARRA funded rotated antenna will be assessed in light of the results. Antenna back plates, side plates, top and bottom plates, and current straps for the rotated antenna have been assembled to allow close inspection of the new antenna. Modification to the bridge region design to improve the new antenna's voltage handling capability are being assessed. The first 34 Faraday rods have been successfully coated with TiCN and baked to 850 C. The rods will be inspected to verify dimensions, and if hey meet specifications, they will be ready to be threaded. Lower Hybrid System ------------------- Results of tests from the new thicker garnet samples for the 4.6 GHz Fast Ferrite Tuner (FFT) look very promising. An FFT using this material should be possible. Diagnostics ----------- Continuing an on-going assessment of the actual neutral current delivered by the C-Mod diagnostic neutral beam (DNB), we have completed an analysis of neutron emission when the DNB is operated in deuterium. The DNB (50 keV, 6 amps ion current) was injected into a deuterium Ohmic plasma, and the beam-target neutron emission exceeded the thermonuclear neutron rate by a factor of ~20. The electron density was ramped during the plasma (from neo = 1 to 2 e20 m-3) to provide a range of beam deposition profiles, ranging from centrally-peaked to relatively flat in radius. The measured neutron rate was compared to calculations based on classical beam thermalization physics using the TRANSP code. The measured neutron rate is observed to be a factor of 2-3 less than predicted by TRANSP. There are at least three possible effects which might be contributing: the full-energy equivalent current is substantially less than expected; there are anomalous fast-ion losses; and/or the beam is partially attenuated by gas before it reaches the plasma edge. Travel and Visitors ------------------- Kevin Tritz, of Johns Hopkins Univ, visited on Friday to give a seminar on electron thermal transport on NSTX. While at the PSFC he had discussions with several team members, including Bob Granetz, Matt Reinke, Luis Delgado-Aparicio, Anne White, Amanda Hubbard, Ted Golfinopoulos, Aaron Bader, Naoto Tsujii and Paul Ennever. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly