Alcator C-Mod Weekly Highlights March 26, 2012 FY2012 weeks of research operations Target: 17 Completed: 5.6 Plasma Shots: 753 Research -------- "Ohmic energy confinement saturation and core toroidal rotation reversal in Alcator C-Mod plasmas" by J. E. Rice, M. J. Greenwald, Y. A. Podpaly, M. L. Reinke, P. H. Diamond, J. W. Hughes, N. T. Howard, Y. Ma, I. Cziegler, B. P. Duval, P. C. Ennever, D. Ernst, C. L. Fiore, C. Gao, J. H. Irby, E. S. Marmar, M. Porkolab, N. Tsujii, and S. M. Wolfe has just been published in Physics of Plasmas: http://link.aip.org/link/?PHP/19/056106 This paper discusses the Ohmic energy confinement saturation that is found to be closely related to core toroidal rotation reversals in Alcator C-Mod tokamak plasmas. Rotation reversals occur at a critical density, depending on the plasma current and toroidal magnetic field, which coincides with the density separating the linear Ohmic confinement regime from the saturated Ohmic confinement regime. The rotation is directed co-current at low density and abruptly changes direction to counter-current when the energy confinement saturates as the density is increased. Since there is a bifurcation in the direction of the rotation at this critical density, toroidal rotation reversal is a very sensitive indicator in the determination of the regime change. The reversal and confinement saturation results can be unified, since these processes occur in a particular range of the collisionality. Neoclassical impurity transport codes NCLASS and NEO have been setup for direct calculation of comparison cases for the wide range of plasmas for which light impurity transport data is available in C-Mod. Neoclassical predictions were calculated for all of the discharges in the boron light impurity transport database including those used as comparisons to the impurity driven driftwave theory of Fu and Horton. The NCLASS work is being done by Ken Liao and Sean Fu, UTex, and the work with NEO by Igor Bespamyatnov, UTex, with advice from Emily Belli, GA, and Matt Landreman, MIT. This work will be presented at TTF 2012. Operations ---------- Alcator C-Mod is presently up-to-air for planned maintenance and upgrades. Refurbishment of the ARRA-funded Field Aligned ICRF Antenna continued. New bellows for the polarimeter shutter have been welded, successfully leak checked, and re-assembly of the shutter has begun. A new CECE mirror has been installed in-vessel to optimize the focal spot location of the diagnostic. ICRF Systems ------------ All candle pins (feed thru center conductors) for the Field Aligned Antenna have been installed and their bolts tightened to their specified torque values, as have those of the bellows, current straps, and outboard Faraday screens. Torques were checked multiple times over several days to ensure that the connections were stable. The FMIT#3 crowbar ignitrons were successfully high-potted last week. One of the two ignitrons in this system is new. Lower Hybrid Systems -------------------- The wall mounted lower hybrid limiter is being prepared for re-installation. Preparations are also being made to clean one of the 64 lower hybrid vacuum windows that has traces of copper and stainless steel deposition. Remote Participation, Travel, and Visitors ------------------------------------------ George Sips, (EFDA-JET Operations Leader, and Integrated Operational Scenarios ITPA Leader) visited March 22-23, and gave a PSFC seminar entitled 'Latest Results from JET and the Integrated Operation Scenario Topical Group'. He had discussions with many C-Mod team members regarding topics of interest to ITPA and JET, including H-mode scenarios experiments, ICRF and LHCD, and possible C-Mod-JET collaborations. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly