Alcator C-Mod Weekly Highlights April 6, 2001 Installation of the J-Port antenna began this week. Work continued on the RF control system, DNB, inner divertor, and Lower Hybrid MIE project. Physics ------- Analysis of neutral particle transport in the main-chamber scrape-off layer (SOL) at the outer midplane has been performed for a small set of discharges using a newly developed neutral transport code, KN1D. This new code is a 1-D space, 2-D velocity kinetic code that treats atomic and molecular transport including molecular dissociation, charge exchange, and elastic collisions between neutral and plasma species. The code takes as input the measured plasma density and temperature profiles in the main-chamber scrape-off layer and the measured molecular neutral pressure near the wall at the midplane. A unity recycling condition on main-chamber limiter and wall surfaces is imposed, consistent with that expected in experiment. In most cases, neutrals contribute to an inward-going heat flux 'pinch' across the separatrix. A comparison with the magnitude of cross-field plasma heat convection in the near and far SOL shows that neutrals play only a minor role in the total heat transported across the scrape-off layer. A meeting was held at MIT on April 3 to investigate the possibility of using Li as a divertor material in Alcator C-Mod. Mike Ulrickson (SNLA), Dennis Whyte (UCSD), Dick Majeski (PPPL) and Jeff Brooks (ANL) all came to participate in this meeting. Participants from C-Mod included Bruce Lipschultz, Brian LaBombard, Jim Terry, Spencer Pitcher, Jim Irby, Earl Marmar and Bob Granetz. Dennis Whyte spent an additional day at C-Mod discussing wall-recycling data taken at DIII-D as part of a joint mini-proposal in which Bruce Lipschultz participated. Progress was made on issues of how to present data from C-Mod and DIII-D jointly and in what format. Discussions with Brian LaBombard included observations and computations of particle and energy fluxes in the SOL of C-Mod and a comparison of fluctuations phenomena observed in the SOL of DIII-D and C-Mod. ICRF Systems ------------ Machining and polishing of all stripline components were completed this week, and copper plating of these components will be completed early next week. Following a vacuum bake, they will then be ready for installation invessel. A picture of one of the long striplines ready for plating can be found at http://www.psfc.mit.edu/cmod/operations/EngImages/RF/ICRF/P0001428.JPG A fitup invessel of the new antenna support plates has been completed and studs have been installed to support the plates. The new J-Port windows and pressure port have been installed on the flange and are ready to be leakchecked. The flange support plate has been taken invessel and punched for drilling at the new diagnostic port locations. The Faraday screen has been aligned on the test stand and will be ready for installation following laser welding of the new gap cover plates. The vessel wall in and around J-Port has been ground and polished to a near mirror finish in preparation for the antenna installation. Testing and calibration was begun this week of the six phase demodulator modules to be used for phase fault detection on the D, E, and J-Port antennas. The new prototype demodulator board is back in house from the vendor and will soon undergo testing. DNB --- The beam was operated in automatic mode for two days this week as we continue the conditioning process. The optical sections of the edge and core CXRS in-vessel optics were cleaned, calibrated, and reassembled. In-vessel backlighting tests demonstrated that the alignment is adequate for the experiments. The shutter assemblies for the two systems are under construction and delivery is expected on Monday. Installation of the shutter actuation cables has begun. Lower Hybrid MIE Project ------------------------ Work continued on the serial fiber optic link. The prototype is working and undergoing tests. Digital I/O definitions are being finalized for the LH phase and amplitude control system. Some hardware/software issues that have caused program crashes are being worked out with the vendor. A 3 kW, 2.45 GHz source is being setup in the LH lab and will be used to test arc detection concepts and electronics. Further progress is being made at PPPL on the design of details of the Lower Hybrid launcher. Advantages are becoming apparent in replacing the original geared chain-driven launcher drive with a hydraulic version. Over the last two weeks, Ron Parker and Montgomery Grimes visited Tore-Supra, JET, and our LH high voltage power supply vendor. At Tore Supra, they discussed recent lower hybrid current drive results and plans for the next campaign including the design of the new launching antenna. At JET, recent progress in the JET lower hybrid experiments was discussed. These experiments had been plagued by coupling problems, especially during high-power auxiliary heating. Recently the coupling has been substantially improved due to a number of factors including better congruence between the coupler and plasma shapes, puffing of CD4 near the launcher to increase the plasma density near the multijunction grill, and four days of dedicated run time during which optimization of the coupling could occur. A "trophy shot" with 3 MW of lower hybrid power and ~ 20 MW of NBI and ICRF power that maintained a reversed shear discharge for ~ 8 s was obtained. Both electron and ion ITB's were formed and the non-inductive current drive has been calculated to be > 80%. The possibility of expanding the collaborative relationship between C-MOD and JET was also discussed. The Lower Hybrid high voltage power supply is progressing on schedule. Preparations for installation and the required acceptance tests were discussed. Inner Divertor -------------- Tiles continue to arrive and machining continues to be done on the new inner divertor. A picture of one of the C-Plates being machined can be found at http://www.psfc.mit.edu/cmod/operations/EngImages/MACHINE/Divertor/Mar30_05.jpg Note the keyways for holding the tiles in place. Power Systems ------------- Work on the EF1U-L Capacitor bank modifications was completed this week. We have started installation of new Hi-Yard instrumentation to better monitor power delivered to the LH, ICRF, and Alternator systems this week. Travel and Visits ----------------- Steve Wukitch attended the US-Japan RF physics workshop in Japan March 22-24. Miklos Porkolab attended the Annual Sherwood Fusion Theory Conference in Santa Fe, NM, on April 2-4. Paul Bonoli also attended the conference. Bob Childs was in Brooklyn, NY supervising copper plating of the stripline components. Martin Greenwald was in Lausanne for an International Database meeting. David Mikkelsen (PPPL) presented a talk on "Turbulent Transport Simulations of C-Mod" at the Confinement Database and Modelling Workshop at CRPP in Lausanne - 2-6 April, 2001.