Alcator C-Mod Weekly Highlights Feb 22, 2005 FY 2005 weeks of research operation planned: 17 weeks, completed: 0.4 weeks. Alcator C-Mod continued Startup and Conditioning operations last week. Four run days were scheduled and three and a half were completed, including one day of research operation. This week will be a scheduled maintenance period. Operations ----------- Plasma operations were conducted Tuesday through Friday last week. A total of 59 plasma discharges were produced, with an overall startup reliability of 74%. Operations began late on Tuesday due to a delay in bringing the alternator up to speed. Runs on Wednesday through Friday maintained the noon to 7:00PM split shift schedule, which provides for additional work time in the cell and power room in the mornings. Two and a half run days were devoted to machine and RF conditioning operations. During Tuesday's run, upper-null discharges were run for the first time in this campaign. This gave us the opportunity to perform some initial tests of the newly installed upper divertor gas baffles, which are meant to simulate a neutral baffle geometry envisioned for an upper divertor cryopump (see http://www.psfc.mit.edu/cmod/sciprogram/ideas2005/Mirror_agenda/ Ideas05_labombard_upper-divertor.pdf) This "plasma conditioning' run quickly contributed some useful plasma results, as we were able to assemble some key information about the behavior of gas flow in the upper chamber. Ohmic L-mode, upper single-null discharges with line-integral densities of 0.6 and 0.8x1020 m^-2 were run. These had the upper strike-point sweeping across the upper divertor target plates. Upper chamber pressures were measured under the baffle (using an in-situ Penning gauge) and at the top of a vertical port (Baratron gauge). The readings were compared to those from a similar set of discharges run during the last campaign (no baffle). The baffle was found to enhance the local pressures by a factor of two as anticipated based on previous experiments. However, the pressure under the baffle was very sensitive to the major radius of the upper strike point location, changing by a factor of 2 or more, while the pressure at the top of the port was not so sensitive. These data suggest simple ways to improve the performance of an upper divertor cryopump system. The use of a series of pumping slots in the ceiling tile structure in place of a pumping duct is now being explored. The run on Thursday was dedicated to MP#406 "Testing of new scanning probe geometry". The new probe design is optimized to record information on cross-field (ExB) as well as parallel plasma flows. The goal of these tests is to identify a probe-head design for a new wall-scanning probe (WASP, see http://www.psfc.mit.edu/cmod/sciprogram/ideas2005/Mirror_agenda/ Ideas05_Smick_New-Probe.ppt) that we are planning to install at the end of the current campaign. Matched discharges in upper and lower-null topologies were run at three plasma densities. The new Mach-probe head on the ASP drive and new power supplies to drive it worked very well. High quality I-V characteristic data from all four electrodes were obtained. We saw clear differences in the relative ion saturation current levels among the four electrodes. These differences changed with density and with LSN/USN topology. The next step is to assemble data analysis tools to compute parallel and perpendicular Mach numbers based on published theoretical models and to compare with previous estimates of these quantities in similar discharges. ICRF System ------------ The E-port dipole antenna (FMIT transmitter#2) was energized during plasma operations last week, and has produced up to 1.2MW into plasma with pulse lengths of up to 0.8 seconds. The D-port antenna (FMIT#1) was also pulsed into plasma, but is not yet providing sustained high power. Tuning of FMIT#3 and #4 (J-port antenna) at 50 MHz also proceeded. Transmitter #4 is now producing up to 1MW into dummy load. The resonant loops for 50 MHz operation of the J-port antenna have been installed and tested. Assembly of the DC breaks and coaxial line to connect the antenna to the transmitters was begun. Lower Hybrid System ------------------- Work continued on preparation of the Lower Hybrid System for plasma operation. The LH high voltage power supply main circuit breaker control station was moved into the C-Mod control room. The LH transmitter operator interface computer was also moved to the C-Mod control room. All 12 waveguide runs are now complete and connected to the launcher. Testing of the integrated timing and data acquisition systems for the lower hybrid was begun. Mdsplus scopes for raw data are in place for TPS, CPS and ACS systems. Diagnostic Neutral Beam Systems ------------------------------- The new DNB has arrived in the US, and we expect delivery to MIT this Monday. The installation team from the Budker Institute (Novisibirsk, Russia) are scheduled to arrive this week and begin working on uncrating and installation of the beam. Travel and Visitors ------------------- Ron Parker (chair), Bruce Lipschultz, and Amanda Hubbard traveled to GA to participate in the DIII-D Progam Advisory Committee meeting. Bruce Lipschultz spent several extra days at GA working with A. Leonard, D. Rudakov, B. Bray and M. Groth on analyzing data from a joint experiment from July 2004. The goal of the experiment was to obtain data for an analysis of radial transport in the SOL during H-mode plasmas. Time-dependent profile data is needed throughout the ELM period for this analysis based on particle balance. Amanda Hubbard attended the IEA Workshop 59 on Shape and Aspect Ratio Optimization for High Beta, Steady-State Tokamak (GA, Feb 14-15), and presented a talk on "Current profile control for high performance steady state tokamaks: Considerations from C-Mod LHCD program". Ron Parker also attended. Stewart Zweben was at C-Mod last week to complete the installation of the PSI-5 fast camera. This camera was installed on the standard GPI view at the outer mid-plane, and reasonably good edge turbulence images were obtained during shots on the afternoon of 2/17/05. The PSI-4 camera was also brought from PPPL to C-Mod for use with the Li pellet experiment. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly