Alcator C-Mod Weekly Highlights February 22, 2010 FY2010 weeks of research operations Base Target: 13 weeks Base Completed: 5.0 weeks ARRA Target: 5 weeks ARRA Completed: 5.0 weeks Plasma Shots: 1040 Operations ----------- Plasma operations continued at Alcator C-Mod last week. Three run days were scheduled and completed. Experiments supported research in the ICRF Physics and Transport topical science areas. A total of 63 plasma discharges were produced with a reliability of about 85%. The run on Friday featured operation at Btor~8 T. Research operations are planned to continue this week. Operation Details ------------------- Wednesday's run was dedicated to MP#598 "Impurity transport studies in L-mode plasmas", and was devoted to continuing a series of parameter scans, including varying density, plasma shape, and toroidal field, in order to investigate the scaling of impurity transport. The principal actuator in these experiments is the laser blow-off system, which was used to inject CaF2. A host of spectroscopic diagnostics were employed to monitor the evolution of the injected impurities across the profile. Experimental configurations included inner wall limited discharges with elongations (kappa) of ~1.1 and 1.4, and upper single null diverted discharges with kappa > 1.7. The toroidal field was varied between 2.6 and 6.5T. These datasets will contribute to the doctoral research of an MIT graduate student. The experiment on Thursday was devoted to MP#562, "Characterization of the decay time of the fast-ion tail", which comprises part of the doctoral research of an MIT graduate student. The goals of this experiment were to measure the rise and decay of the ICRF heated fast ions, using modulation of the ICRF power waveforms (40msec on, 40msec off). The minority proton tail was monitored using the Compact Neutral Particle Analyzers (CNPA). Scans of plasma current and ICRF power were completed, along with some variation in the antenna phasing of the four-strap J-port antenna. A clear difference in the energy of the fast ion tail was observed between 600 kA and 1.2 MA. Higher ICRF power did not result in higher tail energies, but did increase the count rate of fast ions. Variation of the antenna phasing did not seem to affect the fast ion spectrum. The data are being analyzed. Friday's experiment was devoted to MP#508a, "Evaluation of D(3He) Minority Heating", and was carried out with Btor=7.9 T and f~80MHz, with RF power up to 5MW. This run, in combination with the two B~8T runs from the previous week, provide a scan of He^3 concentration and density for characterization of He^3 minority heating regimes. Concentration was varied by adjusting the He^3 puff duration. Localization of the mode conversion signature using the PCI (Phase Contrast Imaging) diagnostic was used to estimate the concentration in the plasma core. The lower He puff rates gave poorer heating performance than 150 ms puff. Increasing the density to nebar~1.6e20/m^3 also reduced the heating but the radiation was significantly lowered. The heating efficiency (as measured with neutron rate and central temperature) appeared sensitive to power level and antenna phase. Overall heating effectiveness appeared better at low plasma density. The majority of the experiments were carried out in L-mode using Upper Single Null discharges. A few Lower Null, H-mode discharges were produced at the end of the run to investigate the PCI response. ICRF Systems ------------ The first 5" feedthrough for the new rotated four-strap ICRF antenna has been received from the vendor and passed incoming inspection. Lower Hybrid System -------------------- Jeff Doody worked with our vendor last week to produce nine more e-beam welded waveguide/window test samples with contaminated alumina surfaces. These samples were used to determine the best process to use to clean the launcher windows. The pH and temperature of the etch solution, as well as the time in the solution, were varied. The lifting fixture needed to hold and orient the launcher during the cleaning process, as well as the fume hood under which the cleaning will be done, have been completed. Active MHD Spectroscopy ----------------------- An upgraded version of the lower Active MHD Spectroscopy antenna amplifier was installed last week. The upgrade allows the amplifier resistance to be modified in discrete steps during a shot to help flatten the current response in the amplifier. In addition, a hardware setup has been created to allow for remote control (via ethernet access from the Control Room) of the ICRF modulation envelope. These enhancements will be tested during an upcoming experimental run. Travel and Visitors ------------------- Amanda Hubbard traveled to Ottawa to participate in a review of proposals as a member of the Physics Grant Selection Committee of the Natural Sciences and Engineering Research Council of Canada (NSERC). Manfred Bitter, Ken Hill and Luis Aparicio-Delgado from PPPL worked on installation of the x-ray fluctuation spectrometer at C-Mod Feb.16-19. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly