Alcator C-Mod Weekly Highlights November 30, 2009 FY2010 weeks of research operations Base Target: tbd ARRA Target: 5 weeks Completed: 4.5 weeks, 548 shots Operations ----------- Plasma operations continued at Alcator C-Mod last week. Two run days were scheduled and completed. A total of 65 plasma discharges were produced with a startup reliability of over 90%. The runs supported experiments from the ICRF Physics topical areas. A successful boronization was carried out on Monday night. Plasma operations are planned to continue this week. Operation Details ----------------- Monday's experiment supported MP#588 "Evaluation of ICRF Sawtooth Pacing Techniques". John Graves of EPFL participated in this experiment remotely from Lausanne, Switzerland. We were able to make good progress investigating sawtooth stabilization/destabilization with He^3 minority absorption near the q=1 surface. We completed a phase scan at low He^3 levels, consistent with the minority heating regime; the Phase Contrast Imaging (PCI) diagnostic saw no evidence of mode converted waves. For -90deg phasing (waves in counter current direction), the sawteeth grew larger with the 3He resonance inside the q=1 surface and shorter with the resonance outside the q=1 surface. For +90deg, the response was reversed. The amplitude was also smaller for +90deg. Heating phasing behaved similarly to +90deg phasing. This phase dependence is opposite from central H minority heating where the sawtooth period can be lengthened/shortened. This suggests the mechanism is not diffusion of fast particles in space. An interesting observation is that the neutron rate was highest for heating phase, next +90deg phase, and the lowest was -90deg phase. On Tuesday, we carried out experiments in support of three miniproposals. The first half of the day was devoted to completion of MP#583 "Optimization of Mode Conversion Flow Drive". The main goal of this part of experiment, which was flow drive in low density H-mode, was not accomplished due to the difficulties in obtaining low density H-mode at high current. Because of the strong linkage between the plasma current and density in H-mode, we were not able to carry out an (Ip/ne) scan in H-mode. Rotation increases were observed during 50 MHz mode conversion heating, but further analysis is needed to separate the MC driven rotation from the intrinsic rotation (with large rise of plasma stored energy). The second part of Tuesday's run was devoted to MP#536 "Evaluation of FWEH, FWCD and MCCD". This run was a successful follow up to previous fast wave (FW) electron heating experiments carried out during the previous week. We were able to obtain several power modulations both faster and slower than sawtooth period, which will enable us to analyze the electron power deposition profile. The PCI only detected fast waves, confirming that there was no residual He3 to complicate the interpretation. Based on preliminary observations, the FW absorption is strong, and the break-in-slope for the central ECE channels is quite obvious at the RF transition. In the last hour of operation, we returned to MP#588 (sawtooth pacing), and successfully developed a discharge at 1 MA for further analysis, along with the 800kA plasmas obtained on Monday. ICRF Systems ------------ On Wednesday, we began the changeover of the J-port antenna and FMIT#3 and 4 transmitters from 50 MHz back to 78MHz. The transmitter cavity dimensions have been returned to their previous settings for 78MHz, and the cabling and software modifications for the frequency change have been completed. Modifications to the coaxial network transmission line are underway. We have completed an inspection of a failed final power amplifier tube, which had accumulated 3508 filament hours. We found that the anode water leak was a pin hole and was not associated with any melt. The screen, grid, and filaments all high potted successfully. We are evaluating different approaches to modify the anode for test purposes. Lower Hybrid System -------------------- Fabrication of the lower hybrid launcher continued last week. All sixteen in-vessel waveguide/splitter assemblies have been cleaned and have successfully passed a final leak-check. The assemblies are now being stacked and prepared for installation on the vacuum flange. We also continued fabrication of the klystron to launcher waveguide runs and the jungle gym assembly that mates the waveguide runs to the launcher. Work also progressed on installation of the rf probes, and the launcher support stand. Travel and Visitors ------------------- Drs Liang Liu and Lianmin Zhao from IPP in Hefei are visiting the PSFC to discuss plans to install Lower Hybrid current drive in the EAST tokamak. They are particularly intersted in learning how to model the interaction between their multijunction antenna and EAST plasmas, and are collaborating with Orso Menghini and Syun'ichi Shiraiwa to adapt their PSFC developed FEM code for this purpose. Ron Parker is host for their visit. John Rice was in Lausanne serving on the committee for a thesis defense on Nov. 24. He also attended the First International Conference on Frontiers in Diagnostic Technologies in Frascati Nov. 25-27, where he gave an invited talk on the spatial imaging high resolution x-ray spectrometer system. Manfred Bitter and Ken Hill from PPPL visited Nov.23-25 to continue work on the x-ray fluctuation diagnostic. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly