Alcator C-Mod Weekly Highlights March 1, 2010 FY2010 weeks of research operations Base Target: 13 weeks Base Completed: 5.90 weeks ARRA Target: 5 weeks ARRA Completed: 5.0 weeks Plasma Shots: 1205 Operations ----------- Plasma operations continued at Alcator C-Mod last week. Four run days were scheduled and completed. Experiments supported research in the Boundary, Transport, and MHD topical science areas, and the Diagnostic Development activity. A total of 102 plasma discharges were produced with a reliability of over 80%. A boronization was performed on Monday night. Research operations are planned to continue this week. Operation Details ------------------- Runs on Tuesday and Wednesday were devoted to MP#591 "Boundary Layer Heat Transport Experiments in H-mode Plasmas". These experiments contribute to the FY2010 OFES Joint Facility Milestone to investigate boundary layer transport and heat flux "footprints". Heat flux datasets, including thermocouple and IR camera measurements, were assembled in steady EDA H-mode conditions with Bt=5.4T and plasma currents of 800 and 500kA. Density and RF power were scanned over the accessible range for both currents. Footprint data were taken with both fixed and swept strikepoints. An L-mode comparison shot was also obtained at 800kA. Finally, several shots were obtained with near double null equilibria for comparison with the LSN cases making up the majority of the dataset. The run on Thursday supported MP#592 "L-H Threshold Dependence on Fueling Location, Density and Neutral Pressure". Inner wall fueling using the NINJA system was compared with standard fueling from the outboard piezovalves, in an effort to reduce the neutral pressure required to obtain a given target density. The cryopump was used to further control the in-vessel particle inventory. Step waveforms of the ICRH power were used to determine the H-mode thresholds over a range of target densities 1 < nebar < 2.5e20/m^3 with Ip=800kA, Bt=5.4T. The observed L-H thresholds did not follow a simple density scaling, but were not systematically very different with low or high field side fueling. However, ICRF operation and L-H transitions were obtained at about 15% higher target density using the inboard fueling. Data were also obtained at Ip=1.1MA (q95~3.15), using inboard fueling. These shots resulted in steady EDA H-modes with n/n_G > 0.7. Two experiments were carried out on Friday. The first half of the day was devoted to MP#502 "HIREX_SR calibration", and addressed the issue of vignetting in the optics of the Spatially Resolving High Resolution X-ray Spectrometer. Argon-seeded ohmic plasmas were used to provide constant plasma conditions, while masking of the crystals in the X-ray spectrometers was used to assess the vignetting . The data indicated that vignetting was taking place in both the H- and He-like systems. The H-like vignetting needs to be compared to ray tracing calculations to see if the brightness profile can be corrected. We also obtained fully covered crystal data for both arrays and first analysis shows that almost all the background is incoherent scattering, not continuum coming directly off the crystal. This result will help inform whether or not background levels can be used to correct for vignetting in past data. The second half-run on Friday was dedicated to MP#590, employing amplitude modulation of the ICRF power to probe Alfven eigenmodes. This experiment employed improved interfacing to the modulation control waveforms. We were able to successfully reproduce the conditions (6T, 800kA, nebar~2e20/m^3, inner wall limited) for which a possible resonance had been identified in a previous run day, and also obtained data for a similar discharge at lower Bt. These data are being analyzed. ICRF Systems ------------ A fast ferrite tuner (E-port antenna) was inoperable this week due to an issue with a power amplifier. The unit will be shipped to the vendor for repair. The E-port antenna continued to operate with one fast ferrite tuner in feedback mode combined with between shot adjustment of the mechanical stub to minimize reflections. During the high density H-mode threshold experiments, we found that the neutral pressure limit could be exceeded by 50-100% when the antenna was operated after L->H transition. Further analysis is required to determine the improved voltage handling at high neutral pressure in H-mode. Lower Hybrid System -------------------- The lower hybrid launcher mounting fixture and an A-Frame with chain falls was used to lift the launcher last week and allow testing of the procedures being developed to clean the windows. Tests will continue early this week. SEM analysis of etched window samples confirm that the braze and other metal components used in the vacuum windows are unaffected by the etching process. High power testing of the new Coupler Protection System (CPS) was begun last week. After some modifications to the software and verification of VSWR and threshold levels, the system performed nominally. Travel and Visitors ------------------- On Tuesday, February 23rd, Catherine Fiore and Matt Fulton hosted a visit to the PSFC by the US Japan Joint Working Group on Fusion Safety. The visitors were Dr. Kiyohiko Nishimura (Professor, Safety & Environmental Research Center. National Institute for Fusion Science), Prof. Yuichi Takase (University of Tokyo), Dr. Tetsuo Seki, (Associate Professor, Department of Large Helical Device Project,National Institute for Fusion Science) and Atsuhiko M. Sukegawa (Dr. Eng. JT-60 Safety Assessment Group, Fusion Research and Development Directorate, Japan Atomic Energy Agency). The group participated in several hours of presentations and discussion of the MIT health and safety programs, followed by a facility tour. Paul Bonoli and Professor Atsushi Fukuyama from Kyoto University hosted a US-Japan Workshop at the MIT Plasma Science and Fusion Center on February 23-25, 2010. This workshop was part of the Joint Institute for Fusion Theory (JIFT) program which is aimed at enhancing US-Japan Fusion Research Collaborations. The JIFT objectives are to advance the theoretical understanding of plasmas and to develop fundamental theory, computational tools, and concepts for understanding nonlinear plasma phenomena. The theme of this JIFT Workshop was integrated modeling. The scope included plasma core phenomena (stability and transport) as well as edge phenomena, heating and current drive, plasma control systems and how these interact. The workshop also reported on progress and issues dealing with integrated modeling of fusion devices. A session was also held on progress in computational frameworks, including a talk from representatives of the climate modeling community on framework activities in that area. Talks that were presented at the workshop can be viewed at the following weblink: http://www.psfc.mit.edu/JIFT09/JIFT09.html Thomas Puetterich from ASDEX-Up started a 6 month visit to MIT to study impurity transport on C-Mod. He will be primarily using the CXRS measurements and the STRAHL code to apply techniques he developed at ASDEX-Upgrade to compare boron transport on C-Mod to He and C transport in ASDEX-Upgrade for the pedestal region. Stewart Zweben was at MIT last week, and installed the second new Phantom 710 high speed camera on C-Mod. This camera now images the X-point region at up to 390,000 frames/sec. He also continued acquisition and analysis of images from the midplane 710 camera, which, at 390,000 frames/sec, is fast enough to track the radial and poloidal motions of turbulence blobs in the SOL. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly