Find weekly highlights below with formatting characters removed: Alcator C-Mod Weekly Highlights October 1st, 2007 FY2008 weeks of research operations: Target: TBD Completed: 0 weeks Non-JOULE Research Milestones for FY07 -------------------------------------- The two C-Mod non-JOULE research milestones for FY2007 were completed on schedule last week with the submission of reports to OFES. The milestones are: A) Investigate particle and density control with the new upper divertor cryopump. A new upper divertor cryopump system has been successfully installed and operated in Alcator C-Mod. The system is a fully integrated divertor and cryopump design that employs a number of unique features including a "pumping-slot" style divertor target and a full toroidal cryogenic loop that acts as a liquid helium "pot". The system is found to function as intended, providing C-Mod with a new high-throughput particle exhaust tool (exceeding 9,000 liters/s for room temperature D2 gas) while minimizing helium consumption and avoiding a complex external cryogenic system. Dedicated experiments were performed during the FY07 run campaign to explore the capability of the pump for particle exhaust and plasma density control as a function of magnetic topology, plasma density and confinement regime. These experiments have provided valuable information, demonstrating the pump's utility for future physics experiments and for expanding the research capabilities of Alcator C-Mod. B) Investigate Lower Hybrid RF in L- and H-Mode plasmas, including study of combined Lower Hybrid RF and Ion Cyclotron RF. We have successfully investigated coupling lower hybrid waves to both L-Mode and H-Mode plasmas in Alcator C-Mod, and studied the interaction between LHRF and ICRF antennas. In addition to these studies we have carried out measurements of the dynamic evolution of the fast electron Bremsstrahlung profile, the non-thermal cyclotron radiation and the current profile. These measurements provide data that are being directly compared with the results of our GENRAY/CQL3D simulations and are stimulating further development of these simulation tools. Physics ------- Eric Edlund, a C-Mod graduate student, has developed a new procedure for toroidal mode number analysis of magnetics data. This procedure uses a fit of a sawtooth function to the phases calculated using a Fourier decomposition. As it is based in a Fourier representation, this method is suitable to the analysis of frequency coherent modes. This technique was first applied to the reversed shear Alfven eigenmodes observed during the current ramp phase of C-Mod discharges and during sawteeth. Low-n mode numbers in the range of 1-5 have been identified using the new technique, as expected from comparison of PCI data to the ideal-MHD code NOVA. Igor Bespamyatnov, a UT-FRC graduate student, has done analysis of the Wide View CXRS diagnostic data during ITB discharges. Density profiles of Boron (B^+5) were found to steepen at the ITB foot. Just inside the foot, the impurity profile steepening is consistent with an increase in inward convection relative to diffusion and with neoclassical estimates. Operations ---------- Maintenance of C-Mod systems continues during the up-to-air period. High voltage switchgear and breaker maintenance was completed in the power room last week. Work on the MIT alternator also continued with removal and inspection of seal oil heat exchangers. Some of the exchanger components have been sent out for refurbishment. In-vessel Work -------------- Two new flux loops have been placed in-vessel and spot welded into position. They have also been prepared for splicing into existing cables. A third loop is ready for installation. Igor Bespamyatnov and Bill Rowan, UT-FRC, completed spatial and intensity calibrations of the wide-view CXRS diagnostic. The Motional Stark Effect Diagnostic in-vessel collection optics has been carefully checked for its sensitivity to thermal and mechanical stress. The polarization angle of an in-vessel polarized light source was recorded by the MSE Diagnostic as the collection optics were heated over a 50 to 80 C range. Changes in polarization angle large enough to explain some of the effects seen during plasma operation were found. The collection optics have been removed from the vessel and are being examined. Lower Hybrid System ------------------- Work continued on refurbishment of the lower hybrid launcher. All jungle gym components are being inspected, cleaned, and high power tested. A loss of tube vacuum has delayed acceptance tests of our #117 klystron. We hope to have a full report from the vendor this week. ICRF Systems ------------ The E-Port antenna stub tuner and phase shifter were removed from the cell, inspected, and refurbished. Pressure seals have been improved on these systems so that SF6 can be used during the next run period to improve their power handling capability. The D-Port coupling loops have also been disassembled, inspected, and reassembled. Travel and Visits ----------------- Earl Marmar attended the International Workshop on Burning Plasma Diagnostics, held in Varenna, Italy, Sept 24-28. He is a member of the program committee for the meeting, and chaired a session on spectroscopic diagnostics. Miklos Porkolab participated in the US ITER Technical Advisory Committee meeting and review in Oak Ridge, TN, on September 25 and 26, 2007. Wayne Solomon, PPPL, visited the PSFC September 27-28 and gave a PSFC seminar. While he was here a roundtable discussion was held on velocity/momentum measurements with the seven graduate students that are involved in these measurements on C-Mod and a number of scientists. Discussion of the similarities and differences between DIII-D and C-Mod measurements, and where the students could provide unique information and studies was very helpful. Amanda Hubbard, Jerry Hughes, and John Rice attended the 11th IAEA Technical Meeting on H-mode Physics and Transport Barriers in Tsukuba, Japan from September 26 to 28. John gave a review talk on "Spontaneous Rotation and Momentum Transport in Tokamak Plasmas". Amanda presented a poster on "Evolution of edge profiles and fluctuations in two-phase L-H transitions in unfavorable magnetic configurations in Alcator C-Mod". Jerry presented a poster on "Studies of H-mode pedestal physics on Alcator C-Mod with enhancements to neutral pumping". Amanda, Jerry, and John will attend the ITPA meeting in Naka, Japan, this week. David Terry and Pat McGibbon travelled to CPI, in Palo Alto, CA, the vendor doing the rebuilds of our klystrons. They spent time with CPI engineers discussing the testing procedures and inspecting the test facilities. T.V. George, LDX project manager, and Barry Sullivan, Magnet R&D and Gyrotron project manager, both from OFES/DoE, visited the PSFC last week, and toured C-Mod. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly