Alcator C-Mod Weekly Highlights October 19, 2009 FY2010 weeks of research operations Base Target: tbd ARRA Target: 6 weeks Completed: 1.2 weeks Operations ----------- Plasma operations continued last week at Alcator C-Mod. Three run days were scheduled and two were completed. The experiments supported research in the Boundary and Transport Physics areas. A total of 55 plasma discharges were produced with a reliability of 83%. On Thursday a fault condition in the alternator drive motor electronics prevented operation. The fault was successfully diagnosed and repaired, and normal operation resumed on Friday. A successful Final Design Review was held for the inspection arm that will be used for inspections of the interior of C-Mod during the short clean vent scheduled for the week of October 26. Plasma operations are planned to continue this week. Operations Details ------------------ Wednesday's run supported MP#584 "Edge Turbulence Approaching and During the L-to-H Transition". This work comprises part of the thesis research of an MIT graduate student, and will also contribute to an invited paper at the upcoming APS DPP Meeting. The purpose of the experiment was to investigate the spectral variation of the electron-diamagnetic-drift-direction propagating turbulence previously identified as a precursor or first phase of the L-H transition, and to clarify the connection of this feature to the improved L-mode (I-mode). The key diagnostic for this study is the edge Gas Puff Imaging (GPI) system. During Wednesday's run we studied Ohmic H-modes (Lower Single Null, 2.7 Tesla) at varying target densities, ICRF-heated H-modes (LSN, 5.4 T) at similar density, and (USN, 5.4T) I-mode discharges, also with a density scan. These data are being analyzed. On Friday, we continued our characterization of the Improved L-mode (I-mode) under MP#579. Experiments this day were carried out at B=5.6 T, Ip=1.35MA and 1.2MA, and included a density scan and impurity seeding (neon) of high performance I-mode discharges. Some shape variations were also undertaken at the higher current, which corresponded to q95 between 2.85 and 3.1. Staircase ICRF power waveforms were employed to establish the H-mode threshold in these upper null (USN) discharges. The best I-mode conditions were obtained at moderate density, contrary to initial expectations. Use of neon seeding had a beneficial effect in reducing injections and resulted in sustained high performance I-modes at 1.2MA (q95~3.3)and nebar~1.7e20/m^3. At 1.35MA, a clear transition to the I-mode, followed by a transition to ELM-free H-mode were observed. Fluctuation data from the reflectometer correlated with formation of the pedestal as seen on electron cyclotron emission (ECE) are being analyzed. Milestones ---------- The final report describing successful completion of the OFES 2009 Joint Facility Milestone on particle control and hydrogenic fuel retention was submitted. Dennis Whyte (C-Mod), Steve Allen (DIII-D) and Charles Skinner (NSTX) were the respective facility coordinators of this effort, and Dennis served as the overall national coordinator. Data Acquisition ---------------- A timing verification system has been deployed on the A- and F-port scanning probes as well as the optical fluctuation diagnostic. The system provides a timing reference signal which can be digitized and used to verify or correct the time stamps of acquired data. ICRF Systems ------------ All three antennas were operational and performed nominally for experiments last week. Testing of phased operation of the J-port four-strap antenna was operationally successful. We also observed that +90 degree and heating phasing resulted in longer sawtooth periods than -90 degree phasing for high power ICRF. Analysis continued in support of the design of the new four-strap antenna. Lower Hybrid System ------------------- We continued our meetings with vendors to define the welding processes required to finish the in-vacuum lower hybrid launcher components. A vacuum chamber extension tube is being fabricated to allow e-beam welding of complete waveguide/transformer/splitter modules. Travel and Visitors ------------------- Perry Phillips (U. Texas) was at MIT last week, working on tuning of the FRCECE electron cyclotron diagnostic. All 32 channels of the FRCECE system are now operational. Catherine Fiore participated in an APS CSWP (Committee on the Status of Women in Physics) at Brown University on Friday. Martin Greenwald traveled to Washington to participate in a briefing of OFES staff on the Fusion Simulation Project. Steve Scott (PPPL) visited the MSE team at Nova Photonics to discuss physics related to the background light seen by the C-Mod MSE diagnostic. The week of Oct 4th, John Wright traveled to Lisbon to attend the 21st International Numerical Simulation of Plasmas conference (ICNSP'09). He gave an invited talk titled, "Challenges in self-consistent full wave simulations of lower hybrid waves." In addition, a poster by Leonardo Patacchini titled,"Ion collection by a sphere in ExB fields", was presented by John. Conference proceedings will be published in IEEE Transactions on Plasma Science on Numerical Simulation of Plasmas early next year. On Oct 13th and 14th, John Wright hosted a TORIC developers meeting at the PSFC. It was attended by Doug McCune and Keshavamurthy Indireshkumar from PPPL, Jim Conboy from JET and Paul Bonoli. Marco Brambilla and Roberto Bilato from IPP and John Cary and Scott Kruger from Tech-X attended remotely. Issues of collaborative development with IPP and integration of parallel TORIC in the Transp and FACETS projects were discussed. Matt Reinke attended the 2009 ADAS-EU Tutorial at IPP-Garching from Oct 8th-16th. Members from the ADAS team instructed a small group on the use of the Atomic Data and Analysis Structure (ADAS) software as well the underlying atomic physics modeling. Also while at IPP he discussed experiments and diagnostics with a number of ASDEX-U researchers, including recent impurity seeded H-modes studies on C-Mod. Josh Stillerman attended the ICALEPS 2009 Conference in Kobe, Japan, and presented a paper on the timing verification system. Steve Wukitch met with Bob Russel of AFT to discuss additional fast ferrite tuners. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly