Alcator C-Mod Weekly Highlights November 5, 2012 FY2013 weeks of research operations Target: tbd Completed: 0.53 weeks Plasma Shots: 61 54th Annual Meeting of the APS Division of Plasma Physics --------------------------------------------------------- Alcator C-Mod personnel, including collaborators, presented 1 invited review, 10 invited orals, 18 contributed orals, and 37 posters last week at the APS meeting in Providence, Rhode Island. An invited review talk on "The Role of the Boundary in Defining Viability of Magnetic Fusion Energy" was given by Dennis Whyte. Invited orals included: "Fluctuating Zonal Flows in I-Mode in Alcator C-Mod", Istvan Cziegler(UCSD) "Nonlinear Upshift of Trapped Electron Mode Critical Density Gradient: Simulation and Experiment", Darin Ernst "Intermittent Fluctuations in the Alcator C-Mod Scrape-Off Layer", O.E. Garcia (U. Tromso, Norway) "Advancing the Predictive Capability for Pedestal Structure through Experiment and Modeling", Jerry Hughes "Edge Sheared Flows and Blob Dynamics", J.R. Myra (Loadstar Research Corporation) "Disruption Mitigation Experiments with One and Two Gas Jets on Alcator C-Mod", Geoff Olynyk "Poloidal Variation of High-Z Impurity Density in ICRF-Heated Alcator C-Mod Plasmas", Matt Reinke (ORISE Fellow) "Multi-Channel/Multi-Field Turbulence and Transport in Alcator C-Mod in L-Mode and I-Mode Plasmas", Anne White "Comparison of Tungsten Fuzz Growth in Alcator C-Mod and Linear Plasma Devices", Graham Wright "Field-Aligned ICRF Antenna Characterization and Performance in Alcator C-Mod", Steve Wukitch All presentations are being made available at http://www.psfc.mit.edu/research/alcator/pubs/APS/APS2012/providence2012index.htm Over 70 presentations at the meeting referenced research done on C-Mod. Undergraduate Award at APS Meeting ---------------------------------- MIT Department of Science and Engineering junior Victoria Winters won an Undergraduate Poster Award at the 54th APS-DPP Meeting for research conducted at Alcator C-Mod this past year as part of the MIT UROP program. The poster was presented in the Tuesday afternoon C-Mod session as JP8.00089, "Exponential Spectra in Alcator C-Mod Edge Turbulence". It has been proposed that exponential power spectra seen in edge turbulence of fusion plasmas is the result of deterministic chaos, and is associated with the presence of Lorentzian pulses in the time series data. Using reflectometer and Gas Puff Imaging (GPI) data from C-Mod, Ms. Winters analyzed exponential power spectra in Ohmic and L-mode plasmas. Both reflectometer homodyne signals and GPI signals measuring density fluctuations just inside or at the Last Closed Flux Surface (LCFS) exhibit exponential power spectra. Theoretically, the characteristic slope of the data on a semi-log plot gives the full width of the underlying Lorentzian pulses. Using a separate fitting routine, individual Lorentzian pulses in the reflectometer time series data have been identified, and the widths of the Lorentzian pulses match the inverse characteristic frequency of the exponential spectra. Preliminary analysis of the waiting times and pulse amplitudes indicate these are randomly distributed, yet the pulse widths have a narrow distribution. This result is consistent with the deterministic chaos model, but further work is in progress to assess the robustness of the results. Victoria's co-authors on this work are Anne White (MIT-PSFC), David Pace (General Atomics), Jim Terry, Arturo Dominguez, Felix Parra and Jerry Hughes (MIT-PSFC). Post APS Tour of the PSFC ------------------------- Last Friday, Nov. 2nd, the PSFC hosted a special tour of the C-Mod, LDX and VTF experiments for APS-DPP attendees after the 2012 APS conference in Providence, RI. Over 50 visitors participated in the tour led by Earl Marmar and Martin Greenwald for C-Mod, Jay Kesner and Darren Garnier for LDX and Jan Egedal for VTF. The program drew visitors from all over the globe; U.S., U.K., India, Germany, Italy, Mexico, Korea, Japan, Spain and Chile. After the tour, participants were invited to enjoy a reception and mingle with PSFC scientists, students and staff. Visitor feedback has been enthusiastically positive and supportive of our work. Operations ---------- Routine maintenance of engineering systems continued last week. Alcator C-Mod remains under vacuum as innovative surface analysis research using the new RFQ accelerator is completed. ICRF Systems ------------ The FMIT#3 transmitter FPA tuning/load element is under repair. A contact finger from the rf gasket had broken off and become jammed in the tuner mechanism. FMIT#4 is set to be tested into dummy load at 50 MHz. Additional tests into vacuum are also planned. Operation at the end of the campaign indicated the FA-antenna system was limited to about 300 kW before faulting occurred. Inspection of FFT#1 has identified the water leak locations in the cooling system. The vendor has indicated that they would like for the entire unit to be shipped back to them for repair. Lower Hybrid System ------------------- Work continued on the 4th cart fiber optic links for the filament control system. Preparations are being made for low power testing of the 8-way splitter for the new lower hybrid launcher (LH3). Diagnostic Neutral Beam Systems ------------------------------- All failed MOVs have been replaced in the high-voltage transformer tank. These components limited DNB operation at the end of the last campaign. Inspections of all o-ring seals for the tank are underway. Remote Participation, Travel, and Visitors ------------------------------------------ Dr. Gregory De Temmerman visited the PSFC November 2-3. He gave a seminar on plasma-surface interaction studies at the FOM/Rijnhuizen Lab in the Netherlands which includes the Pilot-PSI and Magnum-PSI linear plasma facilities. These facilities are unique among linear plasma simulators in achieving C-Mod and ITER divertor densities and thus parallel heat fluxes. Of particular interest is that the recent studies they have done show that the modification of the surface by the impacting D+ ions has a flux dependence. This result is manifested by structural changes in the surface which vary from blistering (more grain size structures) at lower fluxes to smaller structures at higher fluxes. The actual shape of the surface structures is dependent on the lattice orientation. These variations occur above the fluxes normally achieved in linear facilities (and all operating tokamaks other than C-Mod). Dr. De Temmerman also described the effect of simultaneous H+ flux together with ELM-like transient heat loads which, together, lower the damage threshold compared to transient heat loads alone. This points out the importance of the combined characteristics of high fluxes and heat loads to really study the important physics of PSI. Dr. De Temmerman spent time in discussions with C-Mod scientists on the results of the C-Mod experiment and plans for the new divertor. He also spent time with the PSI science center researchers for discussions of ongoing work at both the MIT linear machine (DIONISOS) and the FOM linear machines. Dr. Ralph Dux visited MIT on November 3 to discuss the C-Mod program, including collaborations on diagnostic development for C-Mod and ASDEX-Upgrade. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly