Alcator C-Mod Weekly Highlights October 9, 2012 FY2013 weeks of research operations Target: tbd Completed: 0.53 weeks Plasma Shots: 61 Operations ----------- Plasma operations continued at Alcator C-Mod last week. Two run days were scheduled and completed. A total of 61 plasma discharges were produced with a reliability of 95%. The runs supported research in the Transport Physics, ICRF Physics, and Boundary Physics topical areas. C-Mod has now entered a planned maintenance period. No plasma operations are planned for this week. Milestones ---------- With submission of the final report, the 2012 Joint Research Target milestone was achieved. Research focused on multi-channel core transport, especially experiments that crossed the boundary between electron and ion dominated transport. Work from the 2012 JRT will be featured in the upcoming October meetings, including IAEA papers by: Rice, Reinke, Howard, Fiore, Holland, Doyle, Luce, Guttenfelder, Kaye, Ren; and APS invited talks by White, Ernst, Hillesheim, Waltz, and Scott. Operation Details ----------------- The run on Monday was devoted to MP#695 "Fast ion production and transport in He3 minority heating and mode conversion". This experiment, which supports the thesis research of a University of Texas graduate student, employs a novel Fast Ion Charge eXchange Spectrum (FICXS) diagnostic to measure the energy spectrum and density of He3 ions. He3 minority and mode conversion heating was provided by operation of the field-aligned J-port antenna at 50MHz at powers up to 1.5MW. Up to 2.5MW of additional heating was provided by the D- and E-port antennas operating at 80 and 80.5MHz (proton minority scenario). The He3 concentration was varied to access both mode conversion and minority heating regimes. Scans of RF power, resonance location (toroidal field) and plasma current were performed. Enhancement of the He3 spectrum by the DNB was clearly observed at thermal energies and at energies greater than twice the bulk ion temperature. These data are being analyzed. Three experiments were carried out on Tuesday. The first part of the run was devoted to MP#721 "Study of ICRF mode conversion flow drive and NTM's in high performance I-mode plasmas". Some additional data on NTM behavior was acquired to supplement the results from previous experiments. Due to continued limitations on the power available from the J-port antenna at 50MHz, it was not possible to obtain more data concerning MC flow drive. The second experiment on Tuesday was MP#721 "Controlling sawteeth and core turbulence in I-mode plasmas with off-axis heating". The goal of this experiment was to study the Te profile stiffness, and response of fluctuations to changes in Te, in I-mode plasmas. Gyrokinetic stability analysis finds the dominant core instability is the trapped electron mode driven by the electron temperature gradient. Therefore we applied modulated ICRF heating to look for a signature TEM response to changes in the electron temperature profile and its gradient. To minimize the interference of sawteeth and allow a study of the response of transport and fluctuations to changes in the electron temperature profile, off-axis ICRF heating was applied near the half-radius to obtain I-Modes with small sawteeth. We succeeded both in minimizing sawteeth and maintaining I-Mode through clean and clearly observable power modulations. Profiles were well-documented using a full suite of diagnostics, and extensive fluctuation data were obtained. The third experiment supported MP#723 " Inner wall erosion measured with AGNOSTIC". The goal of this experiment, which supports the research of several MIT graduate students, was to make the first in-situ measurements of plasma-facing surface erosion over the timescale of one to a few shots using the newly developed AGNOSTIC diagnostic. AGNOSTIC was successfully used on a shot-to-shot basis to obtain data about the wall surface properties. In order to document a baseline condition, gamma and neutron spectra at three different locations along the inner wall were obtained. A series of ICRF-heated inner-wall limited discharges were then produced, and again spectra were obtained to document the erosion. The diagnostic was then set up to acquire data between shots, and the first in situ shot-to-shot wall ion beam analysis in a tokamak was produced. Additional data, including a 2D mapping of the inner wall, were obtained during during a no-plasma session on Wednesday morning. ICRF Systems ------------ Following reconfiguration of the external matching network for the J-port antenna, we found that the antenna continued to encounter difficulty operating above 1 MW at 50MHz. The power handling capability further degraded during operation, and the arc detection system indicates the presence of arcing in the J/4 transmission line matching system, probably in the stub tuner. We will carry out a detailed inspection and refurbishment during the extended maintenance period. Lower Hybrid System ------------------- The remaining Collector Over-Temperature System (COTS) fast thermocouple transmitters were calibrated and tested last week. All components (hydraulic fittings, thermocouples, transmitters, boxes, and cables) are now ready for installation in the cell. Diagnostic Neutral Beam Systems ------------------------------- The DNB operated successfully in support of several experiments this past week, at somewhat reduced voltage and current. Now that the campaign has ended, maintenance will be performed on the beam, and any needed repairs will be effected. Diagnostics ----------- Last week the MSE team identified a third wavelength region to use as part of the newly developed real-time polarization background subtraction system. Narrow band-pass filters on loan from JET enabled this measurement. The diagnostic neutral beam was fired with a ~1s long unmodulated pulse into various discharges to demonstrate the use of wavelength interpolation of the polarized background using the new real-time system, instead of the traditional time interpolation across a modulated beam. The results are promising for the future, and analysis is ongoing. Travel and Visitors -------------------- Steve Lisgo (ITER Organization) visited the PSFC for three days, Oct 3-5, to acquire C-Mod data for addressing several issues facing ITER. The subjects were impurity seeding and upper divertor plasma characteristics. Given the similarities in the C-Mod SOL to that of ITER, such ITER simulations of C-Mod plasma will be important in qualifying similar simulations for ITER. Dr. Lisgo also spent time with the C-Mod staff discussing various ways the OSM-Eirenne code combination could be used to model deuterium and impurity physics in the SOL and pedestal regions of both ITER and C-Mod. Dr. Lisgo also presented a PSFC seminar on the status of the ITER project. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly