Alcator C-Mod Weekly Highlights June 4, 2012 FY2012 weeks of research operations Target: 18 Completed: 6.05 Plasma Shots: 1079 Research -------- Dennis Whyte presented a talk at the C-Mod weekly science meeting on "Constraining heat flux widths in ITER". The analysis indicates that reasonable limitation on heat footprints can be established by considering simultaneously pressure limitations at the separatrix and divertor plasma temperature limits based on the thermal stability of open field lines. The result of these constraints is that a very narrow heat width in ITER of 1-3 mm is inconsistent with either pedestal stability or global power exhaust. Operations ---------- Plasma operations continued at Alcator C-Mod last week. Three run days were scheduled and completed. A total of 79 plasma discharges were produced with a reliability of 85%. The runs were devoted to vessel, ICRF antenna, and Lower Hybrid coupler conditioning. Operational Details ------------------- On Wednesday we continued MP355, ICRF Testing and Conditioning. The D and E antennas were conditioned up to the 1 MW level without faulting, while the new Field Aligned antenna was conditioned up to the 2 MW level without faulting. H/D levels are still high and will limit heating efficiency until we boronize the vessel. On Thursday, MP681, Evaluate Field-Aligned Antenna Performance, was conducted. The FA-J antenna was conditioned up to 2.5 MW for 0.4 s in USN discharges. Relatively short pulses at or above 3 MW were run. The maximum voltage reached without faults was 40 kV. Comparison discharges in both USN and LSN were obtained. On Friday, MP605, LH2 Lower Hybrid Launcher Checkout and Conditioning, was run successfully. LH power was increased to ~900 kW for 750 ms at densities conducive to efficient current drive. The first several discharges were at high density (1-1.5e20) as part of the spectrum analyzer probe diagnostic commissioning effort, which is part of a graduate student thesis. Increasing the outer gap to > 2cm seemed to improve high density operation. At low density, the power increased readily all day. Good results were obtained at 90 and 75 deg phasing, while 60 deg phasing had high reflection coefficients that resulted in faulting. ICRF Systems ------------ On Tuesday, the reconfiguration of the Field-aligned antenna transmission system was completed, and the antenna was operated successfully during last week's runs. An issue with the phase locked loop circuit that syncs the two transmitters driving the FA antenna is being addressed. Lower Hybrid System ------------------- The LH system achieved 900 kW net power for 750 ms during plasma conditioning last Friday. Klystrons 1, 2, and 3 were operating at maximum output power during these experiments. TPS firmware version 13 was delivered by the TPS vendor. The new firmware is designed to address issues with asymptotic behavior of the Collector Over Temperature System (COTS) calculation with large heat capacities by increasing the resolution of the calculation. Diagnostics ----------- The DNB performed very reliably and to specification for all runs last week. The MSE was operated successfully along with the DNB on Friday during conditioning of the Lower Hybrid system, including use of the Intershot Calibration System (ISC). Software development has been completed that allows use of the ISC system to compensate for the thermal diagnostic drift over the course of a run day, and the first complete ISC results were obtained. Preliminary analysis indicates that utilizing the ISC data marginally reduces the MSE drift, but there remains shot-to-shot variability that is outside the computed statistical uncertainties. Analysis is ongoing to characterize and understand the residual variability. The Fast Ion Loss Detector (FILD) diagnostic demonstrated improved lower-energy measurement capability in its first operation since the 2012 vent, during which it was moved 5 mm closer to the plasma. Ions from the 50 keV Diagnostic Neutral Beam (DNB) were observed and appear related to prompt-loss deposition. In addition, coherent fast ion losses (f < 30 kHz) were observed and correlated with power modulation of the J-Port ICRF antenna. The new Correlation ECE diagnostic is making measurements near the plasma edge that are most likely related to density fluctuations. Plans to increase the signal-to-noise level for temperature fluctuation measurements are being developed. All ten chords of the new Fast Two-Color-Interferometer (FTCI) are now operational. The demodulator electronics and data acquisition system for the new Differential Two-Color_Interferometer (DTCI) were installed and also made operational last week. The nine channel DTCI system measures the gradient in the line-integrated density. Remote Participation, Travel, and Visitors ------------------------------------------ David Mikkelsen, PPPL, worked at MIT all week on turbulence simulations for a variety of C-Mod plasmas (ITBs, rotation reversals, I-mode), and discussed plans for comparing turbulence simulations with measurements from the correlation electron cyclotron emission diagnostic that will measure electron temperature fluctuations. Josh Stillerman visited the EAST experiment at the Institute of Plasma Physics, Chinese Academy of Sciences (ASIPP), in Hefei China to discuss their use of the MDSplus data system. Discussions were held on both 'best practices' to improve their current operations, and on future collaborative projects for long pulse MDSplus. While there he also gave an overview seminar on MDSplus. David Pace, GA, was at MIT last week to work on the Fast Ion Loss Detector diagnostic. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly