Alcator C-Mod Weekly Highlights Nov 28, 2011 FY2011 weeks of research operations Target: tbd Completed: 0 weeks Plasma Shots: 0 Operations ----------- Plasma startup operations began at Alcator C-Mod last week. Two run days were scheduled and completed. Power systems and other subsystems operated reliably, with only two shots lost to supply faults, out of 65 attempts. Plasma breakdowns were successfully obtained on the other 63 shots. A total of 28 short plasma discharges (breakdown followed by current rise) were produced, with maximum current of 500kA and maximum pulse length of 180msec. All of these plasmas were highly resistive and radiative, with slow current rises and frequent disruptions. None survived long enough to reach their programmed flattop. One discharge was successfully terminated by the control system due to excessive runaway generation. Electron cyclotron discharge cleaning (ECDC) was carried out over the long holiday weekend, along with a 60C bake. Plasma startup operations are planned to continue this week. Physics ------- The paper "Rotation reversal bifurcation and energy confinement saturation in tokamak Ohmic L-mode plasmas", by J. E. Rice, I. Cziegler, P. H. Diamond, et al., has been accepted for publication in Physical Review Letters. Orso Meneghini has successfully defended his doctoral thesis, entitled "Fullwave modeling of lower hybrid waves on Alcator C-Mod", submitted to the MIT Department of Nuclear Science and Engineering. The thesis focuses on several aspects of the Lower Hybrid (LH) wave physics, the common theme being the development of fullwave simulation codes based on Finite Element Methods (FEM) used in support of experiments carried out on the Alcator C-Mod tokamak. Program Planning ---------------- A meeting of the C-Mod Experimental Program Committee (EPC) was held on Monday, Nov 21. Schedule plans for the initial startup and conditioning phase of the campaign were discussed. We anticipate that more than one maintenance day per week may be required in order to efficiently ready new systems, including the ARRA-funded rotated ICRF antenna and the new LH transmitter protection system. Topical group leaders are presently considering priorities for the physics phase of the campaign. Ten miniproposals for near-term experimental runs were reviewed. Eight were approved, some with minor revisions, and two were recommended for more substantial revisions. ICRF System ----------- All four ICRF transmitters have been tested into dummy loads and are ready for operation. The fast ferrite tuner (FFT) system on FMIT#2 driving the E-port antenna is awaiting refilling with coolant prior to final testing. Lower Hybrid System -------------------- Testing continued on the transmitter protection system (TPS) upgrade boards. Gains on all five boards have been modified by the SBIR vendor. New firmware was installed on the collector over temperature system (COTS) CPU board. A test script and formal testing procedure have been established for the testing and documentation of all TPS boards. Ferrite chokes were wound on all 63 TPS upgrade analog input cables. Quotes for ceramic windows for the next lower hybrid launcher (LH3) were received. Diagnostic Neutral Beam System ------------------------------ The DNB continued to operate well during C-Mod operations. A new monitor for the pressure in the DNB beam duct is operational and producing reasonable signals. Requirements for magnetic shielding of the element are being evaluated. Work is proceeding on installation of a vacuum test stand to be used for qualification of spare cathode emitters and development work. Diagnostics ----------- On Monday a vendor representative visited C-Mod to complete the installation and qualification of our upgraded Thomson scattering lasers. Each of these two lasers is now operable at the vendor specification of 1.2 Joules per pulse, at 50 pulses per second. Work is proceeding to interface laser operation with the C-Mod shot cycle, and to align the beams through the C-Mod vessel. The H-port ECE diagnostics (Michelson, GPC, GPC2) are all operational. New GPC preamplifiers, designed and fabricated at the PSFC, were used for the first time to measure startup plasmas. Photovoltaic elements instead of batteries or AC supplies are used to provide bias voltages. The noise is very low, equivalent to about 10 eV of electron temperature, on most channels. This upgrade should improve the s/n and reliability of the GPC diagnostic. The F-port ECE radiometer (FRCECE) is also operational. The Long Wavelength Extreme Ultraviolet Spectrometer (LoWEUS) was operated on C-Mod for the first time last Wednesday. This instrument, deployed as part of a collaboration with LLNL, can cover the 6-40 nm region, with the ability to observe ~18 nm at one time. LoWEUS's primary task will be to monitor the highly-ionized molybdenum line emission, but with better spectral and temporal resolution and reliability than the existing McPherson VUV spectrometer. Simultaneous operation of both spectrometers will occur during this campaign with the eventual goal being to remove the McPherson from C-Mod, freeing up much needed port space. The core CXRS diagnostic is back on-line and acquiring data during the plasma start-up phase of operation. The signal from the new Quasi-Coherent-Mode antenna, configured as a receiver, is being successfully acquired. All three chords of the C-Mod polarimeter are operational with strong signals. Spurious reflections back into the detectors that limited the resolution during the first two days of operation are being reduced with re-alignment and additional absorbing material along the beamlines. Travel and Visitors ------------------- Dr. Christian Theiler visited from CRPP-EPFL (Lausanne, Switzerland) on November 21-23. He gave a talk on his TORPEX research at our weekly turbulence meeting. He has also had multiple discussions with turbulence researchers here (experiment and modelling) about work at Lausanne, at C-Mod and more generally. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly