Alcator C-Mod Weekly Highlights July 6, 2009 FY2009 weeks of research operations Target: TBD Completed: 0.27 weeks Operations ----------- Plasma operations continued on Alcator C-Mod last week with startup and commissioning shots. A total of 34 discharges were produced during two days of plasma operation. On Thursday we completed the first portion of MP#555,"PF error field evaluation and compensation". The purpose of this experiment is to characterize the non-axisymmetric error fields arising from any positioning errors (tilts or shifts) in the poloidal field coils during the recently completed tokamak reassembly. This information is then used to design compensation algorithms to control currents in the C-Mod A-coil system to provide cancellation of the non-axisymmetric field. A series of no plasma pulses were performed with a single PF coil energized on each, and the resulting fields were monitored using the magnetic sensors (BP coils) at 26 poloidal and up to four toroidal locations. These data are being analyzed in terms of rigid tilts and shifts of the PF coil set, using a method developed in 2003. Program Planning ----------------- A meeting of the C-Mod Experimental Program Committee was held on Monday, June 29. The status of major sub-systems was reviewed, and it was agreed that Monday, July 6, will be a maintenance day. MP#556, "Lower Bt Operation, Breakdown and Discharge Development" was reviewed and approved. A subsequent meeting was held to discuss issues associated with experiments to measure the SOL footprint and evaluate the boron coated tiles. In order to avoid compromising these experiments, near-term operation will avoid deliberate high-energy disruptions, and minimize the energy and total power from the ICRF system during conditioning; pulse lengths will be kept relatively short and the waveforms from the different antennas will not be overlapped until needed for the experiments. Internal temperature measurements and molybdenum and boron sources, as well as radiated power, will be monitored. Operation in slide-away regimes should be avoided. ICRF Systems ------------ The D-port antenna has operated up to ~0.9 MW into plasma. The E-port antenna commissioning was delayed by a computer problem with the Fast Ferrite Tuner (FFT) control system but this system is now operational. We have continued to prepare for operation of the four strap J-port antenna. The 6" transmission line network has been assembled and the remaining transmission line work is assembling the 9" network. We plan to tune FMIT#4 to 78 MHz on the next maintenance day. The FMIT#3 transmitter awaits installation of a new tube (in-house) and assembly of the Final Power Amplifier (FPA). Lower Hybrid System ------------------- We continued fabrication of the lower hybrid launcher. Only 3 columns (out of 16) of forward waveguide and vacuum window components remain to be brazed. Work continued on the the lower hybrid control system upgrade, and the new electronics needed for the launcher rf probes. Diagnostic Systems ------------------- The video camera views of the plasma including the D-port antenna, J-port antenna, divertor view and two wide angle views are now operational. The in-vessel capillaries for localized gas puffing were tested. The gas plenum needs to be baked and leak checked. The x-point and midplane views of the Gas Puff Imaging cameras are operational. The inner wall GPI (coupled to fast diodes) is available. The CXRS pedestal toroidal array was installed, spatially and absolutely calibrated. There are 10 chords which intersect the diagnostic neutral beam in the outer midplane with a spatial resolution of 1.2 cm. The F-top poloidal array was installed and spatially calibrated. There are 19 chords intersecting the beam in the range 67.8 < R < 91.0 cm, with spatial resolution of 1.22 cm. The new limiter thermocouple system is now operating, monitoring the temperatures of selected tiles on the GH, AB and K outer limiters. The heat flux instrumentation on the J-divertor is also coming on line. Tile temperatures and calorimeter probe temperatures are now being recorded. The delta-T on these will be used to quantify the heat deposition profiles on the inner and outer divertor surfaces. Six surface temperature thermocouples on the J-port outer divertor are functioning, reporting surface temperature rises during discharges. Travel and Visitors -------------------- Yijun Lin attended the 36th EPS Conference on Plasma Physics, in Sofia, Bulgaria, last week. He presented a poster entitled "ICRF Mode Conversion and Flow Drive on Alcator C-Mod". _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly