Alcator C-Mod Weekly Highlights Dec 27, 2011 FY2011 weeks of research operations Target: 17 weeks Completed: 1.1 weeks Plasma Shots: 209 Operations ----------- Last week was a scheduled maintenance interval at Alcator C-Mod. No plasma operations were planned. A brief helium vent was conducted to allow for a borescope inspection of the J-port field aligned antenna, and to install a gate valve associated with the second gas jet disruption mitigation system at F-port. Following the vent the vessel was pumped down and electron cyclotron discharge cleaning (ECDC) was resumed. This week will also be a planned maintenance period, with no plasma operations scheduled. Physics ------- The paper "Scaling of H-mode threshold power and L-H edge conditions with favorable ion grad-B drift in Alcator C-Mod tokamak" by Y. Ma, et al., has been accepted for publication in Nuclear Fusion. The article "Rotation reversal bifurcation and energy confinement saturation in tokamak Ohmic L-mode plasmas" by J. Rice, et al., has been published online in the 23 December 2011 issue of Physical Review Letters (Vol.107, No.26): http://link.aps.org/doi/10.1103/PhysRevLett.107.265001 Run Planning ------------ The C-Mod Experimental Program Committee met on Tuesday, Dec 20, 2011. Scheduling implications of the performance of the field-aligned J-port antenna in the dipole configuration, and the results of the borescope inspection were discussed. No final decision on an overall long-term schedule was reached, but we anticipate continued operation in the present configuration prior to a manned access this spring. Six miniproposals were reviewed and approved, some with requests for specific revisions. ICRF System ----------- We inspected the ARRA-funded field aligned antenna vacuum transmission line using a video borescope. We found that a bolt connection that attaches the bellows to the feedthrough center conductor has a clear gap. The bellows and center conductor appear to be free of ant damage. A review of the assembly procedure, and inspection of the spare components made in the same fashion as those installed, resulted in identification of issues that may have contributed to the bolt backing out. A repair plan, including fabrication of a modified set of bellows and an improved assembly procedure, is being formulated. An internal review of this connection is planned. Lower Hybrid System ------------------- Work continues on updating PLC logic and interface displays for the LH transmitter protection system (TPS) upgrade. Testing of the PLC changes has started and will continue this week. Modifications to the TPS firmware were made to prevent the cart relays from tripping when the soft fault limit is reached. This modification will prevent excess wear on the high voltage relays. A normal HV shutdown will be initiated when the soft fault limit occurs. Additional changes were made to the grounding scheme to protect sensitive TPS electronic components. Preparations were made for upcoming high power operations. Adjustment and calibration of klystron drive leg power levels is complete. Return leg IQ detectors were calibrated. A defective RF isolator was identified and replaced. The new calibration data tables are documented and in place. The engineer from our TPS Upgrade SBIR vendor visited the PSFC on Monday to help with testing the latest version of the firmware used in the TPS controller boards. Diagnostic Neutral Beam Systems ------------------------------- The DNB was operated into its calorimeter for a series of shots for the purpose of characterizing the beam performance. We scanned the energy by taking shots with 2, 4, 6, 8, or 10 DNB pulses (60 msec on, 40 msec off) at ~50kv and 7.5-8.0 Amps. Data were obtained both with the bending magnet turned on and off. Results of these measurements are being analyzed. Travel and Visitors -------------------- Amanda Hubbard attended a meeting of the FESAC panel on collaborations in San Diego. Manfred Bitter and Ken Hill from PPPL visited MIT on Dec.19-20 to prepare the Pilatus PHA pinhole camera for operation. Bob Ellis (PPPL) visited MIT last week for discussions on the design of the Advanced Divertor. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly