Alcator C-Mod Weekly Highlights July 13, 2009 FY2009 weeks of research operations Target: TBD Completed: 0.52 weeks Discharges: 127 Operations ----------- Plasma operations continued on Alcator C-Mod last week. A total of 80 discharges were produced during four days of plasma operation. On Tuesday and Thursday we continued machine conditioning, including operation in Upper Single Null and Inner Wall Limited configurations. Machine clean-up is progressing satisfactorily, as evidenced by RGA (residual gas analysis), H/D ratios measured during discharges, and by improved startup reliability and robustness. The startup reliability on Thursday was over 90% and disruptivity under 5%. Wednesday's run was dedicated to ICRF checkout and conditioning (MP#355), with power successfully coupled from D- and E-port dipole antennas. On Friday we carried out experiments in support of MP#556, "Lower Bt Operation, Breakdown and Discharge Development". These experiments successfully obtained reliable plasma startup at 3 tesla, with early X-point formation (t_x=0.16sec), as required for experiments planned by the Advanced Scenarios task force. This experiment also succeeded in obtaining the first (ohmic) H-modes in C-Mod so far in this campaign. The low-field startup scanario is also expected to be useful for experiments supporting other research activities, including Transport Physics and support for the ITER half-field H-mode scenarios. Additional experiments on Friday aimed at extending the 3T startup to lower voltage, without the use of solid-state interrupter (commutation) circuits on the OH and EF1 coils. Under these conditions, reliable breakdown was achieved, but current ramp-up was not achieved. Plasma operations are planned to continue this week. Milestones ---------- The 3rd Quarter FY09 Joint Facility Milestone on particle control and hydrogenic fuel retention was successfully completed and reported to the DOE Office of Fusion Energy Science. The Milestone report, coordinated by Dennis Whyte at Alcator C-Mod with key contributions from Steve Allen (DIII-D) and Charles Skinner (NSTX), included new experimental and modeling results from all of the three facilities. Physics -------- A paper, "Comparison of scrape-off layer turbulence in Alcator C-Mod with three dimensional gyrofluid computations", by S.J. Zweben, B.D. Scott, J.L. Terry, B. LaBombard, J.W. Hughes, and D.P. Stotler, has been accepted for publication in Physics of Plasmas. ICRF Systems ------------ The D-port antenna (FMIT#1) was successfully operated into plasma at up to 1MW power. The E-port antenna (FMIT#2), using the fast ferrite tuner (FFT), also operated into plasma with power up to 1 MW, but requires additional conditioning; injections associated with E-port operation above 800kW contributed to increased plasma disruptivity. The FMIT#4 transmitter (J-port) has been successfully retuned to a frequency of 78 MHz. FMIT#3, the other transmitter used for the four-strap J-port antenna, is in the process of being restored to service. DNB System ---------- During beam conditioning a water leak developed in the chamber from the source region. The source was dismounted and disassembled, and repairs are underway. Diagnostic Systems ------------------- The primary Thomson scattering laser was safely aligned through the C-Mod vessel. Following several repairs to the data acquisition system, the first plasma data of the campaign were collected. Additional work is in progress to expand the spatial coverage and include the second laser. The new video view of the G-H outboard limiter is now operational. The WideView Charge eXchange Recombination Spectroscopy (CXRS) Diagnostic was successfully tested using light from plasmas. The diagnostic is calibrated and will is available once the DNB is operational. Most of the bolometry arrays (foil and diode) are operational but not yet calibrated. Four of the reflectometry systems (50, 60, 75, and 88GHz) are online and have been tested with plasma. The swept 110-140 GHz and fixed frequency 140GHz systems are also online and are being tested. The ASP scanning probe has been reinstalled and was operated into plasma for clean-up and conditioning on Thursday. The FSP and inner-wall probes were also operated into plasmas, and will require further conditioning. Bulk temperature increases based on the tile thermocouples in the divertor and main limiter are being routinely analyzed and displayed between shots. The spatially resolving high resolution x-ray spectroscopy (HIREX-SR) diagnostic is online with one of four detectors operational. Travel and Visitors -------------------- Chuck Kessel (PPPL) visited MIT on Thursday and Friday, and served as Session Leader for the experiment on Friday devoted to his MP#556. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly