Alcator C-Mod Weekly Highlights October 26, 2009 FY2010 weeks of research operations Base Target: tbd ARRA Target: 5 weeks Completed: 2.3 weeks Operations ----------- Plasma operations continued last week at Alcator C-Mod. Five run days were scheduled and over four completed. The experiments supported research in the H-mode Scenarios, Transport and ICRF Physics areas. A total of 122 plasma discharges were produced with a reliability of 83%. Boronizations were carried out overnight on Oct 16-17, and again on Oct 20-21. On Friday a fault condition in the AC circuitry of one of the poloidal field power supplies suspended operation after three hours. The supply is under repair. This week is a scheduled maintenance week. No plasma operations are planned. Operations Details ------------------ Runs on Monday and Tuesday supported MP#564 "Power requirements for high confinement H-modes and the role of radiated power spatial distribution". On Monday, neon and nitrogen seeded EDA H-modes were produced; Alberto Loarte (ITER Organisation) participated in the experiment using remote conferencing tools. Effective seeding with N2 was found to require higher plenum pressures than neon, as well as continuous puffing during the H-mode flattop, due to the non-recycling nature of nitrogen. As with neon, high confinement (H89~1.8) along with reduced metallic impurity injections and steady rf performance were obtained with moderate nitrogen seeding. The seeded EDA discharges on Monday resulted in a new one-day record for fusion neutron production on C-Mod. On Tuesday, we attempted to continue the seeding experiments using ELMy discharges in the modified "JFT2-M" shape. However, degraded machine conditions and higher than usual molybdenum radiation prevented reliable ELMy H-mode performance, both with and without neon seeding. Attempts to reproduce the favorable EDA results from the previous day were also unsuccessful, confirming the degraded conditioning. At the end of the day, attempts to reproduce neon-seeded I-mode discharges were successful, reconfirming previous results that I-mode requires neither extensive wall-conditioning nor recent boronization. We will revisit the ELMy H-mode portion of this miniproposal in a future run. The runs on Wednesday and Thursday were devoted to MP#527 "Optimization of H-mode pedestal and performance with magnetic balance control and active pumping". The purpose of this experiment is to study pedestal structure and H-mode confinement in near double null configurations. Prior experiments suggested a notable pedestal degradation at the double null point, with some improvement in slightly upper null cases and substantial improvement in lower null. This observation was largely reproduced and the data set extended with current and power scans. A tantalizing suggestion from the experiment is that the power required for H-mode access can be reduced by making the plasma double null, as has been observed on ASDEX Upgrade and, to a greater extent, on MAST and NSTX. If this effect proves repeatable in future experiments, it would provide additional insight into L-H transition physics. The run on Friday was devoted to MP#581 "High Density Target Plasma Antenna Operation". The goal of this experiment was to attempt to improve the ICRF performance in high density discharges, particularly with respect to the "high neutral pressure limit" which typically results in antenna faulting. Fueling of LSN and DN L-mode targets up to nebar~2.5e20/m^3 using the standard outboard midplane piezo valve was compared to use of the inner-wall capillary "NINJA" gas puff system. As expected, the inner wall puff alone did not significantly reduce the observed neutral pressure for a given density. We did observe that the antenna pressure limit appears to be a function of power, with higher pressures being tolerated at lower power levels. At the neutral pressure limit, the antenna match changes abruptly, likely the cause of the first observed fault. The run day was shortened by a poloidal field power supply problem, and as a result, plans to assess the use of the cryopump to reduce the neutral pressure at the antennas are deferred to a future run. Quarterly Review ---------------- On Friday we held the FY2009 Q4 C-Mod quarterly review by teleconference with DoE. Attendees included Rostom Dagazian, John Mandrekas, John Sauter, Sharon Stevens, Curt Bolton and Ed Synakowski (OFES), Earl Marmar, Bob Granetz, Jim Irby, Steve Wukitch, Dennis Whyte, Brian LaBombard, John Rice, Ian Hutchinson, Miklos Porkolab, Jerry Hughes, Steve Wolfe and Yijun Lin (MIT), Bill Rowan (U. Texas), and Steve Scott (PPPL). Presentations from the review can be found at www.psfc.mit.edu/research/alcator/pubs/quarterlies.html ICRF Systems ------------ We continued operational support for the experiments, delivering up to 6MW to the plasma. On Tuesday FMIT#4 (J-port antenna) failed due to the the 4CM2500KG Final Power Amplifier tube losing vacuum after 3508 filament hours. This tube, and the one in FMIT#2 which is presently at 3300 filament hours will be replaced during the upcoming maintenance period. The D- and E-port antennas continued to perform nominally during experiments for the remainder of the week. Lower Hybrid System ------------------- All preparations required for e-beam welding the lower hybrid launcher in-vacuum components have been completed. The chamber extension tanks that will allow the in-vacuum assembly to be welded as one piece are in-house and have been tested. All sixteen waveguides, flanges, and transformers have been taken to the vendor and welding has begun. Travel and Visitors ------------------- Amanda Hubbard, Paul Bonoli and Chuck Kessel attended the Integrated Operational Scenarios ITPA meeting in Frascati, Italy. Hubbard presented an overview of C-Mod research in support of ITER scenarios and Kessel presented a report on C-Mod ITER-like ramp-up and ramp-down experiments. Bonoli presented an "Update on Static (time) Scenario 4 studies for ITER using ACCOME", and also presented a report on behalf of F. Jaeger entitled "ICRF heating scenarios for the reduced magnetic field, non-nuclear phase of ITER". Andy Pfeiffer and Alan Binus visited UCLA to prepare UCLA's FMIT transmitter for transport back to MIT. This equipment will be used for ICRF related research. Jim Irby served on the Fusion Facility Operation Committee (FFOC) at a meeting held at the DIIID facility in San Diego on 10/19 and 10/20. This time was used to discuss machine operations, planning and budgeting for major projects and upgrades, and safety concerns common to all facilities. Peter Petersen represented DIIID on the committee and organized the meeting, and Al Von Halle represented the NSTX facility. Also attending the meeting were Arnie Kellman and Joe Tooky, both of DIIID. Mark Foster represented DoE at the meeting. On 10/21 Jim visited the Jet Propulsion Laboratory in Pasadena, CA, meeting with Peter Siegel. They discussed the development of FIR detectors and mixers, laser systems, and optical components. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly