Alcator C-Mod Weekly Highlights March 20, 2006 FY2006 weeks of research operations: Planned: 14 weeks Completed: 5.6 weeks Operations ---------- Plasma operations continued at Alcator C-Mod last week. Four run days were scheduled and 2.9 were completed; power system faults forced a delay in the start of Tuesday's scheduled run, and replacement of a laser in the interferometer delayed the experiment on Thursday. A total of 54 plasma discharges were produced with a startup reliability of 62%. Experiments were carried out in support of research in the Divertor/Edge and MHD Stability Topical Science areas. The second quarter FY06 C-Mod target "Install LH launcher, with stainless steel couplers, and continue LH studies (March 31, 2006)" was reached on March 7, 2006. In this run, up to 250 kW of LH power was applied to the plasma for short (10 ms) pulses, with as many as 6 such pulses applied to a single C-Mod shot. The phase was varied electronically from pulse to pulse within a single C-Mod shot and the density at the grill was scanned by moving the coupler radially in and out on a shot-to-shot basis. In this first run with the new SS couplers, an extensive set of reflection coefficient measurements were taken as a function of waveguide phasing and density at the grill. This will allow a detailed comparison with modeling calculations based on Brambilla's LH Coupling code. At the highest powers, clear indications of non-thermal emission from both hard X-Rays and cyclotron emission were observed in agreement with expectations based on ray-tracing (GENRAY) and Fokker-Planck (CQL3D) codes. During inspection on Monday a broken bolt was discovered in the EF3 15KV breaker. A spare breaker was installed and the original was sent out for repair, which was accomplished by Thursday morning. On Tuesday a phase fault indication in the EF3 power supply was traced to a bad switch contact in an SBM switch. Following correction of this fault, one of the four 15kV circuit breakers for the toroidal field power supply also was replaced, because of a broken engagement spring. This breaker, and associated control switch, were replaced with spares; repair of the breaker is now underway. C-Mod plasma operations are planned to continue this week. Run Details ----------- The experiments on Tuesday and Wednesday employed the boron powder injector system to enhance the charge exchange recombination signal of BV for use in measuring poloidal rotation in the near-edge plasma in Upper and Lower single null L-mode discharges. A range of densities and RF powers were explored, particularly in the upper null configuration. We also tested the intra-shot diborane puffing system, using helium in place of the diborane, in preparation for future experiments. The run on Thursday was primarily devoted to MP#409, "SOL Phase Space", and continued this series of experiments aimed at characterizing the relationships between the 'transport state' (profile shapes, gradients, cross-field fluxes, advection velocities, turbulence characteristics) and theory-based 'control parameters' (local collisionality, magnetic field strengths, parallel connection length,...) that may determine that state. The focus of Thursday's run was on obtaining profile and flow data with Ip=1.1MA and Bt=5.4T in upper and lower single null ohmic discharges at a range of densities. One inner-wall limited discharge was also run in support of MP#429 "Turbulence in limited discharges". The run on Friday was devoted to MP#402 "Locked mode threshold at different toroidal phase", which is aimed at improving the characterization of the intrinsic non-axisymmetric error field in C-Mod, and also at clarifying the role of the "sideband" m=1 and m=3 terms in determining the threshold of the m=2 locked mode. These experiments are of particular importance because knowledge of the intinsic error field is crucial to resolving a discrepancy in the determination of the toroidal field scaling of the threshold in C-Mod, which in turn impacts the prediction of the threshold in ITER. Data were obtained in standard 1MA, 5.4T LSN ohmic discharges using four different configurations of the C-Mod A-coil set. These data complement previous results in three other configurations employing similar target plasmas. Additional experiments in this series are planned. Diagnostics ----------- The cryogenic test of the repaired GPC-1 dewar (ECE diagnostic) was successfully completed. Re-installation of the detectors in the dewar can now proceed. ICRF System ----------- The D- and E-port antennas (FMIT transmitters #1 and 2) were employed during the experiments on Tuesday and Wednesday; up to 3MW total power from the two antennas was provided during these experiments. An arc in the stub tuner in the FMIT#3 system (J-port antenna) prevented operation of this system. The coax connection has been removed from the stub tuner and inspection begun. At least two insulators show indications of tracking and arc damage. Repairs are expected to be complete early this week. We have begun characterizing the AFT ferrite tuners with a borrowed power amplifier. This supply can sweep the current +/-120 A in ~4 msec and +/-30 A in 1 msec (the expected current range to match most C-Mod discharges). If increased speed is required, we will purchase a commercially available supply with higher voltage capability. Lower Hybrid System -------------------- The simulation network for the LH launcher was modified to accommodate third harmonic transmission. Simulations revealed that the third harmonic, if generated from a breakdown at any position in the network, should be detected. Recalibration of the #10 drive and monitor leg were completed. Conditioning of klystron #10 continued. A meeting was held to determine near-term improvements for the LH launcher system. It was decided that some modifications to coupler protection system circuits that monitor forward and reflected power just before the launcher would help to better protect the launcher and couplers. After reviewing data from several days of operation it was clear that a 20% reflection trip level was adequate to protect the system. Modifications to the boards are now being made, and trip levels are being set and verified. Travel and Visitors ------------------- Earl Marmar attended the OFES Budget Planning Meeting in Gaithersburg on Tue-Wed of this week. His presentation on "Alcator C-Mod: Highlights, Plans, Budget and Schedule, FY2006-FY2008" can be found at: http://www.psfc.mit.edu/research/alcator/pubs/C-Mod_BPM_presentation-2006.pdf Miklos Porkolab, Martin Greenwald and Ron Parker also attended; Prof. Porkolab gave a presentation entitled "PSFC Institutional Issues". On Monday, Earl Marmar attended and participated in a meeting of the Fusion Facilities Coordinating Committee held at the DoE facility in Germantown, MD. Ron Parker also attended and participated (as chair of the DIII-D PAC); Rich Groebner participated by teleconference (as chair of the C-Mod PAC). On Friday Amanda Hubbard visited the Department of Applied Science at Queen's University, Kingston Ont where she presented a seminar entitled "Fusion Research on the Alcator C-Mod Tokamak: Towards ITER and Fusion Energy" Last week Stewart Zweben (PPPL) was at MIT to continue analyzing GPI data and to continue with the limiter/divertor edge turbulence comparison experiment (MP#429). _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly