Alcator C-Mod Weekly Highlights April 24, 2006 FY2006 weeks of research operations: Planned: 14 weeks Completed: 8.4 weeks Operations ---------- Plasma operations continued at Alcator C-Mod last week. Three run days were scheduled and completed. A total of 78 plasma discharges were produced with a reliability of 94%. Experiments were conducted in support of research in the Transport, Lower Hybrid, and Divertor/Edge/Wall areas. Plasma operations are planned to continue this week. Program ------- The C-Mod Experimental Program Committee met on Tuesday, April 18. Seven Miniproposals for experimental time on C-Mod were reviewed by the EPC. The schedule for the remainder of the FY2006 Experimental Campaign was discussed. A revised block schedule is now available at http://www.psfc.mit.edu/research/alcator/data/operation2006.pdf Run summaries ------------- Wednesday's run was devoted to MP#443 "Temperature scale length measurements using B_tor sweeps". The purpose of this experiment is to use the high resolution ECE radiometer diagnostic to determine the local electron temperature scale length, for comparison with theoretical predictions. A power scan is employed to determine the relationship between the heat flux and Grad(T)/T. The run on Wednesday successfully completed the goals of the Miniproposal. An ICRF power scan from 200kW to 3.5MW was obtained, under conditions with small, high frequency sawteeth, so that sawtooth effects should not complicate the analysis. Thursday's run in support of MP#418, "Lower Hybrid Coupling Studies" successfully demonstrated unambiguous lower hybrid current drive (LHCD) for the first time in Alcator C-Mod. Up to 400kW net power was coupled to the plasma for pulses of 400msec. With the optimum phasing of 90 degrees between adjacent waveguides, the loop voltage dropped by about a factor of two for the 700kA, 7e19/m3 target discharges employed in these experiments. The drop in loop voltage decreased with phasing of 60 and 120 degrees, as expected from modeling. Increasing the field from 5.4 to 6.4T resulted in higher current drive (larger loop voltage drop) for the 60 degree phase, as expected due to improved wave accessibility. The drop in loop voltage was smaller at higher density, as were the hard xray flux and non-thermal electron cyclotron emission, also in agreement with expectations. Friday's run in support of MP#430, "Localization of boronization effect" tested the hypothesis that erosion of the boronization during ICRF heating results from localized RF effects associated with field lines passing in front of the antennas. Between-shot boronizations were carried out, followed by standard 1MA discharges in which either the D&E-port antennas or the J-port antenna were energized at the 2MW level. Field-line tracing indicates that these antennas are connected to surfaces at different toroidal locations. The evidence from this run supports the hypothesis. In particular, after a series of shots using one set of antennas, during which the beneficial effect of the boronization (good confinement, low radiated power, steady EDA H-mode) had clearly degraded, subsequent discharges using the other antenna(s) recovered the improved performance, at essentially the same level as would be observed immediately following the boronization. Apparent systematic differences of erosion from the different antennas are also being investigated. ICRF System ------------ The repair of the FMIT#3 (J-port antenna) phase shifter was successfully completed. Following reassembly, the shifter was filled with a mixture of dry nitrogen and SF6. The J-port antenna operated routinely at 2MW into plasma during Friday's run. Travel and Visitors ------------------- Ian Hutchinson attended the APS April meeting in Dallas. He gave a talk at Texas A&M entitled "Fusion: The Way forward", and attended the Division of Plasma Physics Executive Committee Meeting. Martin Greenwald presented a seminar at the University of Texas in Austin on C-Mod transport research. He then also attended the APS DPP Executive Committee Meeting in Dallas. Perry Phillips (Univ. of Texas, FRC) completed his visit to MIT last week, during which he installed a repaired local oscillator (LO), with a new power supply and added magnetic shielding, in the FRCECE diagnostic. An event recorder was added to monitor the LO current in order to help diagnose any future problems in this component. On Wednesday, Perry led the experiment in support of his MP#443 on determination of temperature gradient scale lengths. Glen Wurden and Leonid Dorf (LANL) completed their visit to MIT on Tuesday, April 18. They installed a new IR spectrometer diagnostic which will be used to examine plasma emission in the spectral range from 700 to 3000 nm. Miklos Porkolab attended the 3rd Hungarian Plasma Physics and Fusion Technology Workshop (Sponsored by the Euratom Fusion Association of the Hungarian Academy of Sciences-HAS) in Visegrad, Hungary, April 20, 21. He gave a keynote invited talk on Alven wave phenomena and Alfven Cascades. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly