Alcator C-Mod Weekly Highlights Nov 24, 2003 Plasma operations continued at Alcator C-Mod last week. Four run days were scheduled, but only two and a half were completed, due to a computer problem. A total of 59 plasma discharges were produced with a startup reliability of over 85%. Experiments were conducted in support of Divertor/Edge, Transport, and RF Group research priorities. Work also continued on Lower Hybrid System Development. Plasma operations are scheduled to continue this week. Operations ----------- Tueday's run was devoted to a continuation of MP#335 on "Edge plasma flows in upper vs lower X-point discharges" begun the previous week. Tne SNU/SNL density scan called for in the MP was completed, leaving the DN scan to be completed. These experiments provide input to Level 1 Milestone SC6-1b, "Compare energy confinement, H-mode threshold and divertor particle dynamics in SN, DN and inner-wall limited discharges in Alcator C-Mod". The run was interrupted for about 4 hours due to a problem with the main data acquisition server. The problem was apparently resolved in time to allow an hour of operation at the end of the day, but the same computer crashed again on Wednesday morning and had to be taken out of service. The experiment planned for Wednesday has been rescheduled for this week. A replacement computer was installed and plasma operations resumed on Thursday. The cause of the computer failure is under investigation. Thursday's run was devoted to MP#350, "ICRF Loading Studies". The primary purpose of this run was to simultanously obtain ICRF coupling measurements and radial density profiles in the core, edge and scrape-off layer using Thomson scattering and the A-port Scanning Probe (ASP). This run was quite successful. Radial profiles were obtained simultanously with coupling measurements for D and E, and we had good data from the probes even with 1 MW of ICRF power. Initial comparison between the measured loading for D- and E-port antennas and the prediction from the 1D model is encouraging. The measured profiles and coupling measurements will also be suitable for more advanced simulations using the TOPICA code. This experiment provides data in support of Level 1 Milestone SC6-1e, "Design advanced, high-power, load tolerant ICRF antenna for C-Mod." Friday's run was devoted to MP#368 "A-coil effect on ohmic EDA operation" and MP#334A "QC mode in ohmic EDA's - radial extent, k-poloidal and high frequency companions". The first portion of the run was spent optimizing and documenting the use of the C-Mod non-axisymmetric control coils (A-coil) to eliminate disruptions which had prevented access to the desired EDA regime (Bt<3T, Ip~800kA, q95<3) when MP#334A had been attempted last July. Non-disruptive operation was obtained for intermediate values of A-coil currents between 1000 and 1400A, corresponding to calculated total B_21 fields based on our model of the intrinsic error-fields of <2 Gauss. The latter part of the run (MP#334A) was dedicated to observations of the Quasi-coherent mode in these EDA plasmas with an array of fluctuation diagnostics, including scanning probes, PCI, reflectometry, BES, and gas puff imaging. Good measurements of the k-spectrum and radial extent of the mode were obtained. The high frequency (1-2MHz) companion predicted by one theory of the QC phenomenon was not observed. With the exception of the computer problem, all tokamak subs-systems performed well last week, and the startup reliability has markedly improved from a week ago. Run Planning -------------- The C-Mod Experimental Program Committee met on Monday, Nov 17, to review MiniProposals for upcoming experiments. The meeting was video-conferenced with participants from MIT, PPPL, and U. Texas. Nine new MP's were approved. One of these, MP#363, is in direct support of the H-mode threshold aspect of Level 1 Milestone SC6-1b. All C-Mod MiniProposals are viewable on the Web at http://www.psfc.mit.edu/cmod/operations/mini_proposals.htm . Lower Hybrid System -------------------- Work continued on the Lower Hybrid launcher. The forward wave guide shroud assembly is in the final stages of machining. The coupler end has been completed, and the rear wave guide end has also been completed and will be inspected 11/24 prior to delivery to PPPL for testing. Diagnostics ----------- Fourteen new channels were added to the CXRS diagnostic. Those put in service were used for poloidal views during this week. Perry Phillips and Alan Lynn (UT-FRC) made Improvements in the FRCECE data programs to handle missing data and to improve calibration. Travel and Visitors -------------------- Rick Goulding (ORNL) and Phil Ryan (ORNL) visited in part to participate in an ICRF antenna design discussion. This discussion was videoconferenced with R. Wilson (PPPL), R. Pinsker (GA), and TV George (DoE). The discussion was centered on developing an antenna concept to replace the D and E-port antennas. The new 4-strap would incorporate the improvements made to J-port and desirable mechanical features of D and E-port antennas. This effort is related to the Level 1 Milestone SC6-1e. David Mikkelsen (PPPL) visited Bill Dorland 11/19-20 at the University of Maryland to discuss changes to the gyrokinetic turbulence simulation code GS2 and simulations of Alcator C-Mod plasmas. The new GS2 will be tested soon at PPPL and should make simulations with many modes faster and more reliably re-startable. Steve Scott (PPPL) and Howard Yuh (MIT) were at General Atomics 11/20-23 to participate in an internal calibration of the DIIID Motional Stark Effect diagnostic. The techniques used, and the experience gained, will be valuable for the planned calibration of the C-Mod diagnostic this winter. Manfred Bitter and Ken Hill were at MIT for the week, continuing to work on the NSTX X-ray Crystal Spectrometer diagnostic. The main problem is still an excessive count rate, leading to detector saturation when ICRF auxiliary heating is applied. Earl Marmar, Miklos Porkolab, and Martin Greenwald attended the FESAC meeting in Washington on Monday-Tuesday. Porkolab and Marmar also attended the Fusion Power Associates annual meeting and Forum on the Future of Fusion on Wednesday-Thursday; Marmar presented a talk entitled "Status of Tokamak Research: Alcator C-Mod and the Path to ITER and Beyond." Amanda Hubbard visited Columbia University on Friday. She gave a Plasma Physics Colloquium entitled "Advanced Tokamak Research on Alcator C-Mod: Towards Profile Control and Long Pulses". Future collaborations on wall stabilization issues were discussed with Columbia researchers.