Alcator C-Mod Weekly Highlights April 4, 2005 FY2005 weeks of research operations Planned: 17 weeks Completed: 3.5 weeks The second quarter target for the Level 1 (JOULE) milestone "Begin measurements of plasma behavior with all high-Z antenna guards during tokamak operation." was completed as of March 18, 2005. The report can be found at http://www.psfc.mit.edu/cmod/sciprogram/FY05_level1_targets/q2_complete.pdf Operations ---------- Plasma operations resumed last week at Alcator C-Mod. Four run days were scheduled and completed. A total of 67 plasma discharges were produced with a startup reliability of 66%. Plasma operations are planned to continue this week. Three run days (Tuesday, Wednesday and Friday) were devoted to MP#417 "Plasma performance, boronization and ICRF heating effectiveness with high-Z antenna guards and all-metal walls", which directly supports our Level 1 JOULE milestone. These experiments were aimed at evaluating and documenting a variety of aspects of tokamak operation with high power ICRF heating (Prf~3MW) with all metal plasma facing components prior to boronization. Scans of RF power, plasma current and density were undertaken, along with determination of L->H transition thresholds, assessment of radiative power, and spectroscopic surveys (VUV) of impurity content. Additional work on this major ongoing research topic is planned. Results will be compared with experiments to be carried out after boronization, with historical data from 1995-96, both before and after the first introduction of boronization in C-Mod, and with data from 1999-2004 which included boronization and boron-nitride protection limiters on the ICRF antennas. The run on Thursday was in support of MP#418, which deals with lower hybrid coupling at low power levels. This run was the first dedicated experiment based on the new C-Mod Lower Hybrid system. The experiments were led by Stefano Bernabei and Randy Wilson (PPPL). Scans in the launched phase over the range -60, -90, -120, and -150 degrees were performed with the coupler located at radii of 1, 3, and 5mm behind the local limiter. For the scans the twelve klystrons, feeding 96 waveguides, were operated at 10kW each with pulse lengths of 20msec. Preliminary data analysis has begun, and more detailed evaluation of the reflection coefficient as a function of phase will be carried out after more calibration work is completed. Physics ------- At the weekly staff meeting, Joseph Snipes presented highlights from his invited talk on Alfven Cascades in Alcator C-Mod to be presented at the Transport Task Force meeting in Napa, CA on 7 April 2005. Previous Nova-K modeling results of the change in the behavior of Alfven eigenmodes (AEs) with ICRF resonance position will be shown together with analysis of the radial structure of the AE's baAgreedsed on core Phase Contrast Imaging (PCI) data and edge magnetics data. The results indicate that higher toroidal mode number Alfven cascades have a more core localized radial structure that is observable on the core PCI data, but makes them only very weakly observed on the edge magnetics. Low n Alfven cascades and the TAEs they evolve into have a more global radial structure that is clearly observed on edge magnetic coils. A nonlinearly excited 2nd harmonic Alfven cascade is more clearly observed with core PCI than with the edge magnetics, while the 2nd harmonic TAE into which it evolves is more clearly observed with the edge magnetics. This result indicates that the 2nd harmonic cascade is more core localized than the 1st harmonic while the 1st and 2nd harmonic TAEs both have more global radial structure out to the edge. Diagnostics ------------ The high frequency 16 channels of the FRCECE electron cyclotron emission diagnostic (0.66m < R <0.75m at B=5.4 T) have been returned to service, with data being acquired using a PCI digitizer. Options for repair of the local oscillator for the 16 lower frequency channels are under investigation. The dewar housing the detectors used by the nine-channel ECE grating polychromator system has been repaired in-house, and this diagnostic has also been returned to service. The C-Mod MSE diagnostic has successfully measured the polarization direction of light through an in-vessel linear polarizer using the plasma as a light source. Excellent data were acquired during a series of highly reproducible plasmas that had been prepared for commissioning of the lower hybrid system. These measurements will be compared to previous in-vessel measurements during the recent vacuum opening to study possible systematic rotation effects in the MSE optics. Long Pulse DNB System --------------------- The beam installation is complete, and testing of all systems has been completed. Many of the final details required for beam operation were being addressed last week. Machining and welding have been completed for the new duct to connect the beam to the C-Mod vacuum vessel. Leveling and alignment of the beam to the machine is required before the DNB is interfaced to the torus gate valve at F-port. The beam cryo pumps have been regenerated and remain warm in preparation for connection to C-Mod. The beam vacuum tank will have to be brought up to atmospheric pressure in order to remove the blank off plate at the output end of the beam tank and attach the duct. ICRF System ----------- The ICRF system was operated in support of experiments on Tuesday, Wednesday and Friday last week. All four transmitters (three antennas) performed nominally with routine long pulse operation at the 3MW level. Lower Hybrid System ------------------- The lower hybrid system with 12 klystrons driving 96 waveguides was successfully operated into C-Mod plasmas during all four runs last week, with a dedicated run on Thursday and piggyback operation on the other days. Waveguide conditioning is ongoing. The Lower Hybrid control system was successfully interfaced to the C-Mod "fizzle detector" signal, which now prevents the klystrons from firing during a shot if the plasma is not present. Travel and Visitors ------------------- Martha Redi (PPPL) visited C-Mod on 3/31 and 4/1 to discuss with Catherine Fiore the upcoming TTF and EPS presentations and their paper on ITB onset physics. David Mikkelsen (PPPL) visited MIT last week to plan an experiment to study changes in temperature gradient scale length, and to relate these to changes in transport. More C-Mod plasmas were studied as candidates for the experiment. Stefano Bernabei and Randy Wilson (PPPL) were at C-Mod on Thursday, and served as Session Leaders for the Lower Hybrid experiment that day. Mark Gilmore, University of New Mexico, visited C-Mod on Friday to discuss a collaboration on FIR Polarimetry with Jim Irby and Earl Marmar. He also discussed reflectometry with Nils Basse, and the new Digital Plasma Control System with Josh Stillerman and Steve Wolfe. Drs. Naoyuki Oyama and Kensaku Kamiya, of JAERI, Japan, are visiting C-Mod to continue their collaboration on comparisons of the JFT2M High Recycling Steady (HRS) H-Mode regime and the C-Mod EDA regime. They will be working with Amanda Hubbard. Web Site ---------- The Plasma Science and Fusion Center has launched a redesigned web site. The new PSFC home page can be found at http://www.psfc.mit.edu/ . The new Alcator C-Mod home page can now be found at http://www.psfc.mit.edu/research/alcator . Many addresses within the site have changed, and links are being modified. Bookmarks within the site will need to be updated. The weekly reports (including this edition) can now be found at: http://www.psfc.mit.edu/cgi-perl/Weekly/cmodhighlights.plx _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly