Alcator C-Mod Weekly Highlights November 16, 2001 The inspection continued this week as did work on the the LH MIE project, ICRF systems, and new diagnostic neutral beam. We continue to make good progress on the new inner divertor. Physics ------- Further comparisons were made between core magnetic MHD mode rotation and core argon impurity ion toroidal rotation in C-Mod. Core MHD mode frequencies typically from sawtooth pre/postcursors generally agree quite well with core impurity ion toroidal rotation measurements from HIREX as has been published by Hutchinson, et al, PRL Vol 84 (2000) 3330. There are some cases, however, when there are large m=2, n=1 modes, that the mode rotation is much slower than the core plasma ion rotation. When these modes are large enough to lock to the wall and couple to a core m=1, n=1 mode, the mode rotation comes to rest and about 50 msec later, the core toroidal ion rotation also comes to rest, within error bars. Magnetic measurements show that core mode rotation, when measurable, begins in the electron direction in L-mode, then rapidly changes to the ion direction after the L-H transition. The modes then continue to rotate in the ion direction until there is an H-L transition and then they slow down until they are no longer measurable on magnetic pick-up coils if the L-mode lasts for more than about 50 msec. In general, core impurity ion rotation also behaves in this way, but the time resolution does not allow as precise measurements at the L-H transition. However, there are cases when the impurity ion rotation clearly rotates in the ion direction even in a long ICRF driven L-mode. In these cases, there were no clear core MHD modes to measure on the magnetic pick-up coils. Inspection ---------- We continued the analysis of the OH coaxes this week. New spring plates for the TF joints needed for reassembly are in house and ready for welding. Voltage tap and thermocouple leads on the TF arms and legs are being refurbished. This process should be complete in about 1 week. Lower Hybrid MIE Project ------------------------ The layout of the Lower Hybrid CAMAC module for TTL to fiber optic conversion is nearly complete. These boards are to be used in the Lower Hybrid timing distribution system. The Triax cable that will deliver power from the HVPS to the cell is being terminated. We continue development of the real-time phase and amplitude control system. New software with possibly somewhat faster loop response time is being tested. The design of the water cooling loops for the water loads and circulators is progressing, in preparation for a design review on Dec 3rd and 4th. The lengths of the 1/4" and 1-1/2" water hoses have been determined, and quotes have been received. The requisition will be released on Monday. The wiring of the pump controller interface has been completed. Wiring of the first transmitter protection and control cabinet is complete. Joel Hosea, Stefano Bernabei, and Doug Loesser, all from PPPL, were at MIT this Friday to review the status of the Lower Hybrid launcher. Suggested resolutions to all the issues raised at the FDR last July were discussed and generally agreed upon. PPPL expects to begin releasing many critical launcher component designs for fabrication over the next few weeks. ICRF Systems ------------ The plasma facing components of all three antennas will be changed somewhat during this up-to-air period to reduce interaction with the plasma. The boron nitride tile design will be finalized over the next two to three weeks. DNB and Related Diagnostics --------------------------- Bill Rowan and Dexter Beals, both from UTexas FRC, visited the University of Wisconsin this week and had detailed discussions with A. Ivanov of the Budker Institute about the RFX diagnostic neutral beam. A schedule for delivery of the beam to MIT was discussed as were many details about the beam design, construction, and installation. Inner Divertor -------------- We continue to prepare new divertor diagnostics for installation. We hope to have the new halo diagnostics installed within the next two weeks. Thermocouples are being fabricated to measure temperature changes in the divertor between shots. Progress continues on the new probe array. Ideas Forum ----------- The Alcator C-Mod Ideas Forum will be held December 12 through 14, 2001, at MIT. The purpose of the Forum is to provide an opportunity for presentation of specific ideas appropriate for experiments during C-Mod's 2002 run campaign. As usual, the Forum will be open to all interested parties, including current and potential future collaborators. Detailed information about the forum can be found at http://www.psfc.mit.edu/people/terry/Ideas_Forum.html Travel and Visits ----------------- Martin Greenwald traveled to PPPL on November 14-15 to participate in a meeting of the NCSX program advisory committee. He took the opportunity to discuss plans for the national fusion collaboratory with NSTX staff. David Mikkelsen (PPPL) visited MIT to discuss q profile measurements and calculations with Earl Marmar and Steve Wolfe. He found that field line pitch angle resolution of 0.1 degrees is required to distinguish between q profiles with similar q but very different magnetic shear near r=a/2. Nonlinear calculations of turbulent transport for these conditions show significant differences, so a direct determination of the magnetic shear is needed.