Alcator C-Mod Weekly Highlights February 16, 2001 We continued work on modifications to the J-Port antenna, maintenance of other rf systems, and fabrication and testing of Lower Hybrid components. A review of the DNB and related diagnostics was held on Thursday, 2/15. Physics ------- John Rice has returned to MIT following 6 weeks of work at LHD. Recent LHD achievements include 1 MJ of stored energy, 4% beta, and a 2 minute steady state discharge. While there John worked on analysis of 'naturally' breathing plasmas, and a comparison with those induced by running the plasma against the stainless steel wall of the LHD vacuum chamber. There is a strong dependence of the breathing frequency on the plasma density. There is also a perturbation on the electron density and radiated power emissivity which modulates at the breathing frequency, located near r/a = 0.5. John also analyzed some CHS titanium x-ray data from an imaging camera system. In the plasma periphery, the emission is dominated by inner shell satellites from B- and C-like titanium, and it can be concluded that the impurity diffusion is very slow in the plasma center, and highly anomalous near the edge. He also attended the large tokamak workshop and review of JT60-SC in Tokai, Feb. 7 and 8, where he presented recent C-Mod results. ICRF Systems ------------ After final checks of the solid model and fitups of the prototypes the first of the stripline component data files was e-mailed to the electric discharge machining (EDM) vendor. The EDM machines will be programmed and final aluminum prototypes will be made and checked here at MIT. The inconel 625 needed for the actual components is now in house. We also made good progress on several small scale modifications to the back plate and Faraday screen this week. A new antenna support bracket has been fit up invessel. Small modifications will be required to the bracket to allow for interference with magnetics diagnostics on the vessel wall. Oak Ridge under the direction of Dave Rasmussen has begun to develop a model of the PPPL J-Port antenna. Phil Ryan and Rick Goulding will work to get the RANT3D and ANTMOD codes up and running on the rather complex antenna geometry. Steve Wukitch has provided them with the data required to implement the codes and also extensive information on the damage we discovered to the antenna components. We continue to inspect, clean, and refurbish rf transmitter cavities in preparation for our next operation period. We successfully tested remote dummy load operation for transmitter #1 and #2. Good progress has been made on the acoustic arc detector. The transducers have shown more than adequate sensitivity to detect 2 kV/4 joule arcs in the transmission line. We have seen phase delays from the mechanical impulse that should allow localization of the arc source. Work on adding new phase balance fault detection for J antenna continues. The fault indicator board construction is complete. The phase balance board construction is still in progress with completion expected next week. DNB --- A review of the DNB and related diagnostics was held at MIT on Thursday, 2/15. The panel members were Fred Levinton (PPPL), Ray Fonck (UWM), Larry Grisham (PPPL), and Al Von Halle (PPPL). Chuck Finfgeld organized the review and represented DoE. Many from MIT attended including Bob Granetz, Earl Marmar, David Terry, Howard Yuh, Jim Irby, Bruce Lipschultz, Jim Terry, and John Rice. Gerd Schilling and Garrit Kramer attended from PPPL. Rostom Dagazien (DoE) participated in the review via video conference. The charges to the panel were: Please comment on the progress in installation and initial operation on Alcator C-MOD of the University of Texas Diagnostic Neutral Beam (DNB), giving due consideration to the financial, material and human resources that have been available. Please comment regarding the difficulties that have been encountered in initial DNB operation, and give every suggestion you can for improving DNB performance. Please provide your best assessment of the potential ultimate performance of the DNB and the resulting prospects for the desired plasma diagnostic measurements, including current density profile (MSE), ion temperature and rotation profiles (CXRS) and internal fluctuations (BES). A complete report will be provided by the committee soon. Earl Marmar has assigned responsibility for coordinating DNB and related diagnostic activity to Bob Granetz, implementing a suggestion made by the C-Mod Program Advisory Committee that a senior staff member take on this challenge. Lower Hybrid Project -------------------- The drawing package provided by Symmes, Maini & McKee Associates (SMMA) regarding the Lower-Hybrid space change is being reviewed. Several problems have been noted mainly with water pipe routing. We are preparing a response. Information of cell layout, launcher/coupler drawings from PPPL, and mezzanine layout from SMMA have been used to create a Lower-Hybrid cell layout drawing. This drawing is to be given to SMMA to assist in water plenum routing to avoid mechanical conflicts. The circulator source selection has been completed and the procurement process has begun. Modifications to and wiring of klystron carts continue. The vector modulator that will be used to control the amplitude and phase of the output power from the klystrons is now in house. A test setup is being assembled to characterize this new component. Work has begun on the LH timing system interface design. Work continued on software tests and development for active controllers. Progress was also made on SFOL fiber optic links. The fiber transmitter will be operational next week. Inner Divertor -------------- Tiles and other components continue to arrive and go through Q/A. Silver plating of fastener hardware is proceeding. The fabrication of the rear girdle and C-plates is on schedule. Power Systems ------------- The rework of the OH commutation capacitor banks is nearly complete. These changes will reduce the strain on the capacitor terminals during commutation.