Alcator C-Mod Weekly Highlights Jan 26, 2004 Research Operations continued at Alcator C-Mod last week. Three run days were scheduled and completed. Progress also continued on the ICRF and Lower Hybrid tasks. Operations are planned to continue this week. Operations ---------- Runs were carried out Wednesday-Friday last week, with scheduled maintenance taking place on Tuesday. A total of 56 plasma discharges were obtained, with a startup reliability of 90%. An additional 27 field pulses were performed during Wednesday's run, which was devoted to calibration shots for the MSE diagnostic (MP#322). The DNB was fired into a gas target at two different toroidal fields and a range of poloidal field settings. Thursday's run was devoted to MP#372, "Further Studies of the Quasi-coherent Mode in EDA H-mode Plasmas" with piggyback MP #369 Experimental Measurement of Neutral Penetration in H-Mode Plasmas". The goal of these experiments was to characterize and understand the Quasi-coherent edge fluctuation (QCM) that is believed responsible for the enhanced particle and impurity transport in EDA H-mode discharges. Excellent data were obtained, accomplishing most of the goals of the day's experiment, and analysis of the results is ongoing. Friday's run was dedicated to MP#375, "Rotation and threshold vs SSEP", which calls for a high resolution scan of the dependence of SOL and core rotation, as well as the L-H threshold, as a function of the SSEP parameter, which measures the magnetic balance between the upper and lower x-points. Physics ------- Some circumstantial evidence from the history trend indicate that the ohmic L-mode plasma performance has degraded since 2000. Correlations with changes to internal hardware, including the installation of the J-Port ICRF antenna and boron-nitride tiles, along with other possible causes, are being investigated. The exact nature of the effect on performance is being sought. ICRF Systems ------------- FMIT#1 and #2 were returned to service after conditioning the new tube installed in FMIT#1 and testing both transmitters into a dummy load. During plasma operation, up to 3 MW were coupled to the plasma from the D and E-port antennas. As a result of the FMIT#4 Jan. 9th incident, an internal review was made of all FMIT operation. A vacuum breaker failure was identified as the root cause of the incident. FMIT#1 and #2 have different breakers and are not subject to the mechanism identified in FMIT#4. An exception event where control of the high voltage is lost is still possible; thus, a high voltage exception event procedure was reviewed and approved before FMIT#1 and #2 were placed back in service. A review of the FMIT#4 Jan. 9th incident was held on Wednesday with Chris Brunkhorst (PPPL), Gerd Schilling (PPPL) and a number of C-Mod physicists and engineers in attendance. The primary fault has been identified as a loss of control of an AC vacuum breaker due to a mechanical failure. A number of actions and modifications which must be carried out before returning FMIT#3 and 4 to service have been identified, repairs are ongoing, and a plan to complete the work has been developed. Lower Hybrid System -------------------- Installation of the circulators continues. The water-cooling lines for all circulators were installed. Preparations for installation of the waveguide switches and dummy loads have also taken place. Additional hardware to accomplish final waveguide hookup has arrived. The forward waveguide assembly was returned to MIT from PPPL on Monday. Gold wire seals were installed with blankoff flanges and a vacuum box, and the unit was successfully leak checked. Further ceramic window braze tests are in progress for the Coupler at a second brazing vendor. Three-window tests are being performed with both CUSIL and GAPASIL alloys. All the PPPL couplers are now at MIT, and preparation work for final rebrazing is being discussed. Electroplating tests of a 3-window prototype are in progress. Diagnostics ----------- Sixteen of the 32 FRCECE channels have not been available recently because of a failed local oscillator in the receiver for those channels. Repairs by the original equiment manufacturer are now complete. The unit will be returned to UT-Austin for installation of new protection circuits. We expect reinstallation at C-Mod during the first week of February. We are now able to observe the MSE spectrum with excellent spectral resolution and to identify the various Stark components contributing to the spectrum. This has been a missing piece in the MSE experimental analysis. This work was accomplished by optimizing the alignment of an MSE fiber bundle with a high resolution spectrometer. The BES system was used for width measurements for the DNB and for some new measurements of the quasicoherent mode. The beam shape can be described as a gaussian which is 0.1 m wide at the 1/e points. The quasicoherent mode was apparent in correlations between poloidally spaced BES channels. More detailed results including comparisons to other diagnostics will follow from continued analysis. Travel and Visitors ------------------- Bruce Lipschultz traveled to the Naka JAERI site in Japan from Jan. 12-19 for two meetings. The first meeting was for the ITPA SOL/divertor group of which he is co-chair. He gave 4 talks during that meeting on topics ranging from D retention, to second separatrix effects to general Mo operational experience. The ITPA meeting was concentrating on comparing a variety of data across machines to, if possible, draw conclusions on similar experiences across machines and the implications for ITER operation. The second meeting was for the Organizing committee of the Plasma Surface Interactions Conference of which he is currently chair for the May 2004 meeting. This meeting was for selection of abstracts to be accepted for the conference as well as which papers were set to be oral, long oral, or poster delivery. Chris Brunkhorst and Gerd Schilling participated in a review on 1/21 of the ICRF transmitter incident. Gerd Schilling stayed at MIT the rest of the week for further discussions and to participate in ICRF experiments. Joe Frangipani and Dave Miller (PPPL) delivered the LH Forward Waveguide assembly to MIT and spent the week cleaning the assembly and preparing it for leak checking. Ron Bravenec (UT-FRC) was at PSFC for the week working with the BES diagnostic.