Alcator C-Mod Weekly Highlights October 2, 2006 FY2007 weeks of research operations: Tentative target: 14 weeks Completed: 0 weeks Physics ------- Joe Snipes has been analyzing low frequency MHD activity in C-Mod during Lower Hybrid Current Drive (LHCD) experiments. Large m=1, n=1 modes were observed last May during LHCD with 90 degree phasing. Changing the phase to 60 degrees or 120 degrees did not have the same effects on the MHD activity in discharges with similar plasma conditions. More recent data taken at 60 degree phasing has found cases where a very large (40 G) m=2, n=1 mode was observed during LHCD. These modes are locked at the start of the LHCD, but it is not clear if they existed before the LH turned on or not. Then, during the ramp up of the LHCD, the modes unlock and rotate slowly ( 2 - 5 kHz) where they are clearly observed on magnetic pick-up coils. In a discharge where 1 MA of current was driven by LHCD, a large mode unlocks and rotates briefly during the ramp-up of the LHCD and then reappears later during the flat-top of the LHCD and persists until the LHCD switches off. A similar brief m=2, n=1 mode was observed in the shot with combined LHCD + ICRF, which seemed to increase in amplitude with the addition of the ICRF to the LHCD. Sawteeth are also observed to either disappear or at least become very small during LHCD indicating a rearrangement of the current profile within or at the q=1 surface as well. Operations ---------- In-vessel work last week was concentrated on removal of diagnostics around F- and K-Ports. MSE, BES, CXRS, and ECE systems have been removed from in-vessel at F-Hor, and the bolometry box and limiter were removed from in-vessel at K-Hor. The F-Hor flange will be removed and modified to allow for the 7 degree toroidal rotation of the DNB. At K-Hor the bolometry system is being upgraded, and the outboard midplane limiter moved back 0.5 cm to better conform to the G/H full limiter position. Numerous upgrades to diagnostics at F-Port are also planned. The refurbishment of the oil lubrication alternator heat exchangers has been completed, and they are back in operation. Following the alternator inspection, the alternator housing was resealed and helium gas is being purged through the alternator to remove atmospheric gases and prepare the alternator for operation. Lower Hybrid System ------------------- The new 24-window double flange coupler design was completed last week and a vendor for production of the couplers selected. Consultations continue with the vendor for the lower hybrid high voltage power supply as we try to understand and repair faults in several of the 68 IGBT modules. A full current, full voltage test stand is being built so that each module can be checked under full load operational conditions. ICRF Systems ------------ Work continues on the FFT protection system including circuit design, wiring of components, and documentation. Servicing of the ICRF UPTEGRAPH high voltage power supply diode stack is complete, and we plan to reinstall the diode stack this week. Travel and Visits ----------------- Earl Marmar and Miklos Porkolab attended the Fusion Power Associates (FPA) Annual Meeting and Symposium held last week in Washington, D.C. Miklos is Chair of the FPA Board of Directors. Earl made a presentation at the Symposium entitled "Alcator C-Mod: Research Highlights and Plans". Links to this and most of the other presentations can be found at http://fire.pppl.gov/fpa_annual_meet.html _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly