Alcator C-Mod Weekly Highlights March 14, 2003 We continue invessel work in preparation for pumpdown early next week. Work on lower hybrid, ICRF, and MSE diagnostic components also continued. Physics ------- John Rice presented data at the weekly Physics meeting indicating that ohmic L-mode discharges which develop into an upper null configuration tend to have substantial (~30 km/s) counter toroidal rotation over most of the core. The amount of power required to produce the equally substantial co-current rotation observed in normal H-mode discharges is large, and may be related to the increased H-mode threshold seen for upper null plasmas. Alan Lynn, U. Texas FRC, also reported at the Physics meeting that the FRC ECE radiometer has observed a high-frequency (~80 kHz) mode during RF centrally heated ITB plasmas at 5.5 T. This mode is localized at or near the on-axis RF resonance location (~70.4 cm) with a FWHM ~2 cm. When sawteeth are present, the mode is suppressed at each sawtooth crash limiting the amplitude to d(Te)/Te < 0.9% . In a few discharges where sawteeth were not present, this mode was able to grow to large amplitudes ( d(Te)/Te ~ 4.8% ). Work is ongoing to further characterize and identify this mode. Operations ---------- We continue to bring up engineering systems in preparation for operation. The TORVAC pumping station and RGA are back on-line. Thermocouple and vessel heater systems are being reconnected and tested. Most invessel work will be completed this weekend, with pumpdown expected early next week. The upgrade of the Active MHD antennas to stand off rf voltages induced by the ICRF antennas has been completed, and the antennas have been installed in vessel. The antennas together with their new triaxial feeds have been designed to handle over 10 kW of rf power coupled from the ICRF antennas and have been successfully hi-potted to over 5 kV. ICRF Systems ------------ Preparations are being made to test operation of the FMIT#3 and #4 transmitters at 53 MHz so that He3 mode conversion heating can be done at a toroidal field of 5.4 T. We continue work on the new transmitter control and protection system. Lower Hybrid MIE Project ------------------------ At MIT, we continue to test and bring on-line the rf control and protection circuits for the klystrons. Work also continues on the low power microwave assemblies and data and timing systems. At PPPL, attachment and calibration of standard waveguide components onto the launcher rear waveguide assembly have continued. All vacuum components have been leak checked successfully separately, and the fully assembled launcher will soon be leak checked on the vacuum test stand. Aluminum mock ups of the BN protection tiles have been fabricated, checked, and found acceptable. The BN tiles are now being fabricated. MSE Diagnostic -------------- We completed fabrication, installation, alignment, and calibration of the disruption-hardened Motional Stark Effect diagnostic on schedule this week at MIT. Two large glass mirrors are now cradled along most of their periphery by a stainless steel "rib" to reduce flexing during disruptions. The backplates are now comprised of Inconel, rather than stainless steel, to increase stiffness and reduce eddy-current forces. Work is resuming on a multi-channel visible Bremsstrahlung background diagnostic that will provide real-time measurements of the VB noise level for subtraction from the MSE signals. This system will improve the capability of MSE to provide q-profile measurements even when the plasma conditions change during the 50-ms neutral beam pulse, e.g. across H-mode and ITB transitions. Travel and Visits ----------------- Benjamin Carreras, ORNL, is visiting MIT. He is working with Amanda Hubbard on L-H dynamics, and Brian LaBombard and Martin Greenwald on edge turbulence.