Alcator C-Mod Weekly Highlights May 29, 2002 First pumpdown of Alcator C-Mod occurred on Monday of last week, followed by several days of leakchecking. Work has continued on the Lower Hybrid High Voltage Power Supply, ICRF systems, and the engineering system required for Plasma operation. Diagnostic calibrations and installations continued. Physics ------- Yijun Lin presented results at the Physics meeting on his analysis of a short wavelength rf wave (SWW) observed by Nelson-Melby during his PhD research. The SSW is a low-field side ion-ion resonance that occurs in a multi-species plasma. This wave also appears in 2-D full wave ICRF simulations, such as TORIC and AORSA. The wave has been recently identified as a slow warm plasma ion cyclotron electromagnetic wave of the 'light' species. The SWW can be calculated by solving the full-electromagnetic dispersion equation together with a cylindrical wave vector transformation due to the poloidal B field. The wave solution can re-produce most features shown in TORIC, such as the wavelength and propagation distance . The root can also be approximately obtained from the slow wave dispersion equation. The wave is damped by both electron Landau damping and ion cyclotron damping. The wave propagation distance is highly sensitive to poloidal B field, and also depends on the plasma composition, density and temperature. Large poloidal B field, high concentration of the 'light' species, low plasma density and low temperature favors the SWW. The SWW is similar to a wave branch found in D-T plasma with minority tritium shown in an early paper [F. W. Perkins, Nuclear Fusion 17(6), 1977]. As shown in the TORIC simulation, the SWW carries comparable (or even larger) power as the mode-converted Ion Bernstein Wave (MCIBW). In the conventional ICRF picture, only the fast magnetosonic wave and MCIBW are thought to be important, therefore, the findings and confirmation of this short wavelength wave have very significant implication on the ICRF mode-conversion physics and other RF applications, such as current drive and plasma flow drive. J. Snipes visited IPP-Garching from 6 - 8 May 2002 to participate in High Density H-mode experiments on the W7-AS stellarator and compare their results with the EDA H-mode on C-Mod. This is a new regime recently discovered on the W7-AS stellarator after divertors were installed, first called Improved Confinement and now called HDH, which has some similarities with the EDA H-mode on C-Mod. It is an improved energy confinement regime that occurs only at high density and is characterized by relatively low particle confinement, which keeps impurities from accumulating in the core of the plasma. Dr. Fritz Wagner requested a visit to W7-AS by a C-Mod scientist to compare this new regime with the EDA H-mode. A clear transition from a low energy confinement mode to a higher energy confinement mode was observed as the target density increased shot-to-shot above about 1.6 x 10^20 m^-3. The energy confinement doubled above this density threshold and the core radiation decreased. No evidence of a Quasi-Coherent Mode (QCM) as found on C-Mod has yet been observed, but their diagnostics are not setup to measure very short wavelength modes. A scanning magnetic probe similar to the one we use on C-Mod is not being built and should be installed within a couple of weeks to be able to measure short wavelength modes in the plasma boundary. Operations ---------- On Monday, 5/21, a first pumpdown of Alcator C-Mod was performed followed by several days of leak checking. Several leaks were found and fixed. On Thursday the vessel was brought back up to air to complete MSE/BES calibrations and to complete other invessel work. All invessel work was completed by Friday evening. Igloo blocks were installed during the week, heater and TC cables were run, and diagnostics continued to be installed and aligned. We continue to checkout and bring on line ACCESS, ECDC, CRYO, HEAT, and other engineering systems. Liquid nitrogen has been added to the sump for the first time, and the LN2 pump operated successfully that supplies nitrogen to the magnets. On Saturday, 5/25, the neutron calibration was performed, and on Tuesday, 5/28, following a re-weld of a leaking tangential port, the machine was pumped down. Preparations are now being made to bake the machine. Lower Hybrid MIE Project ------------------------ Good progress is being made on the HVPS. Several full load pulses without any faults have been obtained. Wire tests are being performed to verify fault protection for the klystrons. ICRF ---- New wiring lists for the RF cell racks were completed, and fault system cabling in RF Cell Rack #2 is in place and connected. DFOL chassis were installed in RF Cell rack, and the wiring was completed. The CAMAC RF auto-tune system wiring was completed. Cross-connect blocks have been also installed in the rack and the wiring has been started. The RF Cell phase-shifter/stub tuner control wiring is in progress. Pressure sensor connectors for the shifter/tuners are ready for wiring. Calibrations continued on the demodulators. RFX DNB ------- The DNB gas system component fabrication is complete and ready for final assembly and a leakcheck. An isolated ethernet connection has been provided for the DNB computer. Isolation is required since the computer operates at the DNB ground potential and proper, safe operation of the DNB requires single point grounding. The data for calibrations for CXRS, MSE, and BES was collected. The data for the CXRS calibrations was completed first, and analysis is nearing completion. Work has started on the LN2 delivery system. The LN2 level sensors that will provide a high level indication at the cryo pumps are assembled. The cryo panel that will mount in the cell behind the DNB is currently being designed. New beam duct bellows supports have been fabricated and installed. Diagnostics ----------- The FRC high resolution ECE diagnostic is almost ready for plasma shots. Waveguide was measured and alignment of the waveguide supports completed; only cutting of the waveguide remains. CAMAC was installed, tested, repaired, re-installed, and is now working. Signal conditioning modules, triggers and PC data acquisition were also installed. Travel and Visits ----------------- Tom Fredian attended a two day National Fusion Collaboratory workshop held at PPPL this week. Perry Phillips, UT-FRC, was here last week working on the ECE radiometer.