Alcator C-Mod Weekly Highlights September 20, 2004 FY 2004 weeks of operation planned: 18 weeks, completed: 18.9 weeks. We are currently up-to-air with the primary goal of installing the lower hybrid launcher. In addition, a large number of in-vessel activities are ongoing in support of ICRF and diagnostic systems. Maintenance and upgrades to diagnostic and power systems are also in progress. Physics ------- Joe Snipes has made calculations using TRANSP/FPPRF/TORIC of the fast particle content of a number of C-Mod ICRF heated plasmas. He compared three discharges with up to 5 MW of ICRF heating during current rise but with three different toroidal fields. The RF resonance location varied from 10 cm inboard, to central, to 10 cm outboard, as the toroidal field was varied. In the inboard case, there were almost no Alfven eigenmodes observed, whereas the central resonance case had strong Alfven Cascades and toroidal Alfven Eigenmodes (TAEs). The outboard resonance case also had Alfven Cascades and TAEs. Calculations showed the inboard and central resonance cases had peak fast ion tail energies up to 300 keV while the outboard case only reached about 100 keV because the average RF power density was not as high in that case. Peak RF power densities were calculated to be around 30 W/cm^3 in the inboard and central resonance cases, but only 7.5 W/cm^3 in the outboard case. The fast ion velocity relative to the Alfven velocity exceeded unity in the inboard and central resonance cases, which is more than sufficient to drive TAEs, but was only marginal in the outboard case just exceeding 0.5. The orbit loss calculated by TRANSP was about the same in the inboard and central resonance cases whereas the lower energy outboard resonance case had negligible orbit loss. Operations ---------- The final five cylindrical heat shield innner wall limiter modules that have been upgraded with tile mounting screw keepers have been installed in-vessel. The Long Pulse Diagnostic Neutral Beam 4160 V power transformer drying process is complete. The transformer will be hi-pot tested up to 5 kV from primary to ground, 1 kV secondary to ground, and 5 kV primary to secondary before power is applied. Documentation of the DNB AC power system controls has begun, including the controls for the power room transformer Limitamp contactor unit, the Hi-Yard 5kV circuit breaker and the interface to the cell PLC. Lower Hybrid System ------------------- The #2 and #3 PPPL couplers, and three 3-window frames were successfully plated and baked last week. Braze wires are being hydrogen fired in preparation for brazing the #2 PPPL coupler. Completion of this coupler, together with the #1 coupler already successfully brazed, will allow preparations of the launcher for high power testing to begin. Cables for the low power microwave control system are being installed and tested. Work continued on fabrication of rf probes for the launcher, and filament control circuitry for the klystrons. ICRF System ----------- We continued maintenance of FMIT transmitters last week. Construction of the test rack needed to do high power testing of the fast ferrite tuners is near completion. The power supplies, fan modules, ac power strip, and card cages are mounted, and fuse block and power wiring is underway. Diagnostics ----------- We continued on upgrade work for the two-color-interferometer. The new AGC amplifier chassis are complete and final testing of the amplifiers has been done. Fabrication of a mount for the new CO2 laser is nearly complete. Travel and Visits ----------------- Earl Marmar and Amanda Hubbard attended a meeting of the FESAC panel on priorities, in Madison, Wisconsin Sept 13-15. _______________________________________________ Cmod_weekly mailing list Cmod_weekly@lists.psfc.mit.edu http://lists.psfc.mit.edu/mailman/listinfo/cmod_weekly