Alcator C-Mod Weekly Highlights 14-Nov-2005 FY2006 weeks of research operations: Planned: 12 weeks (tentative) Completed: 1 week Operations ---------- Alcator C-Mod continued plasma operations last week, with three run days scheduled and completed. A total of 61 plasma discharges were produced with a reliability of 72%. Experiments carried out were in support of MiniProposals from Operations & Diagnostics, MHD, and Divertor/Edge groups. The primary experiments involved ohmic plasmas, while RF conditioning and general machine conditioning proceeded in parallel. Hydrogen levels, which affect the RF minority damping, are decreasing; the rate of decrease is similar to that seen at the beginning of previous campaigns. Plasma operations are planned to continue this week. Physics ------- Tuesday's run was devoted to two diagnostic development miniproposals utilizing the diagnostic neutral beam system. The experiment under MP#265, "CXRS Commissioning", concentrated on measurement of the dependence of the charge exchange recombination photon emission cross section on beam energy. The initial, rough analysis of the beam energy scan indicates that the cross section for charge exchange recombination between the beam neutrals and BVI is not simply described by an interaction of fully stripped boron with full energy hydrogen neutrals in the n=1 state. At least at the high energy end of the scan, other energy components contribute. From the lower energy part of the scan it is appears that hydrogen beam neutrals in states with n>1 contribute to the emission. Further quantitative analysis of these data is under way. The experiment under MP#431 aimed at determining the effect of Faraday rotation in the MSE optics. For these discharges, a wire grid polarizer was positioned immediately in front of the plasma-facing MSE lens to generate a source of linearly polarized light with a fixed polarization direction. MSE measured the apparent polarization direction in discharges with time-varying toroidal field or time-varying plasma current. The results indicate that Faraday rotation is not an important issue for the C-Mod MSE diagnostic: in the polarimeter’s reference frame, the implied Faraday rotation is just -0.002 +/- 0.021 degrees per Tesla of toroidal field, and the implied Faraday rotation associated with the poloidal field is -0.047 +/- 0.104 degrees per megamp of plasma current. Note that both Faraday values are less than the measurement uncertainty, i.e. the measured Faraday rotation values are statistically consistent with zero. These results conclusively rule out Faraday rotation in the optical train as an issue for the MSE diagnostic. Wednesday's run was dedicated to MP#404a "Parametric Dependence of Moderate n Alfvén Eigenmode Damping Rates". This experiment uses the Active MHD Spectroscopy antenna to drive stable Alfven waves and measure their damping. Wednesday's experiment employed inner wall limited plasmas at moderate elongation (kappa=1.6). The density was scanned over a range of 0.6