Multilayer mirror and foil filter AXUV diode arrays on CDX-U spherical torus

Recent upgrades to CDX-U spherical torus diagnostics include two 10-channel AXUV diode arrays. The multilayer mirror (MLM) array measures the lambda 1 50 O VI brightness profile in the poloidal plane using the Mo/B4C synthetic multilayer structures as dispersive elements. The foil filter array has a tangential view and is equipped with interchangeable clear aperture, beryll ium and titanium filters. This allows measurements of radiated power, O VI or C V radial distributions, respectively. The O VI and C V emissivity and the radiated power profiles are highly peaked. A Neoclassical impurity accu mulation mechanism is considered as an explanation. For radiated power meas urements in the T-e less than or equal to 100 eV plasmas, photon energy dep endent corrections must be used in order to account for nonlinear AXUV sens itivity in the range E-phot less than or equal to 20 eV. The arrays are als o used for characterization of resistive MHD phenomena, such as the low m m odes, saw-tooth oscillations and internal reconnection events. Based on the successful operation of the diagnostics, a new ultra soft x-ray multilayer mirror diode AXUV diode array monitoring the 34 A emissivity distribution of C VI will be built and installed on the National Spherical Torus Experim ent. (C) 2001 American Institute of Physics.