High-resolution x-ray crystal spectrometer/polarimeter at torus experimentfor technology oriented research-94

A high-resolution x-ray polarimeter has been installed at the torus experim ent for technology oriented research (TEXTOR-94). The instrument consists o f two spectrometers in Johann geometry, utilizing the dependence of Bragg r eflection on the polarization. The dispersion plane of the so-called horizo ntal spectrometer coincides with the midplane of the tokamak, whereas the d ispersion plane of the so-called vertical spectrometer lies perpendicular t o the midplane of the tokamak. Both spectrometers operate with cylindricall y bent quartz crystals of dimensions 153 mmx38 mmx0.7 mm with a 2d spacing of 4.9130 Angstrom. The radii of curvature of the horizontal and vertical s pectrometer crystals are 3820 mm and 4630 mm, respectively. The detectors a re multiwire proportional counters having a large entrance window of 180 mm x90 mm, with a high count rate capability of up to 2.5x10(5) photons/s, and a spatial resolution of 0.4-0.65 mm, depending on the count rate. The uniq ue data acquisition system makes it possible to record up to 8192 spectra p er TEXTOR-94 discharge to study fast events and impurity transport. The ins truments are sensitive to spurious amounts of argon in hydrogen or deuteriu m discharges and aim for x-ray polarization measurements and other core pla sma diagnostics like electron temperature, ion temperature, plasma rotation , impurity transport, and relative abundance of Ar15+/Ar16+. The first meas urements of toroidal rotation speed, ion and electron temperatures show a v ery good agreement with charge exchange recombination spectroscopy (XRS) an d electron cyclotron emission (ECE) diagnostics available at TEXTOR-94. The measured values of the ratio Ar15+/Ar16+ are higher than that predicted fr om coronal equilibrium. The ratio depends strongly upon the electron densit y both for ohmic and neutral beam injection cases. This suggests that the c harge state distribution is also dependent on diffusion and charge exchange processes in the plasmas. (C) 2001 American Institute of Physics.