Measurement of the ion temperature in the Isar III theta pinch by laser forward scattering
An experiment which allows measurement of a collective scattering spectrum of a plasma in the forward direction (7°) in a single discharge is described. The ion temperatures were determined from the scattering spectra for filling pressures between 10 and 100 μD2. To improve accuracy the electron temperature was also measured by a 90° scattering experiment. In all cases measured spectra agreed within experimental accuracy with those expected of thermal plasmas.The electron temperatures were in all cases approximately 175 eV near the time of maximumB field. However, the ion temperature changed from about 650 eV at 10 μD2 to about 175 eV at 100 μD2. This behaviour is expected from heating and loss mechanisms characteristic of theta pinches.The ion temperature obtained from neutron measurements (1300 eV at 10 μD2) is higher, than that obtained from the laser scattering experiment. A locally varying ion temperature or superthermal fluctuations could explain the discrepancy.