Improved temperature measurement in a plasma focus by means of a cobalt filter

Abstract

The characteristics of cobalt as a soft x-ray filter are investigated. It is found to be a good choice to diagnose 0.5-5 keV hot plasmas in a device like a plasma focus. The focus plasma temperature is found to be filling pressure dependent. The highest temperature recorded is 5 keV at a filling pressure of 2.5 mbar, which gives the highest neutron yield in the 2.3 kJ low-energy Mather-type device under study. The advantage of the cobalt filter is to prevent contamination of the temperature-sensitive continuum radiation by the dominant Cu Kα line radiation. The energy dependence of the detector sensitivity is incorporated to yield a more accurate temperature measurement. The Ni-Co filter combination helps to estimate the Cu Kα line radiation from the device, which is the highest at 0.5 mbar. The emitted energy is estimated to be 1.2 J in the 4π geometry, which corresponds to system efficiency of about 0.045%. The Cu Kα is 90-95% of the total x-ray emission.