Assessment of mixed neutron and photon radiation ratios using a tissue equivalent proportional counter on KSTAR

Abstract

Tokamaks have a mixed radiation field consisting of neutrons, neutron-induced gamma rays, and hard X-rays due to runaway electrons. Neutron and gamma-ray diagnostics for characterization of the mixed radiation fields of tokamak in such an environment is essential for determining neutron emission rate as well as for understanding behaviors of fast ions in plasma operations.The experiment using a tissue equivalent proportional counter (TEPC) based on a microdosimetric technique has performed with the aiming of investigating its application to tokamaks through the measurement of dosimetric quantities at the KSTAR tokamak. For the work, a Bemjamin type of spherical TEPC with a 0.318 cm tissue equivalent wall of Shonka type A-150 plastic has applied to define lineal energy boundaries for secondary particles caused by each radiation component. The TEPC has placed on a deck at a distance of about 20 m from KSTAR tokamak. The mixture distributions have obtained from the measurement of lineal energy spectra. The mixture ratio of neutrons and gammas in the KSTAR tokamak has evaluated to be around 1:4. The present result shows not only the availability of the developed TEPC for the assessment of neutron and gamma components in the tokamak, but also its applicability for fusion reactors even though the application of TEPC on tokamak is still at experimental stage.