Initial result of neutron energy spectrum reconstruction using multi-foil activation method in KSTAR

For the purpose of the fusion power measurement accuracy improvement in KSTAR, multi-foil activation method has been applied on KSTAR neutron activation system (NAS). In order to increase the spectral coverage, in addition to indium and silicon samples which have been routinely used to measure fusion power of deuterium plasma and triton burnup respectively, 3 other sample materials, aluminum, niobium, and nickel are selected based on the calculation of expected activity and gamma-ray counts. Due to the limited accessibility in counting station during the plasma experiment, and in order to maximize gamma-ray counting statistics each sample material is irradiated one by one during the 2016 KSTAR campaign. In this reason, the analysis is carried out under the assumption that neutron emission characteristics on each plasma discharge do not change. MAXED unfolding code has been used in order to reconstruct the default spectrum which is calculated by MCNP5. This initial reconstruction result will be used as criterion for selection of additional appropriate reaction and optimization of strategies of sample irradiation and gamma-ray counting.