Accumulated 2-D neutron flux distribution during KSTAR operation

Since the successful first H-mode in 2010, duration of H-mode is extended to 1 min and the highest stored plasma energy up to 0.6 MJ is obtained by developing hybrid and internal transport barrier (ITB) mode as well as typical H-mode. Major heating system is the neutral beam (NB) of 100 keV with 5.5 MW and it is planned that the new additional 6 MW NBI is installed in 2018. So there is a lot of production of fast neutrons coming from via D (d,n)He-3 reaction and it is found that most of neutrons are 2.45 MeV neutrons coming from deuterium beam plasma interaction and the total neutron fluence during a campaign could be estimated to be about 10(19). In particular, several nickel activation samples are installed inside/outside the vacuum vessel poloidally and toroidally and the total accumulated neutron flux is estimated from 811 keV gamma emission measurement after the campaign. The results show that the neutron activation both inside and outside the vacuum vessel has toroidally non-axisymmetric distribution and it has the highest neutron flux around poloidal limiter area. Considering the prompt ion loss at nominal KSTAR operation including the high beta-p operation, prompt loss ions from 100 keV neutral ion beams hitting on three poloidal limiters was not negligible and the non-uniform distribution is discussed in term of prompt ion loss to the poloidal limiter. In addition, this work reports on the quantitative analysis of poloidal distribution of the neutron emission based on accumulated flux measurements.