Improvement of fuel ion ratio diagnostics performance using anisotropic neutron emission spectrum in NBI heating deuterium-tritium plasma
For the stable operation of the deuterium-tritium (DT) fusion reactor, it is important to measure fuel ion ratio (nT/nD). A method to determine nT/nD from the emission ratio of 14 MeV neutron by DT reaction and 2.45 MeV neutron by DD reaction is being studied. This method has a serious problem that the detection of 2.45 MeV neutron by DD reaction is interfered by slowing-down component of 14 MeV neutron by DT reaction. As a solution to this problem, the technic using the rise in the fraction of the DD to DT reaction rate and modification of neutron emission spectrum by NBI-heating has been studied. Owing to this technic, the measurement was possible even in nT/nD = 1.0. However, the measurable plasma condition is still limited, and further improvement is required. In this study, we consider neutron measurement using the anisotropic neutron spectrum for further improvement of the diagnostics performance. We indicate the effectiveness of the proposed method by discussing the range of measurable plasma condition.