Abstract
A diamond-based neutral particle analyzer (DNPA) array composed of single-crystal chemical vapor deposition (sCVD) diamond detectors was installed on the Large Helical Device (LHD) for measuring the helically trapped energetic particles. In high neutron flux experiments, the unwanted neutron-induced pulse counting rate should be estimated using the neutron diagnostics because a diamond detector is sensitive to neutrons as well as energetic neutral particles. In order to evaluate the quantitative neutron-induced pulse counting rate on the DNPA, the response functions of the sCVD diamond detector for mono-energetic neutrons were obtained using accelerator-based D-D and D-7Li neutron sources in Fast Neutron Laboratory (FNL). As a result of the neutron flux estimation by the Monte Carlo N-Particle code at the NPA position in the LHD and the response function obtained in the FNL experiment, the counting rate of the neutron-induced signal was predicted to be 1.1 kcps for the source neutron emission rate of Sn = 1 × 1015 n/s. In the LHD experiment, the neutron-induced signals were observed by closing the gate valve during the plasma discharges. It is found that the counting rates of the neutron-induced signals proportional to Sn reached 1.1 kcps at Sn = 1 × 1015 n/s. As a result of the quantitative estimation of the neutron-induced signals on the DNPA using other neutron measurements, it has become possible to accurately measure energetic neutral particles in the high neutron flux experiment.
Highlights
In the future fusion reactor, alpha particles should be well confined and used for plasma heating to sustain steady-state without external heating
In order to investigate the behavior of the energetic particles in the experimental devices for fusion research, neutral particle analyzer (NPA) has been developed [1]
We show the results of the neutron-induced signals on the single-crystal chemical vapor deposition (sCVD) diamond detectors for NPA
Summary
In the future fusion reactor, alpha particles should be well confined and used for plasma heating to sustain steady-state without external heating. In the experiment using deuterium gas, the neutron emission produced by the D-D fusion reaction is used for investigating the behavior of the energetic particles because the neutron emission rate depends on the spatial and energy distribution functions of energetic particles. The neutrons produced by D(d,n)3He or by 7Li(d,n)8Be reactions were detected at the sCVD diamond detector with the energy of En+Ebeamcos En of 2.45 MeV with D(d,n)3He reaction was used for evaluating the neutron-induced signals in D-D fusion plasma experiment, and En of 15.0 MeV with 7Li(d,n)8Be reaction was used for measuring the neutrons by DNPA. Quantitative evaluation of neutron-induced signal on diamond detector was observed in FNL.
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