Effect of nuclear elastic scattering on the D(d,n)3He fusion reactivity induced by energetic protons observed in the large helical device

The enhancement of the fusion reaction rate coefficient induced by energetic protons, which isone of the typical nuclear elastic scattering (NES) effects, was observed in the large helicaldevice (LHD) located at the National Institute for Fusion Science. An intense high purityhydrogen beam (the atomic ratio of the contained deuterium was less than 1 ppm) with∼170 keV-energy and ∼10 MW-power was injected into a deuterium plasma with the electrontemperature ∼9 keV and density ∼1019 m−3. After the hydrogen beam injection, the neutrongeneration rate by the D(d,n)3He fusion reaction immediately increased, and an increment ofover one order of magnitude was observed, even though there was no meaningful iontemperature variation. The reasons for the increment in the neutron generation rate arediscussed with reference to the Boltzmann–Fokker–Planck analysis along with LHDexperimental data. It is concluded that the increment was induced by the production ofenergetic deuterons due to the NES of energetic protons.