Investigation on Energy Discrimination in a Direct Energy Converter for Deuterium-Helium-3 Fusion

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We perform a proof-of-principle experiment of a charge separation and energy discrimination in a cusp-type direct energy converter (CUSPDEC), which was proposed as an efficient energy converter from thermal ions poduced by D-^3He fueled fusion reactor directly into electricity. In the CUSPDEC, electrons are separated from the incident plasma stream at the first cusp and the thermal ions are deflected at the second cusp to an energy converter with fusion protons not being affected by the two cusps.We have constructed a basic experimental device for testing the charge separation of electrons from ions and the energy discrimination of thermal and fusion ions. The low enrgy plasma beam is injected to a single cusp and the charge collectors at the line cusp and the point cusp exit monitor the charge flow. When the magnetic field is adjusted to form the cusp, the current to the point cusp becomes positive and that to the line cusp becomes negative showing the separation of electrons and ions. The separation ratio increases with the increased magnetic curvature at the cusp point. A numerical simulation is performed, in which the trajectory of electrons and ions are obtained in the two-dimensional cusp magnetic field. It is found that the charge separation can be obtained under the condition that the incident radius and pitch angle are within a certain value. This result is consistent with the experimental result.The experimental device is equipped with an ion source with variable energy to prove the energy discrimination by the cusp field. The ion current to the point cusp becomes larger than to the line cusp for higher ion energy, showing the proof-of-principle of the energy discrimination.