Measurement of the internal magnetic field of plasmas using an alpha particle source

Abstract

The internal magnetic fields of plasmas can be measured under certain conditions from the integrated v×B deflection of MeV alpha particles emitted by a small radioactive source. The alpha source and large-area alpha particle detector would be located inside the vacuum vessel but outside the plasma. Alphas with a typical energy of 5.5 MeV (241Am) can reach the center of almost all laboratory plasmas and magnetic fusion devices, so this method can potentially determine the q(r) profile of tokamaks or spherical toris (STs). Orbit calculations, background evaluations, and conceptual designs for such α v×B (or “AVB”) detector are described.