Ion Radial Transport due to a Non-Uniform Electrostatic Potential in a Magnetic Mirror

The density around the thermal barrier in a tandem mirror is sustained to be much lower than that in the central cell experimentally, which suggests that the ions trapped in the thermal barrier potential escape from there rapidly. Although the mechanism of radial loss of ions trapped in the axisymmetric end-mirror cells are unknown in the present tandem mirror experiment, the electrostatic potential has been measured to be not axisymmetric around the plug region. Because a numerical calculation reveals that the ion orbits trapped in a non-axisymmetric electrostatic potential (with many high m azimuthal modes around the plug) have a chaotic behavior, the non-axisymmetric electrostatic potential can be a candidate of a large ion radial loss in the axisymmetric end-mirror cells.