Contribution Plenary Presentation
Minimum B mirror trap with guiding center motion on magnetic surface
A properly shaped quadrupolar mirror magnetic field, in combination with a controllable weak radial electric field, is predicted to force each guiding center to move close to its mean magnetic surface. A neoclassical increase of radial transport would then be practically eliminated. The radial electric field may be controlled by biased end plates placed at the end tank outside the confinement region where the magnetic field lines intersect. A radial invariant, the radial Clebsch coordinate of the gyro center, can be used to derive Vlasov equilibria with a finite plasma beta. The minimum B property of the trap is a strong indicator of MHD stability. For a magnetic field ended by two expanders, magnetic field shaping is made aiming at minimum drift and ellipticity. The corresponding magnetic field can be reproduced by superconducting coils up to a mirror ratio of 4 or somewhat higher. Mirror ratios exceeding 10 may be reachable with finite beta effects included. Analytical expressions in closed form are derived. The study addresses potentials for the concept as a fusion neutron source.