Magnetostatic ponderomotive barrier for open field line magnetic confinement configurations*

Open field line configurations, in particular rotating magnetic mirror machines,  are receiving renewed interest. In these devices, field line curvature and centrifugal force add a confining potential on top of the magnetic mirror effect. In this work we propose to add a third type of confining potential for motion along field lines, a ponderomotive potential generated by interaction of the rotating plasma with a static azimuthal magnetic ripple. This ponderomotive effect requires little modification to the rotating mirror concept, and utilizes the existing rotation in order to supply an additional confining potential along the machine axis.

 The Hamiltonian dynamics of a single particle in a rotating plasma column interacting with a magnetic multipole is perturbatively solved for up to second order. The interaction of the rotating and gyrating particle with the multipole generates ponderomotive potentials, one of which is always repulsive, and another which can be of either sign. Additionally, the effective particle mass for the axial degree of freedom is modified. Both the variable sign potential and the variable sign effective mass terms are maximized near resonance, in particular near zero rotation frequency.