Ponderomotive barriers in rotating mirror devices using static fields*

For a-neutronic fusion schemes, it is advantageous to manipulate the fuel species differently from one another, as well as expel ash promptly. The ponderomotive effect can be used to selectively manipulate particles. It is commonly a result of particle-wave interactions and has a complex dependence on the particle charge and mass, enabling species-selectivity [1]. If the plasma is rotating, e.g. due to ExB motion, the ponderomotive effect can be generated using static (i.e., time-independent) perturbations to the electric and magnetic fields, which can be significantly cheaper to produce than time-dependent waves [2]. This feature can be particularly useful in rotating mirror machines where mirror confinement can be enhanced by rotation, both through centrifugal confinement and additionally through a ponderomotive interaction with a static azimuthal perturbation. Some static perturbations generate a ponderomotive barrier, other perturbations can generate either a repulsive barrier or an attractive ponderomotive well which can be used to attract particles of a certain species while repelling another [3, 4]. The viability of each of these effects depends on the specifics of the rotation profile and temperature [5, 6], and the resultant dispersion relation in the rotating plasma [7].

 

[1] A. Gaponov, M. Miller, Potential wells for charged particles in a high-frequency electromagnetic field. Journal of Experimental and Theoretical Physics 34, 242–243 (1958).

[2] T. Rubin et al., Magnetostatic ponderomotive potential in rotating plasma, Phys. Plasmas 30, 052501 (2023).

[3] T. Rubin et al., Guiding center motion for particles in a ponderomotive magnetostatic end plug, Journal of Plasma Physics 89, 905890615 (2023).

[4] T. Rubin et al., Flowing plasma rearrangement in the presence of static perturbing fields, arXiv 2406.03727 (2024).

[5] T. Rubin et al., Finite-difference multiple fluid solution for source-driven rotation in highly magnetized linear plasma device, Phys. Plasmas 28, 122303 (2021).

[6] T. Rubin et al., Fueling limits in a cylindrical viscosity-limited reactor, Phys. Plasmas 29, 082302 (2022).

[7] J.-M. Rax et al., Rotating Alfvén waves in rotating plasmas. J. Plasma Phys. 89, 905890613 (2023).