Maximal ponderomotive potentials for end-plugging

Ponderomotive barriers can be used to enhance confinement in magnetic mirror machines. This enhanced confinement is particularly advantageous because it is independent of the loss cone. Ponderomotive barriers can be generated by radio frequency waves [1], or by static perturbations to the electromagnetic fields when the plasma is rotating in the magnetic mirror machine [2]. These barriers can affect all plasma species [3], or be species-specific [4, 5]. For fusion plasmas, and in particular for the proton-boron 11 reaction due to the high temperature required for the reaction, the required confining potential can be quite large. We present mechanisms that limit the magnitude of a ponderomotive potential barrier, and determine the maximal effect this type of end-plug could achieve.

[1] H. Motz and C. J. H. Watson, Advances in Electronics and Electron Physics, vol. 23, Elsevier, 1967, pp. 153–302.

[2] T. Rubin, J. M. Rax, and N. J. Fisch, Physics of Plasmas, vol. 30, no. 5, p. 052501, May 2023.

[3] T. Rubin, J. M. Rax, and N. J. Fisch, J. Plasma Phys., vol. 89, no. 6, p. 905890615, Dec. 2023.

[4] T. Rubin, I. E. Ochs, and N. J. Fisch, Physics of Plasmas, vol. 31, no. 8, p. 082109, Aug. 2024.

[5] T. Rubin and N. J. Fisch, Physics of Plasmas, vol. 32, no. 6, June 2025