Overcoming Rotation Limits in ExB Plasmas*

In an open-field line configuration, rotation can be produced by imposing an approximately-radial electric field across an approximately-axial magnetic field. Assuming that the magnetic field cannot be reduced below some value, the maximum achievable rotation speed is limited by the size of the electric field. This, in turn, is ultimately limited by the voltage drop that can be tolerated by the material components wherever the field lines intersect the vessel. It turns out to be possible – at least in principle – to circumvent this limit by constructing equilibria in which a large voltage drop is contained within the plasma (that is, the voltage drop does not fully propagate along the field lines to contact the edges of the device) [1]. Here we consider how to find configurations that achieve this voltage-drop isolation while simultaneously meeting the other requirements of a practical confinement device. 

 

[1] E. J. Kolmes, I. E. Ochs, J.-M. Rax, and N. J. Fisch, “Massive, Long-Lived Electrostatic Potentials in a Rotating Mirror Plasma,” Nature Communications 15, 4302 (2024).