The feasibility of viscosity-driven hot ion mode

A radial fuel ion current into the core of a cylindrical plasma, and a quick removal of ash ions, can set up plasma flows leading naturally to a “hot-ion mode” [1]. The heating is the result of the viscous dissipation of the ion fluid. Solutions to the flow profile are obtained using the MITNS code [2], and nontrivial limitations are found: The centrifugal force caused by the rotation empties out the density at the core. The quadratic dependence of the viscosity on the density makes it such that large angular velocity gradients are required in order to produce the viscous shear needed to balance the torque produced by the radial current and the magnetic field. The viscous heating itself, which increases the plasma temperature, further reduces the viscosity coefficient. These effects lead to a runaway behavior when the density at the center approaches 0. The “natural hot-ion mode” is limited at large magnetizations. At small magnetizations, the collisional energy transfer between species and the viscous heating are of similar magnitude.

[1] Kolmes, E. J., et al, Phy. Rev. E 104, 015209 (2021)

[2] Kolmes, E. J., Ochs I. E., and N. J. Fisch. Comp. Phy. Com. 258, 107511 (2021)