Steady-State Confinement of Non-neutral Plasmas by Rotating Electric Fields

We apply “rotating wall” electric fields to spin up a non-neutral plasma in a Penning-Malmberg trap, resulting in steady-state confinement (weeks) of up to ${10}^9{\mathrm{Mg}}^{+}$ ions. The resulting ion columns can be near global thermal equilibrium, with near-uniform temperature and rotation frequency. The equilibrated plasma $\mathbf{E}\times \mathbf{B}$ rotation rate $f_E$ is observed to be somewhat less than the drive frequency $f_w$, with slip $\Delta f\equiv f_w{-f}_E$ depending on temperature as $\Delta f\propto T^{1/2}$ for $0.05\lesssim T\lesssim 5\mathrm{eV}$. Dynamic measurements of applied torque versus slip frequency show plasma spin up and compression for $\Delta f>\mathrm{}0\mathrm{}$ and plasma slowing and expansion for $\Delta f<\mathrm{}0\mathrm{}$. By gradually increasing $f_w$, density compression up to 20% of the Brillouin density limit has been achieved. Heating resonances and hysteresis in plasma parameters are also observed.