Rotating Wall

At UCSD, we have achieved "infinitely" long confinement (weeks) of pure Mg ion plasmas in a Penning-Malmberg trap, by applying a rotating electric asymmetry on a sectored cylindrical wall. The (m=2 or m=1) asymmetry rotates somewhat faster than the rotation of the ion cloud, exerting a positive torque on the plasma; this balances the drag and radial expansion caused by static field errors.

With precision LIF diagnostics, we show that these steady-state plasmas are typically near thermal equilibrium, as characterized by rigid rotation and uniform temperature profiles. Furthermore, the plasma rotation frequency follows that of the applied drive, enabling external control of the ion density and cloud size. By gradually changing the drive frequency, we are able to continuously vary the density of an ion cloud of 10^9 particles from 10^6 to 2*10^8cm¯³,corresponding to 10% of the Brillouin density at B=4T.

Unexplained heating resonances are observed at certain densities, resulting in increased slippage with respect to the drive, and tending to limit further increase in density. When the magnetic field is not properly aligned, hysteresis and bifurcated states are also observed near these resonances. This rotating field technique may be applicable to a number of atomic and plasma physics experiments.

E.M. Hollmann, F. Anderegg, and C.F. Driscoll, "Confinement and Manipulation of Nonneutral Plasmas using Rotating Wall Electric Fields," Phys. Plasmas 7, 2776 (2000).

F. Anderegg, "Steady-State Confinement of Non-Neutral Plasmas Using Trivelpiece-Gould Modes Excited by `Rotating Wall'", Conference on Trapped Charged Particles and Fundamental Physics (1998).


F. Anderegg, E.M. Hollmann, and C.F. Driscoll, "Rotating Field Confinement of Pure Electron Plasmas Using Trivelpiece-Gould Modes," Phys. Rev. Lett. 78, 4875 (1998).


X.-P. Huang, F. Anderegg, E.M. Hollmann, C.F. Driscoll and T.M. O'Neil, "Steady-State Confinement of Non-neutral Plasma by Rotating Electric Fields," Phys. Rev. Lett. 78, 875 (1997).



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