Phase-Locked Rotation of Crystallized Non-neutral Plasmas by Rotating Electric Fields

Abstract

Large numbers of particles with a single sign ofcharge can be trapped and cooled in Penning traps [1,2],which use a combination of static electric and magneticfields for particle confinement. The global rotation ofthese non-neutral plasmas about the magnetic field axisis necessary for the radial confinement [3]. Activecontrol of this rotation prevents plasmas from spinningdown under the ambient drag from static field errorsand background neutrals, and is important for a numberof experiments including Coulomb crystal studies [4,5],precision spectroscopy [6–8], measurements of particleand energy transport [9], trapping of antimatter plasmas[10,11], and storage of highly stripped ions [12]. As anexample, the second-order Doppler (time dilation) shiftdue to rotational velocity in a Penning trap atomic clockcan be minimized by stabilizing the rotation at a particularfrequency [7]. Radiation pressure from laser beams hasbeen used to vary the plasma rotation frequency [13,14].However, this method is limited to the few ion specieswhose atomic transitions are accessible by a laser, and isnot precise due to laser power, frequency, and pointingfluctuations. Recently, rotating azimuthally asymmetric(“rotating wall”) electric fields have been used to applya torque on Mg