Pure electron plasmas in asymmetric traps*

Publisher Website
Google Scholar
Abstract
The equilibrium, stability, and dynamics of pure elec- tron plasmas have been studied extensively."' Tradition- ally, these plasmas are confined in Penning-like traps with cylindrical equipotential walls. Since these traps are azi- muthally symmetric, the canonical angular momentum of the confined plasmas is conserved. This limits the radial expansion of the plasmas and has been thought to be re- sponsible for the excellent confinement properties of these traps.3 However, the azimuthal symmetry can be broken by applying asymmetric electrostatic perturbations on the cylindrical trap wall. Experimental results4 prove that these asymmetries degrade, but do not destroy, the trap confinement properties. Because angular momentum need not be conserved, a new outlook is required to understand these plasmas. In this paper we study the static and dynamic proper- ties of pure electron plasmas confined in such asymmetric traps. The plasma drift dynamics studied here is assumed to occur on a slow time scale ( Td) compared to the cyclo- tron orbit time scale (T,). Furthermore, the plasma is taken to be short and hot. Consequently the axial bounce period (r,> along the magnetic field is also fast compared to the drifts. Thus, we use the guiding center approxima- tion, and the electric field experienced by the electrons can be approximated by the bounce-averaged electric field. The observable dynamics reduce to two-dimensional, bounce-