Confinement of Nonneutral Spheroidal Plasmas in Multi-Ring Electrode Traps

Abstract

A nonneutral spheroidal plasma can be settled in a rigid rotor equilibrium inside a closed conducting cell independently of induced image charges on the cell wall if the electrostatic potential distribution on the wall surface is set equal to the sum of the external hyperbolic potential (r 2 - 2z 2) and the self-potential produced by the plasma. A confinement system equipped with a train of properly biased ring electrodes can approximately generate any axisymmetric potential, including the above field. Experiments on confinement of electron spheroids in such a system showed that the confinement time became the longest when the condition to diminish the image charge effects was satisfied. The observed frequency of the centre-of-mass harmonic oscillation of the plasma in this configuration was in good agreement with the estimated one.

Comparison of non-neutral electron plasma confinement in harmonic and rectangular potentials in a very dense regime

“…An improvement in the confinement may be achieved by canceling the image charge effect. 12 For further investigation of the observed decay in the number of trapped electrons as a function of the s h , the plasma radius R p was measured as a function of the s h . An example of these measurements is shown in Fig.…”

“…We assume the magnetic field axis is the z-axis, so the plasma image is in x-y plane. Since the holding time (s h ¼ 1 s) > the cooling time (s c % 0.2 s), the plasma shape is considered as spheroid and its radius R p can be obtained from fitting the intensity distribution by 12 IðrÞ…”

“…On the other hand, to confine a non-neutral plasmas in a harmonic potential well (HPW) with a long axial extent, a large Penning trap (multi-ring trap, MRT) 12 was used. Cold electron plasmas confined in this type of traps are now being used in several applications, including cooling of highly charged ions, 13,14 cooling of antiprotons for antihydrogen production at CERN, 7,15,16 and for positron accumulation.…”

Atomic collision experiment using ultra-slow antiproton beams

“…We used a Multi-Ring Trap (MRT) [12] consisting of 14 cylindrical electrodes placed coaxially along the magnetic field line. A favorable feature of the MRT compared with a normal Penning trap and a trap with a well-type potential is that a harmonic electric potential can be prepared in a wide region near the trap axis by application of appropriate voltage on each electrode, which enables extremely stable confinement of a large number of charged particles.…”

System of slow highly charged ion beam generation using a cold positron plasma trap at RIKEN

“…Since different nonneutral plasmas as electrons, positrons and HCIs should be manipulated in the trap, a multi-ring electrode trap [2] is adopted, which can produce a variety of axially symmetric configurations of electric field.…”