Trapping Efficiency of a Non-Adidabatic Confinement Device

Abstract

We performed trajectory analysis of beam ions in such a magnetic field structure having a weak magnetic field region over a wide range by canceling the magnetic field created by the solenoid coil with a Helmholtz coil. The rate at which the beam ions injected in the axial direction are trapped in the magnetic field structure is statistically examined. In addition, by adjusting the Helmholtz coil current, the position of the field-null point is changed, and the influence on the ion trapping rate is also investigated. As a result, it is found that the larger the beam dispersion, the higher the trapping rate, and the higher the energy, the lower the trapping rate. Furthermore, it is also found that in the case where the magnetic field is not completely canceled at the center of the device, there is an energy which extremely decreases the trapping rate.

Lyapunov Exponent Analysis for Stochastic Ion Motion in a Non-Adiabatic Trap

“…Figure 4 shows the energy dependence of the fraction of trapped particles. As in the case of Adachi et al [5], it is found that the particle trapped rate becomes a minimum value at 0.05 keV. That is, the Fig.…”

“…Adachi et al simultaneously examined the particle trapping in the state where the Helmholtz coil current was changed and the magnetic field at the center of the device was not zero. In this case, it has been found that there is an energy band where the trapping rate is relatively low [5] and therefore the ions probably tend to exhibit regular motions. In this study, a Lyapunov exponent analysis [4] is carried out to investigate chaotic properties of ion motions in the situation mentioned above.…”

“…This Helmholtz coil current does not completely cancel the magnetic field on the midplane and geometric axis generated by the solenoid. Adachi's research [5] showed that the fraction of trapped particles decreases at specific energies of ions in this magnetic field. The purpose of this study is to investigate properties of stochastic motions of ions with energy around the minimum trapping rate.…”

“…Therefore, it can be used as a particle separation apparatus. Adachi et al calculated trajectories of ions in the trap and obtained the trapping ratio [5]. In Ref.…”

“…In Ref. [5], beam ions were assumed to be spatially dispersed in a Gaussian distribution when they are drawn out from an ion source. Then, when the magnetic field generated by the solenoid is completely canceled by that from the Helmholtz coil, it was found that the trapping ratio is a function of the standard deviation of the beam dispersion divided by the Larmor radius evaluated by the solenoid magnetic field and the beam ion energy.…”