Diagnostics of a charge breeder electron cyclotron resonance ion source helium plasma with the injection ofNa231+ions

Abstract

This work describes the utilization of an injected 23 Na 1þ ion beam as a diagnostics of the helium plasma of a charge breeder electron cyclotron resonance ion source. The obtained data allows estimating the upper limit for the ion-ion collision mean-free path of the incident sodium ions, the lower limit of ion-ion collision frequencies for all charge states of the sodium ions and the lower limit of the helium plasma density. The ion-ion collision frequencies of high charge state ions are shown to be at least on the order of 1-10 MHz and the plasma density is estimated to be on the order of 10 11 cm −3 or higher. The experimental results are compared to simulations of the 23 Na 1þ capture into the helium plasma. The results indicate that the lower breeding efficiency of light ions in comparison to heavier elements is probably due to different capture efficiencies in which the in-flight ionization of the incident 1þ ions plays a vital role.

Plasma instabilities of a charge breeder ECRIS

“…The instabilities are caused by the change of the plasma properties induced by the capture of the 1+ ions. At ∆V < −10.5 V the energy of the injected 1+ ions exceeds the optimum for their thermalization and they can propagate through the oxygen plasma as demonstrated both experimentally [22,35] and numerically [36]. The reduced level of interaction with the oxygen ions causes the instabilities to disappear at high 1+ energies.…”

A novel numerical tool to study electron energy distribution functions of spatially-anisotropic and non-homogeneous ECR plasmas

“…Beyond this, the plasma -being an anisotropic and dispersive medium -presents a 3D dielectric tensor that needs to be in turn included in the calculation of the EM field 20 . The developed code has already proven its validity describing the so-called frequency tuning effect 18 , and reproducing experimental results for light and heavy ion dynamics in ECR-based charge breeding devices 21,22 . When applied to electrons, the kinetic code follows the evolution of N particles for a given simulation time T span , with an integration step T step .…”

Recent improvements of the LPSC charge breeder

“…In order to understand if the efficiencies improvement were caused by an electron density increase, the efficiencies of 1+ and 2+ charge states have been compared to the initial charge breeder configuration results for Na and Rb. They represent the fractions of the 1+ beam that are not captured by the plasma and their yield can be linked directly to the plasma density and ionization rate [15,16]. The values obtained in the two configurations have been found comparable which implies that the electron density has not been modified significantly.…”