Measurement of ionization, charge exchange and ion confinement times in charge breeder ECR ion sources with short pulse 1+ injection of metal ions

Abstract

The Consecutive Transients (CT) method is used for estimating the characteristic times of ionization, charge exchange and confinement within the plasma of a Charge Breeder Electron Cyclotron Resonance Ion Source (CB-ECRIS). The method reveals differences in the characteristic times between different source configurations, with K9+ charge breeding efficiencies of 8.9 % and 20.4 %, and allows qualitative explanation of the improved breeding efficiency. The increase in K9+ efficiency is accompanied by a decrease in ionization time for low charge states, a decrease of charge exchange time for high charge states, and an overall decrease of the ion confinement time, which increases non-linearly with the charge state. The charge exchange time exhibits a minimum near charge state K8+, indicating low neutral density near the plasma core. The CT-method yields a distribution of possible ne and (Ee) corresponding to the spatial distribution of different charge state ions. The results hint at a non-uniform plasma electron density and energy distribution as well as a nested-layer distribution for the ion populations — hot and dense plasma with high charge state ions near the plasma core.

Diagnostics of highly charged plasmas with multicomponent 1+ ion injection

“…We have recently developed a method which satisfies these conditions. The so-called consecutive transients (CT) method [15,16] for estimating the ECR-heated plasma properties, i.e., the electron density, average energy of the EED, characteristic times of ionization, charge exchange, and ion confinement. It is based on causing a small perturbation and monitoring the response of the complex system to it, requiring fewer a priori assumptions than any previous method and, uniquely, accounts for the experimental uncertainty of the electronimpact ionization cross sections employed in the calculations involved in this and similar methods [17][18][19][20][21].…”

Method for estimating charge breeder ECR ion source plasma parameters with short pulse 1+ injection of metal ions

“…The consecutive Transient (CT) method [18,19] is a recently developed method combining computational techniques and experiments for probing the plasma density n e , (warm) electron average energy ⟨E e ⟩, and characteristic times of ion confinement τ conf , charge exchange τ cex and electron impact ionization τ ion in CB-ECRIS plasmas. The CT method is based on short pulse 1+ injection into the ECRIS plasma and the analysis of the resulting N+ ion beam transients extracted from the ECRIS.…”

“…As such, the method either complements existing CB-ECRIS diagnostics while requiring fewer assumptions, or provides information inaccessible through other techniques. For example, it has been shown with the CT method that the ion confinement time is not a linear function but rather increases exponentially with the charge state [18,19], which is commensurate with electrostatic ion confinement in a local potential dip [5,6]. It has been shown that the inherent uncertainties of the CT method can be reduced e.g.…”

“…by two-component injection or overlapping the (⟨E e ⟩ , n e ) solution sets of neighbouring charge states albeit with the caveat of additional assumption [20]. Furthermore, it has been demonstrated that the main contributor to the large relative uncertainty of the CT method is the lack of precise ionization cross section data whereas the presumed EED has a smaller effect [21].…”

“…In this paper we apply the CT method for parametric studies of the CB-ECRIS plasma. We do not detail the method itself but rather refer the reader to the literature [18][19][20][21] for a comprehensive account of the assumptions, computational details and data analysis.…”