Wall-loss distribution of charge breeding ions in an electron cyclotron resonance ion source

Abstract

The ion loss distribution in an electron cyclotron resonance ion source (ECRIS) was investigated to understand the element dependence of the charge breeding efficiency in an electron cyclotron resonance (ECR) charge breeder. The radioactive (111)In(1+) and (140)Xe(1+) ions (typical nonvolatile and volatile elements, respectively) were injected into the ECR charge breeder at the Tokai Radioactive Ion Accelerator Complex to breed their charge states. Their respective residual activities on the sidewall of the cylindrical plasma chamber of the source were measured after charge breeding as functions of the azimuthal angle and longitudinal position and two-dimensional distributions of ions lost during charge breeding in the ECRIS were obtained. These distributions had different azimuthal symmetries. The origins of these different azimuthal symmetries are qualitatively discussed by analyzing the differences and similarities in the observed wall-loss patterns. The implications for improving the charge breeding efficiencies of nonvolatile elements in ECR charge breeders are described. The similarities represent universal ion loss characteristics in an ECR charge breeder, which are different from the loss patterns of electrons on the ECRIS wall.

Charge breeding of light metallic ions: Prospects for SPIRAL

“…[22]). In this respect, the iron plug truncated for passing the RF waveguide in Phoenix should be ideally replaced by a symmetrical one, as recently done at LPSC [31].…”

“…The reason invoked for these results has been that the velocity difference between the plasma ions and the 1þ injected ions has to be minimized for optimizing the capture efficiency [19]. More generally, clues for understanding the lower efficiencies observed for condensable ions compared to rare gases were obtained for higher masses by comparing loss patterns of 111 In 1 þ and 140 Xe 1 þ beams injected into the KEK charge breeder [20]. Compared to EBIS charge breeding, the understanding of the mechanisms involved in the capture in ECR charge breeders is hindered by the difficulty of modeling the interaction of the 1þ beam with realistic plasmas.…”

“…In particular the ECR plasma gross properties such as density, size, location, sheath potential and the hypothetical potential dip, are still difficult to assess experimentally as well as theoretically. Presently only a limited number of attempts were made to model the capture of the 1þ beam into ECR charge breeders taking into account realistic ion-ion collisions [21][22][23], using more or less simplified assumptions.…”