A novel beam-bunching technique has been implemented at a heavy-ion linear accelerator facility by installing a compact two-gap prebuncher and a multilayer beam chopper. A pulsed beam of 2 to 4 MHz, having kinetic energy up to 1:1 MeV=u, is realized by bunching a 2 keV=u continuous beam just upstream of the linac. Around 40% of the continuous beam particles are successively gathered in a single microbunch with a time width of around 15 ns in full width at one-tenth maximum. The number of background beam particles over 250 ns just before the bunched beam is well suppressed to less than 10 À4 of the number of bunched particles. This technique has been adopted to generate intense -particle beams for nuclear astrophysics experiments.
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.
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