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The charge-state distributions and equilibrium charge states of uranium ( 238 U) and xenon ( 136 Xe) ions at 11 MeV=nucleon were determined using a gas charge stripper. A differential pumping system facilitated the increase of the nitrogen gas thickness up to 1:3 mg=cm 2 , which is sufficient for the most probable charge state to attain equilibrium. The charge states of 238 U attain equilibrium at 56.0, 56.6, and 55.7 in N 2 , Ar, and CO 2 media with thicknesses of 125, 79, and 126 g=cm 2 , respectively, while those of 136 Xe attain equilibrium at 40.5, 40.1, and 40.3 in N 2 , Ar, and CO 2 media with thicknesses of 163, 95, and 139 g=cm 2 , respectively. The equilibrium charge states of 136 Xe are acceptable for acceleration by the subsequent cyclotron. The measured data of 238 U were used to devise an empirical formula for the prediction of the equilibrium charge state in gaseous media over the energy region of 0:01-60 MeV=nucleon. The equilibrium charge state of 136 Xe as predicted by the devised formula is in good agreement with the data.

Development of a nondestructive, efficient electric-charge-stripping method is a key requirement for next-generation high-intensity heavy-ion accelerators such as the RIKEN Radioactive-Isotope Beam Factory. A charge stripper employing a low-Z gas is an important candidate applicable to high-intensity uranium beams for replacing carbon-foil strippers. In this study, a high-beam-transmission chargestripping system employing helium gas for 238 U beams injected at 10:8 MeV=u was developed and demonstrated for the first time. The charge-state evolution measured using helium in a thickness range of 0:24-1:83 mg=cm 2 is compared with theoretical predictions. Energy attenuation and energy spread due to the helium stripper are also investigated.

The next generation heavy ion accelerator facility, such as the RIKEN radio isotope (RI) beam factory, requires an intense beam of high charged heavy ions. In the past decade, performance of the electron cyclotron resonance (ECR) ion sources has been dramatically improved with increasing the magnetic field and rf frequency to enhance the density and confinement time of plasma. Furthermore, the effects of the key parameters (magnetic field configuration, gas pressure, etc.) on the ECR plasma have been revealed. Such basic studies give us how to optimize the ion source structure. Based on these studies and modern superconducting (SC) technology, we successfully constructed the new 28 GHz SC-ECRIS, which has a flexible magnetic field configuration to enlarge the ECR zone and to optimize the field gradient at ECR point. Using it, we investigated the effect of ECR zone size, magnetic field configuration, and biased disk on the beam intensity of the highly charged heavy ions with 18 GHz microwaves. In this article, we present the structure of the ion source and first experimental results with 18 GHz microwave in detail.