The RIKEN accelerator complex started feeding the next-generation exotic beam facility radioisotope beam factory (RIBF) with heavy-ion beams from 2007 after the successful commissioning of RIBF at ...the end of 2006. Many improvements made from 2007 to 2010 were instrumental in increasing the intensity of various heavy-ion beams. However, the available beam intensity of very heavy ion beams, especially uranium beams, is far below our goal of 1pμA (6×1012particles/s ). In order to achieve this goal, upgrade programs are already in progress; the programs include the construction of a new 28-GHz superconducting electron cyclotron resonance ion source and a new injector linac. However, the most serious problem, that of a charge stripper for high-power uranium beams, still remains unsolved, despite extensive research and development work using large foils mounted on a rotating cylinder and a N2 gas stripper. A gas stripper is free from problems related to lifetime, though the equilibrium charge state in this stripper is considerably lower than that in a carbon foil, owing to the absence of the density effect. Nevertheless, the merits of gas strippers motivated us to develop a low-Z gas stripper to achieve a higher equilibrium charge state even in gases. We measured the electron-loss and electron-capture cross sections of uranium ions in He gas as a function of their charge state at 11, 14, and 15MeV/nucleon . The equilibrium charge states extracted from the intersection of the lines of the two cross sections were promisingly higher than those in N2 gas by more than 10. Simple simulations of charge development along the stripper thickness were performed by assuming the measured cross sections. The simulation results show that about 1mg/cm2 of He gas should be accumulated to achieve a charge state higher than that of N2 gas, notwithstanding the difficulty in accumulation of this helium amount owing to its fast dispersion. However, we now believe that the following two solutions can overcome this difficulty: a gas cell with a very large differential pumping system and a gas cell with a plasma window. Their merits and demerits are discussed in the paper.
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 charge-stripping system employing helium gas for U238 beams injected at 10.8MeV/u was developed and demonstrated for the first time. The charge-state evolution measured using helium in a thickness range of 0.24–1.83mg/cm2 is compared with theoretical predictions. Energy attenuation and energy spread due to the helium stripper are also investigated.
Since 1997, RIKEN Nishina Center has been constructing the Radioactive Isotope Beam Factory (RIBF) and succeeded in beam commissioning of its accelerator complex at the end of 2006. The world's first ...superconducting ring cyclotron (SRC) is the final booster in the RIBF accelerator complex which is able to accelerate all-element heavy ions to a speed of about 70% of the velocity of light. Assembling of the superconducting sector magnets was completed in August 2005. The superconducting coils were successfully cooled down and excited for tests on many operational aspects: magnetic force, coil protection and quality of magnetic field, showing that they work as designed. After a series of tests the other components were installed and tested under stray fields from the sector magnets. Local magnetic shields were put to the components which could not work under the stray fields. After setups of beam vacuum and radio frequency, beam commissioning started. The first beam was extracted at the end of 2006 and the first uranium beam was extracted in March 2007.
The charge-state distributions of super(238U and ) super(1)36Xe ions at 11 MeV/nucleon were measured using a gas charge stripper to test whether the charge states in gaseous media were acceptable for ...acceleration at the RIKEN RI-Beam Factory (RIBF). A differential pumping system facilitated the increase of the N sub(2 gas thickness to 1.3 mg/cm) super(2); this is sufficient for the most probable charge state to attain equilibrium. The charge states of super(238U attain equilibrium at 56.0, 56.6, and 55.7 in N) sub(2), Ar, and CO sub(2 media with thicknesses of 125, 79, and inline image, respectively, whereas those of ) super(1)36Xe attain equilibrium at 40.5, 40.1, and 40.3 in N sub(2, Ar, CO) sub(2) media with thicknesses of 163, 95, and inline image, respectively. The equilibrium charge states of super(136Xe are acceptable for acceleration by the subsequent cyclotron, whereas those of ) super(2)38U are not acceptable for acceleration without a major remodeling of the accelerator.
The charge-state distributions of
238U and
136Xe ions at 11
MeV/nucleon were measured using a gas charge stripper to test whether the charge states in gaseous media were acceptable for acceleration ...at the RIKEN RI-Beam Factory (RIBF). A differential pumping system facilitated the increase of the N
2 gas thickness to 1.3
mg/cm
2; this is sufficient for the most probable charge state to attain equilibrium. The charge states of
238U 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
μ
g
/
cm
2
, respectively, whereas those of
136Xe attain equilibrium at 40.5, 40.1, and 40.3 in N
2, Ar, CO
2 media with thicknesses of 163, 95, and
139
μ
g
/
cm
2
, respectively. The equilibrium charge states of
136Xe are acceptable for acceleration by the subsequent cyclotron, whereas those of
238U are not acceptable for acceleration without a major remodeling of the accelerator.
Two types of rotating charge strippers were constructed for the acceleration of intense heavy-ion beams at the RIKEN RI-beam factory. One charge stripper rotates a carbon disk using a rotating shaft. ...The other rotates a carbon foil attached onto the end of a rotating cylinder that is connected to hollow-shaft rotary-motion feedthroughs.
We have developed carbon stripper foils, liquid Li strippers, and gas strippers to find the most suitable stripper for high intensity uranium ion beams at the RIKEN RI beam factory (RIBF). The ...lifetime of newly developed polymer coated carbon foils has been measured online with a beam. A water stripper has been developed offline as a test for a liquid lithium stripper. A windowless gas target has been used as a nitrogen gas stripper and tested offline with the gas injected into the target cell. The maximum pressure of the target cell was 9.25
kPa, which corresponds to a thickness of 1.04
mg/cm
2.
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