Abstract
The RIKEN RI (radioactive isotope) Beam Factory (RIBF)
provides the world's most intense heavy ion beams exceeding
345 MeV/u and is the primary facility for in-flight RI beam
generation. The ...RIBF has steadily improved its performance. In
particular, the intensity of the uranium beam, which is critical for
producing in-flight fission RI beams, has been dramatically
increased by a factor of 240 compared to 2008. To further increase
the intensity of the uranium beam, a new acceleration scheme using
charge stripper rings (CSRs) has been proposed as a cost-effective
way to increase charge stripping efficiency. In this paper, we
discuss the key design issues of CSR and required upgrades of
existing ring cyclotrons with the introduction of CSR and
space-charge effects.
The use of charge strippers is almost inevitable for the efficient acceleration of particularly heavy ions such as uranium in heavy-ion accelerator complexes. At the RIKEN RI beam factory (RIBF), the ...total charge stripping efficiency of two strippers, He gas and rotating graphite sheet disk strippers, used for uranium acceleration is less than 5%, which creates a serious bottleneck for potential intensity upgrades in the near future. We have proposed using charge stripper rings (CSRs) as a cost-effective way to enhance the charge stripping efficiency in a multi-stage accelerator complex involving cyclotrons such as the RIBF. In this paper, we present some calculation results on the key design issues of a CSR.
We report here the first successful synthesis of cold antihydrogen atoms employing a cusp trap, which consists of a superconducting anti-Helmholtz coil and a stack of multiple ring electrodes. This ...success opens a new path to make a stringent test of the CPT symmetry via high precision microwave spectroscopy of ground-state hyperfine transitions of antihydrogen atoms.
The total cross sections for single ionization of helium and single and double ionization of argon by antiproton impact have been measured in the kinetic energy range from 3 to 25 keV using a new ...technique for the creation of intense slow antiproton beams. The new data provide benchmark results for the development of advanced descriptions of atomic collisions and we show that they can be used to judge, for the first time, the validity of the many recent theories.
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.
The Radioactive Isotope Beam Factory (RIBF) is a cyclotron-based accelerator facility that is used for nuclear science studies and was completed at the end of 2006. RIBF can produce the most intense ...RI beams using fragmentation or fission of high speed heavy ion beams. Ever since the first beam was produced, effort has focused on increasing the intensity of uranium beams. Ions beams with high intensity and high availability have been used to produce many important scientific achievements. Upgrade programs have been proposed to further expand scientific opportunities. These programs have two goals. The first goal is to find heavier elements than element 118, which is already named. The upgrade program for the heavy ion linac (RILAC), including installation of a superconducting linac, has been funded and is under construction. The second goals is to increase the intensity of uranium ion beams up to 1 pµA, thus facilitating further investigations into the physics of unstable nuclei. This program for uranium beams is still been unfunded. We are pursuing a budget-friendly version without changing the project goals.
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.
The ASACUSA collaboration developed an ultraslow antiproton beam source, monoenergetic ultraslow antiproton source for high-precision investigation (MUSASHI), consisting of an electromagnetic trap ...with a liquid He free superconducting solenoid and a low energy antiproton beam transport line. The MUSASHI was capable of trapping and cooling more than 1×107 antiprotons and extracting them as an ultraslow antiproton beam with energy of 150–250 eV.
A new helium-gas stripper system has been applied at the ~11 A MeV uranium beam of the Radioactive Isotope Beam Factory of the RIKEN accelerator facility. Although the gas stripper is important for ...the heavy-ion accelerator facility, the residual radiation that is generated is a serious problem for maintenance work. The residual dose was evaluated by using three-layered activation samples of aluminium and bismuth. The γ-rays from produced radionuclides with in-flight fission of the 238U beam and from the material of the chamber activated by neutrons were observed by using a Ge detector and compared with the values calculated by using the Monte-Carlo simulation code PHITS.
PDF
