Uranium Ion Beam Research Articles

Producing intense uranium ion beam for RIKEN RI beam factory

Intense highly charged uranium (U) ion beams were produced using RIKEN 28 GHz superconducting electron cyclotron resonance (ECR) ion source in a high-temperature oven (HTO). We used a double-oven system to ensure ample vapor supply. Moreover, we optimized the vapor delivery into the plasma at a constant microwave power input. Consequently, we achieved intense U-ion beams, specifically 250 eμA for U35+, 36 eμA for U46+, and 10 eμA for U54+, at an injected microwave power of approximately 3000 W. This achievement stems from recent advancements, notably the optimization of the material consumption rates aimed at maximizing beam intensity, which we briefly review here.

In-beam test results of the Super-FRS GEM-TPC detector prototype with relativistic uranium ion beam

As an essential part of the Super-FRS particle identification, the GEM-TPC detector in a twin field-cage configuration will provide position information at up to 1 MHz counting rate with a spatial resolution < 1 mm and with tracking efficiency >95 %. This detector is designed to provide particle-beam tracking information of projectiles ranging from protons to uranium. The performance of the GEM-TPC detector in a single field-cage configuration and newly integrated AWAGS readout electronics with a differential output was studied at the FRS for the response to the uranium beam at 850 MeV/u with intensity up to 1000 ions/spill. The result shows that a clusterization algorithm developed for this analysis works properly. The spatial resolution of 0.74–0.81 mm, a detection efficiency >99 %, and a tracking efficiency >96 % were found. This work describes the methodology used to achieve such results in detail.

Stripping of relativistic uranium-ion beams by foils

The dynamics of relativistic uranium-ion beams stripped by foils from Be to Au is investigated in the 100–500 MeV/u energy range. Calculations of the charge-state distributions of uranium fractions as a function of foil thickness are performed using the BREIT code, based on the analytical solution of the balance rate equations for the ion charge-state fractions. Relativistic electron-loss and electron-capture cross sections, required for BREIT as input data, are calculated for interactions of Uq+ ions, q = 65–92, colliding with Be, C, Al, Ti, Cu, Mo, W, and Au atoms. The beam energy losses are found to be rather small, less than 20%, and are not accounted for in calculations. Calculated charge-state distributions are compared with available experimental data, obtained at the GSI (Gesellschaft für Schwerionenforschung) and BEVALAC (Bevatron Linear Accelerator) facilities, and with calculations by the GLOBAL code created at GSI.The optimal conditions are predicted for production of bare, H-like, He-like and Li-like uranium ions with the largest probabilities. Dependencies of the equilibrium thicknesses for uranium charge-state fractions on the initial charge of incident ions are investigated.

Present status of and recent developments at RIKEN RI beam factory

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.

Beam Dynamics Simulation in the LINAC-100 Accelerator Driver for the DERICA Project

The results of uranium ion beam dynamics simulation in front-end and superconducting sections of the accelerator-driver LINAC-100 for the new rare isotope facility DERICA (JINR, Dubna) are presented. The optimum parameters are chosen for the buncher accelerator with radiofrequency quadrupole focusing (RFQ) for uranium ion beam acceleration from the ion source up to the energy of 570 keV/nucleon. LINAC-100 modular superconducting part layout for uranium beam acceleration from 3 to 100 MeV/nucleon is obtained. The energies for the stripper section installation are chosen.

Development of a new high temperature oven for the production of intense metal ion beams with ECR ion sources.

High Temperature Ovens (HTOs) have widely been used to evaporate refractory materials in electron cyclotron resonance ion sources to produce hundreds of microamperes of multiply and highly charged metal ion beams. To meet the demands of milliamperes of multiply charged uranium and other heavy metal ion beams for future accelerators, a new and low-cost HTO is under development at Lawrence Berkeley National Laboratory for better long-term stability at high evaporation rates. ANSYS simulations have been carried out to optimize the new HTO with low heating current to reduce the electromagnetic forces as an HTO is immersed in the strong ECRIS magnetic fields. A larger loading volume is employed to deal with higher material consumption. Off-line tests have shown that the unloaded new HTO operates stably up to 1800-1900 °C with low temperature gradients and good repeatability. This paper presents and discusses the conceptual design features of the new HTO and off-line tests.

Study of heavy ion beam induced damage in tungsten for high power target applications

The spallation material at ESS is pure tungsten, which is cooled by gaseous helium flow. To study the behaviour of tungsten under dynamic beam conditions at ESS, pure tungsten specimens have been irradiated at the M3-beamline of the UNILAC facility at GSI Helmholtz Centre for Heavy Ion Research. Tungsten specimens of two thicknesses, 26 μm and 3 mm, were exposed to pulsed uranium and gold ion beams for fluences up to 7.5 · 1013 ions·cm−2 at 4.8 MeV/nucleon. Nanoindentation tests were performed on the cross section of the irradiated 3 mm sample, and microhardness was measured on the top surface. The measured data are compared with the calculated damage values, and a correlation between the radiation induced damage and the observed mechanical property is presented. Thermal diffusivities of foil samples irradiated up to four different fluences were measured with a Laser Flash Apparatus (LFA). The observed changes in the mechanical and thermal properties of irradiated tungsten were used to estimate the changes of operational temperature and mechanical stresses in the ESS target material with the progress of radiation damage, using coupled thermal and mechanical simulations. From the pulsed beam induced dynamic oscillations of thin tungsten specimens, information on fatigue properties of tungsten under irradiation was drawn. In addition to pure tungsten, oxidised tungsten samples were irradiated. This is to investigate the stability of the adhesive oxide layer under pulsed beam conditions, which would be formed due to oxygen impurities in the helium cooling loop. The irradiated oxide scale was examined using Auger Electron Spectroscopy (AES) and Scanning Electron Microscopy (SEM).

Charge-state dynamics of 1.4- and 11-MeV/u uranium ions penetrating H2 and He gas targets

Abstract Theoretical description and interpretation are presented of the recent experimental data on stripping of fast 238U ions, penetrating H2 and He gaseous targets: obtained in GSI, Darmstadt, Germany at 1.4 MeV/u with a H2 stripper, and in RIKEN, Saitama, Japan at 11 MeV/u with H2 and He strippers. Electron-loss and capture cross sections for uranium ions, interacting with H2 and He targets are calculated and used as input data in the BREIT code to obtain dynamic characteristics of uranium-ion beams: non-equilibrium and equilibrium charge-state fractions, mean and equilibrium charges, and equilibrium thicknesses. Special attention is paid for the calculation of the dynamic characteristics of 1.4-MeV/u uranium ions stripped by a H2 in a windowless gas target at GSI, using a newly designed pulsed gas cell with a pressure changing from ∼ 0.1 to ∼ 100 mbar along the ion beam. To explain the experimental data, a Gaussian pressure model for the H stripper is applied with account for the target-density effect. A possible deviation of the Bragg’s additivity rule for electron-capture cross sections for a H2 target is also considered and we predict that the equilibrium charge of a 1.4-MeV/u uranium beam in atomic hydrogen is larger than in molecular hydrogen, i.e., it is indicated that atomic hydrogen can be a more effective stripper than molecular hydrogen. Charge-changing cross sections and dynamic characteristics of 11-MeV/u uranium ions passing through He and H2 targets are calculated as well. Calculated equilibrium mean charge states q ¯ ( He ) = 67.8 and q ¯ ( H 2 ) = 75.7 are in agreement with RIKEN experimental data within 10%.

Development of rotating beryllium disk stripper

High-intensity uranium (U) ion beams are successfully provided at the RIKEN RI Beam Factory. We have attempted to extend the lifetime of the charge stripper as the U-beam intensity has increased. An attempt to enlarge the irradiated area using a rotating large carbon disk (C-disk) failed in 2006–2007 because no commercially available C-disk with 0.085 mm thickness met our requirements. In 2012, we tested a beryllium (Be) disk (0.1-mm-thick, diameter = 120 mm) as an alternative to the C-disk. The Be disk proved to be an adequate substitute, and has been successfully used during beam-time operation.

Three-dimensional thermal simulations of thin solid carbon foils for charge stripping of high current uranium ion beams at a proposed new heavy-ion linac at GSI

This paper presents an extensive numerical study of heating of thin solid carbon foils by $1.4\text{ }\text{ }\mathrm{MeV}/\mathrm{u}$ uranium ion beams to explore the possibility of using such a target as a charge stripper at the proposed new Gesellschaft f\"ur Schwerionenforschung high energy heavy--ion linac. These simulations have been carried out using a sophisticated 3D computer code that accounts for physical phenomena that are important in this problem. A variety of beam and target parameters have been considered. The results suggest that within the considered parameter range, the target will be severely damaged by the beam. Thus, a carbon foil stripper does not seem to be a reliable option for the future Gesellschaft f\"ur Schwerionenforschung high energy heavy--ion linac, in particular, at FAIR design beam intensities.

Design of the plasma chamber and beam extraction system for SC ECRIS of RAON accelerator

The RAON accelerator is the heavy ion accelerator being built in Korea. It contains a 3rd generation SC ECRIS which uses 28 GHz/18 GHz microwave power to extract 12 puA uranium ion beams. A plasma chamber for that ECRIS is made of aluminum machined from bulk Al. That chamber contains cooling channels to remove dumped power and another access port for microwave introduction and plasma diagnostics. Beam extraction electrodes were designed considering the engineering issues and preliminary beam extraction analysis was done. That plasma chamber will be assembled with a cryostat, and beam extraction experiment will be done.

Effect of Biased Disc on Brightness of Highly Charged Uranium Ions from RIKEN 28 GHz Superconducting Electron Cyclotron Resonance Ion Source

The emittance and beam intensity of highly charged heavy ions were measured as a function of the negative voltage of a biased disc. We observed that the brightness of the highly charged uranium ion beam generated by the RIKEN 28 GHz superconducting electron cyclotron resonance ion source was strongly influenced by the bias voltage.

Production of a highly charged uranium ion beam with RIKEN superconducting electron cyclotron resonance ion source

A highly charged uranium (U) ion beam is produced from the RIKEN superconducting electron cyclotron resonance ion source using 18 and 28 GHz microwaves. The sputtering method is used to produce this U ion beam. The beam intensity is strongly dependent on the rod position and sputtering voltage. We observe that the emittance of U(35+) for 28 GHz microwaves is almost the same as that for 18 GHz microwaves. It seems that the beam intensity of U ions produced using 28 GHz microwaves is higher than that produced using 18 GHz microwaves at the same Radio Frequency (RF) power.

Development of the carbon foils as charge strippers for high-intensity uranium ion beams

A carbon foil (C-foil) is commonly used as a charge stripper in the heavy-ion accelerators. Since 2005, the polymer-coated carbon foils (PCC-foils) have been fabricated at Nishina Center to prepare larger and thicker C-foils than those previously used as charge strippers. However, the multi-layer PCC-foils did not have sufficiently long life-time. Since August 2009, a new magnetron sputtering system is used to fabricate a thick C-foil. The foils coated with polymer are used as strippers. Life-times of the new single-layer PCC-foils under the uranium beam were measured in two configurations: at the first one a small piece of C-foil was attached to a fixed holder and in the second one a large C-foil was attached to a “rotating-cylinder stripper” device. The properties of the new single-layer PCC-foils and the results of the life-time measurements are reported in this contribution.

Generation of plane shocks using intense heavy ion beams: Application to Richtmyer–Meshkov instability growth studies

A design of a novel experiment that allows the generation of a well defined, steady, and strong plane shock wave employing an intense uranium ion beam that is incident on a wedge shaped compound target is presented. This technique will open up the possibility of carrying out unique high energy density physics experiments using these shock waves. One such experiment is to study the growth of Richtmyer–Meshkov instability in fluids as well as in solids, both in the linear and nonlinear regimes, as shown by detailed numerical simulations presented in this paper. The ion beam parameters used in this study correspond to those that will be available at the Facility for Antiprotons and Ion Research (FAIR) at Darmstadt.

Quasispherical fuel compression and fast ignition in a heavy-ion-driven X-target with one-sided illumination

The HYDRA radiation-hydrodynamics code [M. M. Marinak et al., Phys. Plasmas 8, 2275 (2001)] is used to explore one-sided axial target illumination with annular and solid-profile uranium ion beams at 60 GeV to compress and ignite deuterium-tritium fuel filling the volume of metal cases with cross sections in the shape of an “X” (X-target). Quasi-three-dimensional, spherical fuel compression of the fuel toward the X-vertex on axis is obtained by controlling the geometry of the case, the timing, power, and radii of three annuli of ion beams for compression, and the hydroeffects of those beams heating the case as well as the fuel. Scaling projections suggest that this target may be capable of assembling large fuel masses resulting in high fusion yields at modest drive energies. Initial two-dimensional calculations have achieved fuel compression ratios of up to 150X solid density, with an areal density ρR of about 1 g/cm2. At these currently modest fuel densities, fast ignition pulses of 3 MJ, 60 GeV, 50 ps, and radius of 300 μm are injected through a hole in the X-case on axis to further heat the fuel to propagating burn conditions. The resulting burn waves are observed to propagate throughout the tamped fuel mass, with fusion yields of about 300 MJ. Tamping is found to be important, but radiation drive to be unimportant, to the fuel compression. Rayleigh–Taylor instability mix is found to have a minor impact on ignition and subsequent fuel burn-up.

Measurement of trace uranium isotopes using a porous ion emitter

The extent to which thermal ionization mass spectrometry (TIMS) can measure trace quantities of 233U and 236U in the presence of a huge excess of natural uranium is evaluated. This is an important nuclear non-proliferation measurement. Four ion production methods were evaluated with three mass spectrometer combinations. The most favorable combinations are not limited by abundance sensitivity; rather, the limitations are the ability to generate a uranium ion beam of sufficient intensity to obtain the required number of counts on the minor isotopes in relationship to detector background. The most favorable situations can measure isotope ratios in the range of 1 × 10 −10 if sufficient sample intensity is available. These are the triple sector mass spectrometer with porous ion emitters (PIE) and the single sector mass spectrometer with energy filtering.

Charge strippers for high intensity uranium beams in the RIKEN RI beam factory

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.

Simulation of target response due to uranium ion beam impact

Metal targets were irradiated at GSI with a highly focused uranium ion beam with a kinetic energy of 350MeV/u. Out of these targets two copper samples, that had been irradiated multiple times with a maximum intensity of 2.36 · 109 , were chosen for simulations. In order to characterize the behavior of the target under the load of the ion beam, FLUKA was used to generate the initial distribution of deposited energy which was in turn used as an input for ANSYS AUTODYN to calculate the dynamic response of the target. In the simulations of the first sample a good approximation of the so-called hydrodynamic tensile limit, the crucial parameter for target failure, was found to be -1.08 GPa. This acquired value was used for the simulation of the second sample which had been irradiated with two high-intensity shots. These simulations resulted in the full penetration of the sample which was in agreement with metallurgical examinations. This paper presents the performed simulations.

High intensity production of high and medium charge state uranium and other heavy ion beams with VENUS

The next generation, superconducting electron cyclotron resonance (ECR) ion source VENUS (versatile ECR ion source for nuclear science) started operation with 28 GHz microwave heating in 2004. Since then it has produced world record ion beam intensities. For example, 2850 e microA of O(6+), 200 e microA of U(33+) or U(34+), and in respect to high charge state ions, 1 e microA of Ar(18+), 270 e microA of Ar(16+), 28 e microA of Xe(35+), and 4.9 e microA of U(47+) have been produced. A brief overview of the latest developments leading to these record intensities is given and the production of high intensity uranium beams is discussed in more detail.