Stripper Foils Research Articles

Stripping accumulation and optimization of HIMM synchrotron

The design of an injection system for a dedicated carbon-ion therapy synchrotron is presented. Improvements to the particle tracking code ACCSIM are developed to support interactions between heavy ions and stripping foil. The three main improvements are concerned with (a) charge exchange between carbon ions and stripping foil; (b) multiple Coulomb scattering of incident heavy ions on stripping foil; and (c) energy loss in particles passing through the foil, and energy-loss straggling. The accumulation process is then simulated, and the parameters related to the injection system are optimized. A gain of about 140 in the number of particles is achieved, and the emittance and momentum spread growth is obtained, together with a central momentum shift. Finally, the superacceptance of the synchrotron, ε−Δp/p, is tracked. According to the simulation, 1.35×109 actual particles are stored successfully in the synchrotron.

Solenoid Development for an Emittance Transfer Experiment With a Design Environment System

Various solenoids must be developed for different machines of the FAIR-Project. A solenoid design environment (SDE) has been developed to reduce expenditure of design time and work. The design environment is based on an Opera-2d input text file. Most significant physical and technical parameters of a solenoid are considered. Due to the axial symmetry, a two-dimensional solenoid model describes well the main characteristics of a real magnet. The first use of the SDE was the design of a solenoid for an emittance transfer experiment at GSI. The 36 cm long magnet creates a flux density of 1 Tesla at the center. The coil of the solenoid is separated in two halves to allow placing a movable stripping foil on the beam axis. Nevertheless, the magnet design avoids a local flux minimum in the center, since it might act as a trap of electrons. Creating a SDE and a solenoid with this tool takes a little more manpower than designing one solenoid without environment system. But in the future the SDE will help to decrease development time significantly.

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.

Performance characteristics of HBC stripper foils irradiated by 650 keV H− and high intensity DC ion beams

Newly developed Hybrid type Boron mixed Carbon (HBC) stripper foils are extensively used not only for the RCS of J-PARC and PSR of LANL, but also for other low energy, high intensity proton accelerators in medical applications. We had before tested HBC stripper foils with 3.2MeV Ne+ and DC heavy ion beams.In order to further understand characteristics of HBC stripper foils, we measured the following parameters using the KEK-650keV H− and light ion Cockcroft Walton DC accelerator: foil lifetime, thickness reduction, uniformity before and after beam irradiation, and foil deformation. Energy deposition in the present experiment was adjusted to a similar level to that of the HBC foil used in the RCS of J-PARC’. In addition, to understand the reason why the HBC stripper foils have high durability against high intensity beam irradiation, we investigated various physical properties, and compared them between the HBC foils and other tested carbon stripper foils.The sizes of the carbon particles in the HBC foil were found to play a vital role in the lifetime.

Nanodiamond Foils for H- Stripping to Support the Spallation Neutron Source (SNS) and Related Applications

ABSTRACTThin diamond foils are needed in many particle accelerator experiments regarding nuclear and atomic physics, as well as in some interdisciplinary research. Particularly, nanodiamond texture is attractive for this purpose as it possesses a unique combination of diamond properties such as high thermal conductivity, mechanical strength and high radiation hardness; therefore, it is a potential material for energetic ion beam stripper foils. At the ORNL Spallation Neutron Source (SNS), the installed set of foils must be able to survive a nominal five-month operation period, without the need for unscheduled costly shutdowns and repairs. Thus, a single nanodiamond foil about the size of a postage stamp is critical to the entire operation of SNS and similar sources in U.S. laboratories and around the world. We are investigating nanocrystalline, polycrystalline and their admixture films fabricated using a hot filament chemical vapor deposition (HFCVD) system for H- stripping to support the SNS at Oak Ridge National Laboratory. Here we discuss optimization of process variables such as substrate temperature, process gas ratio of H2/Ar/CH4, substrate to filament distance, filament temperature, carburization conditions, and filament geometry to achieve high purity diamond foils on patterned silicon substrates with manageable intrinsic and thermal stresses so that they can be released as free standing foils without curling. An in situ laser reflectance interferometry tool (LRI) is used for monitoring the growth characteristics of the diamond thin film materials. The optimization process has yielded free standing foils with no pinholes. The sp3/sp2 bonds are controlled to optimize electrical resistivity to reduce the possibility of surface charging of the foils. The integrated LRI and HFCVD process provides real time information on the growth of films and can quickly illustrate growth features and control over film thickness. The results are discussed in the light of development of nanodiamond foils that will be able to withstand a few MW proton beam and hopefully will be able to be used after possible future upgrades to the SNS to greater than a 3MW beam.

Cyclotrons with fast variable and/or multiple energy extraction

We discuss the principle possibility of stripping extraction in combination with reverse bends in isochronous separate sector cyclotrons (and/or FFAGs). If one uses reverse bends between the sectors (instead of drifts) and places stripper foils at the sector exit edges, the stripped beam has a reduced bending radius and it should be able to leave the cyclotron within the range of the reverse bend - even if the beam is stripped at less than full energy. We are especially interested in $H_2^+$-cyclotrons, which allow to double the charge to mass ratio by stripping. However the principle could be applied to other ions or ionized molecules as well. For the production of proton beams by stripping extraction of an $H_2^+$-beam, we discuss possible designs for three types of machines: First a low-energy cyclotron for the simultaneous production of several beams at multiple energies - for instance 15 MeV, 30 MeV and 70 MeV - thus allowing to have beam on several isotope production targets. In this case it is desired to have a strong energy dependence of the direction of the extracted beam thus allowing to run multiple target stations simultaneously. Second we consider a fast variable energy proton machine for cancer therapy that should allow extraction (of the complete beam) at all energies in the range of about 70 MeV to about 250 MeV into the same beam line. And third, we consider a high intensity high energy machine, where the main design goals are extraction with low losses, low activation of components and high reliability. The price that has to be paid for these advantages is an increase in size and/or in field strength compared to proton machines with standard extraction at the final energy.

Wrinkle analysis and mounting optimization of the primary stripper foil for CSNS

The primary stripper foil's lifetime is very important for high intensity proton accelerators. Besides high temperature, the wrinkle of the stripper foil is also harmful for the lifetime and the injection efficiency. However, the recent wrinkle simulation is still not perfect. In this paper, a new method for wrinkle analysis has been proposed for the first time, which is integrated with the buckling theory. Based on this method, the wrinkle vibration and the maximum wrinkle shape of the normally mounted foil have been simulated. Then, two mounting schemes for reducing the wrinkle have been contrasted. Finally, the foil mounting structure for CSNS has been designed.

Multi-layer stripper foils containing boron, PLD and CVD produced diamond-like carbon

The Applied Technology Group at TRIUMF operates three accelerators, TR30-1, TR30-2 and CP42 that use 30 MeV proton beams in the generation of commercial radioisotopes. These cyclotrons typically use diamond-like carbon (DLC) stripper foils produced in house of between 2.0 and 3.0 lm to extract particle beams from these cyclotrons. Micromatter (formerly the TRIUMF Carbon Foil Laboratory) manufactures DLC foils in a range of thicknesses from 10 nm to *10 lm using pulsed laser deposition. Continuing our previous work '(Zeisler and Jaggi Nucl Instrum Methods Phys Res A 613:434, 2010)' we further investigated the presence of boron in multilayer DLC foils, specifically DLC/boron/DLC hybrid foils. In this work, we investigated the mechanical properties and lifetime of these stripper foils in cyclotrons with varying thicknesses and boron content as well as a special DLC layer deposited by chemical vapor deposition and find an improvement in flexibility, mechanical strength and lifetime.

Carbon stripper foils for high current heavy ion operation

For the proposed new heavy ion linac@GSI the installation of a carbon foil stripper section is under discussion. High duty factor as well as high current (but low duty factor) heavy ion beams were used for machine experiments. Long term tests were performed to check the carbon foil durability. Relevant beam parameters have been measured in three measurement campaigns. After beam testing stripper foils were analyzed with different offline methods. Additionally promising results of high current beam irradiation of rotating target wheels will be presented. In the transfer line to the SIS 18 the heavy ion beam is stripped to higher charge states in a thick carbon foil. The stripper foil is loaded with 3 % of the beam power. To avoid evaporation in a single beam pulse, the beam is rapidly swept over its width. Experiences collected during the last decade of foil stripper operation at GSI will be presented.

Mirror symmetric optics design for charge-stripping section in Rare Isotope Science Project

The main aim of the Rare Isotope Science Project is to construct a high power heavy-ion accelerator based on the superconducting linear accelerator (SCL). The heavy ion accelerator is a key research facility that will allow ground-breaking research into numerous facets of basic science, such as nuclear physics, astrophysics, atomic physics, life science, medicine and material science. The machine will provide a beam power of 400kW with a 238U79+ beam of 8pμA and 200MeV/u. One of the critical components in the SCL is the charge stripper between the two segments, SCL1 and SCL2, of the SCL. The charge stripper removes electrons from the ion beams to enhance the acceleration efficiency in the subsequent SCL2. To improve the efficiency of acceleration and power in SCL2, the optimal energy of stripped ions in a solid carbon foil stripper was estimated using the code LISE++. The thickness of the solid carbon foil was 300μg/m2. The charge stripping efficiency of the solid carbon stripper in the present study was approximately 87%. For charge selection from the ions produced by the solid carbon stripper, a dispersive section is needed down-stream of the foil. The designed optics for the dispersive section is based on the mirror-symmetric optics to minimize the effect of high-order aberrations.

Sputtering angle effects by Kr mixing in N+ ion beam on the lifetime of nitrided carbon stripper foils

Nitrided carbon stripper (NCS) foils with high nitrogen content were produced by ion beam sputtering of reactive nitrogen gas. Such foils seem to be very useful as strippers in high-intensity heavy ion accelerators. We have conducted comprehensive research, development, and production of such foils with high reproducibility. Krypton, a heavy noble gas, was mixed with the reaction nitrogen gas (IBSRN) in the ion beam sputtering process to produce stripper foils with short sputtering deposition time and long lifetimes in the high intensity ion beam irradiation. With the (N2 + Kr) mixed gas ions we investigated the influence of different sputtering angles (α) on the lifetime of the NCS-foils in case of poly-graphite material. The lifetime measurement of these foils of 20 ± 5 μg/cm2 was performed with a 3.2 MeV Ne+ ion beam as usual. The foils made at a sputtering angle of 15° showed a maximum of 11.0 and 7.5 C/cm2 average charge density, respectively, which corresponded to about 275 and 187 times the lifetime of the best commercially available foils.

Quantitative monitoring of the stripper foil degradation in the 3-GeV rapid cycling synchrotron of the Japan proton accelerator research complex

A hybrid-type boron doped carbon stripper foil of 200 μg/cm2 is used for the present H− injection beam energy of 181 MeV in the 3-GeV rapid cycling synchrotron (RCS) of the Japan Proton Accelerator Research Complex (J-PARC). A stripper foil has a certain lifetime and usually lifetime goes shorter for high power operation. Foil degradation such as foil thinning and pinhole formation caused by the radiation might be a signal of the foil breaking. As a result, one can avoid sudden foil breaking by an efficient monitoring of the foil degradation. We have succeeded measuring even a little change of the stripper foil thickness during user operation of the RCS. It is the main motivation of the present study. A single foil was irradiated with a total of 2.7 × 1021 particles (injected H− itself) during 4 months continuous operation of the RCS but we did not observe any indication of the foil degradation.

Effects of injection beam parameters and foil scattering for CSNS/RCS

The China Spallation Neutron Source (CSNS) uses H− stripping and phase space painting method to fill a large ring acceptance with a small emittance linac beam. The dependence of the painting beam on the injection beam parameters was studied for the Rapid Cycling Synchrotron (RCS). The simulation study was done for injection with different momentum spreads, different rms emittances of the injection beam, and different matching conditions. Then, the beam loss, 99% and rms emittances were obtained, and the optimized injection beam parameters were given. The interaction between H− beam and stripping foil was studied, and the effect of foil scattering was simulated. The stripping efficiency was calculated and the suitable thickness of stripping foil was obtained. In addition, the energy deposition on the foil and the beam loss due to the foil scattering were also studied.

Analysis of Hybrid Type Boron-Doped Carbon Stripper Foils in J-PARC RCS

J-PARC (Japan-Proton Accelerator Research Complex) requires a carbon stripper foil to strip electrons from the H− beam supplied by the linac before injection into the Rapid Cycling Synchrotron (RCS) [1]. The foil thickness is about μm (200μg/cm2) corresponding to conversion efficiency of 99.7% from the primary H− beams of 181MeV energy to H+. We have successfully developed the Hybrid type thick Boron-doped Carbon (HBC) stripper foil, which showed a drastic improvement the lifetime without thickness reduction and shrinkage at the irradiated area. We started to study carbon stripper foils microscopically why carbon foils have considerable endurance for the beam impact by boron-doped. At first step, we made a comparison of ion irradiation effect between normal carbon and HBC by the electric microscope, ion-induced analysis. In particular, it seems that grain size of boron-rich area became much larger by irradiation for HBC. It was also observed that the boron-rich grain grew up by taking around material and generated pinholes more than 100 nm near itself consequently.

Preparation and investigation of diamond-like carbon stripper foils by filtered cathodic vacuumarc

Thin diamond-like carbon (DLC) stripper foils ∼5μg/cm2 in thickness were produced and evaluated as heavy-ion strippers for the Beijing HI-13 Tandem Accelerator. The DLC layers ∼4μg/cm2 in thickness were produced by the filtered cathodic vacuum arc technology onto glass slides coated with betaine–saccharose as releasing agent, which were previously covered with evaporated carbon layers ∼1μg/cm2 in thickness by the controlled ac arc-discharge method. Irradiation lifetimes of the DLC stripper foils were tested using the heavy-ion beams at the terminal of the Beijing HI-13 Tandem Accelerator, and compared with those of the standard carbon stripper foils made by the combined dc and ac arc-discharge method. The measurements indicate that the DLC stripper foils outlast the standard combined dc and ac arc-discharge carbon stripper foils by a factor of at least 13 and 4for the 197Au− (∼9MeV,∼1μA) and 63Cu− (∼9MeV,∼1μA) ion beams, respectively. The structure and properties of the DLC foils deposited onto silicon substrates by the filtered cathodic vacuum arc technology were also evaluated and analyzed by scanning electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy. The scanning electron microscopy images show that the DLC foils contain hardly droplets through the double 90° filters. The X-ray photoelectron spectrum indicates that sp3 bonds of the DLC foils exceed 70%. The integral intensity ratio of the D peak to the G peak (ID/IG) measured by the Raman spectroscopy is0.78.

The feasibility of isobaric suppression of 26Mg via post-accelerator foil stripping for the measurement of 26Al

Most accelerator mass spectrometry measurements of 26Al utilize the Al− ion despite lower source currents compared with AlO− since the stable isobar 26Mg does not form elemental negative ions. A gas-filled magnet allows sufficient suppression of 26Mg thus enabling the use of the more intense 26AlO− ion. However, most AMS systems do not include a gas-filled magnet. We therefore explored the feasibility of suppressing 26Mg by using a post-accelerator stripping foil. With this approach, combined with the use of alternative cathode matrices, we were able to suppress 26Mg by a factor of 20. This suppression was insufficient to enable the use of 26AlO−, however further refinement of our system may permit its use in the future.

Improved 36Cl performance at the ASTER HVE 5 MV accelerator mass spectrometer national facility

The HVE 5MV ASTER AMS national facility at CEREGE was accepted in 2007. Since then we have continued to optimize performance for 36Cl. Cl-36 analyses use AgCl, a Cs negative ion sputter source, Ar stripping to +5 in the terminal of the Tandetron™ accelerator at 5MV and a silicon nitride post-acceleration stripper foil to enhance suppression of 36S relative to 36Cl. The major challenges to obtaining the desired performance for Earth science applications are ion source memory, mass fractionation effects, 36S isobar suppression and sensitivity. Redesign of the SO110 ion source by HVE to change the size of the aperture and the shape of cathode significantly reduced ion source memory to less than ∼0.1%, a level that can be compensated for by matching standards to samples. We observe small systematic drifts in 35Cl/37Cl ratios over time, the source of which is not yet determined. Measurement of standards indicates that this effect limits the precision of 35Cl/37Cl ratio determination to about 2%. 36S is suppressed in several ways. First, the sample chemistry has been designed to reduce S to low levels. Second, cathodes are constructed of low-S nickel, enabling direct target loading without the use of AgBr pre-packing. Third, a post-acceleration Si3N4 stripper foil differentially absorbs energy from 36Cl and 36S. A subsequent electrostatic deflector is then able to suppress 36S by a factor of ∼240 relative to 36Cl. Differential energy loss in the detector further suppresses 36S by about 10−4, for an overall suppression factor of 4×10−7. 36S count rates are typically equivalent to a background 36Cl/Cl of ∼10−15. At typical 35Cl currents of ∼20μA Cl5+ samples with 36Cl/35Cl of 6×10−14 can be measured to ±5% statistical uncertainty with 1h of analysis time. Typical machine blanks have 36Cl/Cl ∼2×10−15.

A first attempt to measure 92Nb/93Nb ratios with Accelerator Mass Spectrometry

An Accelerator Mass Spectrometry (AMS) method for the measurement of the long-lived radionuclide 92Nb has been established at the HI-13 Tandem Accelerator of the China Institute of Atomic Energy (CIAE). Niobium powder mixed with PbF2 by a ratio of 1:2 (in mass) was used as the cathode material. Atomic anions of Nb− were extracted from a Cs-beam sputter source. The terminal voltage of the tandem accelerator was 8.5MV. Nb13+ ions were selected after terminal foil stripping. A multi-anode gas ionization chamber was used for the particle detection. The total suppression factor of the two major interfering isobars, 92Zr and 92Mo, was about 103. A detection limit of about 10−11 was achieved for 92Nb/93Nb ratio measurements on a blank sample.

Graphene stripper foils

Thin carbon and metal foils have been used in heavy ion accelerators for charge stripping. The power dissipated by a particle beam in a foil can be as high as 3 kW or greater, which results in short lifetimes of conventional stripper foils. Graphene stripper foils can overcome critical limitations of other materials due to a unique combination of their exceptional physical properties. The authors have fabricated graphene foils with diameters up to 13 cm and area densities of 0.1 to 3.0 mg/cm2 by reduction of graphene oxide in an aqueous dispersion followed by pressure filtration. The foils were characterized by a number of analytical techniques, including scanning electron microscopy, thermogravimetric analysis, and x-ray photoelectron spectroscopy, and proved their superior mechanical and thermal properties. Preliminary ion beam tests showed that the graphene stripper foils possess up to four times longer lifetime, as opposed to conventional carbon foils.

Study of Total Detection Efficiency (η) of Charge Exchange Analyzer (CXA) in TVD Tokamak

Diagnostic devices detection efficiency consist of many parameters. Contribution of each part in main detection efficiency need to study all aspect of devices and experimentally researches. In this paper experimental results and theoretical study merged to figure out the total detection efficiency of CXA. Most important primary parameters has been recognized (stripping foil thickness, incident energy, etc.) and effect of these parameters in related part studied. For CXA of TVD tokamak total detection efficiency presented and shown for 3 keV this parameter equal to .09 and stripping efficiency is equal 1.1 approximately. Choosing appropriate system for stripping of neutral beam is the most important factor in CXA diagnostic devices specially for high energy beams.