Stripper Foils Research Articles

Modeling multiturn stripping injection and foil heating for high intensity proton drivers

${\mathrm{H}}^{\ensuremath{-}}$ stripping injection into the Fermilab recycler ring, combined with a beam phase painting technique, has been considered. The multiparticle three-dimensional beam dynamics with space charge has been studied numerically, using STRUCT and ORBIT codes, for different painting scenarios. In order to achieve a uniform (quasi-KV) phase-space distribution and to reduce the foil heating, the following parameters were investigated: the number of turns, strengths and temporal forms of kicker magnets, and foil geometry. Performance of the stripping foil is a crucial parameter of the whole injection scheme, so that the latter has been designed to minimize the hit number on the foil. The temperature regime has been evaluated both semianalytically and numerically using Monte Carlo codes MARS and MCNPX, with radiation cooling and transport of $\ensuremath{\delta}$ electrons taken into account. That all results agreed well proves the consistency of the models. It has been shown that the stripping foil can survive during injection with the parameters chosen for Project X at Fermilab.

中国散裂中子源快循环同步加速器主剥离膜设计

中国散裂中子源快循环同步加速器主剥离膜设计

Effect of Incident Energy and Foil Thickness on Foil Stripping and Scattering Efficiency in Charge Exchange Analyzer Detector

Compact neutral particle analyzer (CNPA) is used to measure ion temperature in tokamaks. Calculating of stripping efficiency and scattering efficiency are most important parameters affecting on CNPA performance. We studied the dependent of these parameters with the thickness of carbon foil and incident energy of neutral hydrogen atoms. In low carbon foil thickness variation of the carbon foil stripping efficiency (ηi) and scattering efficiency of the ions (ηsc) with incident energy is very salient. For foil thickness between 200 and 600 angestrom, scattering efficiency of the chamber will be smaller than 0.11.

State of the art online monitoring system for the waste beam in the rapid cycling synchrotron of the Japan Proton Accelerator Research Complex

The 3 GeV rapid cycling synchrotron (RCS) at Japan Proton Accelerator Research Complex is already in user operation stage, delivering a stable and relatively high power beam to the Material and Life Science Experimental Facility as well as to the main ring. RCS utilizes multiturn ${\mathrm{H}}^{\ensuremath{-}}$ charge-exchange injection for which a hybrid-type boron doped carbon stripper foil known as HBC foil with a thickness of around $200\text{ }\text{ }\ensuremath{\mu}\mathrm{g}/{\mathrm{cm}}^{2}$ is used at the present injection beam energy of 181 MeV. It will be changed to $290\text{ }\text{ }\ensuremath{\mu}\mathrm{g}/{\mathrm{cm}}^{2}$ at the near future upgrade and design injection beam energy of 400 MeV. The stripping efficiencies are expected to be 99.6% and 99.7% in the present and the later case, respectively. The remaining 0.4% or 0.3% of the beam is called the waste beam and is transported to the injection beam dump with a capacity of only 4 kW. The full power of the injected beam at 400 MeV is 133 kW, while the waste beam power is calculated to be about 0.4 kW. The raw signal measured by a current transformer placed downstream of the waste beam dump line contains a large noise and it is practically very hard to identify the beam signal. However, a fast Fourier transformation analysis of the raw signal made it possible to clearly identify the beam signal. The power spectrum is calibrated with respect to the known injected beam current. The absolute error of the monitor system is 0.2 mV, which gives the ratio of the waste beam to the injected beam as $(0.38\ifmmode\pm\else\textpm\fi{}0.03)%$. Such an accurate and realtime monitoring system provides quite an efficient method to know the conditions of the stripper foil and the incoming linac beam during the user operation.

Carbon stripper foils for the Australian National University heavy ion accelerator

It is easy to say “Just float and mount the carbon foils“. However learning the art can be more difficult than old masters have shown it to be. In this article we will share our experience of some difficulties we have had at Australian National University (ANU). We also present results from some in beam endurance testing of foils using carbon supplied by Vacuum Technology (Germany), Micromatter (Canada) and those made at the ANU (Australia).

Charge state distribution studies of SrF 3, MnF 3 and CaF 3 molecules using single and double stripping in a Tandem accelerator

High energy beams of high ion currents from a Tandem accelerator are a common requirement in nuclear physics, materials science and Accelerator Mass Spectrometry (AMS) research. In many cases, molecular beams are chosen from the ion source to achieve a high ion source yield for the negative ions, or, as for AMS, to suppress isobaric interference. For this reason we have studied the use of consecutive stripper foils, double stripping, to increase the ion yield in conjunction with increased energy of injected molecular beams through a Tandem accelerator. By this method we could achieve a shift in the yield towards higher charge states.

Recent advances in AMS of 36Cl with a 3-MV-tandem

Accelerator mass spectrometry (AMS) of 36Cl ( t 1/2 = 0.30 Ma) at natural isotopic concentrations requires high particle energies for the separation from the stable isobar 36S and was so far the exclusive domain of tandem accelerators with at least 5 MV terminal voltage. Using terminal foil stripping and a detection setup consisting of a split-anode ionization chamber and an additional energy signal from a silicon strip detector, a 36S suppression of >10 4 at 3 MV terminal voltage was achieved. To further increase the 36S suppression energy loss straggling in various counter gases (C 4H 10, Ar–CH 4 and C 4H 10–Ar) and the effect of “energy focusing” below the maximum of the Bragg curve was investigated. The comparison of experimental data with simulations and published data yielded interesting insights into the physics underlying the detectors. Energy loss, energy straggling and angular scattering determine the 36S suppression. In addition, we improved ion source conditions, target backing materials and the cathode design with respect to sulfur output and cross contamination. These changes allow higher currents during measurement ( 35Cl − current ≈ 5 μA) and also increased the reproducibility. An injector to detector efficiency for 36Cl ions of 8% (16% stripping yield for the 7+ charge state in the accelerator, 50% 36Cl detection efficiency) was achieved, which can favorably be compared to other facilities. The memory effect in our ion source was also thoroughly investigated. Currently our measured blank value is 36Cl/Cl ≈ 3 × 10 −15 when samples with a ratio of 10 −11 are used in the same sample wheel and 36Cl/Cl ≈ 5 × 10 −16 if measured together with samples with a ratio of 10 −12 or below. This is in good agreement with the lowest so far published isotope ratios around 5 × 10 −16 and demonstrates that 3 MV tandems can achieve the same sensitivity for 36Cl as larger machines.

Stripper foil failure modes and cures at the Oak Ridge Spallation Neutron Source

The Oak Ridge Spallation Neutron Source comprises a 1 GeV, 1.5 MW linear accelerator followed by an accumulator ring and a liquid mercury target. To manage the beam loss caused by the ${H}^{0}$ excited states created during the ${H}^{\ensuremath{-}}$ charge-exchange injection into the accumulator ring, the stripper foil is located inside one of the chicane dipoles. This has some interesting consequences that were not fully appreciated until the beam power reached about 840 kW. One consequence was sudden failure of the stripper foil system due to convoy electrons stripped from the incoming ${H}^{\ensuremath{-}}$ beam, which circled around to strike the foil bracket and cause bracket failure. Another consequence is that convoy electrons can reflect back up from the electron catcher and strike the foil and bracket. An additional contributor to foil system failure is vacuum breakdown due to the charge developed on the foil by secondary electron emission. In this paper we detail these and other interesting failure mechanisms and describe the improvements we have made to mitigate them.

Suppression of carbon buildup and lifetime improvement by heating carbon stripper foils

We have successfully developed a new method to reduce the amount of carbon buildup on thin cluster (less than 3.5 μg/cm 2) carbon stripper foils by heating them with infrared radiation during beam bombardment. We studied the carbon buildup and the foil temperature on foil lifetime using a 2.0 ± 0.5 μA beam of 3.2-MeV Ne + ions. It was found that the carbon buildup begins to rapidly suppress at 460 °C; further, at a foil temperature higher than approximately 820 °C, the initial foil thickness did not change until the foil ruptured. We also found that the carbon buildup shortens the lifetime of stripper foils. The foils treated by the newly developed present method could withstand the maximum and average total beam charges of 530 mC/cm 2 and 340 mC/cm 2, respectively, which are approximately 18 and 11 times larger than the values for the best commercially available foils and approximately 3 and 2 times greater than the values for the cluster foils that are not treated by this method.

Laser-assistedH−charge exchange injection in magnetic fields

The use of stripping foils for charge exchange injection can cause a number of operational problems in high intensity hadron accelerators. A recently proposed three-step method of laser-assisted injection is capable of overcoming these problems. This paper presents advances in the physical model of laser-assisted charge exchange injection of ${\mathrm{H}}^{\ensuremath{-}}$ beams and covers a wide field of atomic physics. The model allows the calculation of the evolution of an ${\mathrm{H}}^{0}$ beam taking into account spontaneous emission, field ionization, and external electromagnetic fields. Some new data on the hydrogen atom related to the problem are calculated. The numerical calculations in the model use realistic descriptions of laser field and injection beam. Generally, the model can be used for design and optimization of a laser-assisted injection cell within an accelerator lattice. Example calculations of laser-assisted injection for an intermediate experiment at SNS in Oak Ridge and for the PS2 accelerator at CERN are presented. Two different schemes, distinctively characterized by various magnetic fields at the excitation point, are discussed. It was shown that the emittance growth of an injected beam can be drastically decreased by moving the excitation point into a strong magnetic field.

Measurement of lifetimes of thin carbon stripper foils produced by ion-beam sputtering

Thin carbon stripper foils used in high-intensity proton accelerators and heavy-ion accelerators must have long lifetimes. Thin carbon foils were fabricated by ion-beam sputtering using reactive and inert gas ions. The lifetime of the foils was measured using a KEK 650-keV high-intensity DC H − (negative hydrogen ion) beam; changes in the foil thickness and surface deformations during irradiation were investigated. The lifetime of a typical stripper foil fabricated by heavy-ion-beam (Ar and Kr) sputtering was 60–70 times longer than that of the best commercially available foils. This paper reports a fabrication method for carbon stripper foils, along with an investigation of their lifetimes and changes in foil thickness during beam irradiation.

Influence of carbon material and sputtering angle on stripper foil lifetime

Mixed noble gas (Kr+Ne) was used for ion beam sputtering (MIBS) with the aim to produce stripper foils with long lifetime. Further characteristics of the MIBS method were investigated. Angular thickness distributions were measured for the deposits of three crystalline structures of carbon sputter targets: synthetic diamond, glassy carbon and polycrystalline graphite. In this setup the vertical ion beam hits the horizontal surface of the respective carbon target. Differences are presented for three ion energies. In a second setup the angle of the sputter target relative to the vertical ion beam could be adjusted for preparing carbon deposits with lifetime dependences on the inclination angle α on a glassy carbon surface. Resulting stripper foils were tested for their lifetime depending on sputter material and sputtering angle θ in case of graphite. The lifetime measurements were performed with a 3.2 MeV Ne + ion beam as usual.

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.

Development of carbon foils with a thickness of up to 600 μg/cm 2

Carbon foils are applied as stripper for the heavy-ion accelerator as well as targets in different experiments at GSI. Carbon foils in a thickness range 5–100 μg/cm 2 are routinely produced with good homogeneity and excellent durability. Foils thicker than 100 μg/cm 2 used to be purchased. To overcome problems that emerged and intensified in some applications we started to advance our own carbon production towards higher thickness. We describe the production of carbon foils up to a thickness of 600 μg/cm 2, report on first tests as stripper foils and as targets, and discuss our future plans.

Stripping foils at RHIC

There are two major science programs at the relativistic heavy ion collider (RHIC). These are the heavy ion programs, which collide beams of fully stripped ions, and the polarized proton program. A wide variety of stripper foils and carbon targets are used throughout the RHIC accelerator chain to facilitate these collisions. Each stripper and target has unique properties and functions. Those characteristics will be discussed, as well as recent efforts to improve their performance.

Stripper target lifetime estimations

The problems of stripper target behavior in intense particle beams are considered. The historical sketch on studies of radiation damage failure of carbon targets under ion bombardment is presented. The simple model of target evaporation under intensive pulsing beam is supposed. Lifetimes of stripper targets under intensive nonstationary beams can be described by two failure mechanisms: radiation damage accumulation and evaporation of a target. At maximum temperatures less than 2500 K the radiation damage dominates; at temperatures above 2500 K the mechanism of evaporation of a foil prevails. The proposed approach has been applied to the description of stripper foils behavior in Brookhaven National Laboratory linac and spallation neutron source (SNS) conditions.

Production of stripper foils by laser ablation of carbon–boron sputter targets

The TRIUMF Applied Technology Group operates several high-power industrial cyclotrons for commercial radioisotope production. Two of these accelerators, TR30-1 and TR30-2, can deliver H – beams of 30 MeV and beam currents in excess of 1000 μA. For many years, in-house produced diamond-like carbon (DLC) foils of approximately 2.0–3.0 μm thickness have been utilized to extract proton beams from these accelerators. The TRIUMF Carbon Foil Laboratory uses pulsed laser deposition to manufacture DLC films in a wide thickness range (10 nm to ∼10 μm). It is known that the quality and the composition of the graphite sputter target used in the laser ablation process has a significant effect on the mechanical properties of the deposited film as well as its durability in ion beams. Encouraged by the findings of Sugai et al. [1], we investigated the production of stripper foils by laser ablation of graphite/boron composites as well as multilayer foils using pure graphite and boron targets.

Evaluation of carbon stripper foils produced by a nitrogen ion beam sputtering method

Carbon stripper foils having thicknesses in the range of 5–40 μg/cm2 have been prepared by a nitrogen ion beam sputtering method and their lifetimes have been tested in the Van de Graaff accelerator facility with 3.2 MeV, Ne+ ions. The foils of 21 μg/cm2 thickness had the longest mean lifetime of 1350.0 mC/cm2 (irradiation dose of 8.4×1018 atoms/cm2) which was 50 times longer than that of commercial foils. However, foils with other thicknesses had extremely short lifetimes similar to commercial foils. The nitrogen content of the foils of both long and short lifetimes has been determined using elastic scattering of 3 MeV α-particles.

Study on CYCIAE-100 radiation field and residual radioactivity

The accelerators should be properly designed to make the radiation field produced by beam loss satisfy the dose limits. The radiation field for high intensity H− cyclotron includes prompt radiation and residual radiation field. The induced radioactivity in accelerator components is the dominant source of occupational radiation exposure if the accelerator is well shielded. The source of radiation is the beam loss when cyclotron is operating. In this paper, the radiation field for CYCIAE-100 is calculated using Monte Carlo method and the radioactive contamination near stripping foil is studied. A method to reduce the dose equivalent rate of maintenance staff is also given.

Stripping extraction calculation and simulation for CYCIAE-100

A 100 MeV H- compact cyclotron is under construction at China Institute of Atomic Energy (CYCIAE-100). The proton beams of 75 MeV-100 MeV at an intensity of 200 μA will be extracted in dual opposite directions by charge exchange stripping devices. The crossing point at the switching magnet center is fixed inside the magnet yoke and the stripping points for various extraction energies are calculated by the code CYCTRS. With the code GOBLIN, we can calculate the transfer matrix including the dispersion effects from the stripping point to the switch magnet. The beam distribution just after stripping foil can be obtained from the multi-particle tracking code COMA and the extracted beam parameters after the switch magnet such as emittance, envelope, dispersion, energy spread, bunch length, etc. are given by the extraction orbit simulations.