Carbon Stripper Foils Research Articles

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.

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.

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).

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.

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.

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.

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.

Measurement of carbon sputtering yield by N + ion beam and lifetime dependence of resulting foils on thickness

Carbon stripper foils with a higher nitrogen content were made by ion beam sputtering with reactive nitrogen gas. Such foils seem to be very useful as strippers for high-intensity heavy ion accelerators. To know further characteristics of the lifetime of such carbon foils, we have measured the sputtering yield of the carbon source material at a sputtering voltage of 4–15 kV and the lifetime dependence of such foils on thickness. Lifetime measurement was performed with a 3.2 MeV Ne + ion beam. The sputtering yield on average showed 0.75 atoms/ion at over 9 kV sputtering voltage. The lifetime of the foils noticeably depends on the foil thickness, and the thickness range as practical stripper foil is to be around 15 to 33 μg/cm 2. Two foils made at 13 kV showed extremely long lifetimes of 6800 and 6000 mC/cm 2 at maximum and the foils made above 10 kV lived longer than about 900 mC/cm 2, which correspond to about 270 and 40 times longer than commercially available best foils. We measured the thickness ratio of nitrogen to carbon in each foil made at the different sputtering voltages and at the different irradiation stages (mC/cm 2) by RBS method. We also inspected the structure of a nitrided carbon foil by transmission electron microscopy.

Lifetime improvement of slackened thin cluster carbon stripper foils by suppression of carbon buildup

We control the amount of carbon buildup on slackened thin cluster carbon stripper foils (less than 3.5 μg/cm 2) by heating with a high-power infrared lamp during beam bombardment. Foil lifetime measurements were performed using 2.0±0.5 μA beams of 3.2 MeV Ne + ions and quantified as the total charge/area before breakage. Lifetimes were obtained up to 1286 mC/cm 2 at maximum and 1139 mC/cm 2 on the average; these values are, respectively, approximately 51 times at maximum and 46 times on average greater than the best commercially available foils, when used unheated and unslackened.

New methods for testing cyclotron carbon stripper foils

Carbon foils are used in cyclotrons and other accelerators to strip electrons from fast ions, enabling the extraction or further acceleration of those ions. Lifetimes of stripper foils (extractor foils) need to be as long as possible to maximize the efficiency of accelerator use and minimize radiation exposure of maintenance personnel. A foil's useful lifetime is determined in part by operating temperatures, manufacturing method, and mounting method. We used two methods to test foils in a simulated accelerator environment. These methods involve the heating in vacuum to temperature ranges 500–1750 and 500–4000 K. Either kind of testing can be done in a few minutes instead of the days or weeks typically needed in a cyclotron. Such tests show clearly that foils manufactured by different methods have different responses to elevated temperatures. Because of this fact, optimum mounting techniques depend on the foil type. Results to date are summarized.

Mounting stripper foils on forks for maximum lifetime

While research and development continue to produce forms of carbon for longer lasting stripper foils, relatively little attention has been paid to other factors that affect their survival in use. It becomes apparent that the form of carbon is only part of the issue. Specific mounting methods increase the lifetimes of carbon stripper foils. These methods are determined in part by the specific use and carbon type for a foil. With careful handling, appropriate adhesive, and slack mounting, premature breakage can be avoided. Foil lifetimes are then primarily affected by less easily controlled factors such as high-temperature expansion, shrinkage and evaporation.

Comparison of carbon and corrugated diamond stripper foils under operational conditions at the Los Alamos PSR

To accumulate high-intensity proton pulses, the Los Alamos Proton Storage Ring (PSR) uses the charge-exchange injection method. H − ions merge with already circulating protons in a bending magnet, and then are stripped off their two electrons in a carbon stripper foil. The circulating protons continue to interact with the foil. Despite efforts to minimize the number of these foil hits, like “painting” of the vertical phase space, they cannot totally be eliminated. As a result, foil heating and probably also radiation damage limit the lifetime of these foils. In recent years, LANL has collaborated with KEK to improve the carbon foils in use at PSR, and these foils now last typically for about 2 months. Recently, an alternative in the form of corrugated diamond foils has been proposed for use at SNS. These foils have now been tested in PSR production for a year, and have already shown to be at least as enduring as the LANL/KEK carbon foils. Advantages of the diamond foil concept, as well as some noteworthy differences that we observed with respect to the LANL carbon foils, will be discussed here.

Polymer coating method developed for carbon stripper foils

The problem of handling the fragile carbon foils (mounting on the frame, placing in the stripper changer) that easily break when self-supporting has been solved by coating carbon foils with poly-monochloro- para-xylylene. It was found that the polymer-coating method could also be used to produce carbon foils thicker than 100 μg/cm 2 by alternated deposition of carbon and poly-monochloro- para-xylylene layers. Carbon foil of 500 μg/cm 2 thick and 10 cm in diameter was produced by this method and mounted to a foil holder. Results of lifetime measurement for singly coated foils are also presented.

Carbon stripper foils held in place with carbon fibers

The Spallation Neutron Source (SNS) currently under construction at Oak Ridge National Laboratory, Oak Ridge, Tennessee, is planned to initially utilize carbon stripper foils having areal densities approximately 260 μg/cm 2. The projected design requires that each foil be supported by only one fixed edge. For stability of the foil, additional support is to be provided by carbon fibers. The feasibility of manufacturing and shipping such mounted carbon foils produced by arc evaporation was studied using two prototypes. Production of the foils is described. Fibers were chosen for satisfactory mechanical strength consistent with minimal interference with the SNS beam. Mounting of the fibers, and packaging of the assemblies for shipping are described. Ten completed assemblies were shipped to SNS for further testing. Preliminary evaluation of the survivability of the foils in the SNS foil changer is described.

Strip injection for carbon ion synchrotrons

Requirements and effects of strip injection of C(4+) at 6 MeV/u into carbon ion synchrotrons are studied. The setup is composed of three chicane dipoles, one Lambertson septum, and one carbon stripping foil at a thickness of 60 microg/cm(2). The required length of the injection section is about 4.1 m. The emittance growth due to multiple Coulomb scatterings is studied.

Fabrication of Boron-Mixed Carbon Stripper and Target Backing Foils for High-Power Accelerators

We have succeeded, for the first time, in making long-lifetime boron-mixed carbon stripper foils for high-power accelerators. Foils of 10–1000 µg/cm2 thickness were made by controlled DC arc discharge. The lifetime of the foils was tested using 3.2 MeV Ne+ DC beams of 2.5 µA, by which a significant amount of energy was deposited in the foils. The maximum lifetime was found to be extremely long, 110 and 450 times longer than those of diamond and commercially available carbon foils, respectively. The foils turned out to be free from any shrinkage, and showed an extremely low thickness reduction rate, even at a high temperature of 1800 K.

Development of thick hybrid-type carbon stripper foils with high durability at 1800 K for RCS of J-PARC

The Japan-Proton Accelerator Research Complexes (J-PARC) requires thick carbon stripper foils (250–500 μg/cm 2) to strip electrons from the H − beam supplied by the linac before injection into the Rapid Cycling Synchrotron (RCS). The 200 MeV H − beam from the linac has a pulse length of 0.5 ms with a repetition rate of 25 Hz and an average beam current of 335 μA. For this high-energy and high-intensity beam, conventional carbon stripper foils will break in a very short time and even a diamond foil will be ruptured at around 1800 K by the MW class accelerator. Thus, thick carbon stripper foils with high durability at 1800 K produced by energy deposition in the foil are indispensable for this accelerator. For this purpose, we have been developing carbon stripper foils of 350 μg/cm 2 by means of both the controlled DC and AC/DC arc-discharge methods. Recently, we have successfully developed hybrid type thick boron-doped carbon stripper foils, which showed a drastic improvement not only with respect to the lifetime, but also with respect to thickness reduction and shrinkage at high temperature during long beam irradiation. In this report the preparation procedure and lifetime measurements with a 3.2 MeV, Ne + beam are presented.

Production of carbon stripper foils for high-power cyclotrons

TRIUMF, Canada's National Laboratory for Particle and Nuclear Physics operates three industrial negative ion cyclotrons for commercial radioisotope production. Two of these cyclotrons (TR30 and TR30-2) can deliver 30 MeV protons at beam currents in excess of 1000 μA and are designed for optional dual beam extraction and continuous operation. High-power negative ion accelerators use stripper foils as thick as 500 μg/cm 2. It has been found that very smooth films with nanocrystalline microstructure perform the best in high-current applications. However, high-quality thick foils with good uniformity are difficult to manufacture. To meet our specific requirements, we have developed a carbon arc deposition system capable of producing durable, homogeneous carbon stripper foils. In this paper, we report on the fabrication of carbon foils with a thickness of 100–200 μg/cm 2. The manufacturing equipment capable of producing ∼600 cm 2 of foil in a single run and the process details are described. Properties of these foils and their performance in the cyclotron are discussed.