Carbon Foils Research Articles

High-resolution study of x-rays emitted from highly charged S ions using a bent-crystal spectrometer

We have measured the projectile x-rays from 56 MeV sulphur ions in collision with thin carbon foils using a high-resolution bent-crystal spectrometer. The resolution of the spectrometer is good enough to resolve lines arising from transitions in H-, He- and Li-like ions. The line energies are compared with values from the NIST x-ray database. The data have also been used to generate the approximate equilibrium charge state distribution, which is compared with semi-empirical model predictions.

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.

Tilted foils polarization at REX-ISOLDE

The tilted-foils nuclear-spin polarization method has been evaluated using the REX-ISOLDE linear accelerator at the ISOLDE facility, CERN. A beam of 8Li delivered with an energy of 300keV/u traversed through one Mylar foil to degrade the beam energy to 200keV/u and consequently through 10 thin diamond-like carbon foils to polarize the nuclear spin. The attained nuclear spin polarization of 3.6±0.3% was measured with a β-NMR setup.

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.

Ultra-thin polymer foils for laser-ion acceleration

We report on the development of new materials for laser-ion acceleration applicable for the advanced mechanism of radiation-pressure-acceleration. These targets are ultra-thin with thicknesses of just a few nm. For several years, diamond-like carbon foils in this thickness range can be produced. An alternative material containing more than one ion-species has the potential to further improve the acceleration mechanism. The fabrication and characterization of self-supporting polymer-based targets will be described in this paper. Furthermore, we show the significant influence on a radiation-pressure induced acceleration process by experimental data.

On the small divergence of laser-driven ion beams from nanometer thick foils

We report on experimental studies of divergence of proton beams from nanometer thick diamond-like carbon foils irradiated by a linearly polarized intense laser with high contrast. Proton beams with extremely small divergence (half angle) of 2° are observed in addition with a remarkably well-collimated feature over the whole energy range, showing one order of magnitude reduction of the divergence angle in comparison to the results from μm thick targets. Similar features are reproduced in two-dimensional particle-in-cell simulations with parameters representing our experiments, indicating a strong influence from the electron density distribution on the divergence of protons. Our comprehensive experimental study reveals grand opportunities for using nm foils in experiments that require high ion flux and small divergence.

Positron annihilation lifetime spectroscopy based on secondary electron emission from carbon foil

Using the emission of secondary electron (SE) from a thin carbon foil in transmission geometry guided by a strong radial electric field in the region between the foil and the sample under investigation, a new variable energy positron annihilation lifetime spectroscopy (PALS) system is being implemented. To this end, the SE emission from a carbon foil of 30nm thick has been investigated in transmission geometry. Considerable emission of SE from the foil with peak energy of about 5eV is observed. We have found that both the energy loss and dispersion of the positrons after transmission through the carbon foil are small enough for the proposed positron lifetime-depth profiling PALS system to be realised. These experimental results and the timing simulations of Cai et. al. [1] indicate that the proposed variable PALS based on secondary electrons generated by carbon foil have a high time resolution.

Secondary electron emission from a thin carbon foil induced by H+, He2+ and Li3+ at fixed velocity of 1 MeV/u

The statistical distributions of the number of forward- and backward-emitted secondary electrons (SE’s) from a thin carbon foil have been measured simultaneously in coincidence with foil-transmitted H+, He2+ and Li3+ ions of 1MeV/u in order to examine the forward–backward correlation of the SE emission (refer to as ‘FB correlation’ hereafter). With these projectiles, we have also measured the energy spectrum of SEs emitted from another carbon foil of similar thickness in the direction around 0° with respect to the incident beams. From the emission statistics data, it is found that both of the inclusive forward and backward SE yields divided by the square of the projectile atomic number (Zp) decrease with increasing Zp. This trend is qualitatively consistent with previous works by other authors. On the other hand, it has been certified from the energy spectra that the yields of binary electron scale well with Zp2. As for the FB correlation, the forward- or backward-emitted SE yield decreases gradually with increasing the number of SEs emitted in the opposite directions. This so-called ‘negative FB correlation’ appears to be pronounced for He2+ and Li3+ ions compared with that for H+ ions. Since low energy internal SEs do not contribute to the FB correlation, the observed Zp-dependent FB correlation seems to be consistent with the well Zp2-scaled production of high energy internal SEs and the decrease of the inclusive forward and backward SE yields with respect to this scaling.

Energy Loss and Charge Transfer of Argon in a Laser-Generated Carbon Plasma

This Letter reports on the measurement of the energy loss and the projectile charge states of argon ions at an energy of 4 MeV/u penetrating a fully ionized carbon plasma. The plasma of n(e)≈10(20) cm(-3) and T(e)≈180 eV is created by two laser beams at λ(Las)=532 nm incident from opposite sides on a thin carbon foil. The resulting plasma is spatially homogenous and allows us to record precise experimental data. The data show an increase of a factor of 2 in the stopping power which is in very good agreement with a specifically developed Monte Carlo code, that allows the calculation of the heavy ion beam's charge state distribution and its energy loss in the plasma.

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.

Resonances in the population of circular Rydberg states formed in beam-foil excitation

By directing fast moving 164MeV F2656e12+ ion beam on 90μg/cm2 thick carbon foil we have studied the unresolved decay of short-lived 2p (τ2p≈3.3fs) and long-lived 2s (τ2s≈350.6ps) states of H-like Fe in the time range 1.6×104–9.2×105τ2p, where, τ2p and τ2s are, respectively, radiative lifetimes of the 2p and 2s levels. At such large times four resonances have been observed as the humps riding on the decay curve of the beam-foil-excited 2s state. This unusual behavior is explained as consequence of the sequential cascading of circular Rydberg states (l=n−1) to 2p state, which modifies the time dependent photon intensity, I(t), of the 2p→1s transition from an exponential to hump-like structures for t»τ2p. From the detailed study of the cascading process the relative population of circular Rydberg states is determined. It is observed that certain circular Rydberg states are unexpectedly and profusely populated when fast H-like Fe ions emerge from the back surface of a thin solid foil.

A new differentially pumped plunger device to measure excited-state lifetimes in proton emitting nuclei

A new plunger device has been designed and built to measure the lifetimes of unbound states in exotic nuclei beyond the proton drip-line. The device has been designed to work in both vacuum and dilute-gas environments made possible through the introduction of a low-voltage stepping motor. DPUNS will be used in conjunction with the gas-filled separator RITU and the vacuum separator MARA at the accelerator laboratory of the University of Jyväskylä, Finland, to measure the lifetimes of excited states with low population cross-sections. This is achieved by eliminating the need for a carbon foil to isolate the helium gas of RITU from the beam line thus reducing the background from beam-foil reactions. The inclusion of a high-sampling rate data acquisition card increases further the sensitivity of the device. The plunger will be used to address many key facets of nuclear structure physics with particular emphasis on the effect of deformation on proton emission rates.

Effect of Target Material on Fast-Electron Transport and Resistive Collimation

The effect of target material on fast-electron transport is investigated using a high-intensity (0.7 ps, 10(20) W/cm2) laser pulse irradiated on multilayered solid Al targets with embedded transport (Au, Mo, Al) and tracer (Cu) layers, backed with millimeter-thick carbon foils to minimize refluxing. We consistently observed a more collimated electron beam (36% average reduction in fast-electron induced Cu Kα spot size) using a high- or mid-Z (Au or Mo) layer compared to Al. All targets showed a similar electron flux level in the central spot of the beam. Two-dimensional collisional particle-in-cell simulations showed formation of strong self-generated resistive magnetic fields in targets with a high-Z transport layer that suppressed the fast-electron beam divergence; the consequent magnetic channels guided the fast electrons to a smaller spot, in good agreement with experiments. These findings indicate that fast-electron transport can be controlled by self-generated resistive magnetic fields and may have important implications to fast ignition.

Secondary electron emission from carbon Foils by Ne2+ near Bohr velocity

We have measured secondary electron emission yields in forward and backward directions from the carbon foils with different thicknesses, which are penetrated by Ne2+ ion of an energy from 2 to 25 keV/u. In the experiment, the contributions of projectile potential energy deposition, electronic energy loss and recoil atom to the forward and backward electron emission yields have been studied systematically by changing the projectile ions energy. Results show that the ions potential energy deposition only have the impact on the backward electron emission yield, while the forward and backward electron emission yields increase approximately linearly with the increase of the electron energy loss at the exit and entrance surfaces of the thin film respectively. When the electron energy loss is low, the impact of recoil atoms on the electron emission cannot be neglected.

HITFiL同步加速器剥离注入

A new accelerator dedicated to hadron therapy, the Heavy-Ion Therapy Facility in Lanzhou (HITFiL), is under construction. As the main accelerator of HITFiL, a heavy-ion synchrotron is designed with special attention paid to compact structure, high reliability and low cost. Stripping injection scheme is adopted for the synchrotron, which is more efficient than single-turn injection and less costly than multi-turn injection supported by electron-cooling. Carbon beams are adopted for HITFiL cancer therapy: C5+ ions from an electron cyclotron resonance ion source, are pre-accelerated by a cyclotron, stripped into C6+ ions by a carbon foil located in a main dipole of the ring and injected into the central orbit of the ring at the same time. The detailed injection scheme for the synchrotron is presented, and the stripping injection process is simulated. The injection efficiency, complete beam loss factors and the particle number gain are investigated. In addition, beam properties including beam distribution in real and phase space and emittance growth due to foil traversal are studied, and the required beam intensity is achieved.

A dedicated decay-spectroscopy station for the collinear resonance ionization experiment at ISOLDE

A new decay-spectroscopy station (DSS) has been developed to be coupled to the collinear resonance ionization spectroscopy (CRIS) beam line at CERN-ISOLDE. The system uses a rotatable wheel with ten 20μg/cm2 carbon foils as beam implantation sites for the efficient measurement of charged decay products. Silicon detectors are placed on either side of the carbon foil in an optimal geometry to cover a large solid angle for detecting these charged particles. In addition to the silicon detectors at the on-beam axis position, a second pair of off-beam axis detectors are placed at the wheel position 108° away, allowing longer-lived species to be studied. Up to three high purity germanium detectors can be placed around the chamber for particle-gamma correlated measurement. The radioactive beam is transported through the CRIS beam line before implantation into a carbon foil at the DSS. All materials used in the DSS are UHV-compatible to maintain high vacuum conditions required by the CRIS beam line. This paper describes the DSS and presents the first data collected at the setup during the commissioning run with 221Fr.

Radiative resonant energy transfer process in projectile-like ion formed in beam-foil interaction

The formation of projectile-like M2555n ion during bombardment of a thin carbon foil by V12+2351 ion beam of energies above the Coulomb barrier is inferred through the observation of unresolved 1s2pP2o3→1s2S01 and 1s2pP0o3→1s2S01 transitions of He-like Mn at 6.14keV. From the decay of intensity of this line the measured radiative lifetime of the upper state is found to be 78.7±11.6ps which is close to the theoretical lifetime of the 1s2pP0o3 state (86.18ps), but substantially lower than that of 1s2pP2o3 state (147.1ps). This suggests that the 1s2pP0o3 state is populated more than the 1s2pP2o3 state when He-like Mn exits the carbon foil. This behavior is explained on the basis of radiative resonant energy transfer process in beam-foil excitation as reported recently (Nandi T, et al. J Quant Spectrosc Radiat Transfer 2012;113:783–8).

2D radiation-hydrodynamics modeling of laser-plasma targets for ion stopping measurements

Two-dimensional radiation hydrodynamics calculations were performed to analyze how a homogeneous plasma layer for ion-stopping measurements can be created by direct laser irradiation of thin carbon foils. At the initial stage, the assumed (so as to imitate the discussed experimental conditions) strongly non-uniform intensity distribution in the laser spot leads to the formation of relatively dense and cold clumps in the plasma. However, it is shown that after several nanoseconds the clumpy structure dissipates predominantly due to the energy transport by thermal radiation. Laser irradiation schemes with the fundamental and doubled frequency light, as well as one- and two-sided heating of the target foil are analyzed and compared. We find that the two-sided irradiation with the doubled laser frequency creates a fully ionized plasma layer and allows to reduce the plasma column-density variations to a level of ≲1%.

Vacuum silicon photomultipliers: Recent developments

VSiPMT (Vacuum Silicon PhotoMultiplier Tube) is an innovative design for a modern hybrid, high gain, silicon based photodetector based on the combination of a SiPM with a hemispherical vacuum glass PMT standard envelope. In such a device photoelectrons emitted by the photocathode are accelerated and focused by an electric field towards a small focal area covered by the SiPM which therefore acts as an amplifier, thus substituting the classical dynode chain of a PMT.With a view to the realization of a first prototype of VSiPMT our group is carrying out a preliminary work aimed at the study of SiPM performances as an electron detector, including an accurate Geant4-based simulation of the interaction between SiPM and electron beams. In order to perform a full characterization of the SiPM we developed an experimental setup for the extraction and the acceleration of a beam of backward secondary electrons emitted after the bombardment of a carbon foil by a proton beam extracted in a TTT-3 accelerator.