Thin Carbon Foils Research Articles

Thin carbon foil resistance to differential pressure

Thin carbon foils are used in different environments for various purposes. For example, they are used in vacuum technology to create a barrier between two volumes, in space plasma instrumentation to detect the crossing of a particle passing through them, or as a stripper of electrons for high energy particles. In the case of a change of pressure on either side of the foil, the pressure differential creates mechanical stresses to the foil that can lead to irreversible damage. Few experiments have characterized the survivability of carbon foils as a function of pressure. In this study, we show measurements of the resistance to pressure of carbon foils (CF) up to partial rupture. The focus is on ultra-thin carbon foils (e.g., 0.5–1.0 μg/cm2) that are typically used in space plasma instrumentation. However, our results can be used in other areas of experimental physics. Our results show that the finer the pitch of the supporting grid, the more pressure resistant the foil is, indicating that the CF support grid is perhaps more important in the design trade than the foil thickness. For example, we find that nominal 1.0 μg/cm2 foils mounted on 13.1 lpmm (333 lines per inch) nickel grids can hold a remarkable static pressure of ∼9 kPa (∼1.3 psi) with almost no damage.

Precision Velocity Measurements of Fission Fragments Using the SPIDER Detector

The SPectrometer for Ion DEtermination in fission Research (SPIDER) measures both position and time-of-flight (TOF) of charged particles using a system of thin carbon foils, electrostatic mirrors, microchannel plates, delay-line anodes, and a fast TDC. Tests have been conducted using 229Th and the alpha emitters in its decay chain. To date, timing resolution of 200 ps (FWHM) has been achieved corresponding to roughly 0.5% uncertainty in velocity measurements of fission fragments over a flight path of 52.1 cm. This velocity resolution, in combination with demonstrated fragment energy resolution is sufficient for 1 amu resolution of light mass fragments.

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.

Electron capture at low velocity in the collision of Ar17+ ions with atoms, clusters and solids

Absolute x-ray emission has been measured when Ar17+ ions at 255 keV collide either with atomic gaseous targets of Ar or N2, with Ar clusters or with thin carbon foils. Preliminary results show a strong decrease of the x-ray signal with the backing pressure of the cluster supersonic jet compared to ion-atom interaction. This effect is a clear signature of slow highly charged ions interacting with clusters. Additionally, high resolution x-ray technique gives us access to the charge state distribution of the emitting ions.

Forward–backward correlated secondary-electron emission depending on the angle of emergence of protons transmitted through a thin carbon foil

The statistical distributions of the secondary electrons (SEs) emitted forward and backward from a thin carbon foil have been measured simultaneously, in coincidence with foil-transmitted protons of 1.0 and 2.5 MeV, as a function of the angle of emergence, θem, of the protons. Irrespective of the incident energy, the measured SE yields increase with increasing angle of emergence in both the forward and the backward directions. As for the forward–backward correlation of the SE emission, the forward- and backward-emitted SE yields induced by 2.5 MeV protons increase gradually with increasing number of SEs emitted in the opposite directions. This positive correlation becomes slightly more pronounced with increasing angle of emergence. On the other hand, for 1.0 MeV, a positive correlation observed at θem = 0 mrad changes to a negative one at θem = 1.0 and 2.0 mrad.

Angular scattering of 1–50 keV ions through graphene and thin carbon foils: Potential applications for space plasma instrumentation

We present experimental results for the angular scattering of ~1-50 keV H, He, C, O, N, Ne, and Ar ions transiting through graphene foils and compare them with scattering through nominal ~0.5 μg cm(-2) carbon foils. Thin carbon foils play a critical role in time-of-flight ion mass spectrometers and energetic neutral atom sensors in space. These instruments take advantage of the charge exchange and secondary electron emission produced as ions or neutral atoms transit these foils. This interaction also produces angular scattering and energy straggling for the incident ion or neutral atom that acts to decrease the performance of a given instrument. Our results show that the angular scattering of ions through graphene is less pronounced than through the state-of-the-art 0.5 μg cm(-2) carbon foils used in space-based particle detectors. At energies less than 50 keV, the scattering angle half width at half maximum, ψ(1/2), for ~3-5 atoms thick graphene is up to a factor of 3.5 smaller than for 0.5 μg cm(-2) (~20 atoms thick) carbon foils. Thus, graphene foils have the potential to improve the performance of space-based plasma instruments for energies below ~50 keV.

Observation of2p3d(1Po)→1s3d(1De)Radiative Transition in He-like Si, S, and Cl Ions

We present an experimental determination of the 2p3d(1Po)→1s3d(1De) x-ray line emitted from He-like Si, S, and Cl projectile ions, excited in collisions with thin carbon foils, using a high-resolution bent-crystal spectrometer. A good agreement between the observation and state-of-the-art relativistic calculations using the multiconfiguration Dirac-Fock formalism including the Breit interaction and QED effects implies the dominance of fluorescent decay over the autoionization process for the 2p3d(^{1}P^{o}) state of He-like heavy ions. This is the first observation of the fluorescence-active doubly excited states in He-like Si, S, and Cl ions.

Time-of-flight detector applied to mass measurements in Rare-RI Ring

A large time-of-flight (TOF) detector has been developed for the Rare-RI Ring. This detector consists of a Multi Channel Plate (MCP) and a carbon foil. Secondary electrons from the carbon foil are transported to the MCP by crossed electric and magnetic fields. In order to cover the beam size of the ring, a large and thin carbon foil (100mm×50mm2 and 60μg/cm2) is used as a sensitive material. The time resolution of σ≈130ps, the detection efficiency about 56% and a position dependence of the TOF about 1ns are obtained. A calculated position dependence of TOF adopting experimental (inhomogeneous) electric field and a homogeneous magnetic field is in agreement with the experimental one. These results suggest that the homogeneity of electric field is important to improve the time resolution in the large size detector.

Feasibility studies of a vibration wire monitor and a halo scraper in the J-PARC L3BT

In the Japan Proton Accelerator Research Complex (J-PARC) 3-GeV rapid cycle synchrotron (RCS), transverse beam halo diagnostics and scraping are required to increase the output beam power. Wire scanners and halo scrapers were used to measure the projected beam distributions to determine the extent of beam halo formation at the linac 3-GeV beam transport line (L3BT). In order to determine more details of halo formation, we installed a vibration wire monitor (VWM) in the L3BT for the beam halo measurement. The high sensitivity of the VWM makes it a prospective tool for investigating the beam halo and weak beam scanning. Also, we developed a new vertical scraper system with a thin carbon foil to collimate the beam halo in the L3BT. In this paper, we will report a preliminary result for the beam-halo measurement by using a VWM and a halo scraper at the L3BT, and we will discuss the potential of the VWM for beam-halo diagnostics.

Single-photon emission correlated to double-electron capture by bare ions: background processes

Radiative single- and double-electron capture are one-step processes where a single target electron or two target electrons, respectively, are captured to a bound state of a highly charged projectile with the simultaneous emission of a single photon. In ion–atom collisions, several background processes are likely to contribute to these processes and may interfere with the measured x-rays due to radiative single and double capture. In this study, possible contributions from radiative electron capture to the continuum, secondary electron bremsstrahlung, the two-step process of independent double radiative electron capture, as well as radiative- combined with nonradiative-electron capture are taken into account based on our analysis of the data for 2.21 MeV u−1 F9+ ions colliding with a thin carbon foil.

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.

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.

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.

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%.

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.

Correlated forward-backward electron emission from a thin carbon foil induced by frozen-charged and charge-changed hydrogen penetration

Using 2.5–3.5 MeV H0 and H+ beams penetrating a thin carbon foil, the two-dimensional probabilities of the secondary electron (SE) emission have been investigated as a function of the number of SEs emitted simultaneously in the forward and backward directions. Depending on the charge state of the projectiles in the foil, these probabilities exhibit quite different distributions. The observed difference between the H0 and H+ penetration can be reproduced quite well by a Monte Carlo simulation assuming the frozen charge state of the projectiles in the foil. Furthermore, another simulation elucidates that a small amount for example only 1% of charge-changed H0 projectiles change the forward–backward correlation of the SE emission significantly from that induced by frozen-charged ones.

Bi-Directional Ion Emission from Massive Gold Cluster Impacts on Nanometric Carbon Foils.

Carbon cluster emission from thin carbon foils (5-40 nm) impacted by individual Au(n) (+q) cluster projectiles (95-125 qkeV, n/q = 3-200) reveals features regarding the energy deposition, projectile range, and projectile fate in matter as a function of the projectile characteristics. For the first time, the secondary ion emission from thin foils has been monitored simultaneously in both forward and backward emission directions. The projectile range and depth of emission were examined as a function of projectile size, energy, and target thickness. A key finding is that the massive cluster impact develops very differently from that of a small polyatomic projectile. The range of the 125 qkeV Au(100q) (+q) (q ≈ 4) projectile is estimated to be 20 nm (well beyond the range of an equal velocity Au(+)) and projectile disintegration occurs at the exit of even a 5 nm thick foil.