Carbon Foil Targets Research Articles

Characteristics of laminar ion beams accelerated via a few-joule laser pulse

Laser-driven carbon ion beams from a carbon foil target via a 2.5-J laser pulse are investigated with three-dimensional particle-in-cell simulations. An ion bunch with a narrow energy range exhibits a thin shell shape with a certain diameter. The ion cloud has a layered structure of these ion bunches with different energies. The divergences of the ion bunch in the laser inclination direction and perpendicular to it are different in an oblique incidence laser. In addition, theoretical formulas for the radius of the generated ion beam and the energy spectrum are derived, and they are shown to be in good agreement with the simulation results.

Study of the laser-plasma acceleration of ion beams with enhanced quality: The effects of nanostructured targets

Production of high-quality ion beams by intense laser–plasma interactions represents a rapidly evolving field of interest. In this paper, a nanostructured target is proposed to generate laser-driven quasi-monoenergetic ion beams with considerably reduced energy spread and enhanced peak energy. Linearly polarized, 40-fs laser pulses of intensity 8.5 × 1020 W cm−2 were considered to irradiate simple carbon foil and nanostructured targets. The proposed target consists of a thin layer of relatively high-Z atom (Ti) with a depression on its back surface which is filled by a nanosize disc of a low-Z atom (C). Reliable and reproducible results of multi-parametric Particle-in-Cell simulations show that by using a composed nanostructured target with optimum physical properties, a quasi-monoenergetic ion beam can be generated with a narrow band energy spectrum peaking at energies higher than 20 MeV. In addition, the forward-accelerated beam of low-Z carbon ions exhibits a considerably reduced transverse emittance in comparison with the ion beam obtained in the condition of a simple foil. The proposed nanostructured target can efficiently contribute to the generation of high-quality ion beams which are critical in newly growing applications and physics of laser-plasma accelerators.

Kinetic-energy transfer in highly-charged-ion collisions with carbon

We present an accurate theoretical model for the charge dependence of kinetic energy transferred in collisions between slow highly charged ions (HCIs) and the atoms in a carbon solid. The model is in excellent agreement with experimental kinetic-energy-loss data for carbon nanomembrane and thin carbon foil targets. This study fills a notable gap in the literature of charged-particle energy loss in the regime of low incident velocity (${v}_{p}\ensuremath{\lesssim}2.188\ifmmode\times\else\texttimes\fi{}{10}^{6}$ m/s) where charge states greatly exceed the equilibrium values.

Toward preciseQECvalues for the superallowed0+→0+βdecays ofT=2nuclides: The masses ofNa20,Al24,P28, andCl32

High-precision measurements of superallowed ${0}^{+}\ensuremath{\rightarrow}{0}^{+}$ $\ensuremath{\beta}$ decays of $T=2$ nuclides such as $^{20}\mathrm{Mg}$, $^{24}\mathrm{Si}$, $^{28}\mathrm{S}$, and $^{32}\mathrm{Ar}$ can contribute to searches for physics beyond the standard model of particle physics if the ${Q}_{\mathrm{EC}}$ values are accurate to a few keV or better. As a step toward providing precise ${Q}_{\mathrm{EC}}$ values for these decays, the ground-state masses of the respective daughter nuclei $^{20}\mathrm{Na}$, $^{24}\mathrm{Al}$, $^{28}\mathrm{P}$, and $^{32}\mathrm{Cl}$ have been determined by measuring the ($^{3}\mathrm{He},t$) reactions leading to them with the $^{36}\mathrm{Ar}$($^{3}\mathrm{He},t$)$^{36}\mathrm{K}$ reaction as a calibration. A quadrupole-dipole-dipole-dipole (Q3D) magnetic spectrograph was used together with thin ion-implanted carbon-foil targets of $^{20}\mathrm{Ne}$, $^{24}\mathrm{Mg}$, $^{28}\mathrm{Si}$, $^{32}\mathrm{S}$, and $^{36}\mathrm{Ar}$. The masses of $^{20}\mathrm{Na}$ and $^{32}\mathrm{Cl}$ are found to be in good agreement with the values from the 2003 Atomic Mass Evaluation (AME03) [G. Audi, A. H. Wapstra, and C. Thibault, Nucl. Phys. A 729, 337 (2003)], and the precision has been improved by a factor of 6 in both cases. The masses of $^{24}\mathrm{Al}$ and $^{28}\mathrm{P}$ are found to be higher than the values from AME03 by 9.5 keV ($3.2\ensuremath{\sigma}$) and 11.5 keV ($3.6\ensuremath{\sigma}$), respectively, and the precision has been improved by a factor of 2.5 in both cases. The new $^{32}\mathrm{Cl}$ mass is used together with the excitation energy of its lowest $T=2$ level and the mass of $^{32}\mathrm{Ar}$ to derive an improved superallowed ${Q}_{\mathrm{EC}}$ value of 6087.3(22) keV for this case. The effects on quantities related to standard-model tests including the $\ensuremath{\beta}$-$\ensuremath{\nu}$ correlation coefficient $a$ and the isospin-symmetry-breaking correction ${\ensuremath{\delta}}_{C}$ are examined for the $A=32$ case.

Energy dependence of Xe ion lines produced by beam-foil interaction

Xenon ions are present in stellar atmospheres and in astrophysically interesting plasmas on the ground. Atomic spectra of xenon ions induced by the beam-foil interaction have been recorded in the far-ultraviolet region between 30 and 120 nm. From the relative intensities of Xe II to Xe IX lines that appear in our spectra, we have deduced the first experimental charge state distribution of xenon ions at the exit of a carbon foil target for energies ranging from 0.2 to 1.9 MeV. Our results differ from the predictions of different theoretical models and indicate that xenon is two times easier to ionize than what was predicted by existing models.

Time-resolved measurement of energy loss of low-energy heavy ions in a plasma using a surface-barrier charged-particle detector

We tested an experimental setup for measurement of non-linear stopping of low-energy heavy ions in non-ideal plasmas. In this setup, we used a silicon surface-barrier charged-particle detector (SSBD), which could measure the energy of single ions. For synchronization between the plasma production and the injection of single projectiles, a fast beam kicker was installed in front of the plasma target. In order to test this setup, we used a laser-produced polyethylene plasma target instead of a shock-driven plasma device, which is under R&D process. Results of a preliminary energy loss measurement for low-speed heavy ions in the laser plasma are reported. Performance on the time resolution evaluated by using a carbon-foil target is also presented.

Experimental apparatus for the measurement of non-linear stopping of low-energy heavy ions

We developed an experimental apparatus for the study of non-linear stopping of low-energy heavy ions in non-ideal plasmas. The target plasma was produced by an electromagnetically driven shock tube. A pair of 50- μ m -diameter beam apertures was attached to the shock tube wall. These apertures confined hydrogen gas of ≈ 5 Torr in the tube and sustained the pressure difference ( ∼ 10 5 – 10 6 ) between the tube and the beam line. In order to measure the energy loss in the plasma in the tube, we used a semiconductor charged-particle detector, which could directly measure the kinetic energy of single particles, since the beam transmission through these apertures was very small. To synchronize the plasma production in the shock tube and the injection of projectiles, a fast beam kicker was installed in front of the plasma target. Results of preliminary experiments using thin carbon foil targets showed that the measured energy loss of single projectiles after passing through the target was in agreement with other data. The time resolution of the energy-loss measurement system was ≈ 150 ns , which is enough to measure the projectile energy loss during the life time of the target plasma.

1s2s2p23p 6L–1s2p33p 6P transitions in O IV, F V and Ne VI

We present observations of VUV transitions between doubly excited sextet states in O IV, F V and Ne VI. Spectra were produced by collisions of an O+, (FH)+ and Ne+ beam with a thin carbon foil target. Some observed lines are assigned to the 1s2s2p23p 6L–1s2p33p 6P electric-dipole transitions in O IV, F V and Ne VI, and are compared with the results of multi-configuration Hartree–Fock (with QED and higher-order corrections) and multi-configuration Dirac–Fock calculations. 31 new lines have been identified. The sextet systems of boronlike ions are possible candidates for x-ray and VUV lasers.

Quantum and classical stopping cross-sections of swift heavy ions derived from the evolution with time of the Wigner function

The charge dependent stopping cross-section of partially ionized heavy ions in a carbon target is determined in the energy range of a few MeV/n. It is done by calculating during an ion–atom collision the classical evolution of the Wigner function of the target electrons. A special emphasis in our calculations is put on the contribution of the 1s electrons for which we analyze the influence of the overlapping domain, concerning the impact parameter, of the charge transfer and energy loss processes. We give a detail comparison with the experimental results provided by Blazevic of 2 MeV/n neon ions interacting with a thin carbon foil target.

Electron ejection from solids by heavy ions at high energies (1–100 MeV/u)

Results on electron emission from solids bombarded with swift heavy ions at high energies (from about 1 up to 100 MeV/u) are presented. Three different topics are discussed: (1) The ejection of high energy binary encounter electrons induced by argon ions. (2) Electron yields from thin carbon foil targets. (3) First results on high charge effects in low energy electron spectra from sputter cleaned carbon and the influence of controlled contamination by exposure to nitrogen.

Asymmetries between the production of D− and D+ mesons from 500 GeV/c π− nucleon interaction as functions of x and p2

This paper presents measurements of the production of Ds- mesons relative to Ds+ mesons as functions of x_F and square of p_t for a sample of 2445 Ds decays to phi pi. The Ds mesons were produced in Fermilab experiment E791 with 500 GeV/c pi- mesons incident on one platinum and four carbon foil targets. The acceptance-corrected integrated asymmetry in the x_F range -0.1 to 0.5 for Ds+- mesons is 0.032 +- 0.022 +- 0.022, consistent with no net asymmetry. The results, as functions of x_F and square of p_t, are compared to predictions and to the large production asymmetry observed for D+- mesons in the same experiment. These comparisons support the hypothesis that production asymmetries come from the fragmentation process and not from the charm quark production itself.

Doubly differential secondary-electron yields following 8-MeV/uU68+- and 3.5-MeV/uU38+-ion impact on a thin carbon-foil target

Doubly differential secondary-electron yields following the impact of 8-MeV/u ${\mathrm{U}}^{68+}$ and 3.5-MeV/u ${\mathrm{U}}^{38+}$ ions on 44-\ensuremath{\mu}g/${\mathrm{cm}}^{2}$ carbon-foil targets have been investigated experimentally. Electron emission yields were determined for ejection angles varied between 0\ifmmode^\circ\else\textdegree\fi{} and 157\ifmmode^\circ\else\textdegree\fi{} and electron energies ranging from 10 eV to 8 keV. The experimental data are compared to results from a theoretical model for production and transport of fast electrons in solids.

Dynamical behaviour of angular momentum distributions of autoionizing 1s 22p9 l states of S 12+ ions excited through carbon foils

Coster-Kronig electrons from the autoionizing 1s 22p9 l Rydberg state of sulfur ions have been oberved in the beam direction. Angular momentum ( l) distributions of the Rydberg state produced through collisions of 2 MeV/u S 6+, S 12+, S 13+ and S 14+ projectiles with carbon foil targets of various thicknesses (1.2–9.6 μg/cm 2) were obtained. It is found that l-distributions change with the target foil thickness. A characteristic relaxation time to reach equilibrium in l-distributions in a carbon foil is estimated to be ∼ 10 −15 s for S 12+ injection.

Secondary electron emission in antiproton—carbon-foil collisions

Energy spectra of electrons emitted in the forward direction by antiproton and proton bombardments on carbon foil targets were measured in the incident energy region from 500 to 750 keV. In the spectra for antiproton impact, no sharp anticusp, which is expected in place of the cusp in the case of the proton impact, is recognized and a small bump is found at 50 eV below the cusp energy. The spectral profile in the equivelocity region, including smearing out of the anticusp, together with the energy and intensity of the bump, is consistent with a theoretical prediction for wake-riding electrons based on the classical trajectory Monte Carlo method.

Investigation of delta -electron emission in collisions of highly charged fast Ne projectiles with carbon-foil targets.

The angle and energy dependence of electron emission following the interaction of 70--170-MeV ${\mathrm{Ne}}^{\mathit{q}+}$ (q=7,10) projectiles with 20 and 100 \ensuremath{\mu}g/${\mathrm{cm}}^{2}$ carbon foils has been investigated experimentally. Absolute emission yields were determined for ejection angles ranging from 0\ifmmode^\circ\else\textdegree\fi{} to 180\ifmmode^\circ\else\textdegree\fi{} and electron energies from 10 eV to 6 keV for normal-incidence ion beams. The experimental \ensuremath{\delta}-electron spectra are compared to results from a newly developed theoretical model based on a separation of energy loss and angular scattering for secondary electrons.

Field ionization and quantum interferences of Rydberg levels in fast heavy ions.

Rydberg states in highly stripped fast oxygen and neon ions are formed in the interaction with thin carbon foil and gas targets. They are ionized in the field of an electrostatic parallel-plate spectrometer and produce pronounced structures in the electron energy spectra at apparent energies higher than the cusp peak. The measured electron yield shows marked oscillatory structures in the dependence of the strength of an additional weak electric field in the drift space between target and spectrometer. Fourier analysis of the data reveals the presence of an asymmetric band of fundamental frequencies and contributions from higher harmonics. The oscillations are interpreted in terms of quantum interferences among Stark states which coherently develop in the weak drift-space field. A predominant influence of the experimental arrangement on the shape and the position of the Rydberg structure in the electron spectrum is found through analysis of the data on the basis of a program which calculates the electron trajectories through the fringe fields of the detector. The analysis also reveals that the dependence of the oscillation periods on the detector field strength is influenced by fringe-field effects. The absolute values for the periods and the ionization process in the detector are explainedmore » in the frame of a simple model and conclusions are drawn about the contribution of experiments of the present type in understanding the mechanisms of Rydberg formation.« less

Kinetic energy distribution of ions generated by laser ionization sources

The time of flight (TOF) method has been utilized to measure kinetic energy distributions of ions generated by laser ionization sources. Measurements were carried out on carbon foil targets with pulses from a Q-switched ruby laser in the power density range from 10 6 to 10 10 W cm −2. the onset of plasma formation and appearance of positive and negative energy ions were observed. Interference of neighbouring lines could be resolved by decreasing the light intensity down to the plasma formation threshold. The energy spectrum consisted of a positive energy peak and negative energy tail centered around the ideal symmetrical peak. The appearnace of these characteristics depended on the laser power density applied. The positive energy part of the energy spectrum was related to the shock wave due to laser heating of the foil while the negative energy part could be explained by post-ionization of neutrals in the accelerating region. Shock fitting according to Godunov served as a rough estimate for plasma hydrodynamics, while an optical and charge transfer model as a possible description of the negative part of the energy spectrum were discussed. Encouraging correlations between measured and calculatd data were found.

Effects of external electric fields on high Rydberg states formed in foil and gas interactions of 85-MeV Ne6+ ions.

High Rydberg states in neon ions are formed in interactions of 85-MeV $^{20}\mathrm{Ne}^{6+}$ ions with a thin carbon-foil target and with a helium-gas target. The effect of a weak, transverse, static electric field on the Rydberg states is investigated by measuring the electron yield due to field ionization in the strong electric field of an electron spectrometer. For both targets, marked oscillatory structure is observed in the dependence of the electron yield on the strength of the weak field. The Fourier analysis of the data reveals the dominance of a narrow band of fundamental frequencies in the oscillations and indicates the presence of second-harmonic contributions. The oscillations are interpreted in terms of quantum interferences among Stark states coherently developing in the weak electric field. The relevance of experiments of the present type to the understanding of the mechanisms of Rydberg state formation is discussed.

Absolute excited-state populations of fast carbon ions in solids

The absolute populations of C5+ ions emerging in excited states from carbon foil targets of thicknesses ranging from 10 to 125 atoms.AA2 have been determined for incident beams of 24, 35 and 43 MeV C4+. For a given beam energy the population of 5+ ions emerging in the 2p state was found to follow the total 5+ charge fraction as the foil thickness was increased, suggesting that the cross section for excitation of ground-state electrons was larger than the cross section for electron capture by the bare nucleus. The authors found that in the cases studied, the 2p population formed (17+or-5)% of the total 5+ charge fraction. Populations for other excited states are also reported. The results are consistent with the size of the density effect previously observed in projectile charge-state distributions for the same collision system.

Radiative electron capture in fast ion-atom collisions

Radiative electron capture (REC) has been measured in collisions between 125 MeV sulphur ions and thin carbon-foil targets. Good agreement is found between the experimental cross section and calculations with the impulse approximation and with the strong potential Born theory.