Foil Targets Research Articles

Numerical investigation for shape controlling of ultrathin electron layer

AbstractTo control the shape of the ultra-thin electron layer produced by directly interaction of ultrahigh contrast laser with ultra-thin foil target, we investigated the spacial distribution and temporal evolution of electron layers produced from single and double foil targets through two-dimensional particle-in-cell simulations. Results show that electron layers produced from double foil targets can fly with unperturbed velocity for a much longer time than in the single foil case, which can be explained by the integrated contribution of charge separation field from both the two foils. Further studies show that through adjusting the foil expansion, electron layers with different shapes can be obtained. Detailed studies on the forming process of layers show that electron momentum distribution evolves rapidly along with the pump laser and then the vanishing of electron transverse momentum induced by the reflected laser results in the forming of layer shape. So different foil expansion corresponds to different moments that reflected laser interact with electron layer, when the electron transverse momentum distribution is different. After the reflected laser interact with electron layer, the resultant longitude momentum distribution will finally lead to various electron layer shapes.

Towards Sub-TeV electron beams driven by ultra-short, ultra-intense laser pulses

AbstractEnergetic electron beam generation from a thin foil target by the ponderomotive force of an ultra-intense circularly polarized laser pulse is investigated. Two-dimensional particle-in-cell (PIC) simulations show that laser pulses with intensity of 1022–1023 Wcm−2 generate about 1–10 GeV electron beams, in agreement with the prediction of one-dimensional theory. When the laser intensity is at 1024–1025 Wcm−2, the beam energy obtained from PIC simulations is lower than the values predicted by the theory. The radiation damping effect is considered, which is found to become important for the laser intensity higher than 1025 Wcm−2. The effect of laser focus positions is also discussed.

Feasibility Study of D(3H,3He)nn Experiment Searching for nn Ground State

Possibility of existence of nn ground state was discussed in 2011 by H. Witala and W. Glockle based on anomalous enhancement of nn QFS (Quasi-Free Scattering) cross section in nd breakup at E n = 26 MeV reported in 2002. To search for the nn ground state, we have made a feasibility study of D(3H,3He)nn and D(n, p)nn experiments. 3H and n secondary beams are produced respectively by D(d,3H)p and D(d, n)3He reactions at forward angle, and are injected on a CD2 foil target. If an nn ground state exists, a single peak is observed in the 3He and p energy spectra. We conclude that these experiments are feasible.

Giant half-cycle attosecond pulses

Half-cycle picosecond pulses have been produced from thin photo-conductors, when applying an electric field across the surface and switching on conduction by a short laser pulse. Then the transverse current in the wafer plane emits half-cycle pulses in normal direction, and pulses of 500 fs duration and 1e6 V/m peak electric field have been observed. Here we show that single half-cycle pulses of 50 as duration and up to 1e13 V/m can be produced when irradiating a double foil target by intense few-cycle laser pulses. Focused onto an ultra-thin foil, all electrons are blown out, forming a uniform sheet of relativistic electrons. A second layer, placed at some distance behind, reflects the drive beam, but lets electrons pass straight. Under oblique incidence, beam reflection provides the transverse current, which emits intense half-cycle pulses. Such a pulse may completely ionize even heavier atoms. New types of attosecond pump-probe experiments will become possible.

The Orsay Universal Plunger System

A new plunger device for Recoil-Distance Doppler Shift and Time-Differential Recoil-In-Vacuum measurements has been developed at the CSNSM in collaboration with the IPN Orsay. It is conceived to be easily adapted to different experimental setups and facilities, in particular to the future radioactive beam facility Spiral2. An electronic feedback system keeping the distance between target and stopper foils constant, imperative for precision measurements of short lifetimes, was also developed.The plunger device was commissioned with an experiment performed at the IPN Orsay Tandem accelerator laboratory using the Orgam germanium detector array. Excited states in 76Kr were populated using the reaction 45Sc(35Cl,2p2n)76Kr. The lifetime τ of the 41+ state was determined to 4.3(6)ps, in accordance with previous measurement, confirming the functionality of the new plunger device. The commissioning experiment showed in particular that the electronic feed back system works as foreseen.

Stopping forces of polyimide, vyns, formvar, and polysulfone for Cl, Br, and I ions

The stopping forces of formvar, polysulfone, polyimide, and vyns for 0.1–0.7MeV/u 35Cl ions, 0.1–0.4MeV/u 79Br ions, and 0.1–0.2MeV/u 127I ions have been measured with the transmission technique and thin foil targets. A modified time of flight elastic recoil detection analysis setup and simulation of experimental slowing down energy spectra were employed for obtaining stopping force curves over a continuous range of energies. The results are compared with predictions of widely used parameterization models for the stopping force.

Thrust generation through low-power laser-metal interaction for space propulsion applications

The micro-Newton thrust generation was observed through low-power continuous wave laser and aluminum foil interaction without any remarkable ablation of the target surface. To evaluate the thrust characteristics, a torsion balance thrust stand capable for the measurement of the thrust level down to micro-Newton ranges was developed. In the case of an aluminum foil target with 12.5 micrometer thickness, the maximum thrust level was 15 micro-Newtons when the laser power was 20W, or about 0.75μN/W. It was also found that the laser intensity, or laser power per unit area, irradiated on the target was significantly important on the control of the thrust even under the low-intensity level.

Detection System for Metallic Contaminants by Eight-Channel SQUIDs

We developed a magnetic contaminant detection system for industrial products such as electrode foils of lithium ion battery employing eight high-Tc SQUID gradiometers. The system was based on pre-magnetization of a contaminant in an object under test by means of permanent magnets of 0.5 T, which magnetization direction was horizontal, in order to suppress the edge effect from the object composed of magnetic material. The object was conveyed to pass under the eight-channel gradiometer array, in which a pair of four gradiometers was aligned in two rows to cover target foils of several tens mm in width. The magnetization from the contaminant in the object was detected by the gradiometers of averaged flux white noise level of 25 μϕ0/Hz1/2. In case that an iron ball passed just under one gradiometer, an iron ball of about ϕ30 μm in diameter was successfully detected with a signal to noise ratio (S/N) of 5. From measurement results using an iron ball of about 100 μm in diameter, it was demonstrated that the system had a detectable range of 70 mm in width. There results suggest that the system is a promising tool for the quality control of lithium ion batteries.

Influence of laser irradiated spot size on energetic electron injection and proton acceleration in foil targets

The influence of irradiated spot size on laser energy coupling to electrons, and subsequently to protons, in the interaction of intense laser pulses with foil targets is investigated experimentally. Proton acceleration is characterized for laser intensities ranging from 2×1018-6×1020 W/cm2, by (1) variation of the laser energy for a fixed irradiated spot size, and (2) by variation of the spot size for a fixed energy. At a given laser pulse intensity, the maximum proton energy is higher under defocus illumination compared to tight focus and the results are explained in terms of geometrical changes to the hot electron injection.

Comparison of ion acceleration from ultra-short intense laser interactions with thin foil and small dense target

The comparative efficiency and beam characteristics of high-energy ions generated from the interaction of a petawatt laser pulse with thin foil target and a small solid-density plasma bunch target have been studied by particle-in-cell simulation under identical conditions. It is shown that thin foil and small solid dense target of micrometer size can be efficiently accelerated when irradiated by a laser pulse of intensity >1021 W/cm2. Using direct beam measurements, we find that small solid dense target acceleration produces higher energy particles with smaller divergence and a higher efficiency compared to thin foil target acceleration. The merits of small solid target acceleration can be exploited for potential applications such as its role as ignitor for fast ignition in inertial confinement fusion.

Collimation of laser-driven energetic protons in a capillary

AbstractEnergetic divergent proton beams can be generated in the interaction of ultra-intense laser pulses with solid-density foil targets via target normal sheath acceleration (TNSA). In this paper, a scheme using a capillary to reduce the proton beam divergence is proposed. By two-dimensional particle-in-cell (PIC) simulations, it is shown that strong transverse electric and magnetic fields rapidly grow at the inner surface of the capillary when the laser-driven hot electrons propagate through the target and into the capillary. The spontaneous magnetic field collimates the electron flow, and the ions dragged from the capillary wall by hot electrons neutralize the negative charge and thus restrain the transverse extension of the sheath field set up by electrons. The proton beam divergence, which is mainly determined by the accelerating sheath field, is therefore reduced by the transverse limitation of the sheath field in the capillary.

Excitation functions of proton-induced reactions on natural Nd in the 10–30 MeV energy range, and production of radionuclides relevant for double-β decay

A preferred candidate for neutrinoless double-{\beta} decay, 150Nd, is present in natural neodymium at an abundance level of 5.64%. However, neodymium could be activated by cosmic rays during the period it spends on the Earth's surface. Its activation by protons is therefore of interest when it comes to estimating the possible disturbance effects and increased background during neutrinoless double-{\beta}-decay experiments like Sudbury Neutrino Observatory plus liquid scintillator (SNO+). In most cases, we lack experimental data on proton-induced reactions on neodymium. Therefore, a measurement of cross sections has been performed for the formation of 141Pm, 143Pm, 144Pm, 146Pm, 148Pm, 148Pmm, 149Pm, 150Pm, 140Nd, 141Nd, 147Nd, 149Nd, 138Prm, 139Pr, 142Pr, and 139Ce by 10-30 MeV protons. Oxidation-protected metal foil targets of natural isotopic abundance were irradiated by the usual stacked-foil technique on the external proton beam of the isochronous cyclotron U-120M at the Nuclear Physics Institute at \v{R}e\v{z} near Prague. Special attention was paid to the excitation functions of long-lived radionuclides. The measured data were compared with TENDL-2010 library data (TALYS code).

飞秒激光与薄膜Cu靶作用时质子能谱实验

飞秒激光与薄膜Cu靶作用时质子能谱实验

A fission neutron detector based on helium scintillator

A new neutron detector is designed. Two 235UO2 target foils are used as radiators, and the 4He gas is used as scintillator in the detector. The detector combines the features of 235U and 4He fully, so it has some excellent performances, such as flat energy response to neutrons, better n/γ discrimination, etc. It can be used well to detect neutrons in a pulsed mixture radiation field. In this paper, the principle and structure of the detector are introduced. The energy depositions of different energies of neutrons and γ -rays in 4He gas are calculated. The neutron sensitivity, γ ray sensitivity, n/γ discrimination, and time response of the detector are investigated theoretically and experimentally. The neutron sensitivity is about 10-15 C·cm2, γ ray sensitivity is about 10-17 C·cm2, and time response is about 33.1 ns.

Studies on the production feasibility of 64Cu by (n, p) reactions on Zn targets in Dhruva research reactor

64Cu is an useful radionuclide for both PET imaging and targeted therapy, as it decays by three different modes, namely, electron capture (41%), β− (40%) and positron emission (19%). 64Cu is generally produced by 64Ni (p, n) reaction in a cyclotron for medical use. High specific activity ‘no carrier added’ grade 64Cu by 64Zn (n, p) route is an alternative for research studies and was hence explored. 10 mg zinc foil target (48.63% in 64Zn) was irradiated in the medium flux reactor Dhruva at a thermal neutron flux of ~5.6 × 1013 n cm−2 s−1 for 3 days. The irradiated Zn foil was dissolved in 5 mL 10 M HCl and 64Cu was separated by anion exchange chromatography (Dowex 1 × 8; 100–200 mesh) at 3 M HCl conditions. 64Cu radioactivity content and its radionuclide purity were ascertained by γ-ray spectrometry using HPGe detector coupled to a 4 K multichannel analyser system. Radiochemical separation yielded a radionuclidic purity of 99.9% 64Cu.

Comparison of femtosecond laser-driven proton acceleration using nanometer and micrometer thick target foils

AbstractAdvancement of ion acceleration by intense laser pulses is studied with ultra-thin nanometer-thick diamond like carbon and micrometer-thick Titanium target foils. Both investigations aim at optimizing the electron density distribution which is the key for efficient laser driven ion acceleration. While recently found maximum ion energies achieved with ultra-thin foils mark record values micrometer thick foils are flexible in terms of atomic constituents. Electron recirculation is one prerequisite for the validity of a very simple model that can approximate the dependence of ion energies of nanometer-thick targets when all electrons of the irradiated target area interact coherently with the laser pulse and Coherent Acceleration of Ions by Laser pulses (CAIL) becomes dominant. Complementary experiments, an analytical model and particle in cell computer simulations show, that with regard to ultra-short laser pulses (duration ~45 fs at intensities up to 5 × 1019 W/cm2) and a micrometer-thick target foil with higher atomic number a close to linear increase of ion energies manifests in a certain range of laser intensities.

HAVAR

Abstract Havar is a heat-treatable cobalt-base alloy that provides very high strength. The alloy has excellent comsion resistance and is nonmagnetic. Applications include pressure diaphragms. power springs, gap spacers in magnetic heads, and target foils in nuclear physics. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties. It also includes information on corrosion resistance as well as forming, heat treating, machining, and joining. Filing Code: Co-24. Producer or source: Hamilton Precision Metals.

PEBSI – A Monte Carlo simulator for bremsstrahlung arising from electrons colliding with thin solid-state targets

We present a Monte Carlo code dedicated to the simulation of bremsstrahlung arising in collisions of polarized electrons with thin target foils. The program consists of an electron transport algorithm taking into account elastic electron-nucleus scattering and inelastic collisions with target electrons as well as a treatment of polarized-electron bremsstrahlung emission. Good agreement is found between the predictions of the electron transport code and data stemming from other simulation programs and experiments. In addition, we present first results from the bremsstrahlung simulation which indicate a significant decrease in the degree of linear polarization of bremsstrahlung even for the thinnest gold targets considered.

Simultaneous generation of ions and high-order harmonics from thin conjugated polymer foil irradiated with ultrahigh contrast laser

We report the manufacturing of an (ultra-)thin foil target made of conjugated polymer, poly(9,9′-dioctylfluorene-co-benzothiadiazole) (F8BT), and the simultaneous observation of laser-accelerated ions and second harmonic radiation, when irradiated with ultrahigh-contrast laser pulse at a maximum intensity of 4 × 1019 W/cm2. Maximum proton energy of 8 MeV is achieved along the target normal direction. Strong second harmonic with over 6% energy ratio compared to fundamental is emitted along the specular direction. Two-dimensional particle-in-cell simulations confirm the simultaneous generation of protons and high-order harmonics, which demonstrates the feasibility of applications requiring particle and radiation sources at once, effectively using the same laser and target.

Surface transport of energetic electrons in intense picosecond laser-foil interactions

The angular distribution of energetic electrons emitted from thin foil targets irradiated by intense, picosecond laser pulses is measured as a function of laser incidence angle, intensity, and polarization. Although the escaping fast electron population is found to be predominantly transported along the target surface for incidence angles ≥65°, in agreement with earlier work at lower intensities, rear-surface proton acceleration measurements reveal that a significant electron current is also transported longitudinally within the target, irrespective of incident angle. These findings are of interest to many applications of laser-solid interactions, including advanced schemes for inertial fusion energy.