Beam-target Interaction Research Articles

A dc arc plasma torch as a tailored heat source for thermohydraulic simulation of proton beam–target interaction in ADSS

Currently, research on accelerator driven subcritical systems (ADSS) is gaining significance due to their high safety levels and extremely attractive potential in terms of both thorium utilization and nuclear waste transmutation. While high energy and high current proton beams are being built worldwide, intensive efforts are being undertaken in parallel towards the development of complex lead bismuth eutectic target systems. The major focus is directed towards understanding of the material compatibility and detailed thermohydraulic simulation of the liquid metal flow. The requisite heat flux is being deposited using innovative and easily controllable heat sources. This paper presents an experimental and simulation study to explore the potential of using dc arc plasma torches as a tailored heat source for thermohydraulic simulation of proton beam–target interaction in such systems.

Interaction of a smoothed laser beam with supercritical-density porous targets on the ABC facility

We present the results of experiments on the interaction of laser radiation with low-density porous targets performed on the ABC facility at the ENEA Research Centre (Frascati, Italy). Porous plastic targets with densities of 5 and 20 mg cm-3 were irradiated by a focused neodymium-laser beam at the fundamental frequency (λ = 1.054 μm) at a radiation intensity of 1013 W cm-2 at the target. The beam was preliminarily allowed to pass through an optical system intended to spatially smooth the radiation intensity over the beam cross section. The use a smoothed beam was important to discover in the plasma and in the accelerated dense material the features related to the porous structure of the target under conditions which rule out the effect of the inhomogeneities of the heating beam itself. The spatial plasma structure in the laser beam—target interaction region and at the rear side of the target were investigated by using optical schlieren plasma photography. The time dependent transmission of the laser radiation through the target was also investigated by imaging the target in transmitted radiation to a properly masked photodiode.

Experimental study of the neutron emission mechanisms in a Filippov-type plasma focus device

The results of an experimental investigation of neutron emission characteristics in the Filippov-type plasma focus facility “Dena” (90 kJ, 25 kV, 288 µF) with D2 + %1 Kr as working gas are presented. From the experimental results, one can conclude that both thermonuclear and nonthermonuclear mechanisms are always present in neutron production, but their contributions to the total neutron yield are strongly dependent on the initial pressure and discharge voltage. It has been found that at constant discharge voltages and low pressures the beam—target interaction mechanism plays an important role in the neutron production and with increasing the pressure, its role decreases and the importance of thermonuclear mechanism increases. Also at constant pressures, the contribution of beam—target interaction mechanism in neutron production decreases with increasing the discharge energy. The value of the α index in the empirical neutron yield scaling law Yn ∝ Iα ∝ Eα/2 was found to be about 3.82.

Experiences of operating CELSIUS with a hydrogen pellet target

The CELSIUS ring is equipped with a pellet target used as an internal target for experiments at the WASA-facility. The pellet target generates a stream of frozen hydrogen pellets, the size of which is now reduced to 25–30μm. We discuss the interaction between the pellet target and the stored beam under the influence of RF and electron cooling in terms of measurements and computer simulations. Energy loss measurements using Schottky spectra were performed to measure the effective pellet target thickness. We present Monte Carlo tracking simulations including the beam–target interaction as well as RF and electron cooling. The general behaviour is reproduced but the simulations overestimate the beam lifetime compared to observations.

Numerical modelling of laser beam–target interaction near the plasma-formation threshold

Experimental investigations of laser-produced plasmas often determine plasma parameters as averaged values only and these data cannot be compared with actual conditions at a target surface. In this paper, numerical modelling of target heating with non-constant target material properties was used to estimate the temperature at the surface of the target as a function of time. Three target materials (magnesium, aluminum and silicon) and an experimentally determined laser pulse profile were used for modelling. Gray-body radiation of the target surface and thermal diffusion losses are taken into account during numerical modelling. It was assumed that radiation from the laser impacts perpendicularly onto the target surface. The results obtained by modelling are in good agreement with the experimentally observed plasma parameters and they are consistent with thermal target heating in which the laser beam is treated as a source of very intense input heat energy.

Application of high intensity pulsed ion and plasma beams in modification of materials

Basic mechanisms of modification of materials subjected to irradiation by short (ns-ms), highly intense (105–108W/cm2) plasma or ion pulse beams (HIPIPB) are reviewed. Description of basic phenomena occurring as a result of beam-target interaction, and a representative selection of examples of the HIPIPB processing of semiconductors, metals, ceramics, and other materials described in the literature are given. The HIPIPB processing is compared to the laser processing.

Time of flight electron spectrometry on TIR using natural diamond detector

Natural diamond detectors (NDDs) being developed for the spectrometric applications in tokamak fusion plasma experiments, have been used also for fast x-ray flux measurements and time-of-flight (TOF) electron spectrometry in laser beam-target interaction experiments on the CO2 laser installation TIR (λ=10.6 μm, E=80–95 J, τ∼14 ns). The magnetic field created in front of the detector provided separation of the signals induced by x ray and electrons. The waveform of a NDD current response has been shown to provide an information about energy spectra of the particles generated during laser beam-target interaction. Fast response time (<1 ns), low sensitivity to visible light and x rays, high radiation resistance, and 100% charge collection efficiency of the type IIa diamond samples, make NDDs to be the optimal choice for TOF spectrometry of charged fusion products in inertial confinement fusion experiments.

Electron beam–target interaction and spot size stabilization in flash x-ray radiography

A high current relativistic electron beam incident on a high-Z target to produce bremsstrahlung photons for radiographic applications can be subjected to charge neutralization by target plasma ion production due to energy deposition by the electron beam. This partial charge neutralization can lead to premature focusing of the electron beam at a distance away from the target and subsequent radial divergence. Furthermore, as the ion column continues to expand, the focal point moves upstream along the path of the electron beam, causing the beam spot on the target to grow in time. The increase in radiation spot size is detrimental to the spatial resolution of radiographic images. The ion effects were confirmed via particle-in-cell simulations and analysis, and methods were investigated to suppress the growth of the electron beam spot size in single- and multiple-pulse radiographic applications. The concept of a self-biased target was proposed and validated by computer simulation showing that the electron beam can be used in a configuration to establish an electric potential between the target and the collimator. This potential can effectively trap the ions, limit the ion column length, and thereby maintain the electron beam spot size. Another approach is the placement of a thin metallic foil at 1–2 cm in front of the target, which serves as a barrier to the ions but is essentially transparent to the incoming electron beam. Our study also showed that optimized confinement of plasma ions with the electromagnetic or the mechanical method can provide an additional ion-focusing effect which leads to a desirable further reduction of the beam spot size.

Numerical and experimental studies on synthesis of ultrafine nanosize powders of AlN by ion beam evaporation

Synthesis of ultrafine nanosize powders by ion beam evaporation (IBE) has been studied numerically and experimentally. Theoretical models have been developed, which involve such physical processes as beam-target interaction, plasma expansion, and the synthesis of powders. The macroscopic properties of the ultrafine powders have been predicted. As an application of our models, the macroscopic properties of AlN powders synthesized by IBE with an AlN target have been predicted. The energy density, pulse width, and spot size of the ion beam are 20 J/cm2, 70 ns, and 1 cm2, respectively. The main results have shown that the particle size distribution is log normal and that 70% of all particles exist between 20 and 40 nm. The average diameter and the specific surface area are ∼30 nm and ∼50 m2/g, respectively. Experimentally, the ultrafine AlN powders have been successfully synthesized by IBE, which has been verified by x-ray diffraction and transmission electron diffraction. Furthermore, particle size distributions have been obtained by transmission electron microscopy. The experimental results are found to be in a reasonable agreement with the numerical studies.

Heavy-ion-beam-induced hydrodynamic effects in solid targets.

It is expected that after the completion of a new high current injector, the heavy-ion synchrotron (SIS) at the Gesellschaft für Schwerionforschung (GSI) Darmstadt will accelerate U(+28) ions to energies of the order of 200 MeV/u. The use of a powerful rf buncher will reduce the pulse length to about 50 ns, and employment of a multiturn injection scheme will provide 2 x 10(11) particles in the beam that correspond to a total energy of the order of 1 kJ. This upgrade of the SIS, hopefully, will be completed by the end of the year 2001. These beam parameters lead to a specific power deposition of the order of 1-2 TW/g in solid matter that will provide temperatures of about 10 eV. Such low specific power deposition will induce hydrodynamic effects in solid materials, and one may design appropriate beam-target interaction experiments that could be used to investigate the equation of state of matter under extreme conditions. The purpose of this paper is to propose suitable target designs with optimized parameters for the future GSI experiments with the help of one and two-dimensional hydrodynamic simulations. Cylindrical geometry is the natural geometry for highly focused ion beams, and therefore cylindrical targets are the most appropriate for this type of interaction experiments. The numerical simulations presented in this paper show that one can experimentally measure the characteristic sound speed in beam heated targets which is an important physical parameter. Moreover, one can study the propagation of ion-beam-induced shock waves in the solid materials. Different values for the specific power deposition, namely, 10, 25, 50, and 100 kJ/g, have been used. In some cases the pulse length is assumed to be 40 ns while in others it is considered to be 50 ns. Various materials including lead, aluminum, and solid neon have been used.

Intense ion beam produced plasmas on TIT-RFQ linac

Intense ion beams from an RFQ linac can be used to investigate the plasma experiments. At present, a 4He + beam with the mean current of 2 mA in a macropulse is focused to about 1.1 mm 2 on the target surface. The output-beam is switched from a beam dump to the target within 50 ns by using a fast electrostatic beam kicker. This kicker synchronizes to the RF-pulse, and it is used to control the timing between the beam-target interaction and the diagnostic equipment. The experiments were performed with a gas target. The behavior of the ion beam-produced plasma was observed.

Characterization and modeling of the ablation plumes formed by intense-pulsed ion beam impact on solid targets

An investigation of the properties of the ablation products from intense-pulsed ion beam impact on solid targets is described. Measurements and calculations of the properties of the ablation plume are presented and correlated with incident beam parameters. Experimental techniques include Thomson parabola particle spectroscopy to measure the incident ion beam atomic composition and the energy spectrum of each beam component, thermal imaging to measure the incident-beam energy density, time-resolved photography to measure the plume expansion time history and geometry, and time-resolved energy-density measurements of the plume. The results of a thermal transport model of the beam-target interaction are presented, and a detailed comparison with measurements is made.

Two-dimensional simulations of KALIF beam–target interactions

Beam–target interaction experiments performed at the Karlsruhe Light Ion Facility (KALIF) have previously been simulated by one-dimensional (1D) radiation hydrodynamics in slab geometry, which implies a spacially homogeneous beam power distribution. In this paper the consequences of a non-homogeneous beam power distribution are studied by 2D hydrodynamical simulations. It is shown that – for conditions valid at KALIF – time and space resolved measurements of the target back surface velocity can be used to deduce information on the spacial beam profile.

Intense ion beam optimization and characterization with infrared imaging

We have developed two-dimensional calorimetry with infrared imaging of beam targets to optimize and measure the energy-density distribution of intense ion beams. The technique, which measures a complete energy-density distribution on each machine firing, has been used to rapidly develop and characterize two very different beams—a 400 keV beam used to study materials processing and an 80 keV beam used for magnetic fusion diagnostics. Results of measurements, using this technique, varying the diode applied magnetic field strength and geometry, anode material type and configuration, and anode-cathode gap spacing are presented and correlated with other observations. An assessment of calorimeter errors due to target ablation is made by comparison with Faraday cup measurements and computer modeling of beam-target interactions.

Experimental and theoretical investigation of cumulative laser irradiation effects in YBCO thin film pulsed laser deposition

Compositional and morphological modifications of superconducting YBCO targets under prolonged laser irradiation were investigated by EDS and SEM. Rotated and fixed targets were ablated at different process parameters - laser fluence and oxygen environment. Optical emission spectroscopy was employed for investigation of the evolution of the laser-induced plasma plume. The deposited film thickness distribution over the substrate surface area was examined through the film absorbance. The results can be consistently explained by assuming the existence of an additional effective ablation threshold imposed by the modified surface relief. A one-dimensional theoretical model of the laser beam-target interaction was developed involving temperature-dependent thermophysical parameters and the laser-induced plasma absorption. Reasonable agreement between the experimental and theoretical dependencies of the eroded depth per shot on the pulse energy is found. The model results show a possible influence of the post-pulse evaporation on the target surface stoichiometric deviation found in the experiments.

Equation of state information from beam-target interaction experiments at KALIF

Intense ion beams can be used to generate ultrahigh pressures in condensed matter. Lightion beams generated at the Karlsruhe Light Ion Facility (KALIF) typically have a focus of less than 1-cm diameter. The maximum power density at KALIF achieved so far is of the order of 1 TW/cm2. In the energy deposition zone of the targets, the 1.5-MeV protons of the KALIF beam deposit energy of the order of 100 TW/g or 5 MJ/g. A strongly coupled, hot, dense plasma is thus created by the action of a light ion beam on matter. The high pressure generated in this region has been used to accelerate thin foils to velocities up to 12.5 km/s. A successful interpretation of these experiments can serve as a check of theoretical models and of the equation of state (EOS) data. The present paper contains an investigation of the hydrodynamics of thin aluminum foil accelerated by light ion beams at KALIF using Bθ0-diode. The peak power density in these experiments was 0.15 ± 0.05 TW/cm2. The results of simulations depend mainly on two factors: power density evolution at the target and the EOS for the strongly coupled dense and hot plasma. The beam power density evolution has been carefully remeasured recently. It turned out that the available EOS data do not reproduce experimental results satisfactorily. We have formulated a simple EOS formula in a modified Mie-Grüneisen form. We assume the Grüneisen parameter to be a function of temperature and density. The parameters of this EOS have been adjusted to reproduce experiments at KALIF. In the present paper analysis of beam-target interaction experiments at KALIF is presented using our analytic EOS. We show that such experiments can give information on EOS data in the region of strongly coupled plasma.

Beam-target interaction and chamber propagation

Experiments to study beam plasma interaction phenomena are carried out over a wide range of beam energy. The range extends from a few keV/μ up to and above GeV/μ. They provide detailed insight into interaction phenomena with ionized matter and are relevant to inertial fusion driven by intense ion beams. Chamber propagation and focusing of intense ion beams is a topic which is presently addressed by a number of groups. The present status of beam plasma interaction and chamber propagation physics is reviewed.

Shock-wave physics experiments with high-power proton beams

At the Karlsruhe Light Ion Facility (KALIF) high-power proton beams with power densities up to ∼ 1 TW/cm2 are generated depositing up to 40 kJ of ion energy in a focal spot of 6∼8-mm diameter. With peak proton energies of ∼ 1.7 MeV, specific power densities of up to 200 TW/g and energy densities of several MJ/g can be realized. This is a regime in which experiments providing information on the equation of state (EOS), dynamics of the beam interaction with condensed targets, and properties of solids and plasma at high-energy densities are of particular interest. In the present paper we report on shock-wave experiments using solid targets and high-resolution laser-Doppler velocimetry. The empirical data provided are used to verify code simulations and the used EOS-data in these calculations, to investigate the beam-target interaction, and to perform series of shock-wave measurements of properties of different materials. The ∼40-ns FWHM proton beam can be used to generate, by material ablation or impact of ablatively accelerated flyers, intense shock waves, permitting the investigation of shock compressibility, dynamic failure of solids under nanosecond load duration, phase transitions, and viscosity at strain rates up to ∼108 s-1. Recently an improved line-imaging velocimeter was set up to measure the spatial velocity variation with a maximum resolution of < 10 μm, opening the possibility to address new issues like growth of instabilities or local dynamics of the spall fracture.

Ion irradiation facility for materials research at the 1.4 MeV/u high-charge state injector of GSI

A new 1.4 MeV/u injector for the UNILAC has been in operation for two years in parallel to the Wideröe prestripper accelerator. It consists of an ECR ion source, a 108 MHz RFQ, and a 108 MHz interdigital H structure. This combination has led to a very compact linac providing beams of highly charged heavy ions up to U 28+. High-duty cycle performance together with a beam switching and pulsing system allows to simultaneously provide the UNILAC and an experimental beam line for target irradiations with beam. The technical concept of the experimental beam line including different beam diagnostic tools, beam forming elements, an x− y beam scanning system and a large volume beam-target interaction chamber is outlined. The experimental possibilities are discussed and first experiments with polymer samples irradiated with different ion species are presented.

Inertial fusion targets driven by cluster ion beam: The hydrodynamic approach

Cluster-driven inertial confinement fusion (ICF) is analyzed. A cluster is defined as a charged supermolecule with a charge of one (or of the order 1) and with a very high mass number A, so that Z/A « 1. The energy deposition range is shown to be very small (a few micrometers) for projectiles with a few tens of kev/a.m.u. A significant momentum transfer is therefore possible in its slowing down as it passes through matter. In this case, a high hydrodynamic efficiency seems evident. Three relevant models for cluster beam-target interactions are discussed: (1) the rocket model, where the ablation pressure (Pa) is much larger than the cluster beam direct pressure (II); (2) the hammer model, where Pa « II (in this case, two possibilities are discussed—an impact interaction between the beam and the target, and an impact interaction between one cluster and its absorption volume); (3) an intermediate model, where Pa ~II (in this regime, the hydrodynamic efficiency is maximum). Preliminary simulations were performed and the general features of the models were confirmed. Most relevant for ICF, it was found that approximately 75% of the beam energy is converted into X rays, so that the indirect drive is promising in this context.