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Abstract Direct laser acceleration (DLA) of electrons in plasmas of near-critical density (NCD) is a very advancing platform for high-energy PW-class lasers of moderate relativistic intensity supporting Inertial Confinement Fusion research. Experiments conducted at the PHELIX sub-PW Nd:glass laser demonstrated application-promising characteristics of DLA-based radiation and particle sources, such as ultra-high number, high directionality and high conversion efficiency. In this context, the bright synchrotron-like (betatron) radiation of DLA electrons, which arises from the interaction of a sub-ps PHELIX laser pulse with an intensity of 1019 W/cm2 with pre-ionized low-density polymer foam, was studied. The experimental results show that the betatron radiation produced by DLA electrons in NCD plasma is well directed with a half-angle of 100–200 mrad, yielding (3.4 ± 0.4)·1010 photons/keV/sr at 10 keV photon energy. The experimental photon fluence and the brilliance agree well with the particle-in-cell simulations. These results pave the way for innovative applications of the DLA regime using low-density pre-ionized foams in high energy density research.

A detailed understanding of particle stopping in matter is essential for nuclear fusion and high energy density science. Here, the authors report one order of magnitude enhancement of intense laser-accelerated proton beam stopping in dense ionized matter in comparison with currently used models describing ion stopping in matter.

A number of heavy-ion accelerators are either under construction (e.g., the Facility for Antiproton and Ion Research in Darmstadt and the High Intensity Accelerator Facility in China) or already in operation at many places worldwide. For these accelerators, activation of construction components due to beam loss, even during routine machine operation, is a serious issue, especially with the upcoming high-intensity facilities. Aluminum is one of the most commonly used construction materials in beam lines, collimators, and other components. Therefore, we report here on activation experiments on aluminum samples to verify and benchmark simulation codes. The analysis was performed by gamma spectroscopy of the irradiated targets. Our results on the induced activity measured in samples irradiated by uranium beams at 125 MeV/u and 200 MeV/u and a xenon beam at 300 MeV/u show activation levels significantly lower than those predicted by FLUKA simulations.

The proton-boron (p 11 B) reaction is regarded as the holy grail of advanced fusion fuels, where the primary reaction produces 3 energetic α particles. However, due to the high nuclear bounding energy and bremsstrahlung energy losses, energy gain from the p 11 B fusion is hard to achieve in thermal fusion conditions. Owing to advances in intense laser technology, the p 11 B fusion has drawn renewed attention by using an intense laser-accelerated proton beam to impact a boron-11 target. As one of the most influential works in this field, Labaune et al. first experimentally found that states of boron (solid or plasma) play an important role in the yield of α particles. This exciting experimental finding rouses an attempt to measure the nuclear fusion cross section in a plasma environment. However, up to now, there is still no quantitative explanation. Based on large-scale, fully kinetic computer simulations, the inner physical mechanism of yield increment is uncovered, and a quantitative explanation is given. Our results indicate the yield increment is attributed to the reduced energy loss of the protons under the synergetic influences of degeneracy effects and collective electromagnetic effects. Our work may serve as a reference for not only analyzing or improving further experiments of the p 11 B fusion but also investigating other beam-plasma systems, such as ion-driven inertial confinement fusions. [ABSTRACT FROM AUTHOR]

Astrophysical observations reveal that galaxies and clusters of galaxies are gravitationally held together by vast halos of dark (that is, nonluminous) matter. Theoretical reasoning points to two leading candidates for [...]

The hydrodynamic behavior of a cylindrical solid target, heated by the intense heavy-ion beams, was simulated. The target was of the LAboratory PlAnetary Science (LAPLAS)-type geometry, as described by Tahir (LAPLAS). An iron target irradiated by the intense heavy-ion beams, with parameters available from the planned High Intensity Accelerator Facility or Facility for Antiproton and Ion Research, Society for Heavy Ion Research, Darmstadt, Germany, will transform to the warm-dense state, similar to the situation that exists in the planet interior. The dependence of the achievable state of iron on the outer-shell material and beam location was investigated with Medusa-code simulations. The simulation results show that the compression of inner iron is significantly influenced by the density-to-mass ratio of the outer-shell material and the location of the beam heating. Using the LAPLAS geometry, a uranium beam of 800 MeV/u, and 1.5 x 1011 particles per pulse, our simulations show that the warm-dense-matter regime for iron is obtained. Details depend on the yet unknown equation of state and will be measured when this beam intensity is available in a couple of years. [ABSTRACT FROM AUTHOR]

The hydrodynamic behavior of metal targets when heated by intense proton beams was simulated numerically. The dependence of the achieved warm dense matter state for targets with different materials was investigated by means of a computer code based on two-dimensional fluid models with quantum corrections. Under the irradiation of a proton beam with an energy of 10 MeV, a particle number of 7.9 × 107, and a pulse duration of 10 ps, the numerical simulation results show that the achieved state is significantly influenced by the Winger-Seitz radius rs of materials. [ABSTRACT FROM AUTHOR]

The effect of various electron pressure models on the debris-ambient coupling in a magnetized collisionless shock is demonstrated with a 2-D hybrid code. The simulation specifically models the regime of laboratory shocks launched by laser ablation into a magnetized ambient plasma. A two-electron-fluid model is employed with different polytropic coefficients to vary the electron temperature and pressure gradients and investigate their effects on the shock dynamics, the electric field, and the coupling between debris and ambient ions. The simulations show a significant variation in the radial electric field and ion dynamics with the polytropic index. [ABSTRACT FROM PUBLISHER]

Radioactive decays are of concern in a wide variety of applications using Monte-Carlo simulations. In order to properly estimate the quality of such simulations, knowledge of the accuracy of the decay simulation is required. We present a validation of the original Geant4 Radioactive Decay Module, which uses a per-decay sampling approach, and of an extended package for Geant4-based simulation of radioactive decays, which, in addition to being able to use a refactored per-decay sampling, is capable of using a statistical sampling approach. The validation is based on measurements of calibration isotope sources using a high purity Germanium (HPGe) detector; no calibration of the simulation is performed. For the considered validation experiment equivalent simulation accuracy can be achieved with per-decay and statistical sampling. [ABSTRACT FROM PUBLISHER]

The simulation of radioactive decays is a common task in Monte-Carlo systems such as Geant4. Usually, a system either uses an approach focusing on the simulations of every individual decay or an approach which simulates a large number of decays with a focus on correct overall statistics. The radioactive decay package presented in this work permits, for the first time, the use of both methods within the same simulation framework—Geant4. The accuracy of the statistical approach in our new package, RDM-extended, and that of the existing Geant4 per-decay implementation (original RDM), which has also been refactored, are verified against the ENSDF database. The new verified package is beneficial for a wide range of experimental scenarios, as it enables researchers to choose the most appropriate approach for their Geant4-based application. [ABSTRACT FROM PUBLISHER]

At the GSI Helmholtzzentrum für Schwerionenforschung GmbH (Darmstadt, Germany) intense focused beams of energetic heavy ions are used to generate high-energy-density states in matter [I]. In recent experiments, initially solid tanlalum and tungsten samples (50-901tin thick foils) were uniformly heated in a quasi-isobaric way by a microsecond ion-beam pulses. The temperature of a sample has been observed by a fast multi-channel optical pyrometer during and after the heating. The isobaric heat capacity of the melted metals as well as the enthalpy of fusion have been obtained from the temperature - enthalpy dependence, calculated from measured temperature-time data. A good measurement statistics has been achieved by carrying out a large number of the same experiments with identical targets. The obtained experimental results for liquid tantalum and tungsten heated up to 5000 K are presented and discussed. [ABSTRACT FROM AUTHOR]

A dedicated facility named High Radiation on Materials (HiRadMat) is being constructed at CERN to study the interaction of the 450 GeV protons generated by the Super Proton Synchrotron (SPS) with fixed solid targets of different materials. The main purpose of these future experiments is to study the generation and propagation of thermal shock waves in the target in order to assess the damage caused to the equipment, including collimators and absorbers, in case of an accident involving an uncontrolled release of the entire beam at a given point. Detailed numerical simulations of the beam-target interaction of several cases of interest have been carried out. In this paper we present simulations of the thermodynamic and the hydrodynamic response of a solid tungsten cylindrical target that is facially irradiated with the SPS beam with nominal parameters. These calculations have been carried out in two steps. First, the energy loss of the protons is calculated in the solid target using the FLUKA code [Fasso et al., “FLUKA: A multi-particle transport code,” Report Nos. CERN-2005-10, INFN/TC-05/11, and SLAC-R-773, 2005; Fasso et al., Conference on Computing in High Energy and Nuclear Physics, La Jolla, CA, 24–28 March 2003] and this energy loss data is used as input to a sophisticated two-dimensional hydrodynamic code, BIG2 [Fortov et al., Nucl. Sci. Eng. 123, 169 (1996)], which is based on a Godunov-type numerical scheme. The transverse intensity distribution in the beam focal spot is Gaussian. We consider three different sizes of the focal spot that are characterized by standard deviations, σ=0.088, 0.28, and 0.88 mm, respectively. This study has shown that the target is severely damaged in all the three cases and the material in the beam-heated region is transformed into warm dense matter including a strongly coupled plasma state. This new experimental facility can therefore also be used for dedicated experiments to study high energy density matter. [ABSTRACT FROM AUTHOR]

Physics of high energy density (HED) matter is an ever-expanding field of research with very wide applications to basic and applied physics and with great potential for revolutionary technological and industrial applications. Over the past decades, static as well as dynamic configurations have been widely used to research this interesting field of science. Recent technological advances in the development of high-quality well-focused strongly bunched intense particle beams have led to the idea of generating samples of HED matter using isochoric and uniform heating of solid targets by such intense beams. Theoretical work reported in this paper explores the possibility of carrying out novel experiments using the future Facility for Antiprotons and Ion Research at Darmstadt. [ABSTRACT FROM AUTHOR]

Presents a study which dealt with the characteristics of intense electron beams generated in transient hollow-cathode discharge (THCD). Configurations of THCD; Parameters of generated beams; Description of channel spark produced electron beams.

Pulsed intense electron beams with remarkable parameters are generated in transient hollow-cathode discharges (THCD). The channel spark is different from the other THCD configurations with respect to the low gas pressure and the tube geometry, which consists of a dielectric capillary tube and an anode mounted on its external surface. In this paper, the channel-spark discharge is systematically studied by electrical and fast shutter camera measurements. The buildup of electrostatic field and the equipotential lines are calculated by the numerical code Electrostatic Field (ElFi) 3.0. The influence of the gas pressure, breakdown voltage, and external capacitance on the discharge current and the beam current are outlined. Depending on the gas pressure, two different discharge modes are observed, i.e., the high resistive and the regular modes, which can be distinguished by the shape of the electrical signals. The plasma development in these modes is studied by electrical and fast shutter camera measurements, performed spectrally integrated and with interference filters to separate the emission of the ions originating from the working gas and capillary material. Compared to the pseudospark, the plasma development in channel spark presents similar as well as specific features due to the low gas pressure and to the capacitive anode-plasma coupling [ABSTRACT FROM PUBLISHER]

A letter to the editor is presented in response to the article "Deriving uncertainty factors for threshold chemical contaminants in drinking water," by Leonard Ritter, Kannan Krishnan, and Richard Carrier in the October 2007 issue.

Fast electron transport as well as bremsstrahlung emissions induced by relativistic intense laser solid interactions are investigated with a newly developed particle-in-cell (PIC) simulation code. This PIC code is capable of simulating intense laser-solid interactions by taking into account many coupled physical processes, like laser-plasma interaction, ionization dynamics, collisional dynamics, electron transport and photon emission. The target effects can be distinguished according to their intrinsic atomic properties. In this work, aluminium, copper, and gold targets with different thickness are considered. It is shown that with the fixed laser intensity of 1020 W cm−2, the angular distribution of bremsstrahlung emission, significantly depends on target material and target thickness. For low Z material, the electrons and the emitted photons tend to be collimated along the laser propagation direction. For high Z material, the angular distribution is broader, which is attributed to the self-generated resistive magnetic field-induced electron momentum divergence. Moreover, the simulation result shows that for Al target, the total emission energy increases with decreasing target thickness, because electron refluxing induces considerable backward emission. Comparatively, for Au target, the electron refluxing effect on the total emission energy can be ignored, because the backward emission is somewhat buried within the broad distribution. [ABSTRACT FROM AUTHOR]