High-intensity lasers are an effective source for the acceleration of high-energy particles. Using different interaction configurations, such facilities can be optimized for the acceleration of electrons, protons, heavy ions, high-energy photons, or neutrons. The shielding of these facilities to ensure the safety of personnel has always been a critical requirement and is a fundamental step within the design phase. The knowledge of radiation source terms through both experiments and modelling is now well understood and for the most part can be dealt with through the use of shielding and specialized beam dumps. Unlike most other particle accelerators most high-power laser facilities are still accessed by personnel post shot with little or no remote handling capabilities. As a result, the secondary activation and control of components that lie around the interaction is of great importance to safety. In this paper, we present a 10 year history of activation data on the Vulcan petawatt facility and discuss the primary sources of activation and the potential impact on future laser facilities.

In this paper, a new method for efficient generation of high-energy ion bunches via laser-induced cavity pressure acceleration (LICPA) is examined using one-dimensional particle-in-cell code PIC1D. It is found that for high laser beam intensities of the order of 1022 W/cm2 and for circular light polarization, a substantial increase in parameters of the accelerated ions is obtained when the target is placed inside a special cavity, into which the laser beam is introduced by a small hole. As compared to the pure radiation pressure acceleration scheme, the LICPA scheme leads to an increase in ion energies and the laser-to-ions energy conversion efficiency while the width of the ion energy spectrum are similar for both the schemes. Such a tendency was observed for all carbon targets (from 2 µm to 0.2 µm thick) investigated in the paper. The results of PIC1D simulations agree very well with predictions of the suitably generalized light sail model.

In this work, the generation of a super-short avalanche electron beam (SAEB) in SF6 in an inhomogeneous electric field is studied on two generators with pulse rise times of 0.5 and 2 ns, respectively. The SAEB parameters in SF6 are compared with those obtained in other gases (air, nitrogen, argon, and krypton). It is shown that the SAEB amplitude in SF6 at pressures ranging from 0.05 to 0.2 MPa is commensurable with that in krypton and is much lower than that in air and nitrogen. It is also found that in SF6, SF6 mixture with 2.5% of nitrogen, and other gases, a diffuse discharge is ignited not only at negative polarity but also at positive polarity of the electrode with small curvature radius. Furthermore, the velocity of the ionization wave front in SF6 in an inhomogeneous electric field is studied. Experimental results show that the velocity of the ionization wave front in SF6 is lower than that in air and nitrogen as well as such velocity decreases when the pressure increases from 0.05 to 0.3 MPa in all gases.

We have studied the potential of hard X-ray radiography as a diagnostic in high energy density experiments, proposed for the future Facility for Antiproton and Ion Research (FAIR). We present synthetic radiographic images generated from hydrodynamic simulations of the target evolution. The results suggest that high-resolution density measurements can be obtained from powerful hard X-ray sources driven by a PW-class high-energy laser system. Test measurements of a prototype hard X-ray imaging detector for photon energies above 100 keV are presented.

For a Megawatt class accelerator, classical safety measures may not be sufficient. Precise knowledge of beam loss location and power deposition in the most various scenarios is crucial for the definition of appropriate protection systems. In this work, the case of the Linear IFMIF Prototype Accelerator is studied, where, due to its very high continuous wave beam intensity, the high power part concerns almost the whole accelerator. Beam dynamics simulations are performed to allow the ability to estimate beam losses in all the different situations of the accelerator lifetime: starting from scratch, beam commissioning, tuning or exploration, routine operation, sudden failures. All the results of these studies are given, establishing the catalogue of losses. Recommendations for hot point protection, beam stop speed, beam power limitation are given accordingly.

For very high intensity accelerators, not only beam power but also space charge is a concern. Both aspects should be taken into consideration for any analysis of accelerators aiming at comparing their performances and pointing out the challenging sections. As high beam power is an issue from the lowest energy, careful and exhaustive beam loss predictions have to be done. High space charge implies lattice compactness making the implementation of beam diagnostics very problematic, so a clear strategy for beam diagnostic has to be defined. Beam halo is no longer negligible. Its dynamics is different from that of the core and plays a significant role in the particle loss process. Therefore, beam optimization must take the halo into account and beam characterization must be able to describe the halo part in addition to the core one. This paper presents the advanced concepts and methods for beam analysis, beam loss prediction, beam optimization, beam diagnostic, and beam characterization especially dedicated to very high intensity accelerators. Examples of application of these concepts are given in the case of the IFMIF accelerators.

In this work, we present the spectroscopic studies of the plasma generated at the surface of manganese sulfate by the fundamental (1064 nm) and second harmonic (532 nm) of a Q-switched Nd:YAG laser. The 4s4p 4F7/2→ 4s 2H9/2 at 438.80 nm, 4p 2I11/2 → 4s22I11/2 at 440.80 nm, 4p 4G11/2 → 4s 2H9/2 at 464.27 nm, 4p 4F5/2→ 4s 4D7/2 at 467.16, 4p 4F5/2 → 4s24G 7/2 at 515.08 nm, and 4p 4F7/2 → 4s2 4G 9/2 at 519.65 nm transitions have been used to estimate the electron temperature through the Boltzmann plot method. The number density has been estimated from the Stark broadened profiles of the spectral line 348.30 nm. The spatial behavior of the electron temperature and number density has been examined at different ambient air pressures and with laser irradiance. The temperature and number density are found to be in the range from 9842 K to 9371 K and 1.58 × 1017 to 3.26 × 1016 cm−3 for the 1064 nm laser, from 9668 to 9297 K and 2.27 × 1017 to 5.79 × 1016 cm−3 for the 532 nm laser.

Laser interactions with spray targets (clouds of submicron droplets) are studied here via numerical simulations using two-dimensional particle-in-cell codes. Our simulations demonstrate an efficient absorption of laser pulse energy inside the spray. The energy absorption efficiency depends on the inter-droplet distance, size of the cloud of droplets, and laser pulse intensity, as well as on the pre-evaporation of droplets due to laser pulse pedestal. We investigate in detail proton acceleration from the spray. Energy spectra of protons in various acceleration directions vary significantly depending on the density profile of the plasma created from the droplets and on laser intensity. The spray target can be alternative of foil targets for high intensity high repetition ultrahigh contrast femtosecond lasers. However, at intensities >1021 W/cm2, the efficiency of laser absorption and ion acceleration from the droplets drops significantly in contrast to foils.

High voltage, high current inductors are required for many high pulsed power systems, incorporating capacitor banks. Those inductors simultaneously serve both as a pulse shaping and protection element in R-L-C circuits. A 25 kV/70 kA protection inductor on inductance of 1 mH with low stray field was designed, manufactured, and tested. It was designed as a quasi-toroidal system, consisting of four coils (with 0.25 mH inductance each) evenly distributed in the perimeter of a square. The structure of coils was optimized to withstand a huge electromagnetic force produced by a 70 kA current. The 0.25 mH coil is made as multi-layer solenoid (six layers) from a copper wire (6 × 4 mm2 net cross-section) with fiberglass insulation. Layers are connected in parallel in order to decrease active resistance of the coil. This 0.25 mH coil was tested at 70 kA peak current with a pulse length of about 20 ms, which corresponds to the action integral at about 32 × 106 A2s. Maximum magnetic field inside the coil is about 12 T. A finite element analysis with the ELCUT software was used to calculate the magnetic field, temperature rise, and stresses in the protection inductor. The typical maximum stresses in our design are 100 MPa in copper coils and 140 MPa in fiberglass body tubes; these are both below the yield strength for these materials. Simulations results are compared with the experimental tests and good agreement is observed.

In order to identify the density and material type, high energy protons, electrons, and heavy ions are used to radiograph dense objects. The particles pass through the object, undergo multiple coulomb scattering, and are focused onto an image plane by a magnetic lens system. A modified beam line at the Institute of Modern Physics of the Chinese Academy of Sciences has been developed for heavy-ion radiography. It can radiograph a static object with a spatial resolution of about 65 µm (1 σ). This paper presents the heavy-ion radiography facility at the Institute of Modern Physics, including the beam optics, the simulation of radiography by Monte Carlo code and the experimental result with 600 MeV/u carbon ions. In addition, dedicated beam lines for proton radiography which are planned are also introduced.

We prove that the radiation damping force and the rate of change of the damping energy, in the Landau-Lifshitz forms, in interactions between very intense laser beams and relativistic electron beams, are periodic functions of only one variable, that is the phase of the electromagnetic field. The property is proved without using any approximation, in the most general case, when the degree of polarization of the electromagnetic field, the initial phase of the incident field and the initial energy of the electron have arbitrary values. This property leads to a strong simplification of the calculation of the radiation reaction parameters and of their dependence on the initial electron energy and angular frequency of the laser beam. Our analysis is performed in the proper inertial system of the electron. The radiation reaction is significant for laser beam intensities of the order 1022 W/cm2, and for electron energy greater than 1 GeV. The calculations reveal limitations of the method of generating hard radiations by interactions between laser beams and relativistic electron beams.

The effects of a radiation field (RF) on the interaction process of a relativistic electron beam (REB) with an electron plasma are investigated. The stopping power of the test electron averaged with a period of the RF has been calculated assuming an underdense plasma, ω0 > ωp, where ω0 is the frequency of the RF and ωp is the plasma frequency. In order to highlight the effect of the radiation field we present a comparison of our analytical and numerical results obtained for nonzero RF with those for vanishing RF. In particular, it has been shown that the weak RF increases the mean energy loss for small angles between the velocity of the REB and the direction of polarization of the RF while decreasing it at large angles. Furthermore, the relative deviation of the energy loss from the field-free value is strongly reduced with increasing the beam energy. Special case of the parallel orientation of the polarization of the RF with respect to the beam velocity has been also considered. At high-intensities of the RF two extreme regimes have been distinguished when the excited harmonics cancel effectively each other reducing strongly the energy loss or increasing it due to the constructive interference. Moreover, it has been demonstrated that the energy loss of the ultrarelativistic electron beam increases systematically with the intensity of the RF exceeding essentially the field-free value.

This paper presents a model to study the stimulated Raman scattering (SRS) and stimulated Brillouin scattering (SBS) simultaneously at relativistic laser power. At high intensity, the relativistic mass correction for the plasma electrons becomes significant and the plasma refractive index gets modified which leads to the relativistic self-focusing of the pump beam. This filamentation process affects the scattering processes (SRS and SBS) and at the same time the pump filamentation process also gets modified in the presence of the coexisting SRS and SBS due to the pump depletion. We have also demonstrated that the pump depletion and relativistic filamentation affects the back-reflectivity of scattered beams (SRS and SBS) significantly, for the coexistence case.

As a method to evaluate high-temperature equation of state (EOS) data of fissile materials precisely and safely, we numerically examined an experimental setup based on a sub-range fissile target and a high-intensity short-pulsed heavy-ion beam. As an example, we calculated one-dimensional hydrodynamic motion of a uranium target with ρ = 0.03ρsolid (ρsolid ≡ solid density = 19.05 g/cm3) induced by a pulsed 23Na+ beam with a duration of 2 ns and a peak power of 5 GW/mm2. The projectile stopping power was calculated using a density- and temperature-dependent dielectric response function. To heat the target uniformly, we optimized the experimental condition so that the energy deposition could occur almost at the top of the Bragg peak. The energy deposition inhomogeneity could be reduced to ±5% by adjusting the incident energy and the target thickness to be 2.02 MeV/u and 180 μm, respectively. The target could be heated homogeneously up to kT =7 eV well before the arrival of the rarefaction waves at the center of the target. In principle, the EOS data can be evaluated by iteratively adjusting the data embedded in the hydro code until the measured hydrodynamic motion is reproduced by the calculation. This method is consistent with the conditions of nuclear nonproliferation, because a very small amount of fissile material is enough to perform the experiment, and no shock compression occurs in the target.

One-dimensional particle-in-cell and Monte-Carlo (FLUKA) simulation methods were used together, in order to investigate the production of positrons in lead targets, illuminated by a short-pulse high-intensity laser. The study is focused on lead targets of 1 mm thickness and more and pulses of intensity in the range 1019–1022 W/cm2. The calculations provided an estimate of an absolute number of positrons and the ratio of electrons and positrons emerging from the target. The thickness of the target is scaled in order to find an optimal thickness that could provide a neutral electron-positron beam.

The problem of initial thermal velocity and the space charge effect of electron guns in numerical simulations have been investigated deeply. In general, the current software can meet the engineering requirements. However, the electron's initial thermal velocity and the space charge effect lack sufficient consideration. The above two factors significantly limit the performances of electron guns. Moreover, the parameters of electron guns are approximated based on a limited number of electron trajectories. Thus, the statistical distribution of the beam electron resulting from its initial thermal velocity is not considered adequately in present software. This paper introduces the equivalent meridional projected trajectory equation and the curvilinear axis evolution theory of the current density of toroidal electron sub-beam, and subsequently the current and charge density distributions in electron guns can be derived through iteration calculation. Based upon, the virtual crossover of an electron gun is determined by its current density distribution. As well as, a relevant numerical algorithm is developed and the related program is modified based on the popular commercial software SOURCE. Tungsten cathode guns, LaB6 cathode guns, field mission guns and Pierce guns are simulated respectively by examples. The calculations prove that the modified software is effective and practical.

The paper is directed to the study of high-temperature plasma and ablation plasma formation as well as efficiency of the laser energy transfer to solid targets irradiated by laser pulses with intensities of 1–50 PW/cm2 and duration of 200–300 ps, i.e., at conditions corresponding to the characteristics of the laser spike designed to generate the igniting shock wave in the shock ignition concept. The experiments have been performed at Prague Asterix Laser System. The iodine laser delivered 250 ps (full width at half maximum) pulses with the energy in the range of 100–600 J at the first (λ1 = 1.315 µm) and third (λ3 = 0.438 µm) harmonic frequencies. The focal spot radius of the laser beam on the surface of Al or Cu targets made was gradually decreased from 160 to 40 µm. The diagnostic data collected using three-frame interferometry, X-ray spectroscopy, and crater replica technique were interpreted by two-dimensional numerical and analytical modeling which included generation and transport of fast electrons. The coupling parameter Iλ2 was varied in the range of 1 × 1014−8 × 1016 Wμm2/cm2 covering the regimes of weak to intense fast electron generation. The dominant contribution of fast electron energy transfer into the ablation process and shock wave generation was found when using the first harmonic laser radiation, the focal spot radius of 40–100 µm, and the laser energy of 300–600 J.

The bubble regime acceleration of electrons by a short pulse laser in a carbon nanotube (CNT) embedded plasma is investigated, employing two-dimensional Particle-in-Cell simulations. The laser converts the CNT placed on the laser axis into dense plasma and expels the electrons out, to form a co-moving positive charged sheet inside the bubble. The additional field generated due to sheet enhances the energy of the monoenergetic bunch by about 5% and their number by 5–20%. For a typical 40 fs, 7.5 × 1019 Wcm−2 pulse in an underdense plasma of density n0, CNT of thickness 25 nm and electron density 30n0, produces a monoenergetic bunch of 115 MeV with 5% energy spread. When CNT density is raised to 90n0, the energy gain, energy spread and accelerated charge increases further. The analytical framework supports these features.