A method to design the composite insulation structures in pulsed power systems is proposed in this paper. The theoretical bases for this method include the Weibull statistical distribution and the empirical insulation formula. A uniform formula to describe the reliability (R) for different insulation media such as solid, liquid, gas, vacuum, and vacuum surface is derived. The dependence curves of the normalized applied field on R are also obtained. These curves show that the normalized applied field decreases rapidly as R increases but the declining rates corresponding to different insulation media are different. In addition, if R is required to be higher than a given level, the normalized applied field should be smaller than a certain value. In practical design, the common range of the applied fields for different insulation media should be chosen to meet a global reliability requirement. In the end, the proposed method is demonstrated with a specific coaxial high-voltage vacuum insulator.

We consider the acceleration of electrons in vacuum by means of the circularly-polirized electromagnetic wave, propagating along a magnetic field. We show that the electron energy growth, when using ultra-short and ultra-intense laser pulses (1 ps, 1018 W/cm2, CO2 laser) in the presence of a magnetic field, may reach up to the value 2,1 GeV. The growth of the electron energy is shown to increase proportionally with the increase of the laser intensity and the initial energy of the electron. We find that for some direction of polarization of the wave, the acceleration of electrons does not depend on the initial phase of the electromagnetic wave. We estimate the laser intensity, necessary for the electron acceleration. In addition, we find the formation length of photon absorption by electrons, due to which one may choose the required region of the interaction of the electrons with the electromagnetic wave and magnetic field. We also show that as a result of acceleration of electrons in the vacuum by laser radiation in a magnetic field one may obtain electron beam with small energy spread of the order δε/ε ≤ 10−2.

It is shown that it is possible to accelerate micro-foils to velocities from 108 cm/s up to relativistic velocities without the disturbance of the Rayleigh-Taylor instability. The acceleration occurs due to the radiation pressure of proper high power lasers. In these systems, the ablation force is negligible relative to the ponderomotive force that dominates the acceleration. The laser irradiances of 1017 W/cm2 < IL < 1021 W/cm2 with a pulse duration of the order of 10 picoseconds can accelerate a micro-foil by the laser radiation pressure to velocities as high as 109 cm/s before breaking by Rayleigh Taylor (RT) instability. Similarly, laser irradiances of IL > 1021 W/cm2 with pulse duration of the order of 10 femtoseconds can accelerate a micro-foil to relativistic velocities without RT breaking. Due to the nature of the accelerating ponderomotive force, in both the relativistic and non-relativistic cases, the structure of the accelerated target contains a double layer (DL) at the interface of the laser-target interaction. The DL acts as a piston during the acceleration process. The influence of the DL surface tension on the RT instability is also analyzed in this paper.

Large energy fluxes and energy deposition are often found during off normal events in fusion reactors both magnetic and inertial confinement. Great temperature excursions can be found in the plasma facing components materials resulting in melting, evaporation, and expansion of the target material vapor cloud and successive plasma interaction. A general methodology for the computational solution of this very complex problem is proposed in this paper using a novel approach of the Particle-in-Cell method. This novel approach preserves many of the original Particle-in-Cell methodology proposed by Harlow's but introduces several changes to the method, which makes it particularly suitable in plasma dynamics applications as Tokamaks devices. Benchmarking is done using results from the very well-known and benchmarked HEIGHTS computer package and using available results from the MK200 plasma gun experiments. The general scheme is explained in detail and results and discussion related to the main computational aspects are presented. In particular, the critical importance of the starting computational mesh versus the aimed accuracy is studied and explained. The methodology is different from any other presented in literature because the dynamics of the physical problem dictates that as enough energy is being dumped on the target plate, melting and evaporation of the material takes place. As time progresses, new sample particles are introduced in the system making this boundary a dynamic one along time. Computer time is discussed in relation to the initial sample particle loading, aimed accuracy and importance of the time used for solving the radiation transport at each time step.

We present a new simulation method to predict the maximum possible yield of X-rays produced by electron beams accelerated by petawatt lasers irradiating thick solid targets. The novelty of the method lies in the simulation of the electron refiluxing inside the target implemented with the Monte Carlo code Fluka. The mechanism uses initial theoretical electron spectra, cold targets and refiluxing electrons forced to re-enter the target iteratively. Collective beam plasma effects are not implemented in the simulation. Considering the maximum X-ray yield obtained for a given target thickness and material, the relationship between the irradiated target mass thickness and the initial electron temperature is determined, as well as the effect of the refiluxing on X-ray yield. The presented study helps to understand which electron temperature should be produced in order to generate a particular X-ray beam. Several applications, including medical and security imaging, could benefit from laser generated X-ray beams, so an understanding of the material and the thickness maximizing the yields or producing particular spectral characteristics is necessary. On the other more immediate hand, if this study is experimentally reproduced at the beginning of an experiment in which there is an interest in laser-driven electron and/or photon beams, it can be used to check that the electron temperature is as expected according to the laser parameters.

This paper analyzes the one dimensional shock wave created in a planar target by the ponderomotive force induced by very high laser irradiance. The laser-induced relativistic shock wave parameters, such as compression, pressure, shock wave and particle flow velocities, sound velocity and temperature are calculated here for the first time in the context of relativistic hydrodynamics. For solid targets and laser irradiance of about 2 × 1024 W/cm2, the shock wave velocity is larger than 50% of the speed of light, the shock wave compression is larger than 4 (usually of the order of 10) and the targets have a pressure of the order of 1015 atmospheres. The estimated temperature can be larger than 1 MeV in energy units and therefore very excited physics (like electron positron formation) is expected in the shocked area. Although the next generation of lasers might allow obtaining relativistic shock waves in the laboratory this possibility is suggested in this paper for the first time.

Analytical and numerical investigation of the reflection and transmission of a counter-propagating relativistically strong laser pulse from a relativistically flying dense plasma double-sided mirror is studied. We assume that the incident laser pulse is short, so that we can neglect the slow ion dynamics and consider the electron motion only. Numerical results of the amplitudes of the reflected/transmitted electric fields from a uniformly moving mirror, accelerated mirror, and oscillating mirror are obtained. Fourier spectrum of the reflected intensity from the moving mirror shows that the intensity decreases with increase in the frequency. The reflected pulse has an up-shifted frequency and increased intensity. It is seen that the first few cycles of the reflected radiation exhibit presence of high harmonics, while the later cycles are compressed together with harmonics in comparison with the earlier cycles. The variation of the reflection coefficient for a uniformly moving mirror as a function of the thin foil plasma-density parameter is numerically studied.

Particle acceleration is an important tool in material modification and several other applications. There are multiple techniques to generate and accelerate ion beams. In the current research work, ions emitted from laser induced plasma were accelerated by employing a DC high voltage extraction assembly. The Nd:YAG laser (1064 nm) with 10 mJ energy and 12 ns pulse width was irradiated on Aluminum target. Thomson parabola technique using Solid State Nuclear Track Detector (CR-39) was employed for measurement of ions energy generated from laser induced plasma. In response to a stepwise increase in acceleration potential from 0–10 kV, an evident increase in energy, in the range 627–730 keV, was observed. In order to utilize this facility as an ion source, Aluminum was exposed to these ions. The Optical and AFM micrographs revealed that the damage produced by the ions on Al surfaces, become more prominent with the increase in ion energy. TRIM simulations were performed for the analysis of the damage at the irradiated samples. Changes in the total displacements, target vacancies and replacement collisions, calculated by TRIM simulation, were analyzed for ion irradiations with increasing ion energies.

In order to achieve the truncated amplified spontaneous emission pulse, the method of timeshare quenching was proposed in this paper. When the original pulse of the amplified spontaneous emission is 16.72 ns, the obtained best results show that the pulse width is truncated to 2.48 ns, and the shortening ratio is approximately 6.7. By analyzing the 12 acquisition results of the continuous amplified spontaneous emission truncation, 2.59 ± 0.05 ns amplified spontaneous emission pulse was obtained. The experimental results showed that the stability of the truncated pulse width is well. This method is applicable to truncate the ASE pulse in KrF excimer laser. It is significantly to the research of the inertial confinement fusion.

An extended analytical model for particle dynamics in fields of a highly-nonlinear plasma wakefield (the bubble or blow out regime) is derived. A recently proposed piecewise model is generalized to include a time dependent bubble radius and full field solution in the acceleration direction. Incorporation of the cavity dynamics in the model is required to simulate the particle trapping properly. On the other hand, it is shown that the previously reported piecewise model does not reproduce the formation of a mono energetic peak in the particle spectrum. The mono energetic electron beams are recovered only when the full longitudinal field gradient is included in the model.

The effects of the polarized incident laser pulse on the electrons of the plasma surface and on the reflected pulse in the relativistic laser-plasma interaction is investigated. Based on the relativistic oscillating mirror and totally reflecting oscillating mirror (TROM) regimes, the interaction of the intense polarized laser pulses with over-dense plasma is considered. Based on the effect of ponderomotive force on the characteristic of generated electron nano-bunches, considerable increasing in the localization and charges of nano-bunches are realized. It is found that the circularly polarized laser pulse have Ne/Ncr of 1500 which is almost two and seven times more than the amounts for P-polarized and S-polarized, respectively.

A novel coaxial relativistic transit-time oscillator with low guiding magnetic field is proposed and investigated to generate high power microwave at Ku-band. With the coaxial structure and a quasi body wave adopted as the operating mode, the device has a larger space-charge limiting current, higher power handling capacity, and lower guiding magnetic field. Moreover, for further improving the output power, a coaxial TM02 mode resonant reflector is well designed. Main structure parameters of the device are optimized by particle in cell simulations. A typical simulation result is that, with a 358 keV, 7.25 kA beam guided by a magnetic field of about 0.7 T, an 810 MW microwave pulse at 14.25 GHz is generated, yielding a conversion efficiency of about 31%. The primary experiments are also carried out. At a low guiding magnetic field of 0.7 T, a microwave pulse with power of 400 MW, pulse duration of 30 ns, frequency of 14.3 GHz close to the simulation one, and efficiency of 15.4% is generated.

Laser ablation of graphite materials in the presence of an external magnetic field is studied with the use of the newly developed HEIGHTS-PIC particle-in-cell code and compared with both theoretical and experimental results. Carbon plumes behavior controlled by a strong magnetic field is of interest to evaluate the plume shielding effects to protect the original exposed target from further damage and erosion. Since intense power deposition on plasma facing components is expected during Tokamaks loss of plasma confinement events such as disruptions, vertical displacements event, runaway electrons, or during normal operating conditions such as edge-localized modes, it is critical to better understand the evolving target plasma behavior for more accurate prediction of the potential damage created by these high-energetic dumps which may not be easily mitigated without loss of structural and functional performance of the plasma facing components. Numerical experiments have been performed to provide benchmarking conditions for the HEIGHTS-PIC simulation package originally designed to evaluate the erosion of the Tokamak surfaces, splashing of the melted/ablated-vaporized material, and transport into the bulk plasma with consequent plasma contamination. Evolving target plasma temperature and density are calculated and compared with measured reported values available into literature for similar conditions and show good agreement with the HEIGHTS-PIC package predictions.

This paper presents the results of a statistical and correlation analysis of the energy and energy density of an ion beam formed by a self-magnetically insulated diode with an explosive emission cathode. The experiments were carried out with the TEMP-4M accelerator operating in double-pulse mode: plasma formation occurs during the first pulse (negative polarity, 300–500 ns, 100–150 kV), and ion extraction and acceleration during the second pulse (positive polarity, 120 ns, 250–300 kV). Various arrangements of diodes have been investigated: strip focusing and planar diodes, a conical focusing diode and a spiral diode. The total ion beam energy was measured using both a calorimeter and an infrared camera and the beam energy density was measured by the thermal imaging and acoustic diagnostics. The correlation analysis showed that ion current density is only weakly dependent on the accelerating voltage and other output parameters of the accelerator, with the coefficient of determination <0.3. At the same time, in this paper, we have identified that the total energy of the beam and the energy density is strongly dependant on the accelerator output parameters, since the coefficient of determination >0.9. The mechanism governing stabilization of the beam energy density from shot to shot was discovered and attributed to formation of the neutral component in ion beam as being due to charge exchange between accelerated ions and neutral molecules from a neutral layer near the anode surface. Implementation using a self-magnetically insulated diode with an explosive-emission cathode, having an operational lifetime of up to 106 shots, has promising prospects for various technological applications.

Self-focusing of an intense circularly-polarized laser beam in a hot electron-positron-ion magneto-plasma is studied. Using a relativistic fluid model, nonlinear equation describing laser-plasma interaction in the quasi-neutral approximation is derived. Expanding nonlinear current density in terms of normalized vector potential and saving only the parabolic terms, we investigated the self-focusing phenomenon for right- and left-hand circularly polarized laser beams. The evolution of laser beam spot size with Gaussian profile is considered. Effects of the external magnetic field, fraction of electron-positron pairs, and also the kind of polarization on the self-focusing property are studied. It is shown that a mixture of electron-positron pairs to the ion-electron plasma modifies the behavior of plasma with respect to the external magnetic field.

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.