In electron beams where space charge plays an important role in the beam transport, the beams’ transverse and longitudinal properties will become coupled. One example of this is the transverse–longitudinal correlation produced in a current-modulated beam generated in a DC electron gun, formed through the competition between the time-dependent radial space charge force and the time-independent radial focusing force. This correlation will cause both the slice radius and divergence of the beam extracted from the gun to depend on the slice current. Here we consider the transport of such a beam in a linearly tapered solenoid focusing channel. Transport performance was generally improved with longer taper lengths, minimal initial correlation between slice divergence and slice current, and moderate degrees of initial correlation between initial slice radius and slice current. Performance was also generally improved with lower slice emittances, although surprisingly transport was improved by slightly increasing the assumed slice emittance in certain limited circumstances.

Flux waveforms of aluminum cluster beams supplied from a laser-ablation cluster source were precisely investigated under various source conditions such as background pressure, ablation laser intensity, and nozzle structure. A time-of-flight mass spectroscopy revealed that aluminum clusters with sizes up to 200 were generated and the amount of the clusters could be maximized by choosing a proper background pressure (~2 MPa) and an ablation laser fluence (~40 mJ/cm2). Flux waveforms of clusters having specific sizes were carefully reconstructed from the observed mass spectra. It is found that the pulse widths of the aluminum cluster beams were typically about 100 µs and much smaller than that of the monoatomic aluminum beam, indicating that the cluster formation was limited in a relatively small volume in the laser-ablated vapor. Introducing a conical nozzle having a large open angle was also found to enhance the cluster beam velocity and reduce its pulse width. A velocity measurement of particles in the cluster beam was conducted to examine the velocity spread of the supplied clusters. We found that the aluminum clusters were continuously released from the source for about 100 µs and this release time mainly determined the pulse width of the cluster beam, suggesting that controlling the behavior of an ablated vapor plume in the waiting room of the cluster source holds the key to drastically improving the cluster beam flux.

Ignition with the help of a shock wave is performed by the interaction of accelerated plasma block by a petawatt-picosecond (PW-ps) laser, with a solid-state density fuel that it is a new possibility for achieving controlled fusion by inertial confinement. The unexpected production of plasma blocks provides new access to the ignition of solid-state density fuel according to the Chu hydrodynamic model. When the produced plasma block by the PW-ps laser hits the main fuel due to the density differences between the plasma block and the main fuel of the shock wave, this progressive wave increases the density of solidified fuels and reduces the energy of the ignition threshold and increases the flammability. In this study, a new discovery of shock waves has been observed leading to the resonance phenomenon. Nuclear heat shock waves resonance in the side-on ignition of fuel in the internal layer of fuel at x ≠ 0 appears from the exact solution of the hydrodynamic equations with respect to the density profile. This important finding achieves the required ignition temperature for solid-state fuel deuterium–tritium (D–T) in certain energies, with a significant increase due to the resonance of thermonuclear waves. This discovery will facilitate practical experiments on the ignition of advanced solid-state fuels with the accelerated plasma blocks by a PW-ps laser at certain energies.

A scheme of phase-matched terahertz generation by beating two co-propagating lasers in magnetized plasma, in the presence of a magnetosonic wave (MSW), is developed. The beat frequency ponderomotive force of the lasers imparts an oscillatory drift to electrons. The electron drift velocity couples with the electron density perturbation associated with the MSW to produce an irrotational nonlinear current $\left(\nabla \times {\vec J}\;{}^{\rm NL}\ne 0\right)$ . The beat current density resonantly excites a THz (Terahertz) radiation when the phase-matching conditions are satisfied. The MSW mediates the phase matching. At 9.6 and 10.6 µm wavelengths, and background magnetic field of 285 kG, one may achieve normalized THz wave amplitude of the order of 10−3 and one obtains the ratio of THz power to pump power of the order of 10−6.

We present results of 2D particle-in-cell (PIC) simulations of carbon ion acceleration by 10 petawatt (PW) laser pulses, studying both circular polarized (CP) and linear polarized (LP) pulses. We carry out a thickness scanning of a solid carbon target to investigate the ideal thickness for carbon ion acceleration mechanisms using a 10 PW laser with an irradiance of 5 × 1022 W cm−2. The energy spectra of carbon ions and electrons and their temperature are studied. Additionally, for the carbon ions, their angular divergence is studied. It is shown that the ideal thickness for the carbon acceleration is 120 nm and the cutoff energy for carbon ions is 5 and 3 GeV for CP and LP pulses, respectively. The corresponding carbon ions temperature is ~1 and ~0.75 GeV. On the other hand, the energy cutoff for the electrons is ~500 MeV with LP and ~400 MeV with CP laser pulses. We report that the breakout afterburner mechanism is most likely causing the acceleration of carbon ions to such high energies for the optimal target thickness.

Multi-MeV proton beams can be generated by irradiating thin solid foils with ultra-intense (>1018 W/cm2) short laser pulses. Several of their characteristics, such as high bunch charge and short pulse duration, make them a complementary alternative to conventional radio frequency-based accelerators. A potential material science application is the chemical analysis of cultural heritage (CH) artifacts. The complete chemistry of the bulk material (ceramics, metals) can be retrieved through sophisticated nuclear techniques such as particle-induced X-ray emission (PIXE). Recently, the use of laser-generated proton beams was introduced as diagnostics in material science (laser-PIXE or laser-driven PIXE): Coupling laser-generated proton sources to conventional beam steering devices successfully enhances the capture and transport of the laser-accelerated beam. This leads to a reduction of the high divergence and broad energy spread at the source. The design of our hybrid beamline is composed of an energy selector, followed by permanent quadrupole magnets aiming for better control and manipulation of the final proton beam parameters. This allows tailoring both, mean proton energy and spot sizes, yet keeping the system compact. We performed a theoretical study optimizing a beamline for laser-PIXE applications. Our design enables monochromatizing the beam and shaping its final spot size. We obtain spot sizes ranging between a fraction of mm up to cm scale at a fraction of nC proton charge per shot. These results pave the way for a versatile and tunable laser-PIXE at a multi-Hz repetition rate using modern commercially available laser systems.

Calculations of the spectral coefficients for X-ray absorption and spectral brightness's for X-ray radiation were performed for niobium Z-pinch plasma at the temperature of 1 keV and at different plasma densities to determine the compression degree where the spectral lines become indistinguishable. As known, traditional methods of temperature diagnostics of hot dense radiating plasmas are based on analysis of the spectral line shape in dependence on plasma temperature and density. In this case, the interval of photon radiation energies is used, where the spectral lines are well distinguishable in an experiment. On the other hand, Z-pinch plasma has high compression, and an increase of plasma density leads to the deformation of the spectral line shape because of Doppler broadening, Stark broadening, and so-called “additional” broadening of spectral lines that take place in a quantum statistical ensemble of plasma ions and atoms. The traditional method of temperature diagnostics becomes impossible and different methods, which do not use spectral line characteristics, should be applied. The aim of this paper is to determine the density border where the spectral lines become indistinguishable. Important features of the quantum mechanical model, which is known as ion model of plasma, and which is used for calculations in the presented paper, are considered and discussed. A brief review of the theoretical models that have been earlier developed to calculate the radiative opacity characteristics of hot dense plasma is presented as well.

Nonlinear propagation of ion acoustic waves has been studied in unmagnetized quantum (degenerate) plasma in the presence of an ion beam using the one-dimensional quantum hydrodynamic model. The Korteweg–de Vries (K–dV) equation has been derived by using the reductive perturbation technique. The solution of ion acoustic solitary waves is obtained from the K–dV equation. The theoretical results have been analyzed numerically for different values of plasma parameters and the results are presented graphically. It is seen that the formation and structure of solitary waves are significantly affected by the ion beam in quantum plasma. The solitary waves will be compressive or rarefactive depending upon the values of velocity, concentration, and temperature of the ion beam. The critical value of ion beam density for the nonexistence of solitary wave has been numerically estimated, and its variation with velocity and temperature of ion beam has been discussed graphically. The results are new and would be very useful for understanding the beam–plasma interactions and the formation of nonlinear wave structures in dense quantum plasma.

An analytical formalism of laser absorption in a nanorod embedded dielectric surface has been developed. Nanorods lie in the plane of the dielectric, in the form of a planar array. A laser, impinged on them with an electric field perpendicular to the lengths of the nanorods, imparts oscillatory velocity to nanorod electrons. As the free electrons of a nanorod are displaced, a space charge field is developed in the nanorod that exerts restoration force on the electrons and their drift velocity shows a resonance at ${\rm \omega} = {\rm \omega} _{\rm p}/\sqrt 2 $ , where ωp denotes the plasma frequency of free electrons inside the nanorod. It is inhibited by collisions and nanorod expansion. At the resonance, the electrons are efficiently heated by the laser and laser energy is strongly absorbed, resulting in significant reduction in laser transmissivity. The transmissivity decreases with laser intensity.

The effects of the phase variation, the evolution of the electron beam, the evolution of the radiation intensity, and the higher-order modes due to waveguides on a free-electron laser (FEL) oscillator have been analyzed by using two electron beams of different energies based on the proposed FEL facility which is to be operated in the far-infrared and infrared regions. The three-dimensional (3D) effects on a FEL oscillator due to waveguides and higher-order modes were studied using an extended 3D FEL code with two electron beams that we have developed. The effects of the variation on the amplitude of radiation on the electron beam's emittance and energy spreads were also calculated in the case of waveguide for multi-particle and multi-pass numbers by using a new 3D code. The phase variation, the variation in the beam envelope, the evolution of the amplitude, and power were calculated for the fundamental mode. The results were compared with those of the higher-order modes of the wiggler for various TE and TM modes for determining the FEL's performance which is required for high-quality electron beams.

A transport model for a transverse electron beam-pumped semiconductor laser has been developed. The model incorporates spatial dependencies of the power deposition from the beam as well as a three-dimensional model of the gain medium and the field intensity of the photons produced by stimulated emission in the oscillation cavity. This model accounts for spatial inhomogeneities and has been solved for a variety of pumping strengths. The model was developed so that it can be benchmarked with electron beam pumping. The dominant mechanisms for the production of electron–hole pair production within the semiconductor material is similar to the dominant mechanisms for the production of electron–hole production using ion beams. Thus, the model can be extended to fission fragment ion pumping of semiconductor lasers in order to model a nuclear-pumped laser/reactor system.

Interaction of extreme ultraviolet (EUV) pulses of high intensity with gases results in the creation of non-thermalized plasmas. Energies of the driving photons and photoelectrons are sufficient for creation of excited states, followed by emission of the EUV photons. In most cases, decay times of these states are short comparing to the driving EUV pulse. It means that just after stopping of the driving pulse, the EUV emission corresponding to the excited states should also stop. From our earlier measurements in the optical range, however, it can be concluded that lifetimes of such plasmas exceed a time duration of the driving pulse even two orders of magnitude. Hence, it can be expected that the time duration of the EUV emission can be also significantly longer than the irradiation time. In this work, EUV-induced, low-temperature helium (He), krypton, and xenon plasmas were investigated. EUV emission from these plasmas was studied, using a specially prepared detection system, allowing for time-resolved measurements, in selected spectral ranges. The detection system was based on a paraboloidal collector and a semiconductor photodiode, sensitive for the EUV photons. For spectral selection, the corresponding filters or multilayer mirrors were employed. In most cases, the time duration of the EUV emission was significantly longer than the driving EUV pulse. In case of He plasmas, the emission corresponding to excited atoms was detected even hundreds of nanoseconds after the irradiation. It was also shown that the corresponding time profiles depended on densities of gases to be ionized.

A three-section pulse forming network (PFN) based on Guillemin type-C circuit was developed to meet the challenge of a compact design, high withstand voltage, and high-quality output waveform with fast rise time, flat-top duration, and 100-ns pulse width. A simplified pulse forming circuit was proposed and studied that includes only three LC-sections connected in parallel, with each section containing an inductor and a capacitor connected in series. The effect of the capacitance deviation on the output waveform was investigated. The simulation results show that when the capacitance deviation exceeds +3%, both the flat top and fall time of the output waveform of single PFN module deteriorate greatly. Fortunately, in a multi-stage PFN-Marx circuit, even if the capacitance deviation exceeds +10%, when the average capacitance of the same LC sections is close to the theoretical value, the output waveform maintains a good quality and is in good agreement with the theoretical prediction. The compact three-section PFN developed during this project has a size of only 360 mm × 342 mm × 65 mm, and a maximum withstand voltage of 120 kV. Sixteen PFN stages were assembled to form a Marx generator with design parameters to provide of an output peak power of 12 GW and a maximum peak current of 15 kA. The tested output waveform agrees well with the theoretical results, having a rise time of 31 ns, a flat-top of 104 ns, and a pulse with of 164 ns.

An analytical and numerical study has been carried out for the generation of terahertz (THz) radiation by beating of two intense cosh-Gaussian laser beams (decentered Gaussian beams) in the rippled density magnetized plasma under the relativistic–ponderomotive regime. In this process, both laser beams exert a relativistic–ponderomotive force on plasma electrons at the beat frequency and impart them an oscillatory velocity in the presence of a static magnetic field. Due to coupling between this nonlinear oscillatory velocity with density ripple, nonlinear current is generated that excites the THz radiation at the different frequency. Higher-order paraxial-ray approximation (non-paraxial theory) has been used in this study. The effects of the decentered parameter, magnetic field, and density ripple on the THz radiation generation in ripple density magnetized plasma have been investigated. Further, the effect of beating of laser beams on the THz field amplitude and the efficiency of THz radiation have been studied. The amplitude and efficiency of the emitted radiation are found to be highly sensitive to the decentered parameter, magnetic field, and density ripple. It has been found that the amplitude and efficiency of the generated THz radiation increase significantly with increasing the values of decentered parameter, magnetic field, and density ripple.

We examine the electron acceleration induced by an ultra-relativistic intensity laser–plasma interaction in a two-dimensional plasma channel in the presence of a self-generated transverse magnetic field. We find that the electron dynamics is strongly affected by the laser pulse polarization angle, plasma density, and magnetic field strength. We investigate in detail, the dependencies of the electron acceleration in terms of different parameters and find excellent agreement with non-magnetized plasma in the absence of the magnetic field. The numerical results show that the self-generated magnetic field plays a constructive role in the electron acceleration process. It is shown that electron acceleration is more affected by self-generated magnetic field for the laser radiations with large polarization angles. The numerical results show the maximum enhancement for electron acceleration for a laser radiation with polarization angle θ = π/2.

Self-focusing of Gaussian laser beam has been investigated in quantum plasma under the effect of applied axial magnetic field. The nonlinear differential equation has been derived for studying the variations in the beam-width parameter. The effect of initial plasma electron temperature and the axial magnetic field on self-focusing and normalized intensity are studied. Our investigation reveals that normalized intensity increases to tenfolds where quantum effects are dominant. The normalized intensity further increases to twelvefolds on increasing the magnetic field.

Second-harmonic generation of the relativistic self-focused chirped laser pulse in plasma has been studied with the exponential plasma density ramp profile in the presence of a planar magnetostatic wiggler. It is evident that the exponential plasma density ramp is helpful in enhancing second-harmonic generation as, with the introduction of the exponential plasma density ramp, self-focusing becomes stronger and hence, it leads to enhance the harmonic generation of the second order in the plasma. Also, it is observed that the efficiency of second-harmonic generation enhances significantly with an increase in the value of the chirp parameter. Further, the magnetostatic wiggler helps in enhancing the harmonic generation of the second order. This is due to the fact that dynamics of the oscillating electrons is altered due to the Lorentz force which, in turn, modifies the plasma wave and, hence, results in the efficient second-harmonic generation.

Above-threshold ionization (ATI) is one of the most fundamental processess when atoms or molecules are subjected to intense laser fields. Analysis of ATI process in intense laser fields by a Wigner-distribution-like (WDL) function is reviewed in this paper. The WDL function is used to obtain various time-related distributions, such as time-energy distribution, ionization time distribution, and time-emission angle distribution and so on, of atoms in laser field pulses with different laser parameters. For the linearly polarized laser pulses, the time-energy distribution intuitively shows from a quantum point of view the relationship between the ionization moment and the final energy and clearly reveals the origin of interference structures in the photoelectron spectrum. In particular, for linearly polarized few-cycle laser pulses, all calculated distributions show the dependence of electron behavior on the ionization time, emission direction, and carrier-envelope phase (CEP). For elliptically polarized few-cycle pulses, we calculate the angular distribution, ionization time distribution, and time-emission distribution, which are compared with the semiclassical calculations. Analysis shows that the offset angle (difference between positions of the peaks in the angular distributions obtained by two methods) in the angular distributions does not correspond to the offset time (difference between positions of the peaks in the ionization time distributions obtained by two methods) in the ionization time distributions, which implies that the attosecond angular streaking technique based on this correspondence between the offset angle and time is in principle inaccurate. Furthermore, the offset time cannot be interpreted as tunneling time.

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Efficient electron acceleration by a linearly chirped ultrashort laser pulse in vacuum is investigated using the particle swarm optimization method. By applying this method for optimizing the initial parameters of the laser pulse, a pronounced increase in final energy gain of the electron is obtained compared to that expected from the successive optimization method. Our results also suggest that the value of the optimal chirp parameter is independent of laser polarization and the energy gain could be insensitive to the sign of this parameter when the initial phase is optimally adjusted. In addition, utilizing the chirped laser pulse with optimized conditions for acceleration of an electron bunch reveals that the energy spectrum is shifted to considerably higher energies and the spatial distribution is significantly improved in a polarization-dependent manner.

We study the setting up of relativistic ponderomotive non-linearity in an under-dense collisionless cold plasma. Using the fluid model, coupled system of equations of the laser beam and electron plasma oscillations has been derived. We present the numerical simulation for this coupled system of equations, when the coupling arises through relativistic ponderomotive non-linearity. The filamentation of the laser beam has been found to vary appreciably with perturbation wave number. The results show that with time, localized structures become more complex and the plasma oscillation frequency spectra have several harmonic peaks at terahertz frequencies when the electron plasma frequency is in terahertz range and laser frequency is around 2.35 × 1015 rad/s. We also present the semi-analytical model to capture the underlying physics.

Thermal imaging diagnostics was used as a surface temperature mapping tool to characterize the energy density distribution of a high-intensity pulsed ion beam. This approach was tested on the TEMP-6 accelerator (200–250 kV, 150 ns). The beam composition included carbon ions (85%) and protons, and the energy density in the focus was 5–12 J/cm2. Targets of stainless steel, titanium, brass, copper, and tungsten were examined. Our observations show that the maximum energy density measured with the thermal imaging diagnostics considerably exceeds the ablation threshold of the targets. An analysis of the overheating mechanisms of each target was carried out, including metastable overheating of the target to above its boiling temperature during rapid heating; formation, migration, and the subsequent annealing of fast radiation-induced defects in the target under ion beam irradiation. This expands the range of energy density measurement for this thermal imaging diagnostics from 2–3 J/cm2 up to 10–12 J/cm2 but introduces error into the results of measurement. For a stainless steel target, this error exceeds 15% at an energy density of more than 4 J/cm2. A method of correcting the results of the thermal imaging diagnostics is developed for a pulsed ion beam under conditions of intense ablation of the target material.

The formation of a collisional shock wave by the light pressure of a short-laser pulse at intensities in the range of 1018–1023 W/cm2 is considered. In this regime the thermodynamic parameters of the equilibrium states, before and after the shock transition, are related to the relativistic Rankine–Hugoniot equations. The electron and ion temperatures associated with these shock waves are calculated. It is shown that if the time scale of energy dissipation is shorter than the laser pulse duration a collisional shock is formed. The electrons and the ions in the shock-heated layer may have equal or different temperatures, depending on the laser pulse duration, the material density and the laser intensity. This shock wave may serve as a heating mechanism in a fast ignition scheme.

We present a broad study of linear, clustered, noble gas puffs irradiated with the frequency doubled (527 nm) Titan laser at Lawrence Livermore National Laboratory. Pure Ar, Kr, and Xe clustered gas puffs, as well as two mixed-gas puffs consisting of KrAr and XeKrAr gases, make up the targets. Characterization experiments to determine gas-puff density show that varying the experimental parameter gas-delay timing (the delay between gas puff initialization and laser-gas-puff interaction) provides a simple control over the gas-puff density. X-ray emission (>1.4 keV) is studied as a function of gas composition, density, and delay timing. Xe gas puffs produce the strongest peak radiation in the several keV spectral region. The emitted radiation was found to be anisotropic, with smaller X-ray flux observed in the direction perpendicular to both laser beam propagation and polarization directions. The degree of anisotropy is independent of gas target type but increases with photon energy. X-ray spectroscopic measurements estimate plasma parameters and highlight their difference with previous studies. Electron beams with energy in excess of 72 keV are present in the noble gas-puff plasmas and results indicate that Ar plays a key role in their production. A drastic increase in harder X-ray emissions (X-ray flash effect) and multi-MeV electron-beam generation from Xe gas-puff plasma occurred when the laser beam was focused on the front edge of the linear gas puff.

The multi-petawatt (PW) lasers currently being built in Europe as part of the Extreme Light Infrastructure (ELI) project will be capable of generating femtosecond light pulses of ultra-relativistic intensities (~1023–1024 W/cm2) that have been unattainable so far. Such laser pulses can be used for the production of high-energy ion beams with unique features that could be applied in various fields of scientific and technological research. In this paper, the prospect of producing ultra-intense (intensity ≥1020 W/cm2) ultra-short (pico- or femtosecond) high-energy ion beams using multi-PW lasers is outlined. The results of numerical studies on the acceleration of light (carbon) ions, medium-heavy (copper) ions and super-heavy (lead) ions driven by a femtosecond laser pulse of ultra-relativistic intensity, performed with the use of a multi-dimensional (2D3 V) particle-in-cell code, are presented, and the ion acceleration mechanisms and properties of the generated ion beams are discussed. It is shown that both in the case of light ions and in the case of medium-heavy and super-heavy ions, ultra-intense femtosecond multi-GeV ion beams with a beam intensity much higher (by a factor ~102) and ion pulse durations much shorter (by a factor ~104–105) than achievable presently in conventional radio frequency-driven accelerators can be produced at laser intensities of 1023 W/cm2 predicted for the ELI lasers. Such ion beams can open the door to new areas of research in high-energy density physics, nuclear physics and inertial confinement fusion.

High inductive helical support provides a solution to controlling the alignment error of inner electrodes in magnetically insulated transmission lines (MITLs). Three-dimensional particle-in-cell simulations were performed to examine the current loss mechanism and the effects of structural parameters on electron flow in an MITL with a helical inductor. An empirical expression related to the ratio of electron current loss to anode current and the ratio of anode current to self-limited current was obtained. Electron current loss caused by helical inductor with different structures was displayed. The results indicate that the current loss in an MITL, near an inductive helical support, comprises both the inductor current and the electron current loss. The non-uniform structure and current of a helical inductor cause an abrupt change in the magnetic field near the helical support, which leads to anomalous behavior and current loss of electron flow. In addition, current loss in the inductive helical-supported MITL is negligible when the inductance of the support is sufficiently high. This work facilitates the estimation of electron current loss caused by the inductive helical support in MITLs.

We present low-dimensional functionalization and characterization of electron density of states using highly correlated/precisely guided proton beam trajectories and a silicon nanocrystal as a target, representing at a same time a versatile nanolaser technique capable for coherent control of atomic quantum states and for scanning the interior of an atom with resolution comparable to 10% of the Bohr radius.

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