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The effects of laser and plasma parameters on the proton focusing driven by Coulomb explosion in the interaction of a laser pulse with a thin arched carbon-hydrogen target are investigated by two-dimensional particle-in-cell simulations. The influence of the laser polarization, the laser spot size and the geometrical dimension of the arched target has been examined. It is shown that a linearly-polarized laser pulse contributes to the occurrence of the Coulomb explosion in a shorter time, and a larger focal spot is advantageous to produce a homogeneous Coulomb field. The geometrical property of the arched target and the buffer action of heavy ions are appropriate for the forward proton focusing.

A scheme for a high-yield photonuclear pulsed neutron source is proposed by use of a relativistic femtosecond laser interacting with a microstructure target combined with a high-$Z$ converter. By using three-dimensional particle-in-cell and Monte Carlo simulations, we find that bright $\ensuremath{\gamma}$ rays are emitted by bremsstrahlung radiation when energetic dense electron bunches pulled out from the microstructure target pass through the converter. A large number of neutrons are thus induced via photonuclear reactions. With a laser of intensity of approximately $3.4\ifmmode\times\else\texttimes\fi{}{10}^{21}\phantom{\rule{0.2em}{0ex}}{\mathrm{W/cm}}^{2}$ and energy of approximately $6.2$ J, a neutron pulse of yield as high as $1.9\ifmmode\times\else\texttimes\fi{}{10}^{8}\phantom{\rule{0.1em}{0ex}}{\mathrm{J}}^{\ensuremath{-}1}$ and duration of approximately $45$ ps can be obtained. This scheme could be realized in laboratories with current multipetawatt laser facilities.

Laser-driven positron production is expected to provide a non-radioactive, controllable, radiation tunable positron source in laboratories. We propose a novel approach of positron production by using a femto-second laser irradiating a microstructured surface target combined with a high-Z converter. By numerical simulations, it is shown that both the temperature and the maximum kinetic energy of electrons can be greatly enhanced by using a microstructured surface target instead of a planar target. When these energetic electrons shoot into a high Z converter, copious positrons are produced via Bethe-Heitler mechanism. With a laser (wavelength λ = 1 μm) with duration ~36 fs, intensity ~5.5 × 1020 W/cm2 and energy ~6 Joule, ~109 positrons can be obtained.

Thomson/Compton scattering is well-known as a scattering process between electromagnetic radiation and charged particles, which is found in laboratories and nature. Here, we investigate the radiative properties of nonlinear Thomson scattering with arbitrary incident angle. Based on classical electrodynamics, the analytical universal expressions of the electric field and energy spectrum of the radiation emitted by a relativistic electron scattering of circularly polarized laser field are derived. It is shown that the spatial distributions of the radiation energy of high-order harmonics have annular shapes and the symmetry of the annular shapes is strongly affected by the incident angle, which may relate with the angular momentum of twisted high-order harmonics. These results would help the understanding of the properties of twisted γ/X-ray and high energy electron-laser scattering experiments in laboratory.

The generation and stopping of a laser-driven two-component ion beam are investigated by three-dimensional particle-in-cell simulation and an extended stopping model. It is found that a two-component ion beam with the tunable composition ratio can be obtained from the two-species-ions sandwich target interacting with a relativistic laser pulse. When the generated proton beam mixed with a certain portion of carbon ions is transporting in fully ionized dense plasma, the beam stopping power is significantly enhanced compared to a pure proton beam. The maximum penetration depth is sharply reduced, and the Bragg peak with a higher magnitude appears earlier at the end of their paths, which is beneficial for achieving more localized energy deposition. The effect of heavy ion mixing on proton beam driven fast ignition is also discussed. A simple theoretical model is established, indicating that the required ignition time is relatively delayed for a heavy-ion doping case. For a small hot-spot size, it is possible to achieve the fusion ignition for a low mixed ratio. However, it is difficult to maintain a high fuel temperature due to the growing energy loss originating from mechanical work and thermal conduction.

High-quality ultrashort electron beams have diverse applications in a variety of areas, such as 4D electron diffraction and microscopy, relativistic electron mirrors and ultrashort radiation sources. Direct laser acceleration (DLA) mechanism can produce electron beams with a large amount of charge (several to hundreds of nC), but the generated electron beams usually have large divergence and wide energy spread. Here, we propose a novel DLA scheme to generate high-quality ultrashort electron beams by irradiating a radially polarized laser pulse on a nanofiber. Since electrons are continuously squeezed transversely by the inward radial electric field force, the divergence angle gradually decreases as electrons transport stably with the laser pulse. The well-collimated electron bunches are effectively accelerated by the circularly-symmetric longitudinal electric field and the relative energy spread also gradually decreases. It is demonstrated by three-dimensional (3D) simulations that collimated monoenergetic electron bunches with 0.75° center divergence angle and 14% energy spread can be generated. An analytical model of electron acceleration is presented which interprets well by the 3D simulation results.

Energetic heavy ions with short duration can be generated in the interaction of ultrashort ultraintense (USUI) laser pulse with solid matter. However, the energy conversion efficiency from laser to heavy ions is usually very low. Herein, a novel scheme for efficient transfer of USUI laser energy to the heavy ions of microscopic dust grains in dusty plasma is proposed. Due to the resulting ultraintense space‐charge field, the heavy ions expand isotropically together with the laser heated and expelled grain electrons as a plasma cloud on roughly the ion acoustic timescale. It is found that with 3.1 × 1020 W cm−2 USUI laser, one can produce hundreds‐megaelectronvolt C6+ ions with ≈60% energy transfer efficiency. In fact, up to 300 GeV Au79+ ions with ≈30% energy transfer efficiency can be obtained by using 8.8 × 1023 W cm−2 laser. This result suggests the possibility of using hundreds‐petawatt laser facility to investigate heavy‐ion collisions for nuclear state detection and quantum cardiodynamics phase transition.

In this paper, a scheme is proposed to amplify a seed pulse via non-degenerate four-wave mixing mechanism in plasma. Electron plasma wave excitation and four-wave mixing transmission amplification are examined by two-dimensional particle-in-cell simulations, and the physical factors that affect laser amplification are studied. It is shown that four-wave mixing develops rapidly in dozens of laser cycles and lead to energy transfer between laser beams in the interaction of multiple laser beams and plasma.

Collision of intermediate-energy heavy ions is an important way to investigate the state of high-density nuclear matter and formation of quark gluon plasmas. In this paper, we demonstrate from two-dimensional particle-in-cell simulations that hundreds-GeV Au79+ ions can be generated by ultrashort ∼1022–24 W cm−2 lasers interacting with high-Z grain doped gas. Under extremely intense laser field, strong γ-ray radiation has resulted in massive laser energy loss, and the invoked radiation reaction trapping of electrons weakens the heavy ion acceleration. However, due to hole-boring acceleration and multi-body expansion acceleration of high-Z grains, the energy conversion efficiency from laser to heavy ions is still up to 32%. Our results might provide an effective routine to carry out the experimental explorations of heavy-ion collisions by using hundreds-petawatt laser facilities.

Ion acceleration with linearly polarized 1 petawatt (PW) intense laser pulses interacting with near critical density (NCD) gas targets was demonstrated by using two-dimensional (2D) particle-in-cell (PIC) simulations. The laser parameters considered are comfortably within the capabilities of PW laser facilities, e.g., Extreme Light Infrastructure - Nuclear Physics (ELI-NP), Shanghai Superintense Ultrafast Laser Facility (SULF) and China Academy of Engineering Physics (CAEP). PIC simulation results show that near-100 MeV proton acceleration could be stably achieved within the optimized plasma parameters range, which is a result of the Magnetic Vortex Acceleration (MVA) mechanisms and the longitudinal charge-separation field formed along the filament. Our results indicate that proton energies reaching 100 MeV, benefiting for numerous advanced applications, e.g., the treatment of proton therapy at eyes, are already accessible within the capability of currently laser facilities.

The theoretical model of charged-particle stopping power for the Coulomb logarithm lnΛb ≥ 2 plasma [Phys. Rev. Lett., 20, 3059 (1993)] is extended to investigate the transport of the energetic protons in a compressed deuterium-tritium (DT) pellet mixed with heavy ion dopants. It shows that an increase of mixed-ion charge state and density ratio results in the substantial enhancement of the proton stopping power, which leads to a shorter penetration distance and an earlier appearance of the Bragg peak with a higher magnitude. The effect of hot-spot mix on the proton-driven fast ignition model is discussed. It is found that ignition time required for a small mixed hot-spot can be significantly reduced with slightly increased beam energy. Nevertheless, the ignition cannot maintain for a long time due to increasing alpha-particle penetration distance and energy loss from mechanical work and thermal conduction at high temperatures.

Tunable X-ray sources from a laser-driven wakefield have wide applications. However, due to the difficulty of electron dynamics control, currently the tunability of laser wakefield–based X-ray sources is still difficult. By using three-dimensional particle-in-cell simulations, we propose a scheme to realize controllable electron dynamics and X-ray radiation. In the scheme, a long wavelength drive pulse excites a plasma wake and an off-axis laser pulse with a short wavelength co-propagates with the drive pulse and ionizes the K-shell electrons of the background high-Z gas. The electrons can be injected in the wakefield with controllable transverse positions and residual momenta. These injected electrons experience controllable oscillations in the wake, leading to tunable radiations both in intensity and polarization.

Multiple lasers interacting with a deuterated (D) pitcher-catcher target and neutron generation are investigated using two-dimensional hybrid particle-in-cell and Monte Carlo simulations. It is found that when multiple laser pulses are focused on the front surface of the pitcher layer, D+ ion acceleration by target normal sheath acceleration (TNSA) is enhanced by the interfering overlapped light fields and the resulting periodic target-surface structure. With three laser pulses each of 4.5×1019 W/cm2 intensity, 33 fs duration and ~160 mJ energy, focusing at suitable angles on the pitcher layer, one can obtain 15 MeV D+ ions and ~25% laser-to-D+ ions energy conversion efficiency. As the resulting high-energy-density D+ ions bombard the catcher layer, D-D fusion reactions are triggered. About 3.6×107 neutrons can be produced, with the maximum neutron production rate as high as 3.1×1036 m-3s-1, almost an order of magnitude higher than that from a single laser of the same total energy.

By using three-dimensional particle-in-cell simulations, we demonstrate that an energetic ring-shaped ion beam can be generated by an ultra-intense circularly polarized Laguerre–Gaussian laser pulse interacting with micro-structure targets. The electron and ion dynamics of three different targets including a sleeve–wire target, wire target, and common planar target are investigated. It is found that an optimized sleeve–wire target can provide a remarkable increase in the maximum ion energy and laser-to-ion energy conversion efficiency. The reason can be attributed to the matched transverse profiles between the electric-field distribution of Laguerre–Gaussian laser and sleeve–wire structure, resulting in efficient laser-target energy coupling. In fact, using a laser pulse of intensity 2.74 × 1 0 20 W/cm2, duration 66.7 fs, and energy ∼1 J, one can obtain ∼35 MeV protons, ∼5.8 MeV/u carbon ions, and ∼15% laser-to-ion energy conversion.

When the laser intensity approaches 1022 W cm−2, the recoil force from high-energy photons radiated by relativistic electrons becomes important and may be comparable with the ponderomotive force of the laser pulse. As a result, the electron dynamics are modified greatly. By using particle-in-cell simulations, we show that the polarization of laser pulse has significant influence on the electron behaviors and accompanying radiation in near-critical-density plasmas. Due to the RR force and the pinching effect of self-generated magnetic field, it turns out that much more electrons are trapped in the center of a circularly-polarized (CP) laser pulse than that of a linearly-polarized (LP) laser pulse. Meanwhile, the γ−photon emission is characterized by a two-peak structure in the LP case, while it is dominated in the forward direction in the CP case where electrons keep moving forward along the laser propagating direction. These may serve as a potential signature for radiation trapping effect in forthcoming experiments to be carried out on petawatt laser facilities.

Target-normal sheath acceleration (TNSA) of ions by >100-fs relativistic laser pulses irradiating a multichannel target consisting of a row of parallel long wires and a plane back foil is studied. Two-dimensional particle-in-cell simulations show that the laser light pulls out from the wires a large number of dense hot attosecond electron bunches, which are synergetically accelerated forward by the relativistic ponderomotive force of the laser as well as the longitudinal electric field of a transverse magnetic mode that is excited in the vacuum channels between the wires. These electrons are characterized by a distinct two-temperature energy spectrum, with the temperature of the more energetic electrons close to twice the ponderomotive potential energy. After penetrating through the foil, they induce behind its rear surface a sheath electric field that is both stronger and frontally more extended than that without the channels. As a result, the TNSA ions have much higher maximum energy and the laser-to-ion energy conversion efficiency is also much higher. It is found that a laser of intensity 1.37 × 1020 W/cm2, duration 165 fs, and energy 25.6 J can produce 85 MeV protons and 31 MeV/u carbon ions, at 30% laser-to-ion energy conversion efficiency. The effects of the channel size and laser polarization on the TNSA ions are also investigated.

We propose a novel scheme to generate ultra-bright ultra-short γ-ray flashes and high-energy-density attosecond positron bunches by using multi-dimensional particle-in-cell simulations with quantum electrodynamics effects incorporated. By irradiating a 10 PW laser pulse with an intensity of 1023 W/cm2 onto a micro-wire target, surface electrons are dragged-out of the micro-wire and are effectively accelerated to several GeV energies by the laser ponderomotive force, forming relativistic attosecond electron bunches. When these electrons interact with the probe pulse from the other side, ultra-short γ-ray flashes are emitted with an ultra-high peak brightness of 1.8 × 1024 photons s-1mm-2mrad-2 per 0.1%BW at 24 MeV. These photons propagate with a low divergence and collide with the probe pulse, triggering the Breit-Wheeler process. Dense attosecond e-e+ pair bunches are produced with the positron energy density as high as 1017 J/m3 and number of 109. Such ultra-bright ultra-short γ-ray flashes and secondary positron beams may have potential applications in fundamental physics, high-energy-density physics, applied science and laboratory astrophysics.

Efficient energy boost of the laser-accelerated ions is critical for their applications in biomedical and hadron research. Achiev-able energies continue to rise, with currently highest energies, allowing access to medical therapy energy windows. Here, a new regime of simultaneous acceleration of ~100 MeV protons and multi-100 MeV carbon-ions from plasma micro-channel targets is proposed by using a ~1020 W/cm2 modest intensity laser pulse. It is found that two trains of overdense electron bunches are dragged out from the micro-channel and effectively accelerated by the longitudinal electric-field excited in the plasma channel. With the optimized channel size, these “superponderomotive” energetic electrons can be focused on the front surface of the attached plastic substrate. The much intense sheath electric-field is formed on the rear side, leading to up to ~10-fold ionic energy increase compared to the simple planar geometry. The analytical prediction of the optimal channel size and ion maximum energies is derived, which shows good agreement with the particle-in-cell simulations.

The ionization processes and temporal evolutions of atmosphere ionized by prompt $\gamma $ rays from high-altitude nuclear explosions are studied by numerical simulations. With the increasing of the burst point, the peak energy density of the Compton electrons decreases, but the corresponding altitude of the peak rises, which is 30 km directly below the burst point, and 40 km–50 km below the burst height 1000 km from the burst point following Earth’s surface curvature. It is shown that the prompt $\gamma $ rays have significant ionization effects on the atmosphere from the burst point to several kilometers from the burst point, and the affected area increases with the rising of the burst point. By the secondary ionization, the Compton electrons produce many more low-energy electrons whose lifetime increases with the rising of the altitude.

In this paper, we analytically and numerically studied the impact of the target thickness on the efficiency of laser-plasma based high-order harmonics generation (HHG). The optimal parametric region is acquired where the laser normalized amplitude a 0, the target density n e and thickness d 0 satisfy the relation: a 0 n c / 2 π n e ≤ d 0 / λ ≤ a 0 n c / π n e for n e ≫ a 0 n c . In this region, the laser can partially penetrate the target, leading to efficient acceleration of the target. Meanwhile, the target is thick enough to oscillate along the rising edge of the laser without being broken, which guarantees the occurrence of HHG. Both one-dimensional and two-dimensional particle-in-cell simulation results verify our optimal target thickness theory, and a single attosecond pulse with I = 3.0 × 1020 W cm−2 is generated under the driving of 8.6 × 1020 W cm−2 , which is several hundred times more intense than that from a thick target.

An all-optical method for generating ultra-intense high-order-mode light pulse is investigated with three-dimensional particle-in-cell simulation. We find that the conversion from a short intense circularly polarized incident Gaussian laser pulse into a transverse magnetic (TM) mode occurs as it propagates into a micro plasma waveguide. The strength of the longitudinal electric field of the excited TM modes can be almost two orders of magnitude higher than that of the original laser. The simulation results show that, for the lower-order modes, the trapped electrons lead to their revolving transverse structures. A linear plasma waveguide model is presented to predict the mode pattern and intensity of the longitudinal electric fields, which are in excellent agreement with those in the simulations. Relativistic-intense high-order-mode light can be useful for many applications, including accelerating charged particles to high energies.

Ionization-induced electron injection in a chirped laser pulse driven wakefield acceleration is investigated through particle-in-cell simulations. We find that negative (positive) chirp can longitudinally stretch (compress) laser pulse, and the wakefield amplitude can be enhanced regardless of the chirp sign. On the other hand, the rapid compression of a positively chirped pulse leads to the decrease of the wakefield potential difference, which breaks the ionization injection condition and consequent injection truncation occurs. The effective injection only lasts for a few hundred micrometers and the detailed injection length is determined by the chirp parameter. As a result, a highly tunable quasi-monoenergetic electron beam with narrow energy spread, hundreds of MeV central energy and tens of pC charge can be stably produced by this scheme.

A novel polarizer with a silver nanoribbon added into a traditional waveguide directional coupler is designed to realize the polarized output of TE mode. A high extinction ratio can be obtained because of the selectivity of surface plasmon polaritons (SPPs) on polarization. The effects of the polarizer parameters on coupling efficiency and extinction ratio are discussed. Simulation results indicate that the coupling efficiency for TE mode can reach about 95%, but only 3% for TM mode, with the extinction ratio of TE mode about 15 dB when the light wavelength is 1550 nm. The polarizer may have potential applications in photonic integrated circuits and quantum information technology.

Radially polarized intense terahertz (THz) radiation behind a thin foil irradiated by ultrahigh-contrast ultrashort relativistic laser pulse is recorded by a single-shot THz time-domain spectroscopy system. As the thickness of the target is reduced from 30 to 2 \textmu{}m, the duration of the THz emission increases from 5 to over 20 ps and the radiation energy increases dramatically, reaching $\ensuremath{\sim}10.5\phantom{\rule{0.16em}{0ex}}\mathrm{mJ}$ per pulse, corresponding to a laser-to-THz radiation energy conversion efficiency of $1.7%$. The efficient THz emission can be attributed to reflection (deceleration and acceleration) of the laser-driven hot electrons by the target-rear sheath electric field. The experimental results are consistent with that of a simple model as well as particle-in-cell simulation.

Radially polarized intense terahertz (THz) radiation is measured experimentally behind a thin foil irradiated by ultrashort relativistic intense laser pulse of ultrahigh contrast. As the target thickness is reduced from 30 to 2 μm, the energy of the THz emission increases dramatically, which even reaches up to 10.5 mJ per pulse, corresponding to energy conversion efficiency of 1.7%. This efficient THz emission is attributed to bremsstrahlung radiation of the energetic electrons rapidly refluxing between the target front and back electrostatic sheaths fields created during the laser-target interaction. Analytical modeling and particle-in-cell simulation confirms this interpretation.

Generation of intense coherent THz radiation by obliquely incidenting an intense laser pulse on a wire target is studied using particle-in-cell simulation. The laser-accelerated fast electrons are confined and guided along the surface of the wire, which then acts like a current-carrying line antenna and under appropriate conditions can emit electromagnetic radiation in the THz regime. For a driving laser intensity ∼3×10^{18}W/cm^{2} and pulse duration ∼10 fs, a transient current above 10 KA is produced on the wire surface. The emission-cone angle of the resulting ∼0.15 mJ (∼58 GV/m peak electric field) THz radiation is ∼30^{∘}. The conversion efficiency of laser-to-THz energy is ∼0.75%. A simple analytical model that well reproduces the simulated result is presented.

Nonlinear behaviors of stimulated Raman scattering driven by finite bandwidth pumps are studied by one dimensional particle-in-cell simulations. The broad spectral feature of plasma waves and backscattered light reveals the different coupling and growth mechanisms, which lead to the suppression effect before the deep nonlinear stage. It causes nonperiodic plasma wave packets and reduces packet and etching velocities. Based on the negative frequency shift and electron energy distribution, the long-time evolution of instability can be divided into two stages by the relaxation time. It is a critical time after which the alleviation effects of nonlinear frequency shift and hot electrons are replaced by enhancement. Thus, the broadband pump suppresses instability at early time. However, it aggravates in the deep nonlinear stage by lifting the saturation level due to the coupling of the incident pump with each frequency shifted plasma wave. Our simulation results show that the nonlinear effects are valid in a bandwidth range from 2.25% to 3.0%, and the physics are similar within a nearby parameter space.Nonlinear behaviors of stimulated Raman scattering driven by finite bandwidth pumps are studied by one dimensional particle-in-cell simulations. The broad spectral feature of plasma waves and backscattered light reveals the different coupling and growth mechanisms, which lead to the suppression effect before the deep nonlinear stage. It causes nonperiodic plasma wave packets and reduces packet and etching velocities. Based on the negative frequency shift and electron energy distribution, the long-time evolution of instability can be divided into two stages by the relaxation time. It is a critical time after which the alleviation effects of nonlinear frequency shift and hot electrons are replaced by enhancement. Thus, the broadband pump suppresses instability at early time. However, it aggravates in the deep nonlinear stage by lifting the saturation level due to the coupling of the incident pump with each frequency shifted plasma wave. Our simulation results show that the nonlinear effects are valid in a b...

The development of transverse instability in the radiation-pressure-acceleration dominant laser-foil interaction is numerically examined by two-dimensional particle-in-cell simulations. When a plane laser impinges on a foil with modulated surface, the transverse instability is incited, and periodic perturbations of the proton density develop. The growth rate of the transverse instability is numerically diagnosed. It is found that the linear growth of the transverse instability lasts only a few laser periods, then the instability gets saturated. In order to optimize the modulation wavelength of the target, a method of information entropy is put forward to describe the chaos degree of the transverse instability. With appropriate modulation, the transverse instability shows a low chaos degree, and a quasi-monoenergetic proton beam is produced.

A mechanism of the acceleration and focusing of quasi-monoenergetic proton beams from a thin arched carbon-hydrogen target irradiated by a relativistic-intensity laser pulse is investigated by multi-dimensional particle-in-cell (PIC) simulations. As an intense linearly polarized laser pulse impinges on the thin target, a considerable number of electrons are evacuated, leading to Coulomb explosion in the excess positive charges left behind. Accompanying with the acceleration, the protons are focused ballistically in the Coulomb field, which is mainly contributed by the carbon ions. It is demonstrated that a quasi-monoenergetic proton bunch with the energy-density as high as 1017 J/m3 is produced by using a laser pulse with the intensity of 1021 W/cm2. An analytical model is proposed to predict the proton energy and the focal position, which is fairly consistent with PIC simulations.

A scheme in which carbon ion bunches are accelerated to a high energy and density by a laser pulse (∼1021 W/cm2) irradiating cone targets is proposed and investigated using particle-in-cell simulations. The laser pulse is focused by the cone and drives forward an ultrathin foil located at the cone's tip. In the course of the work, best results were obtained employing target configurations combining a low-Z cone with a multispecies foil transversely shaped to match the laser intensity profile.

An analytical model for energy absorption during the interaction of an ultrashort, ultraintense laser with an overdense plasma is proposed. Both the compression effect of the electron density profile and the oscillation of the electron plasma surface are self-consistently included, which exhibit significant influences on the laser energy absorption. Based on our model, the general scaling law of the compression effect depending on laser strength and initial density is derived, and the temporal variation of the laser absorption due to the boundary oscillating effect is presented. It is found that due to the oscillation of the electron plasma surface, the laser absorption rate will vibrate periodically at $\ensuremath{\omega}$ or 2$\ensuremath{\omega}$ frequency for the $p$-polarized and $s$-polarized laser, respectively. The effect of plasma collision on the laser absorption has also been investigated, which shows a considerable rise in absorption with increasing electron-ion collision frequency for both polarizations.

Simultaneous generation of monoenergetic tunable protons and carbon ions from intense laser multi-component nanofoil interaction is demonstrated by using particle-in-cell simulations. It is shown that, the protons with the largest charge-to-mass ratio are instantly separated from other ion species and are efficiently accelerated in the ”phase stable” way. The carbon ions always ride on the heavier oxygen ion front with an electron-filling gap between the protons and carbon ions. At the cost of widely spread oxygen ions, monoenergetic collimated protons and carbon ions are obtained simultaneously. By modulating the heavier ion densities in the foil, it is capable to control the final beam quality, which is well interpreted by a simple analytical model.

According to the analysis of turbulence on the log-infinitely divisible cascades (LIDC) method, analyzing the GPRS network traffic that obtained from mobile operator, we found that the flow of GPRS is accord with the log-infinitely divisible cascades therefore, we further research the flow data of GPRS. The result indicates that it is very efficiently that the method of LIDC for the flow characteristics of network data. The method which we found could not only analyze the flow of network in full scale but the single scale also. In the basis of analysis frame, we could deeply research other trait, such as the scale of GPRS network has the trait of keeping power-law relations, single scale and scale invariability, etc.

A good traffic model can greatly improve the spectrum efficiency of wireless networks. Conventional traffic models, such as Poisson distribution, only suit for traditional traffics, such as Voice. With the emergency of various kinds of traffics, especially the packet-switched data services of 3G/B3G in Heterogeneous Wireless communication networks, new traffic models are brought to apply increasingly. Long-range dependence (LRD) or self-similarity and multi-fractality are the distinct characteristics of these new traffics, accordingly kinds of traffic models were brought out subsequently. This paper analyzes the principle and the differences of these models, and proposes an optimal traffic modeling algorithm, named Infinitely Divisible Cascades Model (IDC). Further topics on the multi-service traffic modeling for the heterogeneous wireless communication networks are also presented in this paper.

We propose a new scheme to obtain a compact ultra-bright, high-energy-density γ ray source by ultra-intense laser interaction with a near-critical-density (NCD) plasmas filled gold cone-capillary. By using the particle-in-cell code EPOCH, it is shown that NCD electrons are accelerated by the laser ponderomotive force in the gold cone and emit strong radiation. Considering the effect of large radiation back-reaction force, some electrons are kicked into the laser field. The trapped electrons oscillate significantly in the transverse direction and emit ultra-bright γ ray in the forward direction. By attaching a capillary to the gold cone, the trapped electrons are able to keep oscillating for a long distance and the radiation emission can be significantly enhanced. Three-dimensional simulations show that the total γ photon flux with the photon energy in the range of 3 MeV to 30 MeV is approximately 1013/shot, and the corresponding peak brightness is in the order of 1023 photons/s/mm2/mrad2/0.1%BW. The avera...

A scheme for enhancing the electron injection charge in a laser-driven bubble acceleration is proposed. In this scheme, a thin foil target is placed in front of a gas target. Upon interaction with an ultra-intense laser pulse, the foil emits electrons with large longitudinal momenta, allowing them to be trapped into the transmitted shaped laser-excited bubble in the gaseous plasma target. Two-dimensional particle-in-cell simulation is used to demonstrate this scheme, and an electron beam with a total electron number of 4.21×108 μm−1 can be produced, which is twice the number of electrons produced without the foil. Such scheme may be widely used for applications that require high electron yields such as positron and gamma ray generation from relativistic electron beams interacting with solid targets.

It is demonstrated through particle-in-cell simulations that target-normal-sheath-accelerated protons can be well controlled by using a guiding cone. Compared to a conventional planar target, both the collimation and number density of proton beams are substantially improved, giving a high-quality proton beam which maintained for a longer distance without degradation. The effect is attributed to the radial electric field resulting from the charge due to the hot target electrons propagating along the cone surface. This electric field can effectively suppress the spatial spread of the protons after the expansion of the hot electrons.

By using two-dimensional particle-in-cell simulations, we demonstrate enhanced spatially periodic attosecond electron bunches generation with an average density of about 10nc and cut-off energy up to 380 MeV. These bunches are acquired from the interaction of an ultra-short ultra-intense laser pulse with a cone target. The laser oscillating field pulls out the cone surface electrons periodically and accelerates them forward via laser pondermotive force. The inner cone wall can effectively guide these bunches and lead to their stable propagation in the cone, resulting in overdense energetic attosecond electron generation. We also consider the influence of laser and cone target parameters on the bunch properties. It indicates that the attosecond electron bunch acceleration and propagation could be significantly enhanced without evident divergency by attaching a plasma capillary to the original cone tip.

A foil-in-cone target is proposed to enhance stable laser-radiation-pressure-driven proton acceleration by avoiding the beam degradation in whole stage of acceleration. Two and three-dimensional particle-in-cell simulations demonstrate that the guiding cone can substantially improve the spectral and spatial properties of the ion beam and lead to better preservation of the beam quality. This can be attributed to the focusing effect of the radial sheath electric fields formed on the inner walls of the cone, which co-move with the accelerated foil and effectively suppress the undesirable transverse explosion of the foil. It is shown that, by using a transversely Gaussian laser pulse with intensity of ∼2.74 × 1022 W∕cm2, a quasi-monoenergetic proton beam with a peak energy of ∼1.5 GeV/u, density ∼10nc, and transverse size ∼1λ0 can be obtained.

By using two-dimensional particle-in-cell simulations, we propose a scheme for strong coupling of a petawatt laser with an opening gold cone filled with near-critical-density plasmas. When relevant parameters are properly chosen, most laser energy can be fully deposited inside the cone with only 10% leaving the tip opening. Due to the asymmetric ponderomotive acceleration by the strongly decayed laser pulse, high-energy-density electrons with net laser energy gain are accumulated inside the cone, which then stream out of the tip opening continuously, like a jet. The jet electrons are fully relativistic, with speeds around 0.98−0.998 c and densities at 1020/cm3 level. The jet can keep for a long time over 200 fs, which may have diverse applications in practice.

Transport of fast electrons driven by an ultraintense laser through a tracer layer buried in solid targets is studied by particle-in-cell simulations. It is found that intense resistive magnetic fields, having a magnitude of several thousand Tesla, are generated at the interfaces of the materials due to the steep resistivity gradient between the target and tracer layer. Such magnetic fields can significantly inhibit the fast electron propagation. The electrons that can penetrate the first interface are mostly confined in the buried layer by the magnetic fields and cause heating of the tracer layer. The lateral extent of the heated region can be significantly larger than that of the relativistic electron beam. This finding suggests that the relativistic electron divergence inferred from Kα x-ray emission in experiments might be overestimated.

A new scheme of radiation pressure acceleration for generating high-quality protons by using two overlapping-parallel laser pulses is proposed. Particle-in-cell simulation shows that the overlapping of two pulses with identical Gaussian profiles in space and trapezoidal profiles in the time domain can result in a composite light pulse with a spatial profile suitable for stable acceleration of protons to high energies. At ~2.46 × 1021 W/cm2 intensity of the combination light pulse, a quasi-monoenergetic proton beam with peak energy ~200 MeV/nucleon, energy spread