Ultrahigh-intensity lasers (10$^{18}$-10$^{22}$W/cm$^{2}$) have opened up new perspectives in many fields of research and application [1-5]. By irradiating a thin foil, an ultrahigh accelerating field (10$^{12}$ V/m) can be formed and multi-MeV ions with unprecedentedly high intensity (10$^{10}$A/cm$^2$) in short time scale ($\sim$ps) are produced [6-14]. Such beams provide new options in radiography [15], high-yield neutron sources [16], high-energy-density-matter generation [17], and ion fast ignition [18,19]. An accurate understanding of the nonlinear behavior of beam transport in matter is crucial for all these applications. We report here the first experimental evidence of anomalous stopping of a laser-generated high-current proton beam in well-characterized dense ionized matter. The observed stopping power is one order of magnitude higher than single-particle slowing-down theory predictions. We attribute this phenomenon to collective effects where the intense beam drives an decelerating electric field approaching 1GV/m in the dense ionized matter. This finding will have considerable impact on the future path to inertial fusion energy.
The inelastic interaction between heavy ions and an electron plasma in the presence of an intense radiation field (RF) is investigated. The stopping power of the test ion averaged with a period of the RF has been calculated assuming that $ω_{0} >ω_{p}$, where $ω_{0}$ is the frequency of the RF and $ω_{p}$ 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. It has been shown that the RF may strongly reduce the mean energy loss for slow ions while incr…
Impact of ion-beam stopping power on proton-boron fusion yield in the pitcher-catcher scheme driven by ultra-intense laser
State Key Laboratory of Ultra-intense laser Science and Technology, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences（中国科学院上海光学精密机械研究所）；University of Chinese Academy of Sciences（中国科学院大学）；School of Physics, East China Normal University（华东师范大学物理系）；School of Physical Science and Technology, ShanghaiTech University（上海科技大学物理科学与技术学院）
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, $ω_{0} >ω_{p}$, where $ω_{0}$ is the frequency of the RF and $ω_{p}$ 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 …
We study the interaction of intense ultrashort laser pulses with cryogenic He jets using 2d/3v relativistic Particle-in-Cell simulations (XOOPIC). Of particular interest are laser intensities $(10^{15}-10^{20})$ W/cm$^2$, pulse lengths $\le 100$ fs, and the frequency regime $\sim 800$ nm for which the jets are initially transparent and subsequently not homogeneously ionized. Pulses $\ge 10^{16}$ W/cm$^2$ are found to drive ionization along the jet and outside the laser spot, the ionization-front propagates along the jet at a fraction of the speed of light. Within the ionized region, there is a…
In this work, the stopping power of a partially ionized plasma is analyzed by means of free electron stopping and bound electron stopping. For the first one, the RPA dielectric function is used, and for the latter one, an interpolation of high and low projectile velocity formulas is used. The dynamical energy loss of an ion beam inside a plasma is estimated by using an iterative scheme of calculation. The Abel inversion is also applied when we have a plasma with radial symmetry. Finally, we compare our methods with two kind of plasmas. In the first one, we estimate the energy loss in a plasma …
A Monte-Carlo approach to proton stopping in warm dense matter is implemented into an existing particle-in-cell code. The model is based on multiple binary-collisions among electron-electron, electron-ion and ion-ion, taking into account contributions from both free and bound electrons, and allows to calculate particle stopping in much more natural manner. At low temperature limit, when ``all'' electron are bounded at the nucleus, the stopping power converges to the predictions of Bethe-Bloch theory, which shows good consistency with data provided by the NIST. With the rising of temperatures, …
Oblique incidence of a $p$-polarized laser beam on a fully ionized plasma with a low density plasma corona is investigated numerically by Particle-In-Cell and Vlasov simulations in two dimensions. A single narrow self-focused current jet of energetic electrons is observed to be projected into the corona nearly normal to the target. Magnetic fields enhance the penetration depth of the electrons into the corona. A scaling law for the angle of the ejected electrons with incident laser intensity is given.
Intense electric currents called electrojets occur in weakly ionized magnetized plasmas. An example occurs in the Earth's ionosphere near the magnetic equator where neutral winds drive the plasma across the geomagnetic field. Similar processes take place in the Solar chromosphere and MHD generators. This letter argues that not all convective neutral flows generate electrojets and it introduces the corresponding universal criterion for electrojet formation, $\nabla\times (\vec{U}\times\vec{B})\neq\partial\vec{B}/\partial t$, where $\vec{U}$ is the neutral flow velocity, $\vec{B}$ is the magneti…
Utilizing laser plasma wakefield to accelerate ultra-high charge electron beam is critical for many pioneering applications, for example to efficiently produce nuclear isomers with short lifetimes which may be widely used. However, because of the beam loading effect, electron charge in a single plasma bubble is limited in level of hundreds picocoulomb. Here, we experimentally present that a hundred kilo-ampere, twenty nanocoulomb, tens of MeV collimated electron beam is produced from a chain of wakefield acceleration, via a tightly focused intense laser pulse transversely matched in dense plas…
We study the ionization dynamics in intense laser-droplet interaction using three-dimensional, relativistic particle-in-cell simulations. Of particular interest is the laser intensity and frequency regime for which initially transparent, wavelength-sized targets are not homogeneously ionized. Instead, the charge distribution changes both in space and in time on a sub-cycle scale. One may call this the extreme nonlinear Mie-optics regime. We find that - despite the fact that the plasma created at the droplet surface is overdense - oscillating electric fields may penetrate into the droplet under…
A novel radiation pressure acceleration (RPA) regime of heavy ion beams from laser-irradiated ultrathin foils is proposed by self-consistently taking into account the ionization dynamics. In this regime, the laser intensity is required to match with the large ionization energy gap when the successive ionization of high-Z atoms passing the noble gas configurations [such as removing an electron from the helium-like charge state $(\text{Z}-2)^+$ to $(\text{Z}-1)^+$]. While the target ions in the laser wing region are ionized to low charge states and undergo rapid dispersions due to instabilities,…
With the increasing development of laser accelerators, the electron energy is already beyond GeV and even higher in near future. Conventional beam dump based on ionization or radiation loss mechanism is cumbersome and costly, also has radiological hazards. We revisit the stopping power of high-energy charged particles in matter and discuss the associated problem of beam dump from the point of view of collective deceleration. The collective stopping length in an ionized gas can be several orders of magnitude shorter than the Bethe-Bloch and multiple electromagnetic cascades' stopping length in …
Generation and amplification of magnetic fields in plasmas is a long-standing topic that is of great interest to both plasma and space physics. The electron Weibel instability is a well-known mechanism responsible for self-generating magnetic fields in plasmas with temperature anisotropy and has been extensively investigated in both theory and simulations, yet experimental verification of this instability has been challenging. Recently, we demonstrated a new experimental platform that enables the controlled initialization of highly nonthermal and/or anisotropic plasma electron velocity distrib…
To include the bound electron effects in particle-in-cell (PIC) simulation, we propose a model in which the response of the dipole components of partially ionized ions to external electromagnetic fields can be included. Instead of treating the macro-ion particle as a single particle without an internal structure, the ions are considered to have a structure composed of a central nucleus and a bounded electron cloud in our model. The two parts experience the interactions of both the external electromagnetic fields and the internal Coulomb fields. In this way, the laser scattering effects by a pa…
The advent of x-ray free-electron lasers (XFELs) has enabled a range of new experimental investigations into the properties of matter driven to extreme conditions via intense x-ray-matter interactions. The femtosecond timescales of these interactions lead to the creation of transient high-energy-density plasmas, where both the electrons and the ions may be far from local thermodynamic equilibrium (LTE). Predictive modelling of such systems remains challenging because of the substantially different timescales on which electrons and ions thermalize, and because of the vast number of atomic confi…
Proton radiography is used in various high-energy-density (HED) plasma experiments. In this paper, we describe a Monte Carlo and ray-tracing simulation tool called MPRAD that can be used for modeling the deflection of proton beams in arbitrary three dimensional electromagnetic fields, as well as the diffusion of the proton beams by Coulomb scattering and stopping power. The Coulomb scattering and stopping power models in cold matter and fully ionized plasma are combined using interpolation. We discuss the application of MPRAD in a few setups relevant to HED plasma experiments where the plasma …
Experiments were performed to study electron acceleration by intense sub-picosecond laser pulses propagating in sub-mm long plasmas of near critical electron density (NCD). Low density foam layers of 300-500 um thickness were used as targets. The NCD-plasma was produced by a mechanism of a super-sonic ionization when a well-defined separate ns-pulse was sent onto the foam-target forerunning the relativistic main pulse. The effect of the relativistic laser pulse channeling and creation of quasi-static azimuthal magnetic and radial electric fields that keeps electrons in the channel ensured effe…
Particle-in-cell codes are the most widely used simulation tools for kinetic studies of ultra-intense laser-plasma interactions. Using the motion of a single electron in a plane electromagnetic wave as a benchmark problem, we show surprising deterioration of the numerical accuracy of the PIC algorithm with increasing normalized wave amplitude for typical time-step and grid sizes. Two significant sources of errors are identified: strong acceleration near stopping points and the temporal field interpolation. We propose adaptive electron sub-cycling coupled with a third order temporal interpolati…
We study hydrogen plasmas at magnetic fields B ~ 10^{12}-10^{13} Gauss, densities ~ 10^{-3}-10^3 g/cc and temperatures T ~ 10^{5.5}-10^{6.5} K, typical of photospheres of middle-aged cooling neutron stars. We construct an analytical free energy model of the partially ionized plasma, including into consideration the decentred atomic states, which arise due to the thermal motion across the strong field. We show that these states, neglected in previous studies, may contribute appreciably into thermodynamics of the outer atmospheric layers at density below 1 g/cc and typical B and T. We take into …
The processes of energy gain and redistribution in a dense gas subject to an intense ultrashort laser pulse are investigated theoretically for the case of high-pressure argon. The electrons released via strong-field ionization and driven by oscillating laser field collide with neutral neighbor atoms, thus effecting the energy gain in the emerging electron gas via a short-range inverse Bremsstrahlung interaction. These collisions also cause excitation and impact ionization of the atoms thus reducing the electron-gas energy. A kinetic model of these competing processes is developed which predict…
Recent development of Ultra short and Intense laser system paved the way for the generation of short and brilliant proton sources that can be used to study plasmas at extreme conditions in the context of High Energy Density physics. Energy selection, focusing and transport of such sources is still a challenge that is not completely solved. here we present a novel and simple design for a isochrone magnetic selector capable of angular and energy selection of proton sources by drastically reducing the temporal spread if compared with the state of the art. The isochrone selector is demanded for st…
