The electromagnetic radiation pressure becomes dominant in the interaction of the ultra-intense electromagnetic wave with a solid material, thus the wave energy can be transformed efficiently into the energy of ions representing the material and the high density ultra-short relativistic ion beam is generated. This regime can be seen even with present-day technology, when an exawatt laser will be built. As an application, we suggest the laser-driven heavy ion collider.
How electrons get accelerated to relativistic energies in a high-Mach-number quasi-perpendicular shock is presented by means of ab initio particle-in-cell simulations in three dimensions. We found that coherent electrostatic Buneman waves and ion-Weibel magnetic turbulence coexist in a strong-shock structure whereby particles gain energy during shock-surfing and subsequent stochastic drift accelerations. Energetic electrons that initially experienced the surfing acceleration undergo pitch-angle diffusion by interacting with magnetic turbulence and continuous acceleration during confinement in …
We study transverse and longitudinal electron heating effects on the target stability and the ion spectra in the radiation pressure dominated regime of ion acceleration by means of multi dimensional particle-in-cell (PIC) simulations. Efficient ion acceleration occurs when the longitudinal electron temperature is kept as low as possible. However, tailoring of the transverse electron temperature is required in view of suppressing the transverse instability, which can keep the target structure intact for longer duration during the acceleration stage. We suggest using the surface erosion of the t…
A novel regime is proposed where, employing linearly polarized laser pulses at intensities $10^{21}\textrm{Wcm}^{-2}$ as two order of magnitude lower than earlier predicted [T. Esirkepov et al., Phys. Rev. Lett. 92, 175003 (2004)], ions are dominantly accelerated from ultrathin foils by the radiation pressure, and have monoenergetic spectra. In the regime, ions accelerated from the hole-boring process quickly catch up with the ions accelerated by target normal sheath acceleration (TNSA), and they then join in a single bunch, undergoing a hybrid Light-Sail/TNSA acceleration. Under an appropriat…
We study electron acceleration in a plasma wakefield under the influence of the radiation-reaction force caused by the transverse betatron oscillations of the electron in the wakefield. Both the classical and the strong quantum-electrodynamic (QED) limits of the radiation reaction are considered. For the constant accelerating force, we show that the amplitude of the oscillations of the QED parameter $χ$ in the radiation-dominated regime reaches the equilibrium value determined only by the magnitude of the accelerating field, while the averaged over betatron oscillations radiation reaction forc…
Ion beams generated with ultra-intense lasers-plasma accelerators hold promises to provide compact and affordable beams of relativistic ions. One of the most efficient acceleration setups was demonstrated to be direct acceleration by the laser's radiation pressure. Due to plasma instabilities developing in the ultra-thin foils required for radiation pressure acceleration, however, it is challenging to maintain stable acceleration over long distances. Recent studies demonstrated, on the other hand, that specially tailored laser pulses can shorten the required acceleration distance suppressing t…
The radiation pressure acceleration regime of laser ion acceleration requires high intensity laser pulses to function efficiently. Moreover the foil should be opaque for incident radiation during the interaction to ensure maximum momentum transfer from the pulse to the foil, which requires proper matching of the target to the laser pulse. However, in the ultrarelativistic regime, this leads to large acceleration distances, over which the high laser intensity for a Gaussian laser pulse must be maintained. It is shown that proper tailoring of the laser pulse profile can significantly reduce the …
In the ion acceleration by radiation pressure a transverse inhomogeneity of the electromagnetic pulse results in the displacement of the irradiated target in the off-axis direction limiting achievable ion energy. This effect is described analytically within the framework of the thin foil target model and with the particle-in-cell simulations showing that the maximum energy of accelerated ions decreases while the displacement from the axis of the target initial position increases. The results obtained can be applied for optimization of the ion acceleration by the laser radiation pressure with t…
The radiation pressure acceleration (RPA) of charged particles has been considered a challenging task in laser particle acceleration. Laser-driven proton/ion acceleration has attracted considerable interests due to its underlying physics and potential for applications such as high-energy density physics, ultrafast radiography, and cancer therapy. Among critical issues to overcome the biggest challenge is to produce energetic protons using an efficient acceleration mechanism. The proton acceleration by radiation pressure is considerably more efficient than the conventional target normal sheath …
A new regime is described for Radiation Pressure Acceleration of a thin foil by an intense laser beam of above 10^20 W/cm^2. Highly monoenergetic proton beams extending to GeV energies can be produced with very high efficiency using circularly polarized light. The proton beams have a very small divergence angle (less than 4 degrees). This new method allows the construction of ultra-compact proton and ion accelerators with ultra-short particle bursts.
By means of fully kinetic simulations, we investigate electron acceleration during magnetic reconnection in a nonrelativistic proton--electron plasma with conditions similar to solar corona and flares. We demonstrate that reconnection leads to a nonthermally dominated electron acceleration with a power-law energy distribution in the nonrelativistic low-$β$ regime but not in the high-$β$ regime, where $β$ is the ratio of the plasma thermal pressure and the magnetic pressure. The accelerated electrons contain most of the dissipated magnetic energy in the low-$β$ regime. A guiding-center current …
Scaling laws of ion acceleration in ultrathin foils driven by radiation pressure of intense laser pulses are investigated by theoretical analysis and two-dimensional particle-in-cell simulations. Considering the instabilities are inevitable during laser plasma interaction, the maximum energy of ions should have two contributions: the bulk acceleration driven by radiation pressure and the sheath acceleration in the moving foil reference induced by hot electrons. A theoretical model is proposed to quantitatively explain the results that the cutoff energy and energy spread are larger than the pre…
We propose a new acceleration scheme that combines shock wave acceleration (SWA) and light pressure acceleration (LPA). When a thin foil driven by light pressure of an ultra-intense laser pulse propagates in underdense background plasma, it serves as a shock-like piston, trapping and reflecting background protons to ultra-high energies. Unlike in SWA, the piston velocity is not limited by the Mach number and can be highly relativistic. Background protons can be trapped and reflected forward by the enormous "dragging field" potential behind the piston which is not employed in LPA. Our one- and …
The energy of the ions accelerated by an intense electromagnetic wave in the radiation pressure dominated regime can be greatly enhanced due to a transverse expansion of a thin target. The expansion decreases the number of accelerated ions in the irradiated region increasing the energy and the longitudinal velocity of remaining ions. In the relativistic limit, the ions become phase-locked with respect to the electromagnetic wave resulting in the unlimited ion energy gain. This effect and the use of optimal laser pulse shape provide a new approach for great enhancing the energy of laser acceler…
The future applications of the short-duration, multi-MeV ion beams produced in the interaction of high-intensity laser pulses with solid targets will require improvements in the conversion efficiency, peak ion energy, beam monochromaticity, and collimation. Regimes based on Radiation Pressure Acceleration (RPA) might be the dominant ones at ultrahigh intensities and be most suitable for specific applications. This regime may be reached already with present-day intensities using circularly polarized (CP) pulses thanks to the suppression of fast electron generation, so that RPA dominates over sh…
We propose a hybrid laser-driven ion acceleration scheme using a combination target of a solid foil and a density-tailored background plasma. In the first stage, a sub-relativistic proton beam can be generated by the radiation pressure acceleration in the intense laser interaction with the solid foil. In the second stage, this sub-relativistic proton beam is further accelerated by the laser wakefield driven by the same laser pulse in a near-critical-density background plasma with a decreasing density profile. The propagating velocity of the laser front and the phase velocity of the excited wak…
The experimental study of the plasma projectile acceleration in the laser-induced cavity pressure acceleration (LICPA) scheme is reported. In the experiment performed at the kilojoule PALS laser facility, the parameters of the projectile were measured using interferometry, a streak camera and ion diagnostics, and the measurements were supported by two-dimensional hydrodynamic simulations. It is shown that in the LICPA accelerator with a 200-J laser driver, a 4 microgram gold plasma projectile is accelerated to the velocity of 140 km/s with the energetic acceleration efficiency of 15-19 percent…
Magnetic reconnection in strongly magnetized astrophysical plasma environments is believed to be the primary process for fast energy release and particle energization. Currently there is strong interest in relativistic magnetic reconnection, in that it may provide a new explanation for high-energy particle acceleration and radiation in strongly magnetized astrophysical systems. We review recent advances in particle acceleration and reconnection physics in the magnetically-dominated regime. More discussion is focused on the physics of particle acceleration, power-law formation as well as the re…
Radiation Pressure Acceleration relies on high intensity laser pulse interacting with solid target to obtain high maximum energy, quasimonoenergetic ion beams. Either extremely high power laser pulses or tight focusing of laser radiation is required. The latter would lead to the appearance of the maximum attainable ion energy, which is determined by the laser group velocity and is highly influenced by the transverse expansion of the target. Ion acceleration is only possible with target velocities less than the group velocity of the laser. The transverse expansion of the target makes it transpa…
The process of radiation pressure acceleration (RPA) of ions is investigated with the aim of suppressing the Rayleigh-Taylor like transverse instabilities in laser-foil interaction. This is achieved by imposing surface and density modulations on the target surface. We also study the efficacy of RPA of ions from density modulated and structured targets in the radiation dominated regime where the radiation reaction effects are important. We show that the use of density modulated and structured targets and the radiation reaction effects can help in achieving the twin goals of high ion energy (in …
The transverse stability of the target is crucial for obtaining high quality ion beams using the laser radiation pressure acceleration (RPA) mechanism. In this letter, a theoretical model and supporting two-dimensional (2D) Particle-in-Cell (PIC) simulations are presented to clarify the physical mechanism of the transverse instability observed in the RPA process. It is shown that the density ripples of the target foil are mainly induced by the coupling between the transverse oscillating electrons and the quasi-static ions, a mechanism similar to the transverse two stream instability in the ine…
A novel efficient scheme of acceleration and collimation of dense plasma is proposed and examined. In the proposed scheme, a target placed in a cavity at the entrance of a guiding channel is irradiated by a laser beam introduced into the cavity through a hole and accelerated along the channel by the pressure created and accumulated in the cavity by the hot plasma expanding from the target and the cavity walls. Using 1.315-um, 0.3-ns laser pulse of energy up to 200J and a thin CH target, it was shown that the forward accelerated dense plasma projectile produced from the target can be effectivel…
An experimental study on 55fs laser driven plasma accelerator using mixed gas-jet target with varying plasma density is used to identify the role of different acceleration mechanisms, viz. Direct Laser Acceleration (DLA) and wakefield. At lower electron density electron acceleration could be attributed mainly to DLA with ionization induced injection. With increase in density, increasing role of wakefield was observed leading to hybrid regime, and at densities higher than self-injection threshold, observed experimentally for He target contribution of DLA and wakefield was found to be comparable…
We present experimental studies on ion acceleration from ultra-thin diamond-like carbon (DLC) foils irradiated by ultra-high contrast laser pulses of energy 0.7 J focussed to peak intensities of 5*10^{19} W/cm^2. A reduction in electron heating is observed when the laser polarization is changed from linear to circular, leading to a pronounced peak in the fully ionized carbon spectrum at the optimum foil thickness of 5.3 nm. Two-dimensional particle-in-cell (PIC) simulations reveal, that those C^{6+} ions are for the first time dominantly accelerated in a phase-stable way by the laser radiation…
We address the problem of energy dispersion of radiation pressure accelerated (RPA) ion beams emerging from a thin (solid) target. Two different acceleration schemes, namely phase-stable acceleration and multi-stage acceleration, are considered by means of analytical modelling and one-dimensional particle-in-cell simulations. Our investigations offer a deeper understanding of RPA and allow us to derive some guidelines for generating monoenergetic ion beams.
Radiation reaction (RR) effects on the acceleration of a thin plasma foil by a superintense laser pulse in the radiation pressure dominated regime are investigated theoretically. A simple suitable approximation of the Landau-Lifshitz equation for the RR force and a novel leapfrog pusher for its inclusion in particle-in-cell simulations are provided. Simulations for both linear and circular polarization of the laser pulse are performed and compared. It is found that at intensities exceeding $10^{23} \Wcm$ the radiation reaction force strongly affects the dynamics for a linearly polarized laser …
It is shown that well collimated mono-energetic ion beams with a large particle number can be generated in the hole-boring radiation pressure acceleration regime by using an elliptically polarized laser pulse with appropriate theoretically determined laser polarization ratio. Due to the $\bm{J}\times\bm{B}$ effect, the double-layer charge separation region is imbued with hot electrons that prevent ion pileup, thus suppressing the double-layer oscillations. The proposed mechanism is well confirmed by Particle-in-Cell simulations, and after suppressing the longitudinal double-layer oscillations,…
The acceleration of ions from ultra-thin foils has been investigated using 250 TW, sub-ps laser pulses, focused on target at intensities up to $3\times10^{20} \Wcm2$. The ion spectra show the appearance of narrow band features for proton and Carbon peaked at higher energy (in the 5-10 MeV/nucleon range) and with significantly higher flux than previously reported. The spectral features, and their scaling with laser and target parameters, provide evidence of a multispecies scenario of Radiation Pressure Acceleration in the Light Sail mode, as confirmed by analytical estimates and 2D Particle In …
Particle acceleration using ultraintense, ultrashort laser pulses is one of the most attractive topics in relativistic laser-plasma research. We report proton/ion acceleration in the intensity range of 5x1019 W/cm2 to 3.3x1020 W/cm2 by irradiating linearly polarized, 30-fs, 1-PW laser pulses on 10- to 100-nm-thick polymer targets. The proton energy scaling with respect to the intensity and target thickness was examined. The experiments demonstrated, for the first time with linearly polarized light, a transition from the target normal sheath acceleration to radiation pressure acceleration and s…
The production of energetic (multi-GeV) heavy ion beams by acceleration of ultra-thin foils through the application of radiation pressure to a self-generated, imperfect plasma mirror (photon absorption probability η finite) is studied. To evaluate the foil dynamics a relativistic model was developed for a constant and relativistic invariant value of the phenomenological parameter η. The achievable efficiency of kinetic energy transfer to the matter has been evaluated as function of the parameters involved (η, the aimed average foil velocity in unit of the light speed β, etc.). The expected col…
Production of high dynamic pressure using a strong shock wave is a topic of high relevance for high energy density physics, inertial confinement fusion and materials science. Although the pressures in the multi-megabar range can be produced by the shocks generated with a large variety of methods, the higher pressures, in the sub-gigabar or gigabar range, are achievable only with nuclear explosions or laser-driven shocks. However, the laser-to-shock energy conversion efficiency in the laser-based methods currently applied is low and, as a result, multi-kilojoule multi-beam lasers have to be use…
It is shown that the transverse Rayleigh-Taylor-like (RT) instability in the hole boring radiation pressure acceleration can be suppressed by using elliptically polarized (EP) laser. A moderate ${J}\times{B}$ heating of the EP laser will thermalize the local electrons, which leads to the transverse diffusion of ions, suppressing the short wavelength perturbations of RT instability. A proper condition of polarization ratio is obtained analytically for the given laser intensity and plasma density. The idea is confirmed by two dimensional Particle-in-Cell simulations, showing that the ion beam dr…
The generation of compact, high-energy ion beams is one of the most promising applications of intense laser-matter interactions, but the control of the beam spectral quality remains an outstanding challenge. We show that in radiation pressure acceleration of a thin solid target the onset of electron heating is determined by the growth of the Rayleigh-Taylor-like instability at the front surface and must be controlled to produce ion beams with high spectral quality in the light sail regime. The growth rate of the instability imposes an upper limit on the laser pulse duration and intensity to ac…
We study electron acceleration within a sub-critical plasma channel irradiated by an ultra-intense laser pulse ($a_0>100$ or $I>10^{22}~\mathrm{W/cm^2}$). In this regime, radiation reaction significantly alters the electron dynamics. This has an effect not only on the maximum attainable electron energy but also on the phase-matching process between betatron motion and electron oscillations in the laser field. Our study encompasses analytical description, test-particle calculations and 2-dimensional particle-in-cell simulations. We show single-stage electron acceleration to multi-GeV energies w…
When the ions are accelerated by the radiation pressure of the laser pulse, their velocity can not exceed the laser group velocity, in the case when it is less than the speed of light in vacuum. This is demonstrated in two cases corresponding to the thin foil target irradiated by a high intensity laser light and to the hole boring by the laser pulse in the extended plasma accompanied by the collisionless shock wave formation. It is found that the beams of accelerated at the collisionless shock wave front ions are unstable against the Buneman-lke and the Weibel-like instabilities which result i…
It is shown that the transverse Rayleigh Taylor like instability can be well stabilized by using elliptically polarized laser in the hole boring radiation pressure acceleration regime. The $\bm{J}\times\bm{B}$ effect of the laser will thermalize the local electrons and support a transverse diffusion mechanism of the ions, resulting in the stabilization of the short wavelength perturbations, which is quite similar to the ablative Rayleigh Taylor instability in the initial confinement fusion research. The proper range of polarization ratio is obtained from a theoretical model for the given laser…
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,…
Laser-driven proton acceleration from novel cryogenic hydrogen target of the thickness of tens of microns irradiated by multiPW laser pulse is investigated here for relevant laser parameters accessible in near future. It is demonstrated that the efficiency of proton acceleration from relatively thick hydrogen solid ribbon largely exceeds the acceleration efficiency for a thinner ionized plastic foil, which can be explained by enhanced hole boring driven by laser ponderomotive force in the case of light ions and lower target density. Three-dimensional (3D) particle-in-cell (PIC) simulations of …
A short overview of the theory of acceleration of thin foils driven by the radiation pressure of superintense lasers is presented. A simple criterion for radiation pressure dominance at intensities around $5 \times 10^{20} \mbox{W cm}^{-2}$ is given, and the possibility for fast energy gain in the relativistic regime is discussed.
We study the onset of electron heating in intense laser-solid interactions and its impact on the spectral quality of radiation pressure accelerated ions in both hole boring and light sail regimes. Two- and three-dimensional particle-in-cell (PIC) simulations are performed over a wide range of laser and target parameters and reveal how the pulse duration, profile, polarization, and target surface stability control the electron heating, the dominant ion acceleration mechanisms, and the ion spectra. We find that the onset of strong electron heating is associated with the growth of the Rayleigh-Ta…
Radiation pressure acceleration (RPA) is a highly efficient mechanism of laser-driven ion acceleration, with with near complete transfer of the laser energy to the ions in the relativistic regime. However, there is a fundamental limit on the maximum attainable ion energy, which is determined by the group velocity of the laser. The tightly focused laser pulses have group velocities smaller than the vacuum light speed, and, since they offer the high intensity needed for the RPA regime, it is plausible that group velocity effects would manifest themselves in the experiments involving tightly focu…
Polarization and radiation reaction (RR) effects in the interaction of a superintense laser pulse (I > 10^23 W/cm^2) with a thin plasma foil are investigated with three dimensional particle-in-cell (PIC) simulations. For a linearly polarized laser pulse, strong anisotropies such as the formation of two high-energy clumps in the plane perpendicular to the propagation direction and significant radiation reactions effects are observed. On the contrary, neither anisotropies nor significant radiation reaction effects are observed using circularly polarized laser pulses, for which the maximum ion en…
The dynamics of the acceleration of ultrathin foil targets by the radiation pressure of superintense, circularly polarized laser pulses is investigated by analytical modeling and particle-in-cell simulations. By addressing self-induced transparency and charge separation effects, it is shown that for "optimal" values of the foil thickness only a thin layer at the rear side is accelerated by radiation pressure. The simple "Light Sail" model gives a good estimate of the energy per nucleon, but overestimates the conversion efficiency of laser energy into monoenergetic ions.
Magnetic reconnection is thought to be the driver for many explosive phenomena in the universe. The energy release and particle acceleration during reconnection have been proposed as a mechanism for producing high-energy emissions and cosmic rays. We carry out two- and three-dimensional kinetic simulations to investigate relativistic magnetic reconnection and the associated particle acceleration. The simulations focus on electron-positron plasmas starting with a magnetically dominated, force-free current sheet ($σ\equiv B^2/(4πn_e m_e c^2) \gg 1$). For this limit, we demonstrate that relativis…
A scheme with gold cone-capillary is proposed to improve the protons acceleration and involved problems are investigated by using the two-dimensional particle-in-cell simulations. It is demonstrated that the cone-capillary can efficiently guide and collimate the protons to a longer distance and lead to a better beam quality with a dense density $\geq10n_c$, monoenergetic peak energy $E_k \sim 1.51~\mathrm{GeV}$, spatial emittance $\sim0.0088~\mathrm{mm}~\mathrm{mrad}$ with divergence angle $θ\sim 1.0^{\circ}$ and diameter $\sim 0.5\mathrm{μm}$. The enhancement is mainly attributed to the focus…
In this article we report acceleration observed for ions in a forward ablation geometry of 50 nm thick nickel film coated on a glass plate under nanosecond laser ablation. A detailed study with varying background pressure and laser energy of time of flight (TOF) spectra of ionic and other neutral transitions from plasma is undertaken. The results indicate that TOF spectra recorded for different neutral transitions exhibit different dynamical behavior (the slower peak of the neutral emission becomes faster with background pressure). Similar observation is seen for the ionic species as well. The…
Using 1D and 2D particle-in-cell (PIC) simulations of a plasma with a growing magnetic field $\vec{B}$, we show that ions can be stochastically accelerated by the ion-cyclotron (IC) instability. As $\vec{B}$ grows, an ion pressure anisotropy $p_{\perp,i} > p_{||,i}$ arises, due to the adiabatic invariance of the ion magnetic moment ($p_{||,i}$ and $p_{\perp,i}$ are the ion pressures parallel and perpendicular to $\vec{B}$). When initially $β_i = 0.5$ ($β_i \equiv 8πp_i/|\vec{B}|^2$, where $p_i$ is the ion isotropic pressure), the pressure anisotropy is limited mainly by inelastic pitch-angle s…
A superintense laser pulse illuminating a thin solid-density foil can, in principle, accelerate the entire foil, therefore yielding dense, collimated, and quasi-monoenergetic ion beams. These unique features render radiation pressure acceleration in the light sail regime a promising acceleration mechanism suited for applications where dense and high-flux ion beams are required. However, the onset of several instabilities typically results into foil deformation and heating, which cause premature termination of the radiation pressure acceleration stage and strong broadening of the ion spectrum. …
Magnetic reconnection is a leading mechanism for dissipating magnetic energy and accelerating nonthermal particles in Poynting-flux dominated flows. In this letter, we investigate nonthermal particle acceleration during magnetic reconnection in a magnetically-dominated ion-electron plasma using fully kinetic simulations. For an ion-electron plasma with the total magnetization $σ_0=B^2/(4πn(m_i+m_e)c^2)$, the magnetization for each species is $σ_i \sim σ_0$ and $σ_e \sim (m_i/m_e) σ_0$, respectively. We have studied the magnetically dominated regime by varying $σ_{e} = 10^3 - 10^5$ with initial…
High energy ion beams (> MeV) generated by intense laser pulses promise to be viable alternatives to conventional ion beam sources due to their unique properties such as high charge, low emittance, compactness and ease of beam delivery. Typically the acceleration is due to the rapid expansion of a laser heated solid foil, but this usually leads to ion beams with large energy spread. Until now, control of the energy spread has only been achieved at the expense of reduced charge and increased complexity. Radiation pressure acceleration (RPA) provides an alternative route to producing laser-drive…
An oblique-rotating pulsar generates a relativistic striped wind in a pulsar wind nebula (PWN). The termination shock of the PWN compresses the Poynting-flux-dominated flow and drives magnetic reconnection. By carrying out particle-in-cell (PIC) simulations of the termination shock of the PWN, we study the shock structure as well as the energy conversion processes and particle acceleration mechanisms. With the recent advances in the numerical methods, we extend the simulations to the ultra-relativistic regime with bulk Lorentz factor up to γ_{0}=10^{6}. Magnetic reconnection at the termination…
