Reiji Sugaya, Tsunehiro Maehara, Masao Sugawa
It has been proved theoetically and numerically that the highly relativistic electron beam can be accelerated efficiently via the Compton scattering induced by nonlinear Landau and cyclotron damping of the lower-hybrid waves.
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We explore the physics of electron acceleration in a plasma medium in an effective field theory framework. Employing a multiple Compton scattering mechanism, it is found that the acceleration can be sustained in such a medium so as to attain the energies up to the order of $O(100 \rm{MeV})$ within a centimeter. Also, the collimation and mono-energetic electron spectrum can be obtained by proper tuning of the plasma parameters with the photon frequency. The present work is potentially useful in understanding the physics of laser-plasma accelerators.
Plasma wakes driven by Compton scattering: Non-linear regime and particle acceleration
研究通过康普顿散射驱动等离子体激波的非线性机制，揭示其在实验室和天体物理中的加速效应及观测前景。
In the effort of achieving high-energetic ion beams from the interaction of ultrashort laser pulses with a plasma, volumetric acceleration mechanisms beyond Target Normal Sheath Acceleration have gained attention. A relativisticly intense laser can turn a near critical density plasma slowly transparent, facilitating a synchronized acceleration of ions at the moving relativistic critical density front. While simulations promise extremely high ion energies in in this regime, the challenge resides in the realization of a synchronized movement of the ultra-relativistic laser pulse ($a_0\gtrsim 30$…
Collisionless shock acceleration of carbon ions (C$^{6+}$) is investigated in the ultra-relativistic regime of laser-plasma interaction by accounting for the radiation reaction force and the pair production in particle-in-cell simulations. Both radiation reaction force and pair plasma formation tend to slow down the shock velocity, reducing the energy of the accelerated ions, albeit extending the time scales of the acceleration process. Slab plasma target achieves lower energy spread while target with a tailored density profile yields higher ion acceleration energies.
Particle-in-cell (PIC) simulations have shown that relativistic collisionless magnetic reconnection drives nonthermal particle acceleration (NTPA), potentially explaining high-energy (X-ray/$γ$-ray) synchrotron and/or inverse Compton (IC) radiation observed from various astrophysical sources. The radiation back-reaction force on radiating particles has been neglected in most of these simulations, even though radiative cooling considerably alters particle dynamics in many astrophysical environments where reconnection may be important. We present a radiative PIC study examining the effects of ex…
In addition to the ponderomotive acceleration of highly relativistic electrons at interaction of very short and very intense laser pulses, a further acceleration is derived from the interaction of these electron beams with the spontaneous magnetic fields of about 100 MG. This additional acceleration is the result of a laser-magnetic resonance acceleration (LMRA)[1] around the peak of the azimuthal magnetic field. This causes the electrons to gain energy within a laser period. Using a Gaussian laser pulse, the LMRA acceleration of the electrons depends on the laser polarization. Since this is i…
We derive the relativistic kinetic equation for Compton scattering of polarized radiation in strong magnetic field using the Bogolyubov method. The induced scattering and the Pauli exclusion principle are taken into account. The electron polarization is also considered in the general form of the kinetic equation. The special forms of the equation for the cases of the non-polarized electrons, the rarefied electron gas and the two polarization mode description of radiation are found. The derived equations are valid for any photon and electron energies and the magnetic field strength below about …
To clarify the relationship between phase-stable acceleration (PSA) and unlimited relativistic acceleration (URA) (Phys. Rev. Lett. 104, 135003 (2010)), an analytical relativistic model is proposed in the interactions of the ultra-intense laser and nanometer foils, based on hydrodynamic equations. The dependence of the ion momentum on time is consistent with the previous results and checked by PIC simulations. Depending on the initial ion momentum, relativistic RPA contains two acceleration processes: phase-stable limited relativistic acceleration (PS-LRA) and URA. In PS-LRA, the potential is …
High-energy acceleration phenomena in extreme radiation-plasma interactions
本文通过粒子网格模拟研究极端辐射-等离子体相互作用中的高能加速链，揭示康普顿散射、电荷分离场及韦伯不稳定性驱动的电子加速机制，并给出解析描述。
First results are presented from kinetic numerical simulations of relativistic collisionless magnetic reconnection in pair plasma that include radiation reaction from both synchrotron and inverse Compton (IC) processes, motivated by non-thermal high-energy astrophysical sources, including in particular blazars. These simulations are initiated from a configuration known as 'ABC fields' that evolves due to coalescence instability and generates thin current layers in its linear phase. Global radiative efficiencies, instability growth rates, time-dependent radiation spectra, lightcurves, variabili…
A similarity theory is developed for ultra-relativistic laser-plasmas. It is shown that the most fundamental S-similarity is valid for both under- and overdense plasmas. Optimal scalings for laser wake field electron acceleration are obtained heuristically. The strong message of the present work is that the bubble acceleration regime [see Pukhov, Meyer-ter-Vehn, Appl. Phys. B, vol. 74, 355 (2002)] satisfies these optimal scalings.
Many relativistic plasma environments in high-energy astrophysics, including pulsar wind nebulae, hot accretion flows onto black holes, relativistic jets in active galactic nuclei and gamma-ray bursts, and giant radio lobes, are naturally turbulent. The plasma in these environments is often so hot that synchrotron and inverse-Compton (IC) radiative cooling becomes important. In this paper we investigate the general thermodynamic and radiative properties (and hence the observational appearance) of an optically thin relativistically hot plasma stirred by driven magnetohydrodynamic (MHD) turbulen…
We discuss a new compact gamma-ray source aiming at high spectral density, up to two orders of magnitude higher than currently available bremsstrahlung sources, and conceptually similar to Compton Sources based on conventional linear accelerators. This new source exploits electron bunches from laser-driven electron acceleration in the so-called self-injection scheme and uses a counter-propagating laser pulse to obtain X and gamma-ray emission via Thomson/Compton scattering. The proposed experimental configuration inherently provides a unique test-bed for studies of fundamental open issues of e…
The non-thermal acceleration of electrons and ions at an oblique, non-relativistic shock is studied using large scale particle-in-cell (PIC) simulations in one spatial dimension. Physical parameters are selected to highlight the role of electron pre-heating in injection and subsequent acceleration of particles at high Mach number shocks. Simulation results show evidence for the early onset of the diffusive shock acceleration process for both electrons and ions at a highly oblique subluminal shock. Ion acceleration efficiencies of $\lesssim 5\%$ are measured at late times, though this is not th…
A new laser-proton acceleration structure combined by two relativistic electron shells, a suprathermal electron shell and a thermal electron cloud is proposed for $a\gtrapprox80σ_0$, where a is the normalized laser field and $σ_0$ is the normalized plasma surface density. In the new region, a uniform energy distribution of several GeV and a monoenergetic hundreds-of-MeV proton beam have been obtained for $a=39.5$. The first relativistic electron shell maintains opaque for incident laser pulse in the whole process. A monoenergetic electron beam has been generated with energy hundreds of MeV and…
Theoretical investigations are presented, and their results are discussed, of the laser acceleration of a single electron by a chirped pulse. Fields of the pulse are modeled by simple plane-wave oscillations and a $\cos^2$ envelope. The dynamics emerge from analytic and numerical solutions to the relativistic Lorentz-Newton equations of motion of the electron in the fields of the pulse. All simulations have been carried out by independent Mathematica and Python codes, with identical results. Configurations of acceleration from a position of rest as well as from injection, axially and sideways,…
Particle acceleration and magnetic field amplification by relativistic shocks in inhomogeneous media
本文利用三维MHD和测试粒子模拟，发现非均匀介质中相对论激波与致密团块相互作用放大磁场，且上游密度涨落使低能粒子先经下游湍流加速至注入能量，再被激波迅速加速至高能，显著影响粒子加速过程。
Comparative Analysis of Simulation Results of Dielectric Laser Acceleration of Non-relativistic Electrons in Transparent and Reflective Periodic Structures
本文通过数值模拟比较了33.9 keV非相对论电子在透明与反射周期结构中的介质激光加速性能，并提出反射周期结构方案可实现更高加速率。
Particle acceleration at magnetized, relativistic turbulent shock fronts
本文首次通过模拟证明，在轻度相对论性磁化正负电子对激波中，强湍流可在超光速位形下重新激活粒子加速，并产生幂律谱，且高磁化时湍流随机加速可取代激波加速。
Particle energization in shear flows is invoked to explain non-thermal emission from the boundaries of relativistic astrophysical jets. Yet, the physics of particle injection, i.e., the mechanism that allows thermal particles to participate in shear-driven acceleration, remains unknown. With particle-in-cell simulations, we study the development of Kelvin-Helmholtz (KH) instabilities seeded by the velocity shear between a relativistic magnetically-dominated electron-positron jet and a weakly magnetized electron-ion ambient plasma. We show that, in their nonlinear stages, KH vortices generate k…
Particle-acceleration mechanisms in multispecies relativistic plasmas
研究多物种相对论等离子体中粒子加速机制，通过动能学湍流模型分析电子、正电子和质子的加速过程，揭示正电子分数对高能辐射的影响。
We study motion of a relativistic charged particle in a plane slow electromagnetic wave and background uniform magnetic field. The wave propagates normally to the background field. Under certain conditions, the resonance between the wave and the Larmor motion of the particle is possible. Capture into this resonance results in acceleration of the particle along the wave front (surfatron acceleration). We analyse the phenomenon of capture and show that a captured particle never leaves the resonance and its energy infinitely grows. Scattering on the resonance is also studied. We find that this sc…
Intense lasers can accelerate electrons to very high energy over a short distance. Such compact accelerators have several potential applications including fast ignition, high energy physics, and radiography. Among the various schemes of laser-based electron acceleration, vacuum laser acceleration has the merits of super-high acceleration gradient and great simplicity. Yet its realization has been difficult because injecting free electrons into the fast-oscillating laser field is not trivial. Here we demonstrate free-electron injection and subsequent vacuum laser acceleration of electrons up to…
This paper summarizes recent progresses in our theoretical understanding of particle acceleration at relativistic shock waves and it discusses two salient consequences: (1) the maximal energy of accelerated particles; (2) the impact of the shock-generated micro-turbulence on the multi-wavelength light curves of gamma-ray burst afterglows.
While a growing body of research indicates that relativistic magnetic reconnection is a prodigious source of particle acceleration in high-energy astrophysical systems, the dominant acceleration mechanism remains controversial. Using a combination of fully kinetic simulations and theoretical analysis, we demonstrate that Fermi-type acceleration within the large-scale motional electric fields dominates over direct acceleration from non-ideal electric fields within small-scale diffusion regions. This result has profound implications for modeling particle acceleration in large-scale astrophysical…
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…
Relativistic sources, e.g. gamma-ray bursts, pulsar wind nebulae and powerful active galactic nuclei produce relativistic outflows that lead to the formation of collisionless shock waves, where particle acceleration is thought to take place. Our understanding of relativistic shock acceleration has improved in the past decade, thanks to the combination of analytical studies and high level numerical simulations. In ultra-relativistic shocks, particle acceleration is made difficult by the generically transverse magnetic field and large advection speed of the shocked plasma. Fast growing microturb…
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.
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