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Energy gain by laser-accelerated electrons in a strong magnetic field
摘要： This paper deals with electron acceleration by a laser pulse in a plasma with a static uniform magnetic ?eld B?. The laser pulse propagates perpendicular to the magnetic ?eld lines with the polarization chosen such that (Elaser · B?) = 0. The focus of the work is on the electrons with an appreciable initial transverse momentum that are unable to gain signi?cant energy from the laser in the absence of the magnetic ?eld due to strong dephasing. It is shown that the magnetic ?eld can initiate an energy increase by rotating such an electron, so that its momentum becomes directed forward. The energy gain continues well beyond this turning point where the dephasing drops to a very small value. In contrast to the case of purely vacuum acceleration, the electron experiences a rapid energy increases with the analytically derived maximum energy gain dependent on the strength of the magnetic ?eld and the phase velocity of the wave. The energy enhancement by the magnetic ?eld can be useful at high laser amplitudes, a0 (cid:3) 1, where the acceleration similar to that in the vacuum is unable to produce energetic electrons over just tens of microns. A strong magnetic ?eld helps leverage an increase in a0 without a signi?cant increase in the interaction length.
关键词： plasma,laser pulse,dephasing,magnetic ?eld,electron acceleration
更新于2025-09-19 17:13:59
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Characteristics of quasi-unipolar electromagnetic pulses formed in the interaction of high-power laser pulses with nanoscale targets
摘要： A new method is suggested for generating quasi-unipolar electromagnetic IR and terahertz pulses. The method is based on synchronous acceleration of electrons combined to a dense bunch with a charge of up to several tens nanocoulombs, which are forced out from a nanoscale target under an action of a high-power, sharp-leading edge laser pulse. The electromagnetic bunch moving in a field of laser radiation can generate high-power electromagnetic pulses with various spectral composition including terahertz and IR ranges. A physical mechanism underlying the formation of generated quasi-unipolar pulses of electromagnetic radiation is determined and numerically studied. The pulse characteristics are found by numerical simulation, such as amplitude and duration dependences on the angle between the pulse propagation direction and laser beam axis. It is established that in modern laser installations, the amplitudes of quasi-unipolar pulses may reach relativistic values. Reflection of a unipolar pulse from an ideally reflecting surface is numerically analysed. It is shown that the pulse retains its unipolar profile in this case.
关键词： nanoscale targets,generation of terahertz and IR radiation,interaction of high-power laser pulses with matter,electron acceleration by laser pulses
更新于2025-09-16 10:30:52
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Effective production of gammas, positrons, and photonuclear particles from optimized electron acceleration by short laser pulses in low-density targets
摘要： Electron acceleration has been optimized based on 3D particle-in-cell simulations of a short laser pulse interacting with low-density plasma targets to find the pulse propagation regime that maximizes the charge of high-energy electron bunches. This regime corresponds to laser pulse propagation in a self-trapping mode where the diffraction divergence is balanced by the relativistic nonlinearity such that relativistic self-focusing on the axis does not happen and the laser beam radius stays unchanged during pulse propagation in a plasma over many Rayleigh lengths. Such a regime occurs for a near-critical density if the pulse length considerably exceeds both the plasma wavelength and the pulse width. Electron acceleration occurs in a traveling cavity filled with a high-frequency laser field and a longitudinal electrostatic single-cycle field (“self-trapping regime”). Monte Carlo simulations demonstrated that a high electron yield allows an efficient production of gamma radiation, electron–positron pairs, neutrons, and even pions from a catcher-target.
关键词： electron acceleration,photonuclear particles,laser pulse,gamma radiation,positrons,low-density plasma
更新于2025-09-12 10:27:22
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Electron–Ion Recombination Effect on Electron Acceleration by an Intense Laser Pulse
摘要： Electron–ion recombination effect on electron acceleration by a high-intensity laser pulse propagating through a tunnel ionizing gas is investigated in order to observe the actual electron energy gain during acceleration. An intense short-pulse laser with a Gaussian radial pro?le propagates through a vacuum followed by gas. The point at which the peak of the pulse interacts with the electron is the initial point of the gas region. Tunnel ionization causes defocusing of the laser pulse due to high-density plasma formation on the propagation axis. The electron experiences an additional acceleration during the trailing part of the pulse and, thus, gains net energy. In the presence of electron–ion recombination, the laser pulse focuses more, and hence, the net energy gain is affected signi?cantly for speci?c parameters region. A model that self-consistently evolves the laser electron acceleration as it ionizes a neutral gas is presented. The model incorporates the electron–ion recombination effects for multiple ionization stage and for tempospatial variations in the neutral gas density appropriate for studying gas-jet system. The electron energy gain during acceleration is calculated in He gas, where the conditions are appropriate for recombination. It is found that for a given laser intensity, there is always an optimal spot size and focal position with respect to the gas jet, which minimizes the refraction and maximizes the acceleration length for higher energy gain of the electrons. The inclusion of electron–ion recombination is more realistic if the pulse duration is longer in a laser–gas-jet experiment.
关键词： Electron acceleration,gas-jet,energy gain,electron–ion recombination,intense laser pulse
更新于2025-09-11 14:15:04
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Seamless multistage laser-plasma acceleration toward future high-energy colliders
摘要： Multistage laser wakefield accelerators that are coupled with variable-curvature plasma channels make it possible to efficiently accelerate electrons to high energies that exceed dephasing and pump depletion limits. Seamless coupling between laser and particle beams may envisage future energy-frontier colliders of revolutionarily small size and cost.
关键词： high-energy colliders,electron acceleration,plasma channels,laser wakefield accelerators
更新于2025-09-11 14:15:04
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Stochastic electron acceleration in relativistic laser pulse and stationary periodic electric and magnetic fields
摘要： The mechanisms of stochastic electron acceleration in relativistic laser pulses and stationary periodic electric and magnetic fields are investigated by employing a new Hamiltonian approach. The new Hamiltonian is the dephasing rate between the electron and laser pulse such that it is time independent when the stationary fields are absent. The physics underlying stochastic electron motion is clearly revealed, and the conditions for triggering stochastic instability are obtained by finding the Chirikov-like mapping. It demonstrates that if the amplitudes of the stationary fields exceed some threshold values, the Hamiltonian can be randomly changed, and thus, net energy transfer between electrons and the laser radiation are possible. The maximum electron energy gained from the stochastic motion has a weak dependence on the amplitude of stationary fields and can significantly exceed the vacuum ponderomotive energy. All these analytical results have been confirmed by the numerical simulations.
关键词： Chirikov-like mapping,stationary periodic electric and magnetic fields,Hamiltonian approach,relativistic laser pulses,stochastic electron acceleration
更新于2025-09-11 14:15:04
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Influence of the Cathode Material Properties in Reducing the Back-Bombardment Effect in Thermionic RF Gun
摘要： The effect of back-bombardment (BB) electrons is considered one of the main obstacles for extensive use of thermionic RF guns (T-RF). The 10 hexaboride materials named (Ca, Sr, Ba, La, Ce, Pr, Nd, Sm, Eu, and Gd) B6 are investigated in this paper to survey the effect of the cathode material on reducing BB electrons and compare them with LaB6 (which is widely used as a thermionic cathode). A numerical model was used to conduct this paper. Besides the numerical calculations, an experiment has been performed to determine the work functions of CeB6 and LaB6. The results from the numerical calculations revealed that (Ba, Ca, and Nd) B6 are less affected by BB electrons: 42%, 50%, and 59%, respectively, compared with LaB6, for low beam current applications. In contrast, for high beam current duties, (Nd, Ce, and Sm) B6 have minimum influence by BB electrons compared with other hexaborides. The study concluded that BB electrons are strongly affected by the properties of the cathode material, especially thermionic emission and material density. Moreover, the study suggests that it is worthwhile to prepare BaB6, CaB6, NdB6, and SmB6 as cathode materials, then to subject them to a real experimental test using T-RF gun to compare their performance and BB effect against LaB6.
关键词： Back bombardment (BB),radio frequency (RF) guns,electron acceleration,hexaborides,work function,thermionic emission
更新于2025-09-09 09:28:46