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Title: Effects of density gradient on short-bunch injection by wave breaking in the laser wake field acceleration

Abstract

Effects of density gradient on the self-injection of plasma electrons in the phase of laser pulse wake for further acceleration, is studied for moderate laser intensities, a{sub 0}{<=}3. It is shown that transverse wave breaking can shorten the length of accelerated electrons, whereas effective longitudinal wave breaking requiring steep plasma density interface increases their total charge. For the considered range of laser intensities, the total charge of electrons injected by wave breaking rises exponentially with a{sub 0}.

Authors:
; ; ; ;  [1];  [2];  [2]
  1. Nuclear Professional School, University of Tokyo, 2-22 Shirakata-Shirane, Tokai, Naka, Ibaraki, 319-1188 (Japan)
  2. (Japan)
Publication Date:
OSTI Identifier:
20782575
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 13; Journal Issue: 3; Other Information: DOI: 10.1063/1.2181434; (c) 2006 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; ACCELERATION; ELECTRONS; INTERFACES; LASERS; LIGHT TRANSMISSION; PLASMA; PLASMA DENSITY; PLASMA GUNS; PULSES

Citation Formats

Ohkubo, Takeru, Zhidkov, Alexei, Hosokai, Tomonao, Kinoshita, Kenichi, Uesaka, Mitsuru, National Institute of Radiological Sciences, 4-9-1, Anagawa, Inage, Chiba, 263-8555, and Nuclear Professional School, University of Tokyo, 2-22 Shirakata-Shirane, Tokai, Naka, Ibaraki, 319-1188. Effects of density gradient on short-bunch injection by wave breaking in the laser wake field acceleration. United States: N. p., 2006. Web. doi:10.1063/1.2181434.
Ohkubo, Takeru, Zhidkov, Alexei, Hosokai, Tomonao, Kinoshita, Kenichi, Uesaka, Mitsuru, National Institute of Radiological Sciences, 4-9-1, Anagawa, Inage, Chiba, 263-8555, & Nuclear Professional School, University of Tokyo, 2-22 Shirakata-Shirane, Tokai, Naka, Ibaraki, 319-1188. Effects of density gradient on short-bunch injection by wave breaking in the laser wake field acceleration. United States. doi:10.1063/1.2181434.
Ohkubo, Takeru, Zhidkov, Alexei, Hosokai, Tomonao, Kinoshita, Kenichi, Uesaka, Mitsuru, National Institute of Radiological Sciences, 4-9-1, Anagawa, Inage, Chiba, 263-8555, and Nuclear Professional School, University of Tokyo, 2-22 Shirakata-Shirane, Tokai, Naka, Ibaraki, 319-1188. Wed . "Effects of density gradient on short-bunch injection by wave breaking in the laser wake field acceleration". United States. doi:10.1063/1.2181434.
@article{osti_20782575,
title = {Effects of density gradient on short-bunch injection by wave breaking in the laser wake field acceleration},
author = {Ohkubo, Takeru and Zhidkov, Alexei and Hosokai, Tomonao and Kinoshita, Kenichi and Uesaka, Mitsuru and National Institute of Radiological Sciences, 4-9-1, Anagawa, Inage, Chiba, 263-8555 and Nuclear Professional School, University of Tokyo, 2-22 Shirakata-Shirane, Tokai, Naka, Ibaraki, 319-1188},
abstractNote = {Effects of density gradient on the self-injection of plasma electrons in the phase of laser pulse wake for further acceleration, is studied for moderate laser intensities, a{sub 0}{<=}3. It is shown that transverse wave breaking can shorten the length of accelerated electrons, whereas effective longitudinal wave breaking requiring steep plasma density interface increases their total charge. For the considered range of laser intensities, the total charge of electrons injected by wave breaking rises exponentially with a{sub 0}.},
doi = {10.1063/1.2181434},
journal = {Physics of Plasmas},
number = 3,
volume = 13,
place = {United States},
year = {Wed Mar 15 00:00:00 EST 2006},
month = {Wed Mar 15 00:00:00 EST 2006}
}
  • Density effects on the dynamics of a cavity produced in the wake of an ultraintense (a{sub 0}=eE/mc{omega}>>1) and short ({omega}{sub pl}{tau}/{pi}<1) laser pulse and on the duration of accelerated electrons are studied via two-dimensional particle-in-cell simulation. Formation of a nonbreaking cavity is a crucial part of relativistic self-injection of plasma electrons from the front of a laser pulse and their further acceleration leading to a beam-quality femtosecond bunch. This self-injection appears in a uniform plasma when the group velocity of the pulse becomes smaller than the maximal electron velocity accelerated in the ponderomotive bias, {phi}=mc{sup 2}a{sub 0}{sup 2}/2. However withmore » increasing density, this mechanism starts to contend with relativistic wave breaking. Though additional injection due to the relativistic wave breaking increases the total charge of energetic electrons, the duration of the bunch increases to the picosecond range and its energy distribution becomes a Maxwellian.« less
  • Efficient and fast self-injection of plasma electrons into the wake-field acceleration phase can be procured during the transverse wake-wave breaking when the wake-wave is generated by the high-intensity laser pulse propagating in a narrow plasma channel. In the strong focusing regime, when the laser pulse power exceeds critical for the self-focusing power threshold, the injected electron bunch length becomes comparable with the plasma wavelength and the bunch has the femtosecond duration. The total charge of self-injected electrons depends strongly on the laser pulse amplitude.
  • The nonlinear interaction of an ultrashort-pulse laser with a solid target is investigated by using a newly developed particle simulation code, which enables the analysis of laser--plasma interaction in the very steep density gradient in which the laser light penetrates into an overdense plasma. For an ultrashort laser pulse, the plasma density scale length [ital L][sub [ital d]] satisfies [ital L][sub [ital d]][le][ital r][sub 0] for an electron excursion length [ital r][sub 0]. Laser absorption and electron acceleration processes are proposed for the above situation. It is found that the wave breaking is the main mechanism of the electron accelerationmore » and laser absorption, as is discussed in Brunel's paper [Phys. Rev. Lett. [bold 59], 52 (1987)].« less
  • A study is made of a promising method for injecting an electron bunch into an accelerating laser-plasma system. A bunch is injected ahead of the front of a laser pulse generating a wake wave that propagates in a direction collinear with the pulse and has a velocity lower than the pulse group velocity. The influence of the initial nonmonoenergetic character of the bunch on its trapping and acceleration is investigated. By appropriately choosing the laser pulse parameters and the bunch injection energy, it is possible to create such conditions for the trapping of an initially nonmonoenergetic bunch by the wakemore » wave that, over a certain acceleration distance, there will be no energy spread of the bunch due to its initial nonmonoenergetic character, a circumstance that allows compact electron bunches to be accelerated to high energies, with a minimum energy spread.« less
  • The spatial structure of a wake wave excited in a low-density plasma by a laser pulse with a small focal spot radius is studied both analytically and numerically. Numerical study shows that, in a small-amplitude laser field, a wake wave breaks after the formation of an off-axis density maximum, which grows in height away from the pulse to become infinitely high after several periods. Analytical and numerical calculations show that the singularity in the density arises from the intersection of the trajectories of neighboring particles. Numerical simulations demonstrate that, as the laser field amplitude increases, the breaking point of themore » wake wave rapidly approaches the pulse trailing edge. For weakly nonlinear conditions, an analytic dependence of the coordinate of the breaking point on the amplitude and transverse size of the laser pulse is obtained.« less