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Title: Monoenergetic and GeV ion acceleration from the laser breakout afterburner using ultrathin targets

Abstract

A new laser-driven ion acceleration mechanism using ultrathin targets has been identified from particle-in-cell simulations. After a brief period of target normal sheath acceleration (TNSA) [S. P. Hatchett et al., Phys. Plasmas 7, 2076 (2000)], two distinct stages follow: first, a period of enhanced TNSA during which the cold electron background converts entirely to hot electrons, and second, the ''laser breakout afterburner'' (BOA) when the laser penetrates to the rear of the target where a localized longitudinal electric field is generated with the location of the peak field co-moving with the ions. During this process, a relativistic electron beam is produced by the ponderomotive drive of the laser. This beam is unstable to a relativistic Buneman instability, which rapidly converts the electron energy into ion energy. This mechanism accelerates ions to much higher energies using laser intensities comparable to earlier TNSA experiments. At a laser intensity of 10{sup 21} W/cm{sup 2}, the carbon ions accelerate as a quasimonoenergetic bunch to 100 s of MeV in the early stages of the BOA with conversion efficiency of order a few percent. Both are an order of magnitude higher than those realized from TNSA in recent experiments [Hegelich et al., Nature 441, 439more » (2006)]. The laser-plasma interaction then evolves to produce a quasithermal energy distribution with maximum energy of {approx}2 GeV.« less

Authors:
; ; ; ; ; ;  [1]
  1. Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)
Publication Date:
OSTI Identifier:
20975085
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 14; Journal Issue: 5; Other Information: DOI: 10.1063/1.2436857; (c) 2007 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; AFTERBURNERS; ELECTRIC FIELDS; ELECTRON BEAMS; ELECTRONS; GEV RANGE; LASERS; PONDEROMOTIVE FORCE; RELATIVISTIC RANGE

Citation Formats

Yin, L., Albright, B. J., Hegelich, B. M., Bowers, K. J., Flippo, K. A., Kwan, T. J. T., and Fernandez, J. C.. Monoenergetic and GeV ion acceleration from the laser breakout afterburner using ultrathin targets. United States: N. p., 2007. Web. doi:10.1063/1.2436857.
Yin, L., Albright, B. J., Hegelich, B. M., Bowers, K. J., Flippo, K. A., Kwan, T. J. T., & Fernandez, J. C.. Monoenergetic and GeV ion acceleration from the laser breakout afterburner using ultrathin targets. United States. doi:10.1063/1.2436857.
Yin, L., Albright, B. J., Hegelich, B. M., Bowers, K. J., Flippo, K. A., Kwan, T. J. T., and Fernandez, J. C.. Tue . "Monoenergetic and GeV ion acceleration from the laser breakout afterburner using ultrathin targets". United States. doi:10.1063/1.2436857.
@article{osti_20975085,
title = {Monoenergetic and GeV ion acceleration from the laser breakout afterburner using ultrathin targets},
author = {Yin, L. and Albright, B. J. and Hegelich, B. M. and Bowers, K. J. and Flippo, K. A. and Kwan, T. J. T. and Fernandez, J. C.},
abstractNote = {A new laser-driven ion acceleration mechanism using ultrathin targets has been identified from particle-in-cell simulations. After a brief period of target normal sheath acceleration (TNSA) [S. P. Hatchett et al., Phys. Plasmas 7, 2076 (2000)], two distinct stages follow: first, a period of enhanced TNSA during which the cold electron background converts entirely to hot electrons, and second, the ''laser breakout afterburner'' (BOA) when the laser penetrates to the rear of the target where a localized longitudinal electric field is generated with the location of the peak field co-moving with the ions. During this process, a relativistic electron beam is produced by the ponderomotive drive of the laser. This beam is unstable to a relativistic Buneman instability, which rapidly converts the electron energy into ion energy. This mechanism accelerates ions to much higher energies using laser intensities comparable to earlier TNSA experiments. At a laser intensity of 10{sup 21} W/cm{sup 2}, the carbon ions accelerate as a quasimonoenergetic bunch to 100 s of MeV in the early stages of the BOA with conversion efficiency of order a few percent. Both are an order of magnitude higher than those realized from TNSA in recent experiments [Hegelich et al., Nature 441, 439 (2006)]. The laser-plasma interaction then evolves to produce a quasithermal energy distribution with maximum energy of {approx}2 GeV.},
doi = {10.1063/1.2436857},
journal = {Physics of Plasmas},
number = 5,
volume = 14,
place = {United States},
year = {Tue May 15 00:00:00 EDT 2007},
month = {Tue May 15 00:00:00 EDT 2007}
}
  • Using multidimensional particle-in-cell simulations we study ion acceleration from a foil irradiated by a circularly polarized laser pulse at 10{sup 22} W/cm{sup 2} intensity. When the foil is shaped initially in the transverse direction to match the laser intensity profile, three different regions (acceleration, transparency, and deformation region) are observed. In the acceleration region, the foil can be uniformly accelerated for a longer time compared to a usual flat target. Undesirable plasma heating is effectively suppressed. The final energy spectrum of the accelerated ion beam in the acceleration region is improved dramatically. Collimated GeV quasi-monoenergetic ion beams carrying as muchmore » as 19% of the laser energy are observed in multidimensional simulations.« less
  • Experimental data are presented for laser-driven carbon C{sup 6+} ion-acceleration, verifying 2D-PIC studies for multi-species targets in the Break-Out Afterburner regime. With Trident's ultra-high contrast at relativistic intensities of 5 × 10{sup 20} W/cm{sup 2} and nm-scale diamond targets, acceleration of carbon ions has been optimized by using target laser-preheating for removal of surface proton contaminants. Using a high-resolution wide angle spectrometer, carbon C{sup 6+} ion energies exceeding 1 GeV or 83 MeV/amu have been measured, which is a 40% increase in maximum ion energy over uncleaned targets. These results are consistent with kinetic plasma modeling and analytic theory.
  • Laser driven proton acceleration experiments from micron and submicron thick targets using high intensity (2 × 10{sup 21} W/cm{sup 2}), high contrast (10{sup −15}) laser pulses show an enhancement of maximum energy when hydrogen containing targets were used instead of non-hydrogen containing. In our experiments, using thin (<1μm) plastic foil targets resulted in maximum proton energies that were consistently 20%–100% higher than when equivalent thickness inorganic targets, including Si{sub 3}N{sub 4} and Al, were used. Proton energies up to 20 MeV were measured with a flux of 10{sup 7} protons/MeV/sr.
  • It is proposed that laser hole-boring at a steady speed in inhomogeneous overdense plasma can be realized by the use of temporally tailored intense laser pulses, producing high-fluence quasi-monoenergetic ion beams. A general temporal profile of such laser pulses is formulated for arbitrary plasma density distribution. As an example, for a precompressed deuterium-tritium fusion target with an exponentially increasing density profile, its matched laser profile for steady hole-boring is given theoretically and verified numerically by particle-in-cell simulations. Furthermore, we propose to achieve fast ignition by the in-situ hole-boring accelerated ions using a tailored laser pulse. Simulations show that the effectivemore » energy fluence, conversion efficiency, energy spread, and collimation of the resulting ion beam can be significantly improved as compared to those found with un-tailored laser profiles. For the fusion fuel with an areal density of 1.5 g cm{sup –2}, simulation indicates that it is promising to realize fast ion ignition by using a tailored driver pulse with energy about 65 kJ.« less
  • Kinetic simulations of break-out-afterburner (BOA) ion acceleration from nm-scale targets are examined in a longer pulse length regime than studied previously. It is shown that when the target becomes relativistically transparent to the laser, an epoch of dramatic acceleration of ions occurs that lasts until the electron density in the expanding target reduces to the critical density in the non-relativistic limit. For given laser parameters, the optimal target thickness yielding the highest maximum ion energy is one in which this time window for ion acceleration overlaps with the intensity peak of the laser pulse. A simple analytic model of relativisticallymore » induced transparency is presented for plasma expansion at the time-evolving sound speed, from which these times may be estimated. The maximum ion energy attainable is controlled by the finite acceleration volume and time over which the BOA acts.« less