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Title: Laser Acceleration of Ultrashort Ion Bunches and Femtosecond Neutron Sources

Abstract

We have theoretically investigated the acceleration of ions in the interaction of high intensity, circularly polarized laser pulses with overdense plasmas. By using 1D and 2D particle-in-cell (PIC) simulations we find that high-density, short duration ion bunches moving into the plasma are promptly generated at the laser-plasma interaction surface. This regime is qualitatively different from ion acceleration regimes driven by fast electrons, such as sheath acceleration at the back of the target or shock acceleration at the front, which occur for linear polarization. A simple analytical model accounts for the numerical observations and provides scaling laws for the ion bunch velocity and generation time as a function of pulse intensity and plasma density. The present mechanism based on circular polarization of the laser pulse leads to moderate ion energies (in the 100 keV-1 MeV range) but very high ion densities and low beam divergence. These ion bunches might be of interest for problems of compression and acceleration of high-density matter by short pulses as well as for the development of compact neutron sources. We analyzed a scheme based on two-side irradiation of a thin foil deuterated target, where two colliding ion bunches are produced leading to an ultrashort neutron burst.more » We evaluated that, for intensities of a few 1019 W cm-2, more than 103 neutrons per Joule may be produced within a time shorter than one femtosecond. Another scheme based on a layered deuterium-tritium target is outlined.« less

Authors:
 [1];  [2];  [3];  [2];  [4];  [2]
  1. polyLAB, CNR-INFM, Universita di Pisa (Italy)
  2. Dipartimento di Fisica 'E. Fermi', Universita di Pisa (Italy)
  3. (Sweden)
  4. (Germany)
Publication Date:
OSTI Identifier:
20798465
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 827; Journal Issue: 1; Conference: 3. international conference on superstrong fields in plasmas, Varenna (Italy), 19-24 Sep 2005; Other Information: DOI: 10.1063/1.2195213; (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; BEAM BUNCHING; DEUTERIUM; ELECTRONS; ION BEAMS; ION DENSITY; IONS; KEV RANGE; LASERS; MEV RANGE; NEUTRON SOURCES; NEUTRONS; PARTICLE BEAMS; PLASMA; PLASMA DENSITY; PLASMA HEATING; PLASMA SIMULATION; POLARIZATION; PULSES; SCALING LAWS; TRITIUM TARGET

Citation Formats

Macchi, A., Cattani, F., Chalmers University of Technology, Gothenburg, Liseykina, T. V., Ruhr Universitaet, Bochum, and Cornolti, F.. Laser Acceleration of Ultrashort Ion Bunches and Femtosecond Neutron Sources. United States: N. p., 2006. Web. doi:10.1063/1.2195213.
Macchi, A., Cattani, F., Chalmers University of Technology, Gothenburg, Liseykina, T. V., Ruhr Universitaet, Bochum, & Cornolti, F.. Laser Acceleration of Ultrashort Ion Bunches and Femtosecond Neutron Sources. United States. doi:10.1063/1.2195213.
Macchi, A., Cattani, F., Chalmers University of Technology, Gothenburg, Liseykina, T. V., Ruhr Universitaet, Bochum, and Cornolti, F.. Fri . "Laser Acceleration of Ultrashort Ion Bunches and Femtosecond Neutron Sources". United States. doi:10.1063/1.2195213.
@article{osti_20798465,
title = {Laser Acceleration of Ultrashort Ion Bunches and Femtosecond Neutron Sources},
author = {Macchi, A. and Cattani, F. and Chalmers University of Technology, Gothenburg and Liseykina, T. V. and Ruhr Universitaet, Bochum and Cornolti, F.},
abstractNote = {We have theoretically investigated the acceleration of ions in the interaction of high intensity, circularly polarized laser pulses with overdense plasmas. By using 1D and 2D particle-in-cell (PIC) simulations we find that high-density, short duration ion bunches moving into the plasma are promptly generated at the laser-plasma interaction surface. This regime is qualitatively different from ion acceleration regimes driven by fast electrons, such as sheath acceleration at the back of the target or shock acceleration at the front, which occur for linear polarization. A simple analytical model accounts for the numerical observations and provides scaling laws for the ion bunch velocity and generation time as a function of pulse intensity and plasma density. The present mechanism based on circular polarization of the laser pulse leads to moderate ion energies (in the 100 keV-1 MeV range) but very high ion densities and low beam divergence. These ion bunches might be of interest for problems of compression and acceleration of high-density matter by short pulses as well as for the development of compact neutron sources. We analyzed a scheme based on two-side irradiation of a thin foil deuterated target, where two colliding ion bunches are produced leading to an ultrashort neutron burst. We evaluated that, for intensities of a few 1019 W cm-2, more than 103 neutrons per Joule may be produced within a time shorter than one femtosecond. Another scheme based on a layered deuterium-tritium target is outlined.},
doi = {10.1063/1.2195213},
journal = {AIP Conference Proceedings},
number = 1,
volume = 827,
place = {United States},
year = {Fri Apr 07 00:00:00 EDT 2006},
month = {Fri Apr 07 00:00:00 EDT 2006}
}
  • The interaction of a linearly polarized intense laser pulse with an ultrathin nanometer plasma layer is investigated to understand the physics of the ion acceleration. It is shown by the computer simulation that the plasma response to the laser pulse comprises two steps. First, due to the vxB effect, electrons in the plasma layer are extracted and periodic ultrashort relativistic electron bunches are generated every half of a laser period. Second, strongly asymmetric Coulomb explosion of ions in the foil occurs due to the strong electrostatic charge separation, once the foil is burnt through. Followed by the laser accelerated electronmore » bunch, the ion expansion in the forward direction occurs along the laser beam that is much stronger as compared to the backward direction.« less
  • Ion acceleration by ultrashort circularly polarized laser pulse in a solid-density target is investigated using two-dimensional particle-in-cell simulation. The ions are accelerated and compressed by the continuously extending space-charge field created by the evacuation and compression of the target electrons by the laser light pressure. For a sufficiently thin target, the accelerated and compressed ions can reach and exit from the rear surface as a high-density high-energy ion bunch. The peak ion energy depends on the target thickness and reaches maximum when the compressed ion layer can just reach the rear target surface. The compressed ion layer exhibits lateral striationmore » which can be suppressed by using a sharp-rising laser pulse.« less
  • An experimental study of the interaction of ultrashort laser pulses with underdense plasmas in the relativistic regime is presented. A parameter regime of particular interest was found: the so-called bubble regime. In this regime, the laser pulse is focused to relativistic intensities and its pulse duration is comparable to or shorter than the plasma period. A wealth of physical phenomena occurs for such physical parameters. These phenomena have multiple signatures which have been investigated experimentally: (i) the generation of a high quality electron beam (high energy, very collimated, quasimonoenergetic energy distribution); (ii) the laser pulse temporal shortening in nonlinear plasmamore » waves. In addition, experimental results suggest that the electron beam produced in this way has temporal structures shorter than 50 fs.« less
  • Two-step laser acceleration of protons with two foils and two laser pulses is modelled and optimized. It is shown that a nearly mono-energetic distribution of proton bunches can be realized by a suitable parameter choice. Two-step acceleration schemes make it possible to obtain both higher efficiency and energy as compared to the acceleration with only one laser pulse of an energy equal to the sum of the energy of the two pulses. With the aid of our analytical model, the optimal distance between the two targets, the delay between the two laser pulses, and the parameters of the laser pulsesmore » are determined. Estimates and results of the modelling are proven with 2D PIC simulations of the acceleration of proton bunches moving through the second target.« less
  • The problem of ion expansion when a powerful subpicosecond laser pulse is incident upon a solid target is considered in conditions when the mean electron energy in the plasma is the function of time. It is shown that the problem can be solved for the simple case in which the electron has a power-law dependence with time during the laser pulse. The solutions which are obtained are significantly different from the well-known case of isothermal expansion. The ion density profile is much steeper and consequently the ion energy distribution has a very steep gradient in the high-energy tail. For themore » case when [ital v][sub [ital te]]/[ital v][sub os][lt]1 ([ital v][sub [ital te]] and [ital v][sub os] are the thermal and oscillation velocities of electrons, respectively) profile steepening due to the dynamics of the expansion dominates over that caused by the ponderomotive force. The problem considered is relevant to laser--matter interaction experiments where the electron energy has a strong dependence on time during the laser pulse. Some comparisons with recent experiments are presented.« less