Abstract
A two-stage proton acceleration scheme using present-day intense lasers and a unique target design is proposed. The target system consists of a hollow cylinder with conical inner wall, which is followed by the main target with a flat front and a dishlike flared rear surface. At the center of the latter is a tapered proton layer, which is surrounded by side proton layers at an angle to it. In the first acceleration stage, protons in both layers are accelerated by target normal sheath acceleration. The center-layer protons are accelerated forward along the axis while the side protons are accelerated and focused towards them. As a result, the side-layer protons radially compress as well as axially further accelerate the front part of the center-layer protons in the second stage. Two-dimensional (2D) particle-in-cell (PIC) simulations show that a quasimonoenergetic proton bunch with the maximum energy over 250 MeV and energy spread similar to 17% can be generated when such a target is irradiated with an 80 fs laser pulse with focused intensity 3.1 x 10(20) W/cm(2). Three-dimensional (3D) PIC simulation gives the reduced maximum energy similar to 112 MeV but even smaller energy spread similar to 3% under the same laser conditions due to anisotropic electron acceleration with linearly polarized lasers.
Highlights
Generation of high-energy well-collimated proton beams by relativistic intense lasers has attracted much interest in the past decade because its wide potential applications, such as proton oncology [1], medical isotope production [2], proton imaging [3], heavy-ion lithograph [4], as preaccelerated bunch for injection into conventional accelerators [5], fast-ion ignition for inertial confinement fusion [6], etc
When the target front is irradiated by an intense laser pulse, the conical inner wall at the front produces a large number of high-energy electron bunches [20,21,24], which are pushed forward along the cone wall by the laser ponderomotive force
Proton acceleration is accomplished by a two-stage process
Summary
Generation of high-energy well-collimated proton beams by relativistic intense lasers has attracted much interest in the past decade because its wide potential applications, such as proton oncology [1], medical isotope production [2], proton imaging [3], heavy-ion lithograph [4], as preaccelerated bunch for injection into conventional accelerators [5], fast-ion ignition for inertial confinement fusion [6], etc. Ion acceleration with double layer targets by TNSA has been proposed [22] and further investigated theoretically and numerically in different parameter ranges [23]. Such targets provide the possibility to produce quasimonoenergetic proton beams, though the produced maximum proton energy does not change much from single layer targets. We propose a scheme based upon a new target design, which can lead to two-stage acceleration of protons Both two-dimensional (2D) and threedimensional (3D) particle-in-cell (PIC) simulations show that it can result in a well-collimated quasimonoenergetic proton beam with the peak energy over 100 MeV by a readily available laser pulse at the focused intensity $3:1 Â 1020 W=cm
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