Review of Charged Particle Dynamics. Beam Optics and Focusing Systems Without Space Charge. Linear Beam Optics with Space Charge. Self-Consistent Theory of Beams. Emittance Variation. Beam Physics Research from 1993 to 2007. Appendices. List of Frequently Used Symbols. Bibliography. Index.

Theory and Design of Charged Particle Beams

The paper examines the prospects of using laser plasma as a source of high-energy ions for the purpose of hadron beam therapy — an approach which is based on both theory and experimental results (ions are routinely observed to be accelerated in the interaction of high-power laser radiation with matter). Compared to therapy accelerators like synchrotrons and cyclotrons, laser technology is advantageous in that it is more compact and is simpler in delivering ions from the accelerator to the treatment room. Special target designs allow radiation therapy requirements for ion beam quality to be satisfied. (reviews of topical problems)

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Laser ion acceleration for hadron therapy

Outstanding progress has been made in high-power laser technology in the last 10 years with laser powers reaching petawatt (PW) values. At present, there are 15 PW lasers built or being built around the world and plans are afoot for new, even higher power, lasers reaching values of exawatt (EW) or even zetawatt (ZW) powers. Petawatt lasers generate electric fields of 10 12 Vm 1 with a large fraction of the total pulse energy being converted to relativistic electrons with energies reaching in excess of 1GeV. In turn these electrons result in the generation of beams of protons, heavy ions, neutrons and high-energy photons. These laser-driven particle beams have encouraged many to think of carrying out experiments normally associated with conventional nuclear accelerators and reactors. To this end a number of introductory articles have been written under a trial name 'Laser Nuclear Physics' (Ledingham and Norreys 1999 Contemp. Phys. 40 367, Ledingham et al 2002 Europhys. News. 33 120, Ledingham et al 2003 Science 300 1107, Takabe et al 2001 J. Plasma Fusion Res. 77 1094). However, even greater strides have been made in the last 3 or 4 years in laser technology and it is timely to reassess the potential of laser-driven particle and photon beams. It must be acknowledged right from the outset that to date laser- driven particle beams have yet to compete favourably with conventional nuclear accelerator-generated beams in any way and so this is not a paper comparing laser and conventional accelerators. However, occasionally throughout the paper as a reality check, it will be mentioned what conventional nuclear accelerators can do.

https://iopscience.iop.org/article/10.1088/1367-2630/12/4/045005/pdf

Laser-driven particle and photon beams and some applications

An explanation for the energetic ions observed in the PetaWatt experiments is presented. In solid target experiments with focused intensities exceeding 1020 W/cm2, high-energy electron generation, hard bremsstrahlung, and energetic protons have been observed on the backside of the target. In this report, an attempt is made to explain the physical process present that will explain the presence of these energetic protons, as well as explain the number, energy, and angular spread of the protons observed in experiment. In particular, we hypothesize that hot electrons produced on the front of the target are sent through to the back off the target, where they ionize the hydrogen layer there. These ions are then accelerated by the hot electron cloud, to tens of MeV energies in distances of order tens of μm, whereupon they end up being detected in the radiographic and spectrographic detectors.

Energetic Proton Generation in Ultra-Intense Laser-solid Interactions

Electron acceleration to GeV energy by a radially polarized laser

Fast electrons generated in ultra-intense laser interaction with a solid target can produce multi-MeV ions from laser-induced plasmas. These fast ions can have different applications ranging from ion implantation to nuclear reactions. The most important parameter is the efficiency of fast ion production. An analytical model and particle-in-cell simulations were employed to examine acceleration mechanisms that can provide an optimal plasma density distribution due to a laser prepulse. We considered the acceleration of ions leaving a plasma layer with different density gradients, from a step-like overdense plasma to an underdense plasma with a smooth density gradient. The effects of the plasma initial scale length and density on the ion acceleration were analysed, and we found that the optimal case should have some plasma parameters. It is shown that overdense plasmas provide a higher density of accelerated ion energy than underdense plasmas at intensities below 1019 W cm−2.

Effect of a laser prepulse on fast ion generation in the interaction of ultra-short intense laser pulses with a limited-mass foil target

In this paper, suppression of a transverse proton divergence is focused by using a controlled electron cloud. When an intense short pulse laser illuminates a foil plasma target, first electrons are accelerated and they form a strong electrostatic field at the target surface, then ions are accelerated by the strong field. When a target has a hole at the opposite side of the laser illumination, an electron cloud is limited in transverse direction by a neutral plasma at the protuberant part. The proton beam is accelerated and also controlled by transverse shaped electron cloud, and consequently the transverse divergence of the proton beam is suppressed. In 2.5-dimensional particle-in-cell simulations, the transverse shape of the electron cloud is controlled well and the transverse proton beam divergence is suppressed successfully; the transverse emittance is improved by about 28% compared with that in a conventional slab target.

Suppression of transverse proton beam divergence by controlled electron cloud in laser-plasma interactions

Electron ponderomotive acceleration in a vacuum by a short-pulsed laser of TEM (1, 0) + TEM (0, 1) mode is studied in this paper using a 3-dimensional (3D) particle simulation. It was found that the laser can trap electrons in transverse and accelerate them with the longitudinal ponderomotive force at the same time. Through this electron trapping and acceleration scheme of TEM (1, 0) + TEM (0, 1) mode laser, the electron bunch is confined well in transverse and compressed remarkably in longitudinal. Therefore, a high energy, high density, and low emittances electron bunch is generated. For example, the result shows that for a laser with intensity of a0 = eE0 /mωc = 10, the laser spot size of w0 = 15λ, and the laser pulse length of Lz = 10λ, the maximum energy gain reaches 301 MeV and the average energy 57.7 MeV. The electron bunch transverse radius is about 350λ and the longitudinal size about 20λ. The property of this accelerated bunch is improved compared with that generated by the laser of TEM (0, 0) mode.

Electron bunch acceleration and trapping by ponderomotive force of an intense short-pulse laser

A robustness of a thin-foil tailored hole target is demonstrated by particle simulations in laser-produced proton generation. The hole target has a hole at the target rear surface. When an intense short pulse laser illuminates the thin-foil target with the hole, transverse edge fields of an accelerated electron cloud and an ion cloud are shielded by a protuberant part of the hole so that the proton beam divergence is suppressed [Sonobe et al., Phys. Plasmas 12, 073104 (2005)]. This paper presents the robustness of the hole target against laser parameter changes in a laser spot size and in a laser pulse length against a contaminated proton source layer and against a laser alignment error. The 2.5-dimensional particle-in-cell simulations also show that a multiple-hole target is robust against a laser alignment error and a target positioning error. The multihole target may serve as a robust target for practical uses to produce a collimated proton beam.

Robustness of a tailored hole target in laser-produced collimated proton beam generation

A suppression of a transverse divergence of high-energy protons generated by an interaction of a laser with a thin slab foil is investigated in this paper by 2.5-dimensional particle-in-cell simulations. When an intense $(\ensuremath{\sim}{10}^{24}\phantom{\rule{0.3em}{0ex}}\mathrm{W}∕{\mathrm{m}}^{2})$ short-pulse (a few ten femtoseconds) laser illuminates a thin foil target of a hydrogen, foil electrons are accelerated and compressed longitudinally by a laser light pressure and fast electron bunches are produced in the thin foil target. The fast electron bunches pass through the foil target, and a strong magnetic field is produced near the opposite side of the foil target. Because the strong magnetic field confines the electrons, a localization of the electrons is observed at the opposite side of a laser illumination surface. The local electron bunch produces not only a longitudinal electric field, but also a transverse electric field, which is directed toward the laser axis. Protons are accelerated and extracted from the foil, and the proton bunch divergence is successfully suppressed by the transverse electric field.

R. Sonobe

Papers

Effect of a laser prepulse on fast ion generation in the interaction of ultra-short intense laser pulses with a limited-mass foil target

Suppression of transverse proton beam divergence by controlled electron cloud in laser-plasma interactions

Electron bunch acceleration and trapping by ponderomotive force of an intense short-pulse laser

Robustness of a tailored hole target in laser-produced collimated proton beam generation

High-energy proton generation and suppression of transverse proton divergence by localized electrons in a laser-foil interaction.