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Author

H. Ruhl

Bio: H. Ruhl is an academic researcher from General Atomics. The author has contributed to research in topics: Laser & Electron. The author has an hindex of 11, co-authored 32 publications receiving 2264 citations.
Topics: Laser, Electron, Plasma, Ion, Pulsar

Papers
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Journal ArticleDOI
TL;DR: An intense proton beam to achieve fast ignition is proposed, produced by direct laser acceleration and focused onto the pellet from the rear side of an irradiated target and can be integrated into a hohlraum for indirect drive ICF.
Abstract: The concept of fast ignition with inertial confinement fusion (ICF) is a way to reduce the energy required for ignition and burn and to maximize the gain produced by a single implosion. Based on recent experimental findings at the PETAWATT laser at Lawrence Livermore National Laboratory, an intense proton beam to achieve fast ignition is proposed. It is produced by direct laser acceleration and focused onto the pellet from the rear side of an irradiated target and can be integrated into a hohlraum for indirect drive ICF.

1,171 citations

Journal ArticleDOI
TL;DR: In this article, a wide range of laser-plasma interaction conditions of relevance for inertial confinement fusion (ICF)/fast ignition has been explored, including the electric field distribution in laser-produced long-scale plasmas of ICF interest, the measurement of highly transient electric fields related to the generation and dynamics of hot electron currents following ultra-intense laser irradiation of targets, and the observation in underdense Plasmas, after the...
Abstract: Due to their particular properties, the beams of the multi-MeV protons generated during the interaction of ultraintense (I>1019 W/cm2) short pulses with thin solid targets are most suited for use as a particle probe in laser-plasma experiments. The recently developed proton imaging technique employs the beams in a point-projection imaging scheme as a diagnostic tool for the detection of electric fields in laser-plasma interaction experiments. In recent investigations carried out at the Rutherford Appleton Laboratory (RAL, UK), a wide range of laser-plasma interaction conditions of relevance for inertial confinement fusion (ICF)/fast ignition has been explored. Among the results obtained will be discussed: the electric field distribution in laser-produced long-scale plasmas of ICF interest; the measurement of highly transient electric fields related to the generation and dynamics of hot electron currents following ultra-intense laser irradiation of targets; the observation in underdense plasmas, after the ...

375 citations

Journal ArticleDOI
TL;DR: In this article, the effect of electron recirculation on the rear side sheath acceleration is discussed and it is found that the peak proton energy increases in inverse proportion to the target thickness.
Abstract: The generation of high energy protons from the interaction of a short laser pulse with a dense plasma, accompanied by a preformed low density plasma, has been studied by particle-in-cell simulations. The proton acceleration toward the laser direction in the preformed plasma is characterized by a time-dependent model and the peak proton energy is given. The effect of electron recirculation on the rear side sheath acceleration is discussed and it is found that the peak proton energy increases in inverse proportion to the target thickness. These results shed light on the peak proton energy dependence on laser intensity, laser pulse length, and target thickness. Finally the optimal parameters of the laser pulse for large ion peak energy and conversion efficiency are discussed.

258 citations

Journal ArticleDOI
TL;DR: In this article, it is shown that the laser light is optically guided inside the conical target and focused at the tip of the cone, where the convergence of hot electrons to the head of a cone is observed as a consequence of the surface electron flow guided by self-generated quasistatic magnetic fields and electrostatic sheath fields.
Abstract: The laser light propagation inside the conical target had been studied by three-dimensional particle-in-cell simulations. It is found that the laser light is optically guided inside the conical target and focused at the tip of the cone. The intensity increases up to several tens of times in a several micron focal spot. It is the convergence of hot electrons to the head of the cone that is observed as a consequence of the surface electron flow guided by self-generated quasistatic magnetic fields and electrostatic sheath fields. As a result, the hot electron density at the tip is locally ten times greater than the case of using a normal flat foil.

185 citations

Journal ArticleDOI
TL;DR: In this paper, particle-in-cell simulations of the three-dimensional regime of proton acceleration in the interaction of laser radiation with a thin spherical target are presented, and it is shown that the density of accelerated protons can be several times higher than that in conventional accelerators.
Abstract: Results from particle-in-cell simulations of the three-dimensional regime of proton acceleration in the interaction of laser radiation with a thin spherical target are presented. It is shown that the density of accelerated protons can be several times higher than that in conventional accelerators. The focusing of fast protons created in the interaction of laser radiation with a spherical target is demonstrated. The focal spot of fast protons is localized near the center of the sphere. The conversion efficiency of laser energy into fast ion energy attains 5%. The acceleration mechanism is analyzed and the electron and proton energy spectra are obtained.

81 citations


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Journal ArticleDOI
TL;DR: In this paper, a number of consequences of relativistic-strength optical fields are surveyed, including wakefield generation, a relativistically version of optical rectification, in which longitudinal field effects could be as large as the transverse ones.
Abstract: The advent of ultraintense laser pulses generated by the technique of chirped pulse amplification (CPA) along with the development of high-fluence laser materials has opened up an entirely new field of optics. The electromagnetic field intensities produced by these techniques, in excess of ${10}^{18}\phantom{\rule{0.3em}{0ex}}\mathrm{W}∕{\mathrm{cm}}^{2}$, lead to relativistic electron motion in the laser field. The CPA method is reviewed and the future growth of laser technique is discussed, including the prospect of generating the ultimate power of a zettawatt. A number of consequences of relativistic-strength optical fields are surveyed. In contrast to the nonrelativistic regime, these laser fields are capable of moving matter more effectively, including motion in the direction of laser propagation. One of the consequences of this is wakefield generation, a relativistic version of optical rectification, in which longitudinal field effects could be as large as the transverse ones. In addition to this, other effects may occur, including relativistic focusing, relativistic transparency, nonlinear modulation and multiple harmonic generation, and strong coupling to matter and other fields (such as high-frequency radiation). A proper utilization of these phenomena and effects leads to the new technology of relativistic engineering, in which light-matter interactions in the relativistic regime drives the development of laser-driven accelerator science. A number of significant applications are reviewed, including the fast ignition of an inertially confined fusion target by short-pulsed laser energy and potential sources of energetic particles (electrons, protons, other ions, positrons, pions, etc.). The coupling of an intense laser field to matter also has implications for the study of the highest energies in astrophysics, such as ultrahigh-energy cosmic rays, with energies in excess of ${10}^{20}\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. The laser fields can be so intense as to make the accelerating field large enough for general relativistic effects (via the equivalence principle) to be examined in the laboratory. It will also enable one to access the nonlinear regime of quantum electrodynamics, where the effects of radiative damping are no longer negligible. Furthermore, when the fields are close to the Schwinger value, the vacuum can behave like a nonlinear medium in much the same way as ordinary dielectric matter expanded to laser radiation in the early days of laser research.

1,459 citations

Journal ArticleDOI
TL;DR: An overview of the state of the art of ion acceleration by laser pulses as well as an outlook on its future development and perspectives are given in this article. But the main features observed in the experiments, the observed scaling with laser and plasma parameters, and the main models used both to interpret experimental data and to suggest new research directions are described.
Abstract: Ion acceleration driven by superintense laser pulses is attracting an impressive and steadily increasing effort. Motivations can be found in the applicative potential and in the perspective to investigate novel regimes as available laser intensities will be increasing. Experiments have demonstrated, over a wide range of laser and target parameters, the generation of multi-MeV proton and ion beams with unique properties such as ultrashort duration, high brilliance, and low emittance. An overview is given of the state of the art of ion acceleration by laser pulses as well as an outlook on its future development and perspectives. The main features observed in the experiments, the observed scaling with laser and plasma parameters, and the main models used both to interpret experimental data and to suggest new research directions are described.

1,221 citations

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TL;DR: An intense laser-plasma interaction regime of the generation of high density ultrashort relativistic ion beams is suggested and it is suggested that the laser energy is transformed efficiently into the energy of fast ions.
Abstract: An intense laser-plasma interaction regime of the generation of high density ultrashort relativistic ion beams is suggested. When the radiation pressure is dominant, the laser energy is transformed efficiently into the energy of fast ions.

951 citations

Journal ArticleDOI
TL;DR: In this paper, the authors considered strong field effects in laboratory and astrophysical plasmas and high intensity laser and cavity systems related to quantum electrodynamical (QED) photon-photon scattering.
Abstract: Strong-field effects in laboratory and astrophysical plasmas and high intensity laser and cavity systems are considered, related to quantum electrodynamical (QED) photon-photon scattering. Current state-of-the-art laser facilities are close to reaching energy scales at which laboratory astrophysics will become possible. In such high energy density laboratory astrophysical systems, quantum electrodynamics will play a crucial role in the dynamics of plasmas and indeed the vacuum itself. Developments such as the free-electron laser may also give a means for exploring remote violent events such as supernovae in a laboratory environment. At the same time, superconducting cavities have steadily increased their quality factors, and quantum nondemolition measurements are capable of retrieving information from systems consisting of a few photons. Thus, not only will QED effects such as elastic photon-photon scattering be important in laboratory experiments, it may also be directly measurable in cavity experiments. Here implications of collective interactions between photons and photon-plasma systems are described. An overview of strong field vacuum effects is given, as formulated through the Heisenberg-Euler Lagrangian. Based on the dispersion relation for a single test photon traveling in a slowly varying background electromagnetic field, a set of equations describing the nonlinear propagation of an electromagnetic pulse on a radiation plasma is derived. The stability of the governing equations is discussed, and it is shown using numerical methods that electromagnetic pulses may collapse and split into pulse trains, as well as be trapped in a relativistic electron hole. Effects, such as the generation of novel electromagnetic modes, introduced by QED in pair plasmas is described. Applications to laser-plasma systems and astrophysical environments are also discussed.

930 citations