Ultrahigh intensity lasers can potentially be used in conjunction with conventional fusion lasers to ignite inertial confinement fusion (ICF) capsules with a total energy of a few tens of kilojoules of laser light, and can possibly lead to high gain with as little as 100 kJ. A scheme is proposed with three phases. First, a capsule is imploded as in the conventional approach to inertial fusion to assemble a high‐density fuel configuration. Second, a hole is bored through the capsule corona composed of ablated material, as the critical density is pushed close to the high‐density core of the capsule by the ponderomotive force associated with high‐intensity laser light. Finally, the fuel is ignited by suprathermal electrons, produced in the high‐intensity laser–plasma interactions, which then propagate from critical density to this high‐density core. This new scheme also drastically reduces the difficulty of the implosion, and thereby allows lower quality fabrication and less stringent beam quality and symmet...

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Ignition and high gain with ultrapowerful lasers

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.

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Optics in the relativistic regime

http://absimage.aps.org/image/DAMOP12/MWS_DAMOP12-2012-000066.pdf

Optics in the Relativistic Regime

Complex (dusty) plasmas: current status, open issues, perspectives

Analytic theory of the linear and nonlinear behavior of the one‐dimensional Brillouin and Raman scattering instabilities is given. Results are presented for the problems of an infinite homogeneous plasma and of a finite inhomogeneous plasma. Nonlinear fluid equations can predict backscatter energies the order of the incident laser energy; however, the size of the interaction region and nonlinear effects on the excited electrostatic wave are very important in determining the amount of backscatter. In many cases of contemporary interest for a high power laser incident on a target plasma, the latter effects can play a crucial role in reducing backscatter to a tolerable level.

Theory of stimulated scattering processes in laser‐irradiated plasmas

The nonlinear propagation of a very intense laser beam in a cold overdense plasma is analytically investigated; the laser beam is assumed to be intense enough to cause the directed component of electron velocity to be comparable to the velocity of light. Special attention has been given to the case when coupled longitudinal‐cum‐transverse modes propagate in the plasma. An interesting result is that the beam can readily propagate through the overdense plasma, in contrast to what would be expected on the basis of a linear theory of laser propagation.

Relativistic Nonlinear Propagation of Laser Beams in Cold Overdense Plasmas

The interaction of relativistic laser light with overdense plasmas is studied by three-dimensional particle-in-cell simulations. Generation of layered current sheets and quasistatic magnetic fields is observed near the target surface owing to anisotropic laser filamentation and Weibel instabilities. Later these current sheets tear into filaments that partially merge with each other to form isolated magnetic channels penetrating into the dense plasmas. It is found that fast electron energy flow is not only inside the magnetic channels but also it is widely distributed outside the channels. This is possible because of electron anomalous diffusion across self-generated magnetic fields. Consequently, the total hot electron current exceeds a few hundred kiloamperes and is much larger than the Alfven current. Hence a considerable amount of energy flows towards the plasma core. Significant heating of the bulk plasma electrons is also observed.

Three-dimensional particle-in-cell simulations of energetic electron generation and transport with relativistic laser pulses in overdense plasmas.

Recent experiments on strongly coupled plasmas in a magnetic field and a background of neutrals have revealed that the dust component exhibits a rigid rotation of order a fraction of a radian/s. The rotation arises spontaneously and seems to be in the direction of ion rotation (which in turn is determined by a competition between E×B and diamagnetic rotations of the ions in the collisional magnetized plasma). In this Letter a possible interpretation of these results, based on the use of fluid equations, is offered.

Rotation in collisional strongly coupled dusty plasmas in a magnetic field

The deconfining ponderomotive force exerted by an intense electromagnetic wave on a linearly inhomogeneous plasma layer has been analytically investigated. Since the ponderomotive force maximizes near the region where the dielectric constant e′ → 0, an exact solution of the wave equation is required for a correct estimate of the maximum force. For the case of oblique incidence with the electric vector in the plane of incidence, the solution of the exact wave equation leads to an interesting resonance effect which predicts a force higher than that obtained by earlier workers using a WKB procedure. Physically, this enhanced ponderomotive force arises because of the large nonuniform longitudinal fields that are generated in the region e′ ≈ 0 for this geometry.

Ponderomotive Force on Laser‐Produced Plasmas

Instabilities of dust acoustic waves in a plasma with a significant background pressure of neutrals have been investigated. A long wavelength mode is found to be unstable due to recombination of electrons and ions on the surface of dust particles. At short wavelengths, a dissipative instability driven by relative drift between ions and the dust particles is found to be important. Nonlinearly, the short wavelength modes lead to the formation of K{minus}dV solitons whereas the long wavelength end is dominated by modulational instabilities. {copyright} {ital 1997} {ital The American Physical Society}

Predhiman Kaw

Papers

Relativistic Nonlinear Propagation of Laser Beams in Cold Overdense Plasmas

Three-dimensional particle-in-cell simulations of energetic electron generation and transport with relativistic laser pulses in overdense plasmas.

Rotation in collisional strongly coupled dusty plasmas in a magnetic field

Ponderomotive Force on Laser‐Produced Plasmas

Collisional Instabilities in a Dusty Plasma with Recombination and Ion-Drift Effects