Stable relativistic/charge-displacement channels in ultrahigh power density (≈10 ²¹ W/cm ³ ) plasmas

Abstract

Robust stability is a chief characteristic of relativistic͞charge-displacement self-channeling. Theoretical analysis of the dynamics of this stability (i) reveals a leading role for the eigenmodes in the development of stable channels, (ii) suggests a technique using a simple longitudinal gradient in the electron density to extend the zone of stability into the high electron density͞high power density regime, (iii) indicates that a situation approaching unconditional stability can be achieved, (iv) demonstrates the efficacy of the stable dynamics in trapping severely perturbed beams in single uniform channels, and (v) predicts that Ϸ10 4 critical powers can be trapped in a single stable channel. The scaling of the maximum power density with the propagating wavelength is shown to be proportional to ؊4 for a given propagating power and a fixed ratio of the electron plasma density to the critical plasma density. An estimate of the maximum power density that can be achieved in these channels with a power of Ϸ2 TW at a UV (248 nm) wavelength gives a value of Ϸ10 ), a range that can approach Ϸ100 W͞atom. These conditions provide new possibilities for the production and regulation of many highly energetic physical processes, including hard x-ray generation, the initiation of nuclear reactions, particle acceleration, and the fast ignition of fusion targets. The key to the production of these exceptional conditions is the stable compression of the spatial distribution of powerful (P 0 Ϸ 1 TW-1 PW) pulses of radiation into very narrow plasma channels. Specifically, a complex mechanism, which is triggered by pulses whose power exceeds a critical value P cr and involves both relativistic electron motions and the relative spatial separation of the electron and ion densities caused by the radiation pressure of the intense wave, produces the conditions necessary for channel formation. In brief (1), the ponderomotive radial displacement of the electrons and the contrasting inertial confinement of the ions cooperate to produce the two chief characteristics of the channels. They are (i) the refractive self-focusing action of the displaced electrons, which confines the propagating radiation, and (ii) the high spatial stability of the channels, the feature produced by the immobile electrostatic spine formed by the fixed ions. These narrow channels, which typically have a diameter of a few microns, represent an example of a new, largely unexplored class of strongly nonequilibrium excited matter that combines a very high energy density with a well-ordered structure.The existence of dynamic stability is essential for the control of high power density plasmas. Of particular importance are the physical limits of stable behavior and the corresponding implications on the maximum achievable power density. The overall result of this study is that exceptionally robust stability is a chief characteristic of the relativistic͞charge-displacement self-channeling mechanism. Specifically, the six key findings are: (i) the discovery of the ...

Relativistic and ponderomotive effects on evolution of dark hollow Gaussian electromagnetic beams in a plasma

“…Experimental as well as theoretical observations of relativistic self-focusing and ponderomotive self-channeling have been reported in a number of investigations (Faenov et al, 2007;Chessa et al, 1998;KurkiSuonio et al, 1989;Abramyan et al, 1992;Tzeng & Mori, 1998;Monot et al, 1995;Krushelnick et al, 1997;Konar & Manoj, 2005;Wagner et al, 1997;Chen et al, 1998;Borisov et al, 1998). The dynamics of ponderomotive channeling in underdense plasma has recently been studied experimentally (Borghesi et al, 2007).…”

Interaction between parallel Gaussian electromagnetic beams in a plasma with weakly relativistic-ponderomotive regime

“…Self-focusing and filamentation are among the most dangerous nonlinear phenomena which destroy the uniformity of overall irradiation required for directdrive fusion experiment as well as leads to seeding and growth of hydrodynamic instabilities. Experimental as well as theoretical observations of relativistic self-focusing and ponderomotive self-channeling have been reported in a number of investigations [25][26][27][28][29][30][31][32]. The dynamics of ponderomotive channeling in underdense plasma has recently been studied experimentally [33].…”

Optimization of power compression and stability of relativistic and ponderomotive self-channeling of248nmlaser pulses in underdense plasmas

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