How much laser power can propagate through fusion plasma?

A nonlinear Langmuir wave in the kinetic regime kλD 0.2 may have a filamentation instability, where k is the wavenumber and λD is the Debye length. The nonlinear stage of that instability develops into the filamentation of Langmuir waves which in turn leads to the saturation of the stimulated Raman scattering in laser-plasma interaction experiments. Here we study the linear stage of the filamentation instability of the particular family [1] of Bernstein-Greene-Kruskal (BGK) modes [2] that is a bifurcation of the linear Langmuir wave. Performing direct 2+2D Vlasov-Poisson simulations of collisionless plasma we find the growth rates of oblique modes of the electric field as a function of BGK's amplitude, wavenumber and the angle of the oblique mode's wavevector relative to the BGK's wavevector. Simulation results are compared to theoretical predictions.

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“…(26) and (27) becomes k max x ∝ (φ eq ) 1/4 and fails to agree with numerical results for k max x somewhat well as seen in Fig. 17.…”

Section: A Simulation Settings and Methodsmentioning

confidence: 77%

“…(32). They include different estimates of ∆ω, from Rose's model (26), Dewar's model (27) and measured ∆ω N U M . The equation (38) …”

Section: A Simulation Settings and Methodsmentioning

confidence: 99%

Langmuir wave filamentation in the kinetic regime. I. Filamentation instability of Bernstein-Greene-Kruskal modes in multidimensional Vlasov simulations

2017

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“…Near the singularity z = z c , NLSE looses applicability, and either dissipative or non-dissipative effects must be taken into account. Such effects can include the optical damage and formation of plasma in the Kerr media, inelastic scattering in * Electronic address: plushnik@math.unm.edu the BEC, or plasma density depletion in high temperature laser-plasma interactions [9,10].…”

Section: Introduction and The Main Resultsmentioning

confidence: 99%

Beyond leading-order logarithmic scaling in the catastrophic self-focusing of a laser beam in Kerr media

2013

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We study the catastrophic stationary self-focusing (collapse) of laser beam in nonlinear Kerr media. The width of a self-similar solutions near collapse distance z = zc obeys (zc − z) 1/2 scaling law with the well-known leading order modification of loglog type ∝ (ln | ln(zc − z)|) −1/2 . We show that the validity of the loglog modification requires double-exponentially large amplitudes of the solution ∼ 10 10 100 , which is unrealistic to achieve in either physical experiments or numerical simulations. We derive a new equation for the adiabatically slow parameter which determines the system self-focusing across a large range of solution amplitudes. Based on this equation we develop a perturbation theory for scaling modifications beyond the leading loglog. We show that for the initial pulse with the optical power moderately above ( < ∼ 1.2) the critical power of self-focusing, the new scaling agrees with numerical simulations beginning with amplitudes around only three times above of the initial pulse.

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“…Since the threshold depends on the optic f/#, or in other words, on the laser's coherence (speckle) length, any LPI that affects this coherence will obscure interpretation of an observed SRS threshold with the predictions of our theory. Therefore, sufficient laser bandwidth is needed 36 to suppress speckle self-focusing and sufficient ion-acoustic damping is required to suppress collective 37…”

Section: Discussionmentioning

confidence: 99%

Diffraction-controlled backscattering threshold and application to Raman gap

Rose

Mounaix

2011

Physics of Plasmas

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The range of stimulated Raman scattering (SRS) frequencies covers a domain which at the low end abuts ! min = ! 0 2 , according to the simplest SRS theories, corresponding to scatter from electron densities near ¼ critical. Experiments, on the other hand, clearly point to ! min > ! 0 2 : SRS is not observed in a frequency gap between ! 0 2 and ! min , indicating a drastic disruption of scatter from Langmuir waves as electron densities approaches ¼ critical from below. Several one-dimensional mechanisms, linear and nonlinear, have been proposed to explain this "Raman gap". In this paper we release the one-dimensional constraint by allowing diffraction of the scattered light. In the linear convective regime we find that diffractive effects on SRS from a wide speckled laser beam tend to increase the SRS threshold with increase of density, so long as the interaction length is comparable to or larger than a speckle length. This may lead to a new, diffraction controlled, contribution to the Raman gap. 52.38.Bv

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How much laser power can propagate through fusion plasma?

Cited by 28 publications

References 38 publications

Langmuir wave filamentation in the kinetic regime. I. Filamentation instability of Bernstein-Greene-Kruskal modes in multidimensional Vlasov simulations

Langmuir wave filamentation in the kinetic regime. I. Filamentation instability of Bernstein-Greene-Kruskal modes in multidimensional Vlasov simulations

Beyond leading-order logarithmic scaling in the catastrophic self-focusing of a laser beam in Kerr media

Diffraction-controlled backscattering threshold and application to Raman gap

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