Anomalous Absorption of Very High-Intensity Laser Pulses Propagating through Moderately Dense Plasma

Adam, J. C.; Héron, A.; Guérin, S.; Laval, G.; Mora, P.; Quesnel, B.

doi:10.1103/physrevlett.78.4765

Cited by 41 publications

(15 citation statements)

References 16 publications

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“…The initial temperature of electrons is 4 keV. We verify that this choice, related to numerical stability reasons, is justified as, in the simulation, the interaction pulse heats in tens of fs the surroundings of the channel at a mean energy above 100 keV by parametric instabilities [10]. The laser beam is incident from the left and has a shape, intensity, and polarization (which is parallel to the surface of the images shown in Fig.…”

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confidence: 76%

Dynamics of Subpicosecond Relativistic Laser Pulse Self-Channeling in an Underdense Preformed Plasma

et al. 1998

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The formation and evolution of density channels created by the interaction of a short bright (600 fs, 5 3 10 18 W cm 22 mm 2 ) laser pulse with a preformed plasma are studied by means of experiments and 2D particle-in-cell (PIC) simulations. Hollow density channels are observed by interferometry, and a fast radial expansion ͑5 3 10 8 cm͞s͒ is measured. Magnetic fields around 50 MG inferred from Faraday rotation measurements suggest the occurrence of self-focusing. The PIC simulations support this hypothesis and show ion depletion during the laser pulse as well as radial expansion in agreement with experiments. [S0031-9007(98)05299-5] PACS numbers: 52.40.Nk, 52.25.Rv, 52.50.Jm, 52.70.Kz With the progress of compact short-pulse multiterawatt laser systems [1], it has become possible to explore the domain of relativistic laser pulse propagation and channel formation in an underdense plasma. These are topics of considerable interest for the fast ignitor (FI) concept [2], relevant to the inertial confinement fusion (ICF) studies. Indeed, the ultimate interest of this concept relies on the penetration of a short and bright laser pulse in the overdense core and the generation of the electrons that will ignite the fuel. However, to cross the underdense corona without energy losses, this pulse is planned to propagate into a hollow channel. Channel formation has been observed for several years with subrelativistic laser pulses [3]. Density depression in the channel and density increase on its walls are caused by the combined effects of transverse ponderomotive force, space-charge fields, and plasma heating. The channel formation process can be enhanced [4] by the cumulative effects of ponderomotive and relativistic self-focusing [5] which increase drastically the laser intensity, as shown recently in 3D simulations [6]. Moreover, the evacuated channel can act as a beam selfpropagation guide, as seen recently [7].In this Letter, we present direct measurements and 2D particle-in-cell (PIC) simulations that show the dynamics of subpicosecond relativistic laser pulse self-channeling in a fully ionized underdense plasma in the presence of a density gradient. The PIC simulations quantitatively reproduce the experimental results at early and long times. Therefore we rely on the PIC simulation to describe the channel formation during the laser pulse since this is not directly accessible by interferometry. These results are complementary to the ones of Borghesi et al.[7] as we put in evidence (i) the local dynamics of channel formation (ion depletion during the laser pulse), (ii) the local dynamics of channel evolution (radial expansion of the channel after the laser pulse), and (iii) the existence via Faraday rotation of relativistic electron currents accelerated in the forward direction during the laser pulse. Among other consequences, these results suggest the self-focusing of the laser pulse and a strong local heating of the plasma.The experiments are performed with the P102 CPA laser system [1] at CEA͞LV. A long creation la...

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confidence: 76%

Dynamics of Subpicosecond Relativistic Laser Pulse Self-Channeling in an Underdense Preformed Plasma

et al. 1998

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“…The laser energy is either directly deposited at the critical surface (use of Lambert-Beer's law, 100 keV hot spot generation, energy transport by an electronic heat wave [10]) or converted at the critical surface into a collimated beam of fast electrons which subsequently deposit their energy in the plasma (ballistic model, use of a Bethe-like energy loss formula [11], including a self-consistent electric field which drives the return current, in analogy to [12]). There are indications for the formation of collimated beams of relativistic electrons under certain conditions in experiments [13] and simulations [7,14,15] and their breaking up into numerous filaments [7,14,16]. At present, neither merging into a single beam ("superchannel") nor splitting into filaments is understood.…”

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confidence: 97%

Fast Ignition without Hole Boring

Hain

Mulser

2001

Phys. Rev. Lett.

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A fast-ignitor scheme for inertial confinement fusion is proposed which works without hole boring. It is shown that a thermonuclear burn wave starts from the pellet corona when an adequate amount of energy (typically 10 kJ) is deposited in the critical layer by a petawatt laser ("coronal ignition"). Burn efficiencies as high as predicted for standard central spark ignition are achieved. In addition, the scheme is surprisingly insensitive to large deviations from spherical precompression symmetry. It may open a new prospect for direct drive.

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“…The transverse ponderomotive force should be dominant, which means that the interaction is multidimensional and transverse effects such as Raman sidescattering are important. Also, because there are a number of plasma periods (t p 2p͞v p ) within the pulse envelope, various instabilities such as Raman processes and laser-envelope modulations can cause laser beam breakup [10,11] and complicate the interpretation of the origin of electron acceleration [9,[12][13][14]. For instance, a recent analysis shows that the occurrence of Raman scattering and plasma heating will suppress both ponderomotive expulsion and RSF [15].…”

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“…This is in agreement with Refs. [12,14,22], in which numerical simulations are reported, showing that electrons accelerated in a filament can have high energies and small angular spreads. In combination with the S/PMT measurement, we estimate that, for n e 0.06n c , the number of electrons with kinetic energies above 1 MeV is about 10 5 , and the number of electrons in the main beam component is ϳ5 3 10 4 .…”

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Electron Acceleration and the Propagation of Ultrashort High-Intensity Laser Pulses in Plasmas

et al. 2000

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Anomalous Absorption of Very High-Intensity Laser Pulses Propagating through Moderately Dense Plasma

Cited by 41 publications

References 16 publications

Dynamics of Subpicosecond Relativistic Laser Pulse Self-Channeling in an Underdense Preformed Plasma

Dynamics of Subpicosecond Relativistic Laser Pulse Self-Channeling in an Underdense Preformed Plasma

Fast Ignition without Hole Boring

Electron Acceleration and the Propagation of Ultrashort High-Intensity Laser Pulses in Plasmas

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