100 research outputs found
The Collisonal Tearing Mode Instability in a Quasi-stational Plasma
The behaviour of a small perturbation in the diffuse neutral sheet is analysed in a frame of MHD equations. It is shown that the normal magnetic component perpendicular to the current sheet does not contribute to the stability of the tearing instability in both the cases of high coductivity limit and low conductivity limit.The plasma flow expanding along the sheet can effectively stabilize the tearing instability.The nonlinear stage of this mode is estimated. It is shown that the secondary stationary flow with a hyperbolic pattern is structed.Tearing不安定は,天体プラズマ及び実験室プラズマでの応用と関連して,多くの研究がある。この不安定は,MHD的扱いのみならずCollisionlessプラズマでも起こる。又,この不安定は,太陽大気でのフレアー現象や,地球磁気圏での爆発的現象(substorm)と関連して,そして又,トカマクプラズマでのdisruptive不安定と関連しており,重要な不安定として研究されている。我々は,本稿で,MIlD領域でtearingmodeが安定化されないことを示す。論文の終わりで,tearing modeの非線形段階で現われる2次的な流れの効果についても述べる
Relativistic Laser-Matter Interaction and Relativistic Laboratory Astrophysics
The paper is devoted to the prospects of using the laser radiation
interaction with plasmas in the laboratory relativistic astrophysics context.
We discuss the dimensionless parameters characterizing the processes in the
laser and astrophysical plasmas and emphasize a similarity between the laser
and astrophysical plasmas in the ultrarelativistic energy limit. In particular,
we address basic mechanisms of the charged particle acceleration, the
collisionless shock wave and magnetic reconnection and vortex dynamics
properties relevant to the problem of ultrarelativistic particle acceleration.Comment: 58 pages, 19 figure
Transverse Dynamics and Energy Tuning of Fast Electrons Generated in Sub-Relativistic Intensity Laser Pulse Interaction with Plasmas
The regimes of quasi-mono-energetic electron beam generation were
experimentally studied in the sub-relativistic intensity laser plasma
interaction. The observed electron acceleration regime is unfolded with
two-dimensional-particle-in-cell simulations of laser-wakefield generation in
the self-modulation regime.Comment: 10 pages, 5 figure
Coulomb implosion mechanism of negative ion acceleration in laser plasmas
Coulomb implosion mechanism of the negatively charged ion acceleration in
laser plasmas is proposed. When a cluster target is irradiated by an intense
laser pulse and the Coulomb explosion of positively charged ions occurs, the
negative ions are accelerated inward. The maximum energy of negative ions is
several times lower than that of positive ions. The theoretical description and
Particle-in-Cell simulation of the Coulomb implosion mechanism and the evidence
of the negative ion acceleration in the experiments on the high intensity laser
pulse interaction with the cluster targets are presented.Comment: 4 page
The reflectivity of relativistic ultra-thin electron layers
The coherent reflectivity of a dense, relativistic, ultra-thin electron layer
is derived analytically for an obliquely incident probe beam. Results are
obtained by two-fold Lorentz transformation. For the analytical treatment, a
plane uniform electron layer is considered. All electrons move with uniform
velocity under an angle to the normal direction of the plane; such electron
motion corresponds to laser acceleration by direct action of the laser fields,
as it is described in a companion paper. Electron density is chosen high enough
to ensure that many electrons reside in a volume \lambda_R^3, where \lambda_R
is the wavelength of the reflected light in the rest frame of the layer. Under
these conditions, the probe light is back-scattered coherently and is directed
close to the layer normal rather than the direction of electron velocity. An
important consequence is that the Doppler shift is governed by
\gamma_x=(1-(V_x/c)^2)^{-1/2} derived from the electron velocity component V_x
in normal direction rather than the full \gamma-factor of the layer electrons.Comment: 7 pages, 4 figures, submitted to the special issue "Fundamental
Physics with Ultra-High Fields" in The European Physical Journal
Stability improvement of a laser-accelerated electron beam and the pulse width measurement of the electron beam
Laser wakefield acceleration has the possibility to generate an ultrashort electron beam of the order of femtoseconds or less. In applications of these laser accelerated electron beams, stable and controllable electron beams are necessary. A high stability electron bunch is generated by laser wakefield acceleration with the help of a colliding laser pulse (optical injection). Stable and monoenergetic electron beams have been generated in the self-injection scheme of laser acceleration by using a Nitrogen gas jet target. The electron interaction with the laser field results in transverse oscillations of the electron beam. From the electron oscillation period dependence on the electron energy we find that the electron beam width is equal to 1.7 fs (rms).В процессе ускорения кильватерными волнами возможна генерация сверхкоротких электронных пучков фемтосекундной длительностью. Для приложений требуются электронные пучки с воспроизводимыми и котролируемыми параметрами. Оптическая инжекция, использующая сталкивающиеся лазерные импульсы, обеспечивает высокую воспроизводимость параметров пучков ускоренных электронов. Моноэнергетические пучки электронов с воспроизводимыми параметрами были получены при «самоинжекции» в кильватерную волну в экспериментах, использующих в качестве мишени струю азота. Взаимодействие электронов с излучением лазерного импульса приводит к поперечным осцилляциям электронного пучка. Анализ наблюдаемой в эксперименте зависимости периода осцилляций от энергии электронов позволяет найти длительность электронного пучка, равную 1.7 фс.В процесі прискорення кільватерними хвилями можлива генерація надкоротких електронних пучків фемтосекундної тривалості. Для додатків потрібні електронні пучки з відтворюючими і котролюючими параметрами. Оптична інжекція, що використовує зіштовхуючі лазерні імпульси, забезпечує високу відтворюваність параметрів пучків прискорених електронів. Моноенергетичні пучки електронів з відтворюваними параметрами були отримані при «самоінжекції» в кільватерну хвилю в експериментах, в яких в якості мішені використовувалася струмінь азоту. Взаємодія електронів з випромінюванням лазерного імпульсу призводить до поперечних осциляцій електронного пучка. Аналіз спостерігаючої в експерименті залежності періоду осциляцій від енергії електронів дозволяє знайти тривалість електронного пучка, яка дорівнює 1.7 фс
Current-sheet formation in incompressible electron magnetohydrodynamics
The nonlinear dynamics of axisymmetric, as well as helical, frozen-in vortex
structures is investigated by the Hamiltonian method in the framework of ideal
incompressible electron magnetohydrodynamics. For description of current-sheet
formation from a smooth initial magnetic field, local and nonlocal nonlinear
approximations are introduced and partially analyzed that are generalizations
of the previously known exactly solvable local model neglecting electron
inertia. Finally, estimations are made that predict finite-time singularity
formation for a class of hydrodynamic models intermediate between that local
model and the Eulerian hydrodynamics.Comment: REVTEX4, 5 pages, no figures. Introduction rewritten, new material
and references adde
Precision tests of QED and non-standard models by searching photon-photon scattering in vacuum with high power lasers
We study how to search for photon-photon scattering in vacuum at present
petawatt laser facilities such as HERCULES, and test Quantum Electrodynamics
and non-standard models like Born-Infeld theory or scenarios involving
minicharged particles or axion-like bosons. First, we compute the phase shift
that is produced when an ultra-intense laser beam crosses a low power beam, in
the case of arbitrary polarisations. This result is then used in order to
design a complete test of all the parameters appearing in the low energy
effective photonic Lagrangian. In fact, we propose a set of experiments that
can be performed at HERCULES, eventually allowing either to detect
photon-photon scattering as due to new physics, or to set new limits on the
relevant parameters, improving by several orders of magnitude the current
constraints obtained recently by PVLAS collaboration. We also describe a
multi-cross optical mechanism that can further enhance the sensitivity,
enabling HERCULES to detect photon-photon scattering even at a rate as small as
that predicted by QED. Finally, we discuss how these results can be improved at
future exawatt facilities such as ELI, thus providing a new class of precision
tests of the Standard Model and beyond.Comment: 15 pages, 2 figures. Corrected few mistakes in section and 4. Results
unchanged. Added a referenc
Observation of Burst Intensification by Singularity Emitting Radiation generated from relativistic plasma with a high-intensity laser
Coherent x-rays via the Burst Intensification by Singularity Emitting Radiation (BISER) mechanism are generated from relativistic plasma in helium gas target. A broad modulation of the BISER spectrum, which is significantly wider than the harmonic order, is observed and characterized. In particular, we found that the modulation period can be as large as 41 eV
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Controllable Laser Ion Acceleration
In this paper a future laser ion accelerator is discussed to make the laser-based ion accelerator compact and controllable. Especially a collimation device is focused in this paper. The future laser ion accelerator should have an ion source, ion collimators, ion beam bunchers, and ion post acceleration devices [Laser Therapy 22, 103(2013)]: the ion particle energy and the ion energy spectrum are controlled to meet requirements for a future compact laser ion accelerator for ion cancer therapy or for other purposes. The energy efficiency from the laser to ions is improved by using a solid target with a fine sub-wavelength structure or a near-critical density gas plasma. The ion beam collimation is performed by holes behind the solid target or a multi-layered solid target. The control of the ion energy spectrum and the ion particle energy, and the ion beam bunching would be successfully realized by a multistage laser-target interaction
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