151 research outputs found
Radiation Emission by Extreme Relativistic Electrons and Pair Production by Hard Photons in a Strong Plasma Wakefield
Radiation spectrum of extreme relativistic electrons and a probability of
electron-positron pair production by energetic photons in a strong plasma
wakefield are derived in the framework of a semiclassical approach. It is shown
that that the radiation losses of the relativistic electron in the plasma
wakefield scale as in the quantum limit when the
energy of the radiated photon becomes close to the electron energy, . The quantum effects will play a key role in future plasma-based accelerators
operating at ultrahigh energy of the electrons.Comment: 10 pages, 2 figure
Landau damping in thin films irradiated by a strong laser field
The rate of linear collisionless damping (Landau damping) in a classical
electron gas confined to a heated ionized thin film is calculated. The general
expression for the imaginary part of the dielectric tensor in terms of the
parameters of the single-particle self-consistent electron potential is
obtained. For the case of a deep rectangular well, it is explicitly calculated
as a function of the electron temperature in the two limiting cases of specular
and diffuse reflection of the electrons from the boundary of the
self-consistent potential. For realistic experimental parameters, the
contribution of Landau damping to the heating of the electron subsystem is
estimated. It is shown that for films with a thickness below about 100 nm and
for moderate laser intensities it may be comparable with or even dominate over
electron-ion collisions and inner ionization.Comment: 15 pages, 2 figure
The Averaged EMGs Recorded from the Arm Muscles During Bimanual “Rowing” Movements
The main purpose was to analyze quantitatively the the average surface EMGs of the muscles that function around the elbow and shoulder joints of both arms in similar bimanual ‘rowing’ movements, which were produced under identical elastic loads applied to the levers (‘oars’). The muscles of PM group (‘pulling’ muscles: elbow flexors, shoulder extensors) generated noticeable velocity-dependent dynamic EMG components during the pulling and returning phases of movement and supported a steady-state activity during the hold phase. The muscles of RM group (‘returning’ muscles: elbow extensors, shoulder flexors) co-contracted with PM group during the movement phases and decreased activity during the hold phase. The dynamic components of the EMGs strongly depended on the velocity factor in both muscle groups, whereas the side and load factors and combinations of various factors acted only in PM group muscles. Various subjects demonstrated diverse patterns of activity redistribution among muscles. We assume that central commands to the same muscles in two arms may be essentially different during execution of similar movement programs. Extent of the diversity in the EMG patterns of such muscles may reflect the subject’s skilling in motor performance; on the other hand, the diversity can reflect redistribution of activity between synergic muscles, thus providing a mechanism directed against development of the muscle fatigue
Analytical model for electromagnetic cascades in rotating electric field
Electromagnetic cascades attract a lot of attention as an important QED
effect that will reveal itself in various electromagnetic field configurations
at ultrahigh intensities. We study cascade dynamics in rotating electric field
analytically and numerically. The kinetic equations for the electron-positron
plasma and gamma-quanta are formulated. The scaling laws are derived and
analyzed. For the cascades arising far above the threshold the dependence of
the cascade parameters on the field frequency is derived. The spectra of
high-energy cascade particles are calculated. The analytical results are
verified by numerical simulations.Comment: 14 pages, 10 figure
On radiative damping in plasma-based accelerators
Radiative damping in plasma-based electron accelerators is analyzed. The
electron dynamics under combined influence of the constant accelerating force
and the classical radiation reaction force is studied. It is shown that
electron acceleration cannot be limited by radiation reaction. If initially the
accelerating force was stronger than the radiation reaction force then the
electron acceleration is unlimited. Otherwise the electron is decelerated by
radiative damping up to a certain instant of time and then accelerated without
limits. Regardless of the initial conditions the infinite-time asymptotic
behavior of an electron is governed by self-similar solution providing
unlimited acceleration. The relative energy spread induced by the radiative
damping decreases with time in the infinite-time limit
QED cascades induced by circularly polarized laser fields
The results of Monte-Carlo simulations of electron-positron-photon cascades
initiated by slow electrons in circularly polarized fields of ultra-high
strength are presented and discussed. Our results confirm previous qualitative
estimations [A.M. Fedotov, et al., PRL 105, 080402 (2010)] of the formation of
cascades. This sort of cascades has revealed the new property of the
restoration of energy and dynamical quantum parameter due to the acceleration
of electrons and positrons by the field and may become a dominating feature of
laser-matter interactions at ultra-high intensities. Our approach incorporates
radiation friction acting on individual electrons and positrons.Comment: 13 pages, 10 figure
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