Electron-positron pair creation in the electric fields generated by micro-bubble implosions

We show that electron-positron pair production from the vacuum is possible via the strong Coulomb fields generated by micro-bubble implosions induced by ultra-high intensity lasers. Even in the case where the Coulomb fields are lower than the pair creation threshold, externally injected high energy electrons or photons could be used to generate pairs.     

On refractive processes in strong laser field quantum electrodynamics

Refractive processes in strong-field QED are pure quantum processes, which involve only external photons and the background electromagnetic field. We show analytically that such processes occurring in a plane-wave field and involving external real photons are all characterized by a surprisingly modest net exchange of energy and momentum with the laser field, corresponding to a few laser photons, even in the limit of ultra-relativistic laser intensities. We obtain this result by a direct calculation of the transition matrix element of an arbitrary refractive QED process and accounting exactly for the background plane-wave field. A simple physical explanation of this modest net exchange of laser photons is provided, based on the fact that the laser field couples with the external photons only indirectly through virtual electron–positron pairs. For stronger and stronger laser fields, the pairs cover a shorter and shorter distance before they annihilate again, such that the laser can transfer to them an energy corresponding to only a few photons. These results can be relevant for the future experiments aiming to test strong-field QED at present and next-generation facilities.     

Large amplitude electron plasma oscillations

We consider a cold plasma in order to find new large-amplitude wave solutions in the long-wavelength limit. Accordingly we derive two generic coupled equations which describe the energy exchange between the electrostatic and electromagnetic waves. A new kind of quasi-periodic behavior is found. Our derivations may be considered as a prerequisite to extended studies of stimulated Raman scattering for cases where the wave amplitudes are so large that standard perturbation techniques are not applicable.     

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利用朗缪尔探针和发射光谱两种诊断手段,测量了某固体工质等离子体发生器的喷流流场参数。结果表明,在输入功率为2kW时,发生器可持续稳定工作300s;发生器燃烧室内最高温度为800K。稳定工作时,发生器壳体结构正常,没有发现损毁现象;等离子体喷流的电子密度为1011～1012cm–3量级,电子温度为1.5～3.5eV。     

Electron-positron pair production in a strong asymmetric laser electric field

By solving the quantum Vlasov equation, electron positron pair production in a strong electric field with asymmetric laser pulses has been investigated. We consider three different situations of subcycle, cycle and supercycle laser pulses. It is found that in asymmetric laser pulse field, i.e.. when the pulse length of one rising or falling side is fixed while the pulse length of the other side is changed, the pair production rate and mnnber density can be significantly modified comparable to symmetric situation. For each ca,se of these three different cycle pulses, when one side pulse length is constant and the other side pulse length becomes shorter, i.e., the whole pulse is compressed, the more pairs can be produced than that in tile vice versa case, i.e., the whole pulse is elongated. In compressed pulse case there exists an optimum pulse length ratio of asylnmetric pulse lengths which makes the pair number density maximunn. Moreover, the created maximum pair number density by subcycle pulse is larger than that by cycle or/and supercycle pulse. In elongated pulse case, however, only for supercycle laser pulse the created pairs is enhanced and there exists also an optimum asymmetric pulse length ratio that maximizes the pair number density. On the other hand. surprisingly, in both cases of subcycle and cycle elongated laser pulses, the pair number density is monotonically decreasing as the asymmetry of pulse increases.     

X-ray production by a laser plasma in a strong electric field

The X-ray emission of a laser plasma from metal targets in a 26 kV cm^–1 electric field is investigated experimentally. A substructure of the X-ray pulse, corresponding to the laser pulse train period is found. The spectrum of the radiation in the range 2–25 keV is measured.     

Commensurability oscillations in a quasi-two-dimensional electron gas subject to strong in-plane magnetic field

We report on a theoretical study of the commensurability oscillations in a quasi-two-dimensional electron gas modulated by a unidirectional periodic potential and subject to tilted magnetic fields with a strong in-plane component. As a result of coupling of the in-plane field component and the confining potential in the finite-width quantum well, the originally circular cyclotron orbits become anisotropic and tilted out of the sample plane. A quasi-classical approach to the theory, that relates the magneto-resistance oscillations to the guiding-center drift, is extended to this case.     

On a kinetic approach to the modulational stability of envelope solitons in a relativistic plasma in an external electric field

Summary The formation of envelope solitons is discussed in a relativistic plasma under the influence of a fluctuating electric field. We use the kinetic-theory approach for our analysis. Due to the larger inertia, only the electrons are considered to be relativistic and the ions to be nonrelativistic. A NLS equation is derived describing the motion of the solitary wave. This NLS equation actually comes from an approximation of a pair of equations which can be considered to be a relativistic generalisation of the Zakharov equation. We next discuss the exact form of the envelope solitary-wave solution of the NLS equation and the modulation stability of such a wave. When the density, momentum and energy of such wave packets are fixeda priori, conditions are derived for the parameters of the problem from such stability consideration.     

Time behaviour of electron oscillations in a plasma

Summary This paper analyses the transient part in the dynamical behaviour of electron oscillations in a partially ionized plasma. The influence of electron-neutral collisions on time evolution is pointed out. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

On the polarizability of a pair of cylinders in a transverse electric field

A sequential scheme for calculating the polarizability of a pair of parallel cylinders with an arbitrary (but fairly symmetric) form is suggested. An infinite set of algebraic equations is derived for coefficients involved in an expression for the potential. The numerical solution of this set makes it possible to find the polarizability with any degree of accuracy. This method is unrelated to the cylinder shape. The electrostatic properties of the cylinders are described in terms of the multipolar polarizability matrix.     

Electron oscillations in a plasma: Effect of collisions on Landau damping

Summary Electron oscillations in a plasma are analysed starting from the integral form of Boltzmann-Vlasov equation. The effects of collisions on Landau damping are shown. The conditions for Landau damping existence are derived.

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Riassunto Onde elettrostatiche in un plasma sono studiate ricorrendo alla forma integrale dell'equazione di Boltzmann-Vlasov. In particolare, sono stati evidenziati gli effetti prodotti sul Landau damping dalle collisioni. Si è ricavato che in certe condizioni le collisioni possono impedire il Landau damping e si sono ottenuti i valori di soglia.

     

Radial oscillations of neutron stars in strong magnetic fields

The eigen frequencies of radial pulsations of neutron stars are calculated in a strong magnetic field. At low densities we use the magnetic BPS equation of state (EOS) similar to that obtained by Lai and Shapiro while at high densities the EOS obtained from the relativistic nuclear mean field theory is taken and extended to include strong magnetic field. It is found that magnetized neutron stars support higher maximum mass whereas the effect of magnetic field on radial stability for observed neutron star masses is minimal.     

Neutrino pair creation in a strong magnetic field

An expression for the probability of neutrino pair creation by an electron in an ultrastrong magnetic field is obtained. The calculations are done using the exact solutions of the Dirac equation in a magnetic field in the low energy approximation of the Weinberg-Salam model.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 39–41, September, 1982.     

Electron-positron pair creation by a strong tightly focused laser field

The analytical calculation of the electron-positron pair creation yield by an extremely strong focused laser pulse in the vacuum is presented. In particular, dependence of the total yield of the pair production on the focusing parameter and the polarization properties of the laser pulse are analyzed. Comparison with the previous consideration of N.B. Narozhny, V.S. Popov, V.D. Mur, and S.S. Bulanov is given and discussed. As a result, we confirm their conclusion that the electron-positron pair production can be observed in principle at the level of intensity of 10²⁷ W/cm².     

dc Magnetic field generated by an electric dipole antenna in an anisotropic plasma

dc magnetization generated by an ac electric dipole in a magnetized plasma is considered. The main result is the expression of the induced dc magnetic field in a system with axial symmetry. It has a general form valid for any ac source with the same symmetry.     

On the hopping conduction mechanism of amorphous semiconductors in a strong electric field

The theory of the hopping conduction by the radiative tunnel transitions (RTT) in a strong electric field is applied to amorphous silicon and germanium. On the basis of numerical estimations we suggest that the relative contribution of the RTT mechanism into the total strong electric field hopping conductivity of an amorphous semiconductor could be significant.     

Polaron in a strong alternating electric field

The solution is found for the transport equation for a Feynman polaron having arbitrary coupling interacting with the acoustic oscillations in an alternating electric field. In the low-frequency case, this solution cannot be normalized — there are runaway polarons. For high frequencies, this effect is absent. Equations are obtained for the electrical conductivity of polaron semiconductors for various particular cases, including the runaway regime.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 45–49, April, 1979.