Dispersion in a relativistic degenerate electron gas

Relativistic effects on dispersion in a degenerate electron gas are discussed by comparing known response functions derived relativistically (by Jancovici) and nonrelativistically (by Lindhard). The main distinguishing feature is one-photon pair creation, which leads to logarithmic singularities in the response functions. Dispersion curves for longitudinal waves have a similar tongue-like appearance in the relativistic and nonrelativistic case, with the main relativistic effects being on the Fermi speed and the cutoff frequency. For transverse waves the nonrelativistic treatment has a nonphysical feature near the cutoff frequency for large Fermi momenta, and this is attributed to an incorrect treatment of the electron spin. We find (with two important provisos) that one-photon pair creation is allowed in superdense plasmas, implying relatively strong coupling between transverse waves and pair creation.Comment: 17 pages, 9 figures. Submitted to Physical Review

Dispersion and damping of potential surface waves in a degenerate plasma

Potential (electrostatic) surface waves in plasma half-space with degenerate electrons are studied using the quasi-classical mean-field kinetic model. The wave spectrum and the collisionless damping rate are obtained numerically for a wide range of wavelengths. In the limit of long wavelengths, the wave frequency $\omega$ approaches the cold-plasma limit $\omega=\omega_p/\sqrt{2}$ with $\omega_p$ being the plasma frequency, while at short wavelengths, the wave spectrum asymptotically approaches the spectrum of zero-sound mode propagating along the boundary. It is shown that the surface waves in this system remain weakly damped at all wavelengths (in contrast to strongly damped surface waves in Maxwellian electron plasmas), and the damping rate nonmonotonically depends on the wavelength, with the maximum (yet small) damping occuring for surface waves with wavelength of $\approx5\pi\lambda_{F}$, where $\lambda_{F}$ is the Thomas-Fermi length.Comment: 22 pages, 6 figure

Shielding of a moving test charge in a quantum plasma

The linearized potential of a moving test charge in a one-component fully degenerate fermion plasma is studied using the Lindhard dielectric function. The motion is found to greatly enhance the Friedel oscillations behind the charge, especially for velocities larger than a half of the Fermi velocity, in which case the asymptotic behavior of their amplitude changes from 1/r^3 to 1/r^2.5. In the absence of the quantum recoil (tunneling) the potential reduces to a form similar to that in a classical Maxwellian plasma, with a difference being that the plasma oscillations behind the charge at velocities larger than the Fermi velocity are not Landau-damped.Comment: 9 pages, 11 figures. v3: Fixed typo, updated abstrac

Measurement of qutrits

We proposed the procedure of measuring the unknown state of the three-level system - the qutrit, which was realized as the arbitrary polarization state of the single-mode biphoton field. This procedure is accomplished for the set of the pure states of qutrits; this set is defined by the properties of SU(2) transformations, that are done by the polarization transformers.Comment: 9 pages, 9 figure

К МЕТОДИКЕ ОПРЕДЕЛЕНИЯ РЕОЛОГИЧЕСКИХ СВОЙСТВ МЕТАЛЛОВ ИСПЫТАНИЯМИ НА КРУЧЕНИЕ

The quality of results of mathematical modeling the pressure treatment of metals (PTM) substantially depends on the exactness of the initial data, which include the rheological properties of the billet material. The traditional procedure of their testing is based on the assumption that the sample temperature remains constant during testing. However, it is known that strain sample heating occurs during isothermal loading. Modern plastometers do not foresee monitoring the sample temperature during testing, which introduces the substantial error when calculating the deformation resistances and, correspondingly, temperaturefields and energy-power parameters of PTM processes. In connection with this, the procedure and results of the experimental investigation into the heat liberation in the samples made of the VT-6 titanium alloy under torsion using a laboratory torsion plastometer in a temperature range of 800–1000 °C at deformation rates of 0,01–10,0 s–1 (1–600 rpm) are presented in this article. The temperature of the sample surface was monitored using a photopyrometer during testing. It is established that the sample surface substantially heats at relatively high loading rates, and the temperature increment to the destroy instant can reach 50–60 °C at the testing rate of the order of 10 s–1 and initial temperature of 850 °C. The error in determining the strain resistance is of the order of 30 %.Качество результатов математического моделирования процессов обработки металлов давлением (ОМД) существенно зависит от точности исходных данных, к числу которых относятся реологические свойства материала заготовки. Традиционная методика их определения основана на допущении, что температура образца в процессе испытания сохраняется постоянной. Вместе с тем известно, что при изотермических условиях нагружения имеет место деформационный разогрев образца. Современные пластометры не предусматривают контроль температуры образца в ходе испытания, что вносит существенную погрешность при расчете сопротивления деформации и, соответственно, температурных полей и энергосиловых параметров процессов ОМД. В связи с этим в настоящей работе приводятся методика и результаты экспериментального исследования тепловыделения в образцах из титанового сплава ВТ-6 при кручении на лабораторном торсионном пластометре в интервале температур 800–1000 °C при скоростях деформации 0,01–10,0 с–1 (1–600 об/мин). В процессе испытаний температуру поверхности образцов контролировали фотопирометром. Установлено, что при относительно больших скоростях нагружения имеет место существенный разогрев поверхности образца, который, например, при скорости испытания порядка 10 с–1 и начальной температуре 850 °С к моменту разрушения может достичь 50–60 °С. При этом погрешность в определении сопротивления деформации составляет около 30 %

Properties of electrons scattered on a strong plane electromagnetic wave with a linear polarization: classical treatment

The relations among the components of the exit momenta of ultrarelativistic electrons scattered on a strong electromagnetic wave of a low (optical) frequency and linear polarization are established using the exact solutions to the equations of motion with radiation reaction included (the Landau-Lifshitz equation). It is found that the momentum components of the electrons traversed the electromagnetic wave depend weakly on the initial values of the momenta. These electrons are mostly scattered at the small angles to the direction of propagation of the electromagnetic wave. The maximum Lorentz factor of the electrons crossed the electromagnetic wave is proportional to the work done by the electromagnetic field and is independent of the initial momenta. The momentum component parallel to the electric field strength vector of the electromagnetic wave is determined only by the diameter of the laser beam measured in the units of the classical electron radius. As for the reflected electrons, they for the most part lose the energy, but remain relativistic. There is a reflection law for these electrons that relates the incident and the reflection angles and is independent of any parameters.Comment: 12 pp, 3 fig

Stochastic Theory of Relativistic Particles Moving in a Quantum Field: II. Scalar Abraham-Lorentz-Dirac-Langevin Equation, Radiation Reaction and Vacuum Fluctuations

We apply the open systems concept and the influence functional formalism introduced in Paper I to establish a stochastic theory of relativistic moving spinless particles in a quantum scalar field. The stochastic regime resting between the quantum and semi-classical captures the statistical mechanical attributes of the full theory. Applying the particle-centric world-line quantization formulation to the quantum field theory of scalar QED we derive a time-dependent (scalar) Abraham-Lorentz-Dirac (ALD) equation and show that it is the correct semiclassical limit for nonlinear particle-field systems without the need of making the dipole or non-relativistic approximations. Progressing to the stochastic regime, we derive multiparticle ALD-Langevin equations for nonlinearly coupled particle-field systems. With these equations we show how to address time-dependent dissipation/noise/renormalization in the semiclassical and stochastic limits of QED. We clarify the the relation of radiation reaction, quantum dissipation and vacuum fluctuations and the role that initial conditions may play in producing non-Lorentz invariant noise. We emphasize the fundamental role of decoherence in reaching the semiclassical limit, which also suggests the correct way to think about the issues of runaway solutions and preacceleration from the presence of third derivative terms in the ALD equation. We show that the semiclassical self-consistent solutions obtained in this way are ``paradox'' and pathology free both technically and conceptually. This self-consistent treatment serves as a new platform for investigations into problems related to relativistic moving charges.Comment: RevTex; 20 pages, 3 figures, Replaced version has corrected typos, slightly modified derivation, improved discussion including new section with comparisons to related work, and expanded reference

Modelling the effects of the radiation reaction force on the interaction of thin foils with ultra-intense laser fields

The effects of the radiation reaction (RR) force on thin foils undergoing radiation pressure acceleration (RPA) are investigated. Using QED-particle-in-cell simulations, the influence of the RR force on the collective electron dynamics within the target can be examined. The magnitude of the RR force is found to be strongly dependent on the target thickness, leading to effects which can be observed on a macroscopic scale, such as changes to the distribution of the emitted radiation and the target dynamics. This suggests that such parameters may be controlled in experiments at multi-PW laser facilities. In addition, the effects of the RR force are characterized in terms of an average radiation emission angle. We present an analytical model which, for the first time, describes the effect of the RR force on the collective electron dynamics within the 'light-sail' regime of RPA. The predictions of this model can be tested in future experiments with ultra-high intensity lasers interacting with solid targets