A new combination of scattering mechanisms for transverse runaway (TR) of hot electrons

A new combination of energy and momentum scattering mechanisms has been found at which the transverse runaway (TR) of hot electrons takes place. Up to now only two combinations of scattering mechanisms at which TR occurred have been known. These two combinations were obtained by analytical solution of a complex integral equation at certain approximations. In the present work, using modern numerical methods, with no above-mentioned approximations, a solution of the integral equation for a new combination of scattering mechanisms has been found.In the work physical conditions responsible for dominance of corresponding scattering mechanisms are also analyzed.     

A Mechanical Model for Analyzing the Runaway Solutions in the Radiation Reaction Problem

In order to understand the rise of runaway solutions in the radiation reaction problem a mechanical model is used. An alternative demonstration of Daboul’s theorem, through Hurwitz’s criterion, is given. The origin of runaway solutions in electrodynamics is discussed. They arise when the particle has a negative mechanical mass or when approximations are used in the equation of motion. In the 1-dimensional mechanical model an exact and linear equation of motion for the particle is obtained, the corresponding exact solution is again runaway when the mechanical mass is negative. The exact solution is not runaway when the mechanical mass is positive. However, the use of approximations leads to an equation of motion which has runaway solutions. It is exhibited that the use of approximations in the 3-dimensional mechanical model is completely necessary because the general equation of motion for the particle is non-linear. The analysis of this case proceeds in a very similar way to the one carried out in electrodynamics. This means that the number of dimensions also plays an important role in the analysis.     

Transverse runaway of hot electrons and the electron-temperature approximation

This paper discusses the transverse runaway effect in the electron-temperature approximation. The combinations of scattering mechanisms and the corresponding threshold electric fields for which transverse runaway develops are determined. It is shown that the transverse-runaway effect is not associated with any approximation. Zh. éksp. Teor. Fiz. 113, 688–692 (February 1998)     

磁化等离子体中逃逸电子的临界速度

根据等离子体动力论,分析了在磁化等离子体中逃逸电子的临界速度,并在托卡马克参数下作了数值计算。计算表明,有磁场时,逃逸电子所受到的摩擦力,在纵向速度较大时比无磁场时的为大,这相应于逃逸电子临界速度的提高,因而高能的逃逸电子也较难产生。当磁场增大时,摩擦力略有减小。在纵向速度较高时,逃逸电子的横向速度分量对临界速度的影响较明显,横向速度越大,临界速度也越大。 关键词：     

Simulations of plasma formation in the cathode sheath of an efficient excimer lamp

Based on the available experimental data and computer simulations, analytical approximations of the quantities characterizing electron multiplication in the cathode sheath are proposed. The critical electric field is found above which runaway electrons are observed. Using the approximations proposed, the dependences of the plasma parameters (the electron and ion densities and currents and the electric field strength) on the distance from the cathode are analyzed. Simple formulas for the total current, the cathode sheath thickness, and the cathode potential drop as functions of the electric field on the cathode surface are derived.     

Quantum theory of transverse galvano-magnetic phenomena

A quantum theory of electrical conduction in crosfsed electric and magnetic fields is given for the limit of very weak scattering. A density matrix formulation of the problem is used, and an arbitrary scattering mechanism is considered. The theory is found to be completely equivalent to theories given earlier by and by and .

Formulae are given for the resistivity in the quantum limit for both longitudinal and transverse orientations of electric field, for degenerate and non-degenerate statistics, and for several different scattering mechanisms. The oscillatory conductivity is calculated for acoustical and ionized-impurity scattering mechanisms. Formulae obtained for the quantum transport effects are in disagreement with the formulae of and of . The discrepancy is attributed to unwarranted approximations in those authors' treatments of scattering.     

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.     

Linear response theory for thermoelectric transport coefficients of a partially ionized plasma

Electrical conductivity, thermopower and thermal conductivity for a partially ionized plasma are expressed within an extended Zubarev approach by equilibrium correlation functions. The Green function technique is used to evaluate the correlation functions in different approximations. Improvements of the Lenard-Balescu approximation are considered, which account for dynamical screening effects and higher Born approximations for the electron-electron, electron-ion and electron-atom interaction.     

Comparison of relativistic runaway electron avalanche ratesobtained from Monte Carlo simulations and kinetic equation solution

New computer simulations of the relativistic runaway electron avalanche mechanism were carried out to remove prior approximations and reassess the space and temporal scales predicted by previous Boltzmann calculations. Two Monte Carlo techniques, a finite-difference solution, and a finite-volume solution of the kinetic equation for high-energy electrons were employed. Results obtained for the length and time scales at sufficiently high electric fields by the different methods are consistent with each other and with analytical estimates. The physical reason for the remaining discrepancy at small fields is discussed     

Bessel–Gauss beam optical resonator

In a simple picture, a Bessel beam is viewed as a transverse standing wave formed in the interference region between incoming and outgoing conical waves. Based on this interpretation we propose an optical resonator that supports modes that are approximations to Bessel–Gauss beams. The Fox–Li algorithm in two transverse dimensions is applied to confirm the conclusion.     

Dynamical conductivity of type-I semiconductor superlattices

We calculated longitudinal and transverse macroscopic as well as microscopic dynamical conductivity for a modulation-doped type-I superlattice. Our computed long wavelength macroscopic conductivity significantly differs from Drude conductivity in the low-frequency regime (microwave and infrared radiations). Macroscopic conductivity shows oscillatory behaviour along the direction of growth of the superlattice. Propagation of transverse electromagnetic waves in a superlattice has been studied for all possible values of frequency and wavevector. It is found that microscopic transverse conductivity exhibits poles along both real and imaginary axes of frequency. Depending on the values of wavevector components, along and perpendicular to the direction of the superlattice, both poles can lie on real or imaginary axes of frequency. We also find that there can be more than one penetration depth for a superlattice and one of them decreases with frequency for frequencies below the microwave regime.     

Electronic thermal Hall effect in silicene

We theoretically investigate the electronic thermal Hall effect in silicene via a discrete four-band model. Based on the linear response theory, a formalism to address the transverse thermal conductivity is developed. In the absence of an exchange field, the transverse thermal conductivity vanishes due to the time-reversal symmetry. The transverse conductivity becomes finite in the presence of an exchange field and exhibits several peaks with opposite signs. The peak values increase as the field becomes strong. However, as the temperature becomes high, the peak values begin to decay. The results may be helpful in exploring spin caloritronics based on silicene.     

Simple formulas for the oscillating component of the electrical conductivity of layered chargeordered crystals

In the present paper, oscillations of the longitudinal component of the electrical conductivity of layered crystals are examined in electric and quantizing magnetic fields perpendicular to the layers. It is demonstrated that frequencies and amplitudes of longitudinal conductivity oscillations can be determined with sufficient accuracy through the chemical potential of the electron gas and effective width of the miniband caused by the charge ordering. In addition, based on an analysis of formulas for the transverse conductivity, it is established that the applicability limits for the transverse conductivity in the semiclassical approximation (for the magnetic field induction) in the field perpendicular to the layers are much wider than for the longitudinal conductivity. An immediate reason for this is the zero longitudinal velocity of current carriers in the extreme cross sections, which leads to the field dependence of the amplitudes of longitudinal conductivity oscillations stronger than of transverse ones. Calculated results are used to interpret experimental data obtained for the β-(ET)2IBr2 synthetic metals. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 34–43, May, 2006.     

Effect of a transverse magnetic field on the generation of electron beams in the gas-filled diode

The effect of a transverse magnetic field (0.080 and 0.016 T) on generation of an electron beam in the gas-filled diode is experimentally investigated. It is shown that, at voltage U = 25 kV across the diode and a low helium pressure (45 Torr), the transverse magnetic field influences the beam current amplitude behind a foil and its distribution over the foil cross section. At elevated pressures and under the conditions of ultrashort avalanche electron beam formation in helium, nitrogen, and air, the transverse magnetic field (0.080 and 0.016 T) has a minor effect on the amplitude and duration of the beam behind the foil. It is established that, when the voltage of the pulse generator reaches several hundreds of kilovolts, some runaway electrons (including the electrons from the discharge plasma near the cathode) are incident on the side walls of the diode.     

New approach to the small polaron conductivity problem

A model of electrons coupled to the damped lattice-oscillators is made the basis for calculation of the small polaron conductivity in the infrared frequency range. The inclusion of damping prevents the occurrence of singularities. Under the assumption of a weak damping a closed formula for the real part of conductivity is deduced which unifies the low-temperature as well as the high-temperature approximations.     

Role of bremsstrahlung radiation in limiting the energy of runaway electrons in tokamaks

Bremsstrahlung radiation of runaway electrons is found to be an energy limit for runaway electrons in tokamaks. The minimum and maximum energy of runaway electron beams is shown to be limited by collisions and bremsstrahlung radiation, respectively. It is also found that a massive injection of a high-Z gas such as xenon can terminate a disruption-generated runaway current before the runaway electrons hit the walls.     

Hot electron transverse conductivity in quantizing magnetic fields

In this work the general expression of the electron transverse conductivity tensor of an electron-phonon system being in crossed strong electric and quantizing magnetic fields is considered starting from the Kubo-Kalashnikov formula. An explicit formula for the hot electron transverse conductivity σ _xx is obtained and it is compared to a Titeica-type formula with the temperature of electrons replaced by an effective electron temperature depending on the electric field.     

Observation of trapped and passing runaway electrons by infrared camera in the EAST tokamak

In EAST, synchrotron radiation is emitted by runaway electrons in the infrared band, which can be observed by infrared cameras. This synchrotron radiation is mainly emitted by passing runaway electrons with tens of Me V energy. A common feature of radiation dominated by passing runaway electrons is that it is strongest on the high field side. However,the deeply trapped runaway electrons cannot reach the high field side in principle. Therefore, in this case, the high field side radiation is expected to be weak. This paper reports for the first time that the synchrotron radiation from trapped runaway electrons dominates that from passing runaway electrons and is identifiable in an image. Although the synchrotron radiation dominated by trapped runaway electrons can be observed in experiment, the proportion of trapped runaway electrons is very low.     

Transverse spectra of waves in random media

We consider the statistics of the transverse spectra of forward-propagating waves in a stationary random medium. A short-range perturbation solution is used to derive the difference equations that govern the long-range evolution of the ensemble-averaged transverse wave spectrum and coherence. The conditions under which these equations may be approximated by differential and integro-differential equations are given, and it is shown that the approximation is valid for the treatment of beam propagation provided that the transverse dimension of the beam is sufficiently large, and at ranges where the transverse coherence length of the beam remains larger than a wavelength. The equations that are derived are not limited by the parabolic approximation, and are amenable to numerical solution by marching techniques. We use the equation that governs the spectral density of the total energy flux, and also the propagation of waves which are statistically homogeneous in transverse planes, to show the conditions under which previously studied approximations derive from the present formulation, and to illustrate the numerical solution of the problem.     

Synchrotron radiation intensity and energy of runaway electrons in EAST tokamak

A detailed analysis of the synchrotron radiation intensity and energy of runaway electrons is presented for the Experimental Advanced Superconducting Tokamak(EAST). In order to make the energy of the calculated runaway electrons more accurate, we take the Shafranov shift into account. The results of the analysis show that the synchrotron radiation intensity and energy of runaway electrons did not reach the maximum at the same time. The energy of the runaway electrons reached the maximum first, and then the synchrotron radiation intensity of the runaway electrons reached the maximum.We also analyze the runaway electrons density, and find that the density of runaway electrons continuously increased. For this reason, although the energy of the runaway electrons dropped but the synchrotron radiation intensity of the runaway electrons would continue rising for a while.