Nonlocal Electron Transport Research Articles

Nonlocal electron transport in the presence of high-intensity laser irradiation.

We investigate electron transport in a plasma heated by spatially modulated laser irradiation. When the heating rate is greater than the electron-electron collision rate, the thermal conductivity is reduced by a factor of 3 to 4 from the Spitzer-Haerm [Phys. Rev. 89, 977 (1953)] value for [ital K][lambda][sub [ital e]][lt]0.01 and is less affected by nonlocal heat-transport effects for [ital k][lambda][sub [ital e]][much gt]1, where [lambda][sub [ital e]] is the electron mean free path and [ital k] is the perturbation wave number. Implications for thermal filamentation will be discussed.

Modified formula of nonlocal electron transport in a laser-produced plasma.

A nonlocal heat-transport formula for electrons is derived to include the terms associated with the electrostatic potential and \ensuremath{\partial}/\ensuremath{\partial}v(${\mathit{f}}_{0}$,${\mathit{f}}_{1}$) in the Fokker-Planck (FP) equation. Then the FP equation for a strongly inhomogeneous plasma is solved. It is found that the behavior of the electron thermal conductivity at a large temperature gradient is considerably affected by the electrostatic field, and the thermal conductivity \ensuremath{\kappa}/${\mathrm{\ensuremath{\kappa}}}_{\mathrm{SH}}$ for electrons scales as 1/k in a large temperature gradient k when there exists a non-negligible electrostatic field, where ${\mathrm{\ensuremath{\kappa}}}_{\mathrm{SH}}$ is the Spitzer-H\"arm heat coefficient.

Quenching of non-local electron transport in tilted magnetic fields

A variety of transport phenomena observed at laterally confined two- dimensional electron systems (2DES) prove the occurrence of non-local contributions to the electronic conductance in these systems. However, this non-local regime accompanied by a non-equilibrium population of the edge states with respect to the 2D bulk state is quenched at rather low values of current-driving electric fields. We analyse the non-Ohmic behaviour of SdH oscillations at GaAs/GaAlAs Quantum Hall conductors on the basis of a model including edge and bulk conduction and deduce the non-equilibrium population of edge and bulk states quantitatively. The spatial separation between edge and bulk states was changed by tilting the samples with respect to the magnetic field. The resulting angular dependences of equilibration parameters could be quantitatively explained by the change of the ratio of spin splitting to cyclotron energy being present in 2DES in tilted magnetic fields. PACS index numbers: 73.20.Dx; 73.40.Hm

Theory and three-dimensional simulation of light filamentation in laser-produced plasma

A desire to interpret recent experiments on filamentation with and without beam-smoothing techniques led to the development of a three-dimensional fluid model that includes the effects of nonlocal electron transport and kinetic ion damping of the acoustic waves. The damping of the electron-temperature perturbations that drive thermal filamentation by nonlocal electron conduction, valid in the diffusive limit, is supplemented in the present model by electron Landau damping in the collisionless limit when the wavelength of the perturbation is much less than the electron–ion scattering mean-free path. In this collisionless limit, Landau damping of the ‘‘temperature’’ fluctuations makes ponderomotive forces universally more important than thermal forces. Simulations in plasmas of current interest illustrate the relative importance of thermal and ponderomotive forces for strongly modulated laser beams. Although thermal forces may initiate filamentation, the most intense filaments are associated with ponderomotive forces. The present simulations of filamentation model well the density perturbations observed in experiments [Young et al., Phys. Rev. Lett. 61, 2336 (1988)]. In addition, a simple criterion is obtained analytically and supported by simulations for stabilization of filamentation by laser beam-smoothing techniques such as induced spatial incoherence and random phase plates [Eq. (1)].

Nonlocal heat transport effects on the filamentation of light in plasmas

The nonlocal nature of electron heat transport in hot coronal plasmas is investigated. Its effect on the linear theory of laser filamentation is reviewed. The nonlinear evolution of filaments is modeled with the two-dimensional Fokker–Planck code spark, for the conditions of recent filamentation experiments. Simulation results agree with experimental data and imply the dominance of thermal over ponderomotive filamentation. The increased importance of the thermal filamentation mechanism is attributed to heat flux inhibition arising from nonlocal electron transport. The potential implications of filamentation for inertial-confinement-fusion target designs are discussed.

The Benedicks effect: Nonlocal electron transport in metals.

The Benedicks effect is the voltage difference between two points in a solid that are at the same temperature. A nonzero value may be obtained if the temperature profile between the points is asymmetric. We derive the nonlocal transport theory of a metal from the Boltzmann equation, and use the results to discuss the Benedicks effect. The nonlocal theory is needed whenever the electron mean free path has the same size as variations in the gradients of the voltage, temperature, or chemical potential.