Spin Contribution to the Ponderomotive Force in a Plasma

Abstract

The concept of a ponderomotive force due to the intrinsic spin of electrons is developed. An expression containing both the classical as well as the spin-induced ponderomotive force is derived. The results are used to demonstrate that an electromagnetic pulse can induce a spin-polarized plasma. Furthermore, it is shown that for certain parameters, the nonlinear back-reaction on the electromagnetic pulse from the spin magnetization current can be larger than that from the classical free current. Suitable parameter values for a direct test of this effect are presented.PACS numbers: 52.35. Mw, The use of the spin properties of material constituents for e.g., carrying information is currently an important paradigm [1]. However, the spin properties of the material constituents also make its presence felt through collective effects. In particular, recent findings point to the possibility of observing quantum plasma effects [2] through the electron spin [3] in regimes otherwise thought to be classical [4]. Such results are due to the complex interplay between collective plasma effects and the system nonlinearities. In classical plasmas, nonlinear effects play an important, sometimes a crucial, role. For example, the density fluctuations induced by the ponderomotive force of an electromagnetic (EM) wave lead to an electrostatic wake field [5], as used in advanced particle accelerator schemes [6]. In other regimes, the back-reaction on the EM-wave due to the density fluctuations leads to phenomena such as soliton formation, self-focusing or wave collapse [7]. Such radiation pressure-like effects are widely used in high-intensity laser experiments [8], and generalizations to include certain types of quantum plasma effects have recently been made [9]. However, to our knowledge the possibility of spin induced contribution to the ponderomotive forces has not been explored.In the present work we will solve the full set of equations for the spin dynamics of charged particles in the presence of a weakly nonlinear EM wave pulse, propagating parallel to an external magnetic field, in order to find the contribution to the ponderomotive force. In the classical limit, we recover the well-known expression first derived by Karpman and Washimi [14]. The spin contribution to the ponderomotive force will in general act in opposite directions for spin-up and spin-down populations. As a consequence, an EM-pulse (due to, e.g., a laser or a microwave source) may induce a spin-polarized plasma. In particular, it is demonstrated that this mechanism can induce large spin-polarization for a laser source in the UV-regime. For this case it should be noted that the effect of the external magnetic field is negligible as the laser frequency is much higher than the cyclotron frequency, but our general expression applies also for lowfrequency (lf) waves in magnetized plasmas.When combined with the high-frequency (hf) oscillations, the classical lf density response generates a hf current that results in a cubical nonlinearity. This classical nonlinearit...

Kinetic analysis of spin current contribution to spectrum of electromagnetic waves in spin-1/2 plasma. II. Dispersion dependencies

“…The spin-1/2 quantum hydrodynamics containing the Fermi spin current (1) or (2) (see for instance [1]) is a generalization of the spin-1/2 quantum hydrodynamics suggested earlier [5][6][7][8][9][10][11][12][13][14].…”

Kinetic analysis of spin current contribution to spectrum of electromagnetic waves in spin-1/2 plasma. I. Dielectric permeability tensor for magnetized plasmas

“…All these features of the separated spin evolution are obtained in Refs. [25], [26] and [28], while a two fluid model of electrons was mention in literature earlier [29], [30], [31]. Incompleteness of earlier model bound to incorrect coefficients in spin depending terms [32].…”

Hydrodynamic and kinetic models for spin-1/2 electron-positron quantum plasmas: Annihilation interaction, helicity conservation, and wave dispersion in magnetized plasmas

“…Electron-positron and electron-positron-ion spin-1/2 quantum plasmas and their wave properties have been under consideration in recent years [45]- [54].…”