Dissipative surface waves in plasma
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LLATIONS AND WAVES IN PLASMA
Dissipative Surface Waves in Plasma I. N. Kartashov and M. V. Kuzelev Department of Physics, Moscow State University, Moscow, 119991 Russia email: [email protected], [email protected] Received November 19, 2013; in final form, February 10, 2014
Abstract—Debatable aspects of the theory of nonpotential surface waves propagating along the boundary of a dissipative medium with frequency dispersion are discussed. On the basis of the known theoretical results and theoretical analysis carried out in this work, a theory of surface waves that is valid for any dissipation of the perturbation energy in the medium is developed. It is shown that, if dissipation is sufficiently strong, there can be surface waves the physical nature and dispersion law of which differ radically from those of ordinary surface waves. The damping rate of such waves is low even at large dissipation in the medium, and their group and phase velocities exceed the speed of light. In particular, surface waves on the interface between vacuum and cold collisional electron plasma are considered. The existence of such surface waves for different media of laboratory and natural origin is discussed. DOI: 10.1134/S1063780X14070046
1. INTRODUCTION The physics of surface waves has been actively dis cussed in the scientific literature nearly since their the oretical prediction by A. Sommerfeld in 1896 [1]. This is not surprising, because many types of surface waves have been discovered that are very important for vari ous applications. In particular, plasma surface waves are employed in Cherenkov electronbeam microwave oscillators [2–7]. The possibility of using dissipative beam–plasma instability in surface waves in such oscillators was discussed in [8, 9]. Surface waves in plasma are used to sustain gas discharges [10]. Strong spatial inhomogeneity of surface waves and their local ization near the interface find wide application in the new actively developing area of nanophysics—nano plasmonics [11, 12]. In spite of the long time that has passed since the prediction of surface waves and their intensive study and numerous applications, there are questions of the theory of surface waves that still remain unresolved. In particular, in [13–15], the detection of surface waves on the boundary of a con ducting medium (Zenneck waves) was reported, whereas in [16], the very possibility of existence of such waves was called into question. In recent work [17], it was noted that, under certain conditions, the group velocities of Zenneck surface waves [18, 19] can exceed the speed of light c, from which it was con cluded that such waves cannot exist. In this case, a simplified model of the medium with a frequency independent complex permittivity was used. In our opinion, taking into account frequency dispersion (i.e., the frequency dependence of the permittivity of the medium) in the theory of surface waves is very important and it is incorrect to completely negate the existence of surface waves with group velocities
exceeding c. It w
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