Plasma channel created by ionization of gas by a surface wave
- PDF / 624,653 Bytes
- 4 Pages / 612 x 792 pts (letter) Page_size
- 102 Downloads / 167 Views
MPERATURE PLASMA
Plasma Channel Created by Ionization of Gas by a Surface Wave V. N. Konovalov, G. P. Kuz’min, I. M. Minaev, A. A. Rukhadze, and O. V. Tikhonevich Prokhorov General Physics Institute, Russian Academy of Sciences, ul. Vavilova 38, Moscow, 119991 Russia e-mail: [email protected] Received July 10, 2014; in final form, February 9, 2015
Abstract—Conditions for gas ionization in the field of a slow surface wave excited by a microwave source are considered. The gas ionization rate and the plasma density distribution over the radius of the discharge tube were studied by the optical method. The experiments were conducted in a dielectric tube with a radius much smaller than the tube length, the gas pressure being ~1–3 Torr. It is shown that the stationary distribution of the plasma density is determined by diffusion processes. DOI: 10.1134/S1063780X15090068
1. INTRODUCTION Theoretical analysis, numerical simulations, and laboratory experiments show that an extended highfrequency discharge in a gas-discharge tube filled with a rarefied gas can be excited and sustained by using an axisymmetric running surface wave (SW) [1–3]. In [4], the conditions were considered in which the gas is initially ionized at the input of gas-discharge tube by the radiation field with a frequency ω. The SW is excited at the plasma–vacuum interface after the electron density in plasma reaches a value satisfying the condition [5]
ω pl ≥ 2ω,
(1)
where ω pl = (4π nеe 2 / m)1/2 is the plasma frequency; nе is the electron density; e and m are the charge and mass of an electron, respectively; and ω is the circular frequency of radiation. In [6], the required plasma density was determined by solving the problem on the propagation along the z axis of a surface E-wave with nonzero field components Ex, Вy, and Ez, decaying in both directions away from the plane plasma boundary x = 0 . It was assumed that the plasma density at the boundary dropped abruptly to zero. The region x < 0 was occupied by a plasma with the permittivity ε(ω), depending on the field frequency ω, while the region х > 0 was in vacuum. The spatial distribution of the SW field near the plane medium–vacuum interface is schematically shown in Fig. 1. In [1], a cylindrical problem with similar boundary conditions was considered. In actuality, the plasma density varies from zero on the dielectric surface to values at which an SW can propagate, i.e., there is a
transition layer at the plasma boundary. Thus, an extended high-frequency discharge sustained by the electric field Е sw of a propagating axisymmetric SW is excited in a plasma column the radius of which is smaller than the radius of the dielectric tube by the thickness of the transition layer. Due to the presence of the transition layer, the plasma density does not exceed values corresponding to condition (1). The radius of the transition layer can be determined from the measured intensity distribution of visible radiation over the cross section of the discharge tube, because gas ionization is accompanied by the exc
Data Loading...
