摘要:

Using a normalized set of nonlinear equations, which describe a free‐electron laser (FEL) oscillator, the efficiency of energy extraction from the electron beam to the radiation can be optimized. The optimum values of this efficiency are presented for (a) an untapered and (b) a tapered wiggler FEL oscillator.

ISSN:0899-8221    

DOI:10.1063/1.859158

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

The drift kinetic approximation (DKA) is developed by combining the macro‐ and microdynamics of guiding center plasmas. It is shown that the DKA provides a better description for collisionless processes in plasmas than the Chew–Goldberger–Low approximation. A new theory of the Kelvin–Helmholtz instability (KHI) in collisionless space plasmas is established. Calculations show that the general pattern of the growth rate of the KHI versus flow velocity in the DKA is similar to that in compressional magnetohydrodynamics. However, the critical velocity decreases if pressure is anisotropic, and the growth rate and energy flux are reduced in the presence of wave–particle interactions.

ISSN:0899-8221    

DOI:10.1063/1.859159

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

A numerical study is done of a plasma in contact with a solid surface that reemits some fraction of the incident plasma as neutral gas. The calculation uses a steady‐state, kinetic treatment of the transport equations in one space dimension and one or two velocity dimensions to determine self‐consistently the distribution functions of the interacting species and the electrostatic potential. The dominant phenomena are the ionization of the neutral gas and the acceleration of the resulting ions away from a potential maximum that is predicted to form in the ionization region. Other effects involved are a Debye sheath structure between the solid surface and the potential maximum, and collisional trapping and untrapping of electrons in the well represented by the potential maximum. Results are presented from a nondimensional model with a monatomic returning neutral species, and for diatomic molecular deuterium returning from the surface. For each set of physical parameters chosen, a one parameter family of solutions is obtained. A hypothesis is presented for the choice from this family of solutions that would be found experimentally.

ISSN:0899-8221    

DOI:10.1063/1.859160

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

The set of coupled integrodifferential equations describing the low frequency electromagnetic perturbation in a finite ion temperature plasma of slab geometry is reduced to a single simple integral equation. The equation is described in terms of a localized variable, and the boundary condition is clear and easy to implement, particularly for the tearing mode. As an application of the formalism, collisionless tearing modes are studied numerically, and the results are compared with previous analytic works.

ISSN:0899-8221    

DOI:10.1063/1.859161

出版商:AIP    

年代:1989

数据来源: AIP

摘要:

A two fluid model is used to derive an analytical equilibrium for elongated field reversed configurations containing shear in both the electron and ion velocity profiles. Like some semiempirical models used previously, the analytical expressions obtained provide a satisfactory fit to the experimental results for all radii with a few key parameters. The present results reduce to the rigid rotor model and the infinite conductivity case for a specific choice of the parameters.

ISSN:0899-8221    

DOI:10.1063/1.859162

出版商:AIP    

年代:1989

数据来源: AIP