A theoretical and experimental investigation of instability phenomena in synthesized plasmas is carried out. In the theoretical analysis the space charge and potential distributions are obtained for an idealized one‐dimensional model. The model consists of two face‐to‐face electrodes each emitting ions and electrons in any ratio and with a Maxwellian velocity distribution. The calculations show that no stable zero‐field solution is possible; instead, distributions with either a potential maximum or minimum in the center are obtained. For a range of values of the ratio β of injected ion to electron space‐charge density near unity (0.81 ≤β<1.235), double‐valued solutions to the problem are obtained. The actual solution into which the system settles depends on whether this range of β values is approached from above or below. Transitions from one such state to the other can occur at the limits of this β range. In the experimental investigation of a synthesized plasma, these instabilities, or state‐to‐state transitions, were found to be in good agreement with the theory. Oscillations triggered by state‐to‐state transitions were observed with a frequency corresponding to the ion transit time through the interelectrode space. These oscillations are not described by the steady‐state analysis.

Space Charge Instabilities in Synthesized Plasmas

Publisher Summary This chapter focuses on the thermionic energy conversion with description of idealized model of a thermionic converter and work function of various surfaces. A thermionic converter is a device which converts heat energy into electrical energy by utilizing the thermionic emission of electrons. The close-spaced high-vacuum converter appears to have neared the limit of its development at a power output of 1 watt/cm2 and an efficiency of approximately 5%. Three electrode gas-filled devices should allow relatively low temperature operation, for example, in the range 1300–1700 K. Although the rare gases have a lower electron-neutral cross-section (that is, lower resistance), a Cs filling has the advantage that a low anode ϕ is maintained and that lower auxiliary-discharge voltages are required. Cesium-filled diodes are probably the most promising type of thermionic converter. Two promising approaches are now being explored for improving cesiated-cathode converters. The first of these is the use of electrode surfaces with the optimum crystallographic orientation. The second is the addition of gases such as halogens, oxygen, or hydrogen which increases the cathode emission and decrease the anode work function.

Thermionic Energy Conversion

Publisher Summary his chapter examines the velocity distribution in electron streams. The method of approach adopted is based exclusively on the powerful concept of electron density in a six-dimensional space composed of configuration and momentum spaces joined together. It is found that when the collisions or in the case of electrons, the short-range interactions are neglected and the flow in the six dimensional phase space becomes continuous. The change in the shape of electron trajectories with time is now represented by the corresponding variations in the density function. The electrons with zero velocity can play a prominent role in the composition of the velocity distribution function, the function often having a maximum at the origin, however they contribute nothing to the current density function. It is found that in symmetrical distributions, due to the cancellation of contributions from equal but oppositely directed velocities, the total current density at a given point may be zero in spite of a very large local electron density. The electron density at the surface of a plane emitter is also elaborated.

Velocity Distribution in Electron Streams

During the last decade much interest has been shown in various methods of direct conversion of heat into electricity. The advantages of direct-conversion devices are discussed and the basic physical principles of thermoelectric conversion and thermionic conversion are explained. A review is given of the present state of knowledge and an assessment is made of prospects for future applications of direct-conversion devices.

http://iopscience.iop.org/article/10.1088/0031-9120/3/6/003/pdf

The direct conversion of heat into electricity. Thermoelectric conversion and thermionic conversion

3 – vacuum chambers for radiation measurement

This paper gives the derivation of expressions for the space charge and potential distribution between two plane parallel emitting electrodes. Numerical calculations are carried out for the case when an external potential difference φext is applied between the electrodes, both being at the same temperature T. It is shown that all possible potential distributions can be represented by a single family of curves, the parameter of the family being.A=(—eφext/kT). Thus for a given φext the same general curve of potential distribution applies, whatever the values of the electrode work functions. Changing the work functions merely shifts the end points of the potential distribution along the curve.

F. W. Parker

Papers

Potential Distribution between two Plane Emitting Electrodes