V. I. Sitnov

Ultra‐High Temperature Thermionic System for Space Solar Power Applications

Theoretical and experimental investigations made to date at the Ioffe Physico‐technical Institute on ultra‐high temperature thermionic energy converter (TEC) have demonstrated the possibility of significantly increasing the efficiency of such a converter when operating in the Knudsen mode. In the arc mode of inevitable scattering losses make up about 50%. The TEC efficiency rises sharply when operating in high and ultra‐high emitter temperature range (2500 – 3000 K). As a result, it is possible, in principle, to fabricate a TEC with emitter temperature of 2500 – 2600 K and having an efficiency of about 25% and long life. If design and engineering problems are solved, such a TEC in combination with a solar concentrator can be used to serve as a spacecraft power system. It can be also used as a high temperature stage of a terrestrial solar power station. This paper presents some of the features of a Cs‐Ba high emitter temperature TEC and a conceptual design of a 5 kWe solar thermionic power system.

Bimodal solar system based on a ultra-high-temperature TEC

The paper considers an ecological, solar, bimodal system with ultra‐high temperature thermionic energy converter (TEC). The solar bimodal Space Electric Propulsion System (SEPS) characteristics are presented.

Next generation solar bimodal systems

One of the principal advantages of a solar thermal propulsion system as compared to a conventional chemical propulsion one is high specific impulse which is proportional to the square root of a propellant temperature. Obviously, next generation solar propulsion and bimodal systems must take advantage of high and ultra-high temperatures. This requires use of an appropriate energy conversion system capable to take advantage of high temperature potentially achievable in a solar receiver. High efficiency and power density of a high temperature thermionic converter open new perspectives in the development of advanced bimodal power systems having performance significantly higher than that achievable by the state-of-the-art technology. The paper presents an innovative concept of a cascaded solar bimodal power system with a high temperature Cs-Ba thermionic converter. The paper shows that the use of high temperature Knudsen cesium-barium thermionic converter in a solar bimodal system allows to eliminate thermal insulation sleeve, generate electrical power in the propulsion mode, and precise control thermal state of the solar receiver. In the Cs-Ba thermionic converter, an electron instability and high amplitude current oscillations develop. These effects can be used to obtain alternate current power directly in the converter. Possibility and potential advantage of such a generator are discussed.

Terrestrial solar power system based on Cs-Ba thermionic converter

A new concept of terrestrial, environmentally friendly solar cogeneration system is described. Power generation is accomplished by a cascaded system with the high temperature stage being a Cs-Ba thermionic converter. Its heating is accomplished by a two-stage solar concentrator with a mirror and focon. Thermal efficiency of such a system is close to 100% because all the heat supplied to the heat receiver is utilized.

Current-voltage characteristics of underneutralized Knudsen thermionic converters with electron emission from the collector

Calculations of the potential distribution are used to study the current-voltage (I-V) characteristics of unneutralized Knudsen thermionic converters with unlimited electron emission from the collector. It is shown that the optimum work function of the collector satisfies the condition of unlimited emission. The effect of a number of characteristic parameters of a converter on its I-V characteristics are studied: the degree of neutralization, the ratio of the emitter and collector temperatures, and the work functions of the emitter and collector.

study of the reverse current range in a knudsen diode with surface ionization under overneutralized conditions in the presence of electron emission from the collector: Part II. Small electrode spacing

A Knudsen diode with surface ionization under overneutralized conditions is studied in the range of reverse current. The electrode spacing is assumed to be small, which causes the potential jumps near the electrodes to overlap. The asymptotic behavior of the current under high negative voltage is investigated.

The influence of electron emission from the collector on the potential distribution within a Knudsen diode with surface ionization in the underneutralized regime

This paper gives a theoretical treatment of the distribution of potentials within a Knudsen diode with surface ionization in the underneutralized regime in the presence of electron emission from the collector surface. A method is derived to calculate the potential distribution. It is shown that if the emission from the collector is sufficiently strong, spatially oscillatory (“wavelike”) potential distributions do not form; instead, a continuous transition occurs from a distribution with a virtual anode to one with a virtual cathode. Particular attention is focused on the neighborhood of the transition point from one of these distributions to the other.