Lennart Lundgren

Semiconducting low‐pressure, low‐temperature cesium plasma with unidirectional conduction

In a low‐temperature, low‐pressure cesium plasma environment, special conditions have been found which exhibit unidirectional conduction of a current over a physical interelectrode space of a size up to 1 mm between two plane parallel electrodes. The spacing is determined by the need to maintain a high enough cesium pressure in the present setup. The cesium emitter has a temperature of 800 K or lower. Current densities of 100–200 A cm−2 during steady state and up to 500 A cm−2 under non‐steady‐state conditions are reported. The experiments give a semiconducting resistivity between the electrodes as low as 10−3 Ω m, usually around 10−2 Ω m. The special plasma conditions are probably due to excited states of cesium atoms, which condense to form an excited state of matter. Such a type of matter has been predicted to exist on theoretical grounds by Manykin et al. and was stated to have metallic electrons. We propose that the conduction observed involves electron transfer from the cold electrode, through the e...

Numerical simulations of the capacitance of forward-biased Schottky-diodes

Abstract The semiconductor transport equations, including the energy balance equations, are used to numerically model the forward-bias capacitance of Schottky-barrier diodes on n-GaAs. The differential capacitance is determined from the change of electric charge in the semiconductor for an incremental voltage change. The capacitance calculated from this model is compared to capacitance determinations only by solving Poissons equation. The transport model must be used when the electric current through the device influences the carrier distribution which happens at a forward voltage of approximately 0.8 V.

The formation of double‐valued sheaths in thermionic converters

A theory for the sheath in an ignited thermionic converter is presented. The theory includes the effect of the velocity spread of the particles but the charge‐particle collisions are neglected. Conditions for the appearance of a virtual emitter are given. The theory is compared with a beam approximation theory and a hydrodynamic theory. All three theories give almost the same condition for the appearance of a virtual emitter in an ignited thermionic converter.

Pump efficiency and saturation effects in waveguide lasers

The cross‐sectional variation of the energy density in a waveguide gas laser results in a transversely varying saturation if the molecules are stationary. At a transversely constant excitation of the upper laser level, the varying saturation reduces the efficiency and power output compared to the case when rapid molecular movements make the saturation constant. Near threshold, the reduction factor is approximately 2. The cross‐sectional saturation has, however, little influence on the optimization of the output coupling.

A comparison between arc drops in ignited thermionic converters with and without ion reflections at the emitter

The output performance of two thermionic energy converters is compared. One converter has a normal emitter, working with zero field at the emitter which is close to the optimum working point, and the other has a low work function emitter and ion reflection at the emitter. A simple model of the plasma and the sheaths shows that a converter working with a low work function emitter and ion reflections gives a worse performance than a similar converter with a normal emitter.

High‐frequency capacitance of bipolar resonant tunneling diodes

The high-frequency characteristics of bipolar resonant tunneling diodes are experimentally investigated at room temperature. The electron accumulation and discharging in these resonant tunneling light-emitting diodes are studied at frequencies up to 35 GHz. The experiments show capacitance peaks due to electron charge disappearing from the quantum well. The measurements are found to be in agreement with our theoretical model for the calculation of the high-frequency characteristics of resonant tunneling devices. The high-frequency characteristics of the bipolar light-emitting resonant tunneling diode are compared to the unipolar resonant tunneling diode and the resonant interband tunneling diode. The comparison shows a similar discharging characteristic of the quantum well, but a different overall variation of the capacitance.

Theoretical and experimental investigation of leakage power in microwave transmit–receive switches

A theoretical and experimental investigation is made of the leakage power in microwave transmit–receive switches. The peak leakage power is shown to be independent of incident peak power but to depend on the rise time of the incident pulse. The plateau leakage power through the switch is also estimated and shown to be independent of incident peak power. The theoretical predictions for peak leakage power and plateau leakage power are compared and found to be in good agreement with experimental results.

Spike‐mode oscillations in flashlamp pumped Nd lasers

Regular spiking‐mode oscillations have been investigated theoretically and experimentally. Stable and regular spiking oscillations can be obtained if the modulation signal is phase locked to the output pulse. Experimental investigation of intracavity loss modulation of a flashlamp pumped Nd‐YAG (yttrium aluminum garnet) laser is reported.

Ion trapping in the emitter sheath in thermionic converters

The effect of ion trapping in the emitter sheath in ignited thermionic converters is studied. The ion trapping prevents the emitter‐sheath barrier from being higher than approximately 0.1 eV, when the current decreases in the converter. This gives a condition for the constriction of the arc. I‐V curves are calculated for an ignited thermionic converter with a hydrodynamic plasma theory that takes into account the effect of Coulomb scattering and volume recombination, but assumes that the electron temperature is constant in the plasma.