Interplay of current crowding and current self-quenching effects in planar cold cathodes Space-charge effects and current self-quenching in a metal/CdS/LaS cold cathode Effects of space charge on the current-voltage characteristics of field emitter arrays AIP Conf.Microfabricated field emitter arrays ͑FEAs͒ can provide the very high electron current densities required for rf amplifier applications, typically on the order of 100 A/cm 2 . Determining the dependence of emission current on gate voltage is important for the prediction of emitter performance for device applications. Field emitters use high applied fields to extract current, and therefore, unlike thermionic emitters, the current densities can exceed 10 3 A/cm 2 when averaged over an array. At such high current densities, space charge effects ͑i.e., the influence of charge between cathode and collector on emission͒ affect the emission process or initiate conditions which can lead to failure mechanisms for field emitters. A simple model of a field emitter will be used to calculate the one-dimensional space charge effects on the emission characteristics by examining two components: charge between the gate and anode, which leads to Child's law, and charge within the FEA unit cell, which gives rise to a field suppression effect which can exist for a single field emitter. The predictions of the analytical model are compared with recent experimental measurements designed to assess space charge effects and predict the onset of gate current. It is shown that negative convexity on a Fowler-Nordheim plot of I anode (V gate ) data can be explained in terms of field depression at the emitter tip in addition to reflection of electrons by a virtual cathode created when the anode field is insufficient to extract all of the current; in particular, the effects present within the unit cell constitute a newly described effect. ͓S0021-8979͑97͒03214-3͔

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Vacuum microtriode RF amplifi er performance, based upon a unit cell with a conical field emitter tip, gate, and anode, was evaluated via computer simulation. Electron emis sion was calculated from the Fowler-Nordheim equation. The dependence of emitted current, transconductance, and field en hancement upon geometrical factors, e.g., tip sharpness, tip height, cone half-angle, and gate hole radius, is shown. The device design parameters of transconductance, cutoff fre quency, small signal gain, and efficiency, have been calculated. Electron streamlines and current flux are shown for time-de pendent RF input. Because a compact electron beam source has wide application, the normalized beam emittance, brightness, and beam quality are calculated for a typical case. Potential difficulties with anode power deposition are noted.

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We introduce and analyze the concept of a wakeless triple-soliton accelerator in a plasma fiber. Under appropriate conditions the triple soliton with two electromagnetic and one electrostatic waves in the beat-wave resonance propagates with velocity c leaving no plasma wake behind, while the phase velocity of the electrostatic wave is made also c in the fiber.