Spontaneous electrical polarization of ferroelectric materials can be changed either by reversal or by phase transition from a ferroelectric into a non-polar state or vice versa. If spontaneous polarization changes are induced at a submicrosecond time-scale, strong uncompensated surface charge densities and related fields are generated, which may lead to the intense self-emission of electrons from the negatively-charged free surface areas of the ferroelectric cathode. The nature of this self-emission differs essentially from other methods of ferroelectric electron emission and from conventional electron emission in that the latter methods are only achieved by extracting electrons with externally applied electric fields. When electron guns are constructed with ferroelectric cathodes, new design criteria have to be taken into account. The intensity, the energy, the temporal and spatial distribution and the repetition rate of the emitted electron beams can be adjusted within wide limits. The advantages of ferroelectric cathodes and the technological difficulties arising during their production, preparation, and operation are identified and discussed and solutions to the problems are proposed. Experiences with a few applications of ferroelectric electron emission are reported and suggestions for further applications are made.

No abstract

No abstract

No abstract

Sealed-off, metal-ceramic pseudospark switches are currenfly developed as a replacement of conventional thyratrons in pulsed gas discharge lasers. The gross performance of pseudospark switches exceeds that of thyratrons in many facts, like peak current, current reversal capability and rate of current rise. One of the major problems which has to be solved is the increase of lifetime of the pseudospark switch which should be comparable to that of conventional thyratrons. In this contribution the performance of different type of pseudospark switches at different load conditions typical for pulsed gas discharge lasers will be discussed. Experiments were performed at a low inductive 1 Q water pulse line at holdoff voltages of up to 32 kV with a dJ/dt of 6* 1 A/s (10% -90 %) and a maximum current of 30 kA. Switch parameters like delay, jitter, misfiring rate and current rise were continuously recorded at repetition rates of up to 100 Hz. By adjusting the reservoir current and herewith the gas pressure of the switch to the applied voltage a jitter of less than 5ns can be achieved. The delay is dependent on the rise time of the trigger pulse and is 650 ns at a voltage rise of 5 kV/600 ns and has a minimum of 200 ns with a trigger pulse of 5 kV/18 ns voltage rise. By biasing an auxiliary electrode, which is mounted inside of the hollow cathode, the jitter can be decreased to values below 1 ns. SPIE Vol. 2206/219Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/24/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx