H. Gundel

Time‐dependent electron emission from ferroelectrics by external pulsed electric fields

Results of experiments investigating the influence of the amplitude, the growth rate, and the repetition rate of the exciting electric field pulses on the electron current and charge density emitted from ferroelectrics are reported. The behavior of two types of lead‐lanthanum‐zirconium‐titanate (PLZT) ceramics, 2/95/5 and 8/65/35, was studied. The temporal shift between the applied HV pulses and the emitted electron current pulses was different for the two materials. Regular electron emission was observed at repetition rates of up to 2 MHz in the PLZT‐2/95/5 material, showing that the recovery of the emitting sample back to the original state may happen in less than a microsecond.

Copious electron emission from PLZT ceramics with a high zirconium concentration

Abstract We describe the experimental method and report the results of electron emission from PLZT-2/95/5 ceramics subjected to rectangular HV pulses. The influence of HV amplitude, of gas pressure, and of temperature on electron beam current-density and charge was investigated. The kinetic energy was estimated by applying a decelerating field. Emitted current-density pulses of several A/cm2 and charges of 1 μC/cm2 are measured. A tentative interpretation is given.

Low‐pressure hollow cathode switch triggered by a pulsed electron beam emitted from ferroelectrics

A new type of low‐pressure gas switch is described. The switch is triggered by an electron beam that is emitted from the surface of a ferroelectric sample. The electron beam is generated within the hollow cathode and ejected through a hole of arbitrary shape into the main gap of the switch. The beam current and the electron energy can be chosen such that breakdown is achieved with small jitter. The switch with its ferroelectric trigger requires neither heating nor an auxiliary gas discharge. The fast spontaneous polarization change ΔPs, which is the cause of electron emission, is induced by a high‐voltage pulse from an electronic switching circuit.

Fast polarization changes in ferroelectrics and their application in accelerators

Abstract Several mechanisms are described which change the polarization in ferroelectric material. Provided the change is too rapid for the related surface charges to be screened or neutralized, the high charge density can lead to strong electric fields. The fields may possibly be used for emission and acceleration of electrons. First results of experiments are reported in which fast spontaneous polarization changes by reversal or phase transition have been demonstrated. Electrons of 25 keV energy have been observed, emitted from triglycine sulfate (TGS) crystals during phase transition while being slowly heated across the Curie temperature. With fast polarization changes, electron beams of even higher energy and density are expected.

Pulsed electron emission from PLZT ceramics

Abstract New experimental results on electron emission from PLZT ceramics of composition 2/95/5, subjected to rectangular high-voltage pulses are reported. The dependence of the emitted electron charge on the electric field strength and temperature was investigated. The energy of the emitted electrons was estimated by applying a decelerating potential to an auxiliary grid electrode. Emitted current densities of several A/cm2 and emitted charges up to ∼ 1 μC/cm2 (∼1013 electrons/cm2) were observed.

Intense laser‐induced electron emission from prepoled lead‐lanthanum‐zirconium‐titanate ceramics

A sample of lead‐lanthanum‐zirconium‐titanate (PLZT 9/65/35) has been exposed to 6‐ns‐long laser pulses of 266 nm wavelength. The maximum output pulse energy of the laser beam was 300 μJ, the output power density on the sample 5×105 W/cm2, and the beam diameter 3 mm. By applying a moderate extraction voltage of several kilovolts, intense electron beam pulses are emitted from the free sample surface. Their time structure corresponds to the time structure of the laser pulse. Electron beam current intensities of up to 0.1 A and 2 A/cm2 and total charges of 1 nC (corresponding to 20 nC/cm2 ) were measured with a simple Faraday cup. In the range where the parameters of laser intensity and of extraction voltage could be varied their influence on the emitted electron beam current amplitude was determined.

Fast polarization changes in PZT ceramics by high-voltage pulses

Abstract Experiments on fast spontaneous polarization changes in PZT ceramics are described. The interactions between spontaneous polarization Ps and space-charge polarization Psp.ch. are discussed. The fast polarization changes are made with the aim of producing electron beam emission and acceleration from ferroelectric surfaces.

The use of ferroelectrics for acceleration of charged particles

Several mechanisms are described which lead to fast polarization changes in ferroelectric materials. The resulting surface charges may ultimately generate electric field spikes on the order of 1 GV/m. The fast response of ferroelectric materials to phase transitions under the influence of external electrical and/or mechanical stress allows the design of structures which emit and accelerate charged-particle beams. >

Correlated light emission during polarization reversal in ferroelectric crystals

Abstract The light emitted during polarization reversal of different ferroelectric single crystals (FEs) has been studied quantitatively by using a technique from nuclear spectroscopy. The time spectra contain characteristic features and indicate strong correlation between the switching process and the light emission. The duration of each light pulse is 10−7-10−8 s. These signals can be used for defining each particular polarization reversal.

Time-variable dielectric constant in ferroelectric crystals

Abstract Abstract The polarization reversal in thick ferroelectric crystals has been performed with pulsed HV. A time-dependent dielectric constant e has been observed in the (ms-μs) range. The time variable e can also be used for making visible the polarization reversal of the crystal.