J. Phys. D: Appl. Phys. 31 (1998) 1375–1382. Printed in the UK PII: S0022-3727(98)89669-1 A high-perveance ferroelectric cathode with a narrowed electron energy spread D Shur†, G Rosenman†, Ya E Krasik‡ and R Advani§ † Tel-Aviv University, Faculty of Engineering, Department of Electrical Engineering – Physical Electronics, Tel-Aviv 69978, Israel ‡ Technion, Physics Department, Haifa 32000, Israel § Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, MA 02139-4294, USA Received 2 December 1997 Abstract. A pulsed ferroelectric electron cathode with a current density of up to 45 A cm −2 based on (Pb, La)(Zr, Ti)O 3 ceramic is presented. The experimental set-up for the cathode triggering allowed us to achieve a perveance of more than 65 µP and an energy spread in the generated electron beam as low as 100 eV (FWHM). 1. Introduction High-current metal–dielectric plasma cathodes have been known since the late 1960s [1, 2]. A dense plasma formed by a dielectric surface discharge was used as the electron source. These cathodes, based on materials with high dielectric permittivity, were used for high-current pulsed electron accelerators [2]. Extensive studies of cathodes based on various ferroelectric PLZT ceramic compositions have been conducted by several research groups [3–13]. Typical current densities provided by these ferroelectric cathodes are up to 100 A cm −2 . It has recently been shown that the total current emitted by ferroelectric cathodes may be as high as 1 kA [14]. In the majority of the papers this rather strong electron emission was ascribed to a fast spontaneous polarization switching of ferroelectric ceramics according to a mechanism proposed earlier in [15]. This model assumes that electrons are emitted into vacuum due to a high electric field generated by an uncompensated charge at a polar ferroelectric surface during polarization reversal. However, a strong electron emission has also been observed without any polarization switching from 12/65/35 PLZT ceramic [13] whose composition does not possess a macroscopic spontaneous polarization [16]. It has been suggested that there is a plasma contribution to the strong electron emission from ferroelectrics [11, 12]. It has been demonstrated that the strong electron emission occurs from a surface flashover plasma caused by a high-voltage stress applied to the PLZT ceramic [13] or BaTiO 3 ceramic [17, 18] on a nanosecond time scale. Other data are also consistent with the formation of a plasma on the surface of the ferroelectric cathode [19]. A dual-mode mechanism of electron emission from ferroelectric ceramics, which implies that the emission is stimulated either by a surface plasma or polarization switching, has been proposed in [20]. In an alternative emission mechanism [21, 22] it has been shown directly that a surface plasma of ferroelectric origin (existing in the ferroelectric phase only) may be induced by polarization switching under applied voltages as low as 100 V on a microsecond time scale or even under a sinusoidal (50–100 Hz) voltage [21]. Ferroelectric cathodes could be an important electron source for high-power microwave tubes. The electron energy spread is one of the important quality factors for any electron source. To the best of our knowledge, thorough studies of electron energy spectra for ferroelectric cathodes have not been conducted yet. The electron energy spectrum may play a crucial role in potential applications of these cathodes for microwave generation. It is known that electrons emitted from ferroelectrics due to a spontaneous change in polarization may have rather high initial energies [23, 24]. Emission of electrons from a ferroelectric cathode into vacuum during polarization reversal is governed by the dynamically changing surface potential [21, 22]. To determine whether the influence of such a dynamic surface potential can be avoided, we have studied electron energy spectra and other parameters of ferroelectric cathodes using the PLZT 12/65/35 ceramic composition, which is not spontaneously polarized at room temperature [16]. Particular conditions for ferroelectric cathode operation which provide a narrow spectrum of electron energies and high perveance have been found. 2. Experimental techniques A silver paint contact (diameter 6 mm) was deposited onto the rear surface of a rectangular PLZT 12/65/35 ceramic 0022-3727/98/111375+08$19.50 c  1998 IOP Publishing Ltd 1375