Search

The technology for manufacturing large size shielded metal-ceramic cold cathodes is described. It has been shown that the use of a shielded metal-ceramic cathode allows to significantly increase the impedance of the vacuum diode and to form an electron beam of constant cross-sectional size or of the required size (up to 400 mm wide) with a fairly uniform electron beam current density distribution (≤15%). It has been found that the emission decline of the shielded metal-ceramic cathode, like that of the metal-dielectric cathode operating at a high repetition rate (≥100 pps), is significant at the beginning of the process and then slows down, allowing continuous operation for up to 40 h. Both cathodes require periodic cleaning of the plates, which is more difficult for metal-ceramic plates. At the same time, a metal-ceramic cathode works better at low vacuum, allowing twice as much current to be generated (in the same geometry) as a metal-dielectric cathode, while reducing the accelerating voltage by ∼15%. However, metal-ceramic plates are about 100 times more expensive to manufacture than dielectric plates for a metal-dielectric cathode. Therefore, the choice of cathode type for vacuum diode accelerators is not a trivial problem, but depends on many factors that must be taken into account in each case and for each radiation technology. • A shielded cathode has been designed to produce an electron beam with a cross-section of up to 400 mm. • It is possible to have a fairly uniform electron beam current density distribution (≤15%). • The beam size of the shielded metal-ceramic cathode can be practically constant. • The shielded metal-ceramic cathode works better at low vacuum than a metal-dielectric cathode. [ABSTRACT FROM AUTHOR]

We present results of the investigation of a metal-ceramic cathode suitable for technological applications. The cathode was tested in electron diodes powered by two different high-voltage generators (500 kV, 50 ns, 300 Ω, ≤200 Hz and 300 kV, 250 ns, 84 Ω, ≤5 Hz). The metal-ceramic cathode which was made in a form of a disk was composed of TiO[sub 2] ceramics with stainless steel spherical particles uniformly inserted inside. It was shown that already at relatively low accelerating fields (E ≤ 5 kV/cm) fast cathode plasma formation occurs as a result of surface flashover. This surface flashover is initiated in triple points located in micropores which were formed during the process of cathode preparation due to the different thermal expansion coefficients of the ceramic and the metal. Experimental data concerning the uniformity of the light emission from the cathode surface and inside the anode-cathode gap and divergence of the generated electron beams are presented. Also, it is shown that the uniformity of the generated electron beam depends strongly on the duration of the accelerating pulse. [ABSTRACT FROM AUTHOR]

The characteristics of a metal-ceramic (MC) cathode designed for nanosecond electron accelerators are studied in relation to the size of metal particles, their density on the ceramic surface, and the type of ceramics. A high emissivity of the MC cathode at a moderate electric field in the diode tube is demonstrated. This allows one to significantly sharpen the electron beam and increase its current (power). The possibility of controlling the emissivity of the MC cathode by varying the composition of the MC plate is established. © 2003 MAIK “Nauka / Interperiodica”. [ABSTRACT FROM AUTHOR]