Investigations of the field emission current from bismuth ceramic cathodes

In this work the investigations of the emission current from Bi ₂Sr₂Ba₂Cu₃O_x and Bi₂Sr₂BaCu₂O_x ceramic cathodes are presented. Experiments were carried out in the vacuum chamber at pressure within the range of 10^-8 Tr (10^-6 Pa), with DC high-voltage power supply and high-class digital electrometer. Current-voltage and Fowler-Nordhelm characteristics for the superconducting cathodes at liquid nitrogen temperature were obtained for various distances between electrodes. Current vs. temperature characteristics were also measured. For some measurements the transparent anode technique was employed in order to provide information about emission origin point. Emission current was registered for the electron emission originating from a single emission center. Superconducting state did not influence current-voltage dependences. It was observed for superconducting cathodes that emission current abruptly changes in the vicinity of the superconducting transition temperature T _c. Emission current was stable and practically constant for the temperatures below T_c and became unstable and noisy for the temperatures above T_c. Emission current rate depends on the temperature range of the superconducting transition ΔT_c . Superconducting parameters of the cathodes: critical temperature T_c, temperature range of the superconducting transition ΔT_c and critical current density j_c were also measured. It was found that sorbtion phenomena on the surface of cathodes during cooling and heating influence emission current values and play a major role in the emission phenomena