| 摘要 |
PROBLEM TO BE SOLVED: To control the local heating of a spiral type cathode, stably discharge electrons, and improve the life, by arranging lead wires for retaining the cathode and applying a voltage, in three or more portions, i.e., both end portions of the spiral cathode and a portion except both of the end portions of the spiral cathode. SOLUTION: Lead wires 3, 3' which apply a voltage and retain a direct heat impregnation type cathode 1 are connected with both ends 2, 2' of the direct heat impregnation type cathode 1. A lead wire 3' is connected with a portion in the central part of the direct heat impregnation type cathode 1. By this constitution, a voltage is applied from three points to the direct heat impregnation type cathode 1, which can be retained. Thereby, at the time of operation start, a voltage is applied from both of the end portions of a spiral type cathode, the whole of the spiral type cathode is heated, and a discharge beam is generated. After stabilization, the applied voltage is controlled to restrain the local temperature rise generated by ion collision, by independent circuits formed between adjacent contacts of lead wires of both end portions of the spiral type cathode and a part except both of the end portions. |
