Cathode-ray tube having an ion trap

摘要

Positive ions which are generated in a vacuum tube (1) and can adversely affect the electron emission of a cathode (3) are collected for the major part by a screen grid or diaphragm (5), which forms part of a positive electron lens (4,5). In the case of a semiconductor cathode having a circular emission region (13) having a diameter larger than that of the opening in the screen grid (5), this emission region (13) is struck only by positive ions generated in a small region between the cathode (3) and a first grid (4). These ions moreover have a comparatively low energy so that the emission behavior is to only a limited extent adversely affected by sputtering by positive ions which would remove cathode material (33), such as cesium.