| 摘要 |
<p>A dual-mode electron gun (110) for a traveling-wave tube which selectively generates an electron beam of two different cross-sectional areas. The electron gun (110) includes radially inner (118) and annular (120) control grids as well as a shadow grid (122) disposed between the cathode (112) and the control grids (118, 120) along the electron beam path (115). The shadow grid (122) is provided with a suppressor ring (170) which precludes electron emission from an annular portion (184) of the cathode (112) immediately radially outwardly of the cathode region over which the inner control grid (118) projects, thereby eliminating generation of a spurious beam portion radially outwardly from the desired smaller cross-section beam.</p> |
