Emission characteristics of a directly heated, rod-shaped LaB₆ hot cathode has been studied in a multi-dipole confinement device. It is found that contrary to predictions from the conventional space-charge limited emission theory, emission current is not simply limited to a maximum value but eventually extinguished by space-charge related effects. In addition, directional preference of electron emission towards the positive lead of the applied heating voltage can be visibly observed. Results suggest that thermionically emitted electrons trapped in the virtual cathode are pumped towards the high voltage lead of the applied heating, and that the magnetic effects for filament heating currents exceeding 50 A may be the underlying mechanism of extinguishment; that is, the gyromotion of surface emitted electrons for sufficiently great heating currents may prevent electrons from escaping the virtual cathode. Geometrical effects are also briefly discussed.

直接加热的棒状LaB _6的发射特性已经在多偶极限制装置中研究了热阴极。发现与常规空间电荷限制发射理论的预测相反，发射电流不仅被简单地限制为最大值，而且最终被与空间电荷相关的效应所消除。另外，可以明显观察到电子发射朝向所施加的加热电压的正极引线的方向偏好。结果表明，捕获在虚拟阴极中的热电子发射电子被泵向所施加加热的高压引线，并且灯丝加热电流超过50 A的磁效应可能是其熄灭的潜在机制。也就是说，对于足够大的加热电流，表面发射电子的旋转会阻止电子逸出虚拟阴极。