History of Vacuum Electronics and Vacuum Electron Sources and Future Development Trends

The historical rise of vacuum electronics (VE) was enabled by the availability of electrical power and by improved vacuum techniques, but its further progress relied on improved electron sources and their control. The development of VE has been pushed by several technological waves/cycles, starting with incandescent lamps, continuing with the radio tube era and then followed by the cathode-ray tubes. Yet vacuum electronics is still alive and has specific advantages in the high-power, high-frequency domain. The improvement trends of cathodes over time, related to specific and also advanced application requirements will be addressed.