Backbombardment

Backbombardment is a phenomenon observed in certain types of vacuum tubes, particularly in cathode ray tubes (CRTs) and magnetrons. It refers to the process where high-energy electrons from the electron beam strike the target or cathode surface and then reflect back towards the electron source or other internal components of the device. These reflected electrons, often referred to as backscattered electrons or secondary electrons, possess significant kinetic energy.

In CRTs, backbombardment can lead to several issues. It can contribute to the degradation of the phosphor screen, reducing its brightness and lifespan. The reflected electrons can also cause unwanted secondary emissions from other internal structures, potentially leading to electrical discharge or interference. In magnetrons, used in microwave ovens and radar systems, backbombardment can reduce the efficiency of the device and increase the risk of internal damage.

Minimizing backbombardment is a design consideration in vacuum tube engineering. Techniques employed to reduce its effects include optimizing the shape and material of the cathode and anode structures, implementing suppressor grids, and carefully controlling the beam voltage and current. The energy and angle of incidence of the primary electron beam play crucial roles in determining the extent of backbombardment. Understanding and mitigating this phenomenon is important for ensuring the performance, longevity, and reliability of these electronic components.