Beam control for electron beam welder - has beam focus and stability controlled by periodically deflecting beam

摘要

An electron gun produces a collimated and accelerated beam of electrons via the collimator and accelerating anode respectively. The beam is focussed onto a workpiece by coils and is deflectable by further coils. A water cooled probe (or a Faraday slit) is positioned adjacent the beam and, by a periodic signal generated as a saw tooth wave by the generator, the beam is periodically deflected across the probe. The dwell time of the beam on the probe is a signal proportional to the dia. of the beam and hence its focus. The current induced in the probe is compared with a reference signal from a generator and the beam focus adjusted accordingly by an operational amplifier acting on the focus coils.