Gas-discharge electron beam guns
Gas-discharge electron beam guns of the BTP series
Electron emission in gas-discharge EB gun results from ion bombardment of a cathode. Ions are emitted by plasma which occurs in high-voltage glow discharge between cathode and anode. Initial forming of electron beam is provided by design features of cathode and anodic assembly. Then by operating of focusing and deflection coils electron beam are been focusing on the processed surface and been scanning on it with specified frequency and path (sweep).
The main specialty features of gas-discharge EB gun are following:
Gas-discharge EB guns are successfully used in Ukraine, Russia, Estonia and USA for melting of titanium, niobium, tantalum and other materials.
Design of gas-discharge EB gun includes the following main parts and units:
The construction scheme of the gas-discharge EB gun of the BTP series (1- Cathode assembly; 2 – anodic assembly; 3 - insulator; 4 – beam transmitter; 5 – focusing coils; 6 – deflection coil)
At operation of gas-discharge EB gun an operating gas mixture (hydrogen and oxygen in specified propotrion) is supplied to discharge chamber of a gun. High-voltage glow discharge burns in discharge chamber of a gun under accelerating voltage between cathode and anode.
Plasma generating under discharge emits positive ions which are accelerated by electric field in zone of cathode potential drop and bombard the cathode, causing electron emission. The same field accelerates electrons and forms a converging electron beam which passes to focus-and-scanning system through a hole in bottom of the anode.
The magnetic field created by the first focus coil forms an electron beam under the form close to cylindrical. Hereupon it passes to the melting chamber through focus-and-scanning system practically without power losses. By means of the second focus coil the beam is focused on a heating surface. Specified scanning of a beam is carried out by the deflection coil.
Current of the electron beam is controlled by regulation of operating gas pressure in a gun. The quick-response gas supply control system is applied for the efficient control of the electron beam current and for stabilization of operating mode of a gun. Control of gas supply in this system is carried out by means of electromagnetic regulators of gas outflow.
Supporting systems for gas-discharge EB guns of the BTP series
Availability of the following systems is necessary for providing of gas-discharge EB gun operation:
Scheme of supporting systems for gas-discharge EB guns of the BTP series
System for preparation and supply of operating gas mixture and gun's cooling system consist of commercial equipment which is used for the same technical purposes.
Any unrestricted high-voltage power supply can be used if it ensures maximal protection from short circuit. Also such power supply should provide rapid recovery of parameters of output current and voltage in case of breakdown in EB gun.
Gun's control system should provide control for gas outflow regulators (in fact it is control of beam power), control for focusing and path of electron beam, and also provide continuous automatic monitoring of EB gun parameters.