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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: 

  • It does not demand separate high-vacuum pumps for additional evacuation of gun’s chamber. Gas-discharge EB gun can stable operate under residual pressure in the gun’s chamber in the range 10…0.01 Pa. 
  • It is insensitive to pressure variations in operating chamber, to action of metal vapor and even spray during running of melting process. This feature allows stable melting of gas-saturated stock of refractory and reactive metals, for example titanium sponge.
  • It has compact construction and light weight, it is simple and reliable at operation. ·
  • Cathode of gas-discharge EB gun has long service life (up to 1000 hours).
  • Gas-discharge EB guns have attractive prices due to using of inexpensive materials for production and maintenance of them.

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:

  • Cathode assembly (including a cathode);
  • Anodic assembly;
  • Insulator;
  • Focus-and-scanning system (including two focusing coils and one deflection coil)

 

 


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.

 

 

Gas-discharge EB gun BTP-30

Gas-discharge EB gun BTP-60 and BTP-100

Gas-discharge EB gun BTP-300

Gas-discharge EB gun BTP-450

Gas-discharge EB gun BTP-600/40


 

Technical data of gas-discharge EB guns of the BTP series 

 

  BTP-30 BTP-60 BTP-100 BTP-300 BTP-450 BTP-600/40
Maximum beam power, kW 30 60 100 300 450 600
Power regulation limits, kW 0...30 0...60 0...100 0...300 0...450 0...600
Nominal accelerating voltage, kV 30 40
Maximum deflection angle of electron beam from axis 20° 30°
Operating residual pressure in the operating chamber, Pa 5…0,01
Maximum operating gas consumption at pressure of 0,1 MPa, l/sec 1•10-3 2•10-3 3•10-3 8•10-3 11•10-3 14•10-3
Minimum operating time of the cathode, hours 300
Cooling water consumption, l/sec 0.05 0.10 0.15 0.5 0.75 1.25
Height, mm (approximate) 380 420 480 460 550 670
Weight, kg (approximate) 14 18 22 43 60 65

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:

 

  • High-voltage power supply;
  • System for preparation and supply of operating gas mixture;
  • Gun's cooling system;
  • Gun's control system;
  • Control equipment.

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.

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