Electron beam generator for an electron beam gun

In the electron beam generator the cathode (3) the control electrode (4) and the anode (5) are provided with easily replaceable parts (12, 13, 14, 28, 29) so as to be able, by exchanging the parts, to optimize the electron beam generator in a simple manner for a selected power range within the working range of the electron beam gun.

BACKGROUND OF THE INVENTION 
The invention relates to an electron beam generator for an electron beam 
gun, having a cathode, a control electrode and an anode which are disposed 
in an evacuable acceleration chamber. 
Electron beam generators of the stated kind are used in metallurgy. They 
generate an electron beam which, being focused by an electromagnetic 
focusing system, is directed against a workpiece for the purpose, for 
example, of removing material therefrom, or of melting it. The need in 
this case arises for adapting its power to various working procedures and 
materials, for example by varying the accelerating voltage and the beam 
current. It has been found, however, that the known electron beam 
generators can be operated in an optimum manner only within a narrow range 
of power. This optimum power range is defined by the emittance--the 
product of the focus radius times the solid angle--which varies with the 
beam current. To make optimum use of the entire working range of an 
electron beam gun it has therefore been necessary to replace the gun from 
one case to the next. 
SUMMARY OF THE INVENTION 
The invention is addressed to creating an electron beam generator of the 
kind described above, which can be adapted by simple means to the selected 
power range within the range of operation of the electron beam gun. 
The cathode, the control electrode and the anode have easily 
interchangeable parts which contribute by their shape and size to the 
formation of the electron beam. An assortment of different parts is 
provided for the cathode, the control electrode and the anode, these parts 
being interchangeable. 
By the installation of the interchangeable parts provided for the power 
desired in each case, the invention permits optimum beam formation. In 
this manner the quality of the beam is substantially improved throughout 
the power range. In the case of production equipment, the electron beam 
generator can be optimized for a specific use and it becomes easier to 
achieve repeatable results. The interchangeable parts can be manufactured 
at reasonable cost and can therefore be kept on hand in sufficiently fine 
gradations of size and shape. 
In a further development of the invention, provision can be made for 
optimizing the external shape of the electron beam generator electrodes, 
which cannot be varied by interchangeable parts, to achieve minimum field 
strength. This version results in great reliability of operation and 
enables the electron beam generator to be adapted to all applications by 
varying the parts which are interchangeable. 
The control electrode preferably consists of a pot-shaped, hollow 
cylindrical jacket with a central bore passing through its bottom, into 
which an annular insert designed as an interchangeable part can be 
installed to vary the shape of the central bore. Preferably the insert 
consists of a material of high permeability. Provision can furthermore be 
made in invention for a cathode holder in the form of an interchangeable 
part and held by an insulator to be installed as an interchangeable part 
in the jacket. The anode can advantageously consist, of an interchangeable 
anode body and an interchangeable anode spacing ring. Furthermore, an 
annular diaphragm in the form of an interchangeable part can be provided 
in back of the anode with respect to the direction of the beam.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
In the electron beam generator in the drawing, a cathode 3 and a control 
electrode 4 are disposed on a insulator 2 in the center of an evacuable 
acceleration chamber 1, and can be connected to a high-voltage generator 
by electrical conductors inside of the insulator 2. At a distance from the 
cathode 3 is an annular anode 5 which is coaxial therewith and is borne by 
a plate 6 and is at ground potential with the accelerating chamber 1. A 
diaphragm 8 is provided in a second plate 7 at a distance from the anode 
5. 
The control electrode 4 has a pot-shaped, cylindrical jacket 9 whose 
external shape has been optimized to achieve minimum field strengths. The 
jacket 9 is borne by a flange 10 on which it is held by a catch for easy 
release. One over another, in a central, cylindrical bore 11 in the jacket 
9, are an insert 12, a supporting ring 13, and a cathode holder 14, which 
rest on one another and thus have a precise geometrical relationship to 
one another. The insert 12 is in the shape of a cylindrical pot and is 
centered by its cylindrical exterior in the bore 11 in the jacket 9. By 
means of a set screw 15 engaging a groove, the insert 12 is locked in the 
bore 11, in contact with the bottom 16 of the jacket 9. A central bore 17 
flaring conically in the direction of the beam is provided in the bottom 
16 for the passage of the electron beam. The central bore 17 is adjoined 
by an opening -8 in the insert -2, which is smaller in diameter and 
surrounds the area of emission of the cathode 3. The opening -8 flares 
conically toward the cathode holder 14. In its diameter and in its shape, 
the opening 18 is adapted to a cathode size suitable for a certain 
specific power range. If a cathode of a different size is installed for a 
different power range, the insert 12 is replaced with one that is adapted 
to this other cathode. 
The supporting ring 13 surrounds the cathode holder 14 and provides for its 
precise axial positioning with respect to the insert 12 of the control 
electrode 4. An insulator 20 of the cathode holder 14 is optically 
shielded from the electron beam by a radially inwardly directed flange 19. 
The cathode holder 14 has two connecting terminals 21, 22, of a 
substantially mirror-image configuration, which are held in the insulator 
20 and bear at their bottom ends clamps 23, 24, for fastening the two ends 
of the cathode 3. The terminals 21, 22, are connected to the heater 
circuit of the electron beam generator by plug contacts 25, 26. Just like 
the insert 12 and the supporting ring 13, the cathode holder 14 is an 
interchangeable part which is provided so as to fit different cathode 
sizes. The cathode holder 14 is fastened in the jacket 9 by a set screw 
27. 
The anode 5 has a replaceable anode sleeve 28 having a threaded projection 
which is screwed into a threaded bore in plate 6. The anode sleeve 28 and 
the anode spacing ring 29 are replaceable parts. To optimize the electron 
beam for a specific power range, therefore, the appropriate anode sleeve 
can be selected from a plurality of anode sleeves 28 of various bore 
diameter and the acceleration length can be optimized with an anode 
spacing ring 29. Furthermore, diaphragms 8 of different diameters can be 
inserted into plate 7 in order to achieve the desired beam quality. 
To set up the electron beam generator for a specific use, the housing of 
the accelerating chamber 1 is swung open, making the electrodes easily 
accessible. To set up the cathode 3 and the control electrode 4, the 
jacket 9 can be removed from the mounting flange 10 and equipped in the 
desired size with an insert 12, a supporting ring 13 and a cathode holder 
-4 with a cathode 4. At the same time the appropriate anode sleeve 28, 
anode spacing ring 29 and diaphragm 8 can be installed. These measures can 
be performed simply and quickly and involve no more than a small parts 
cost. Thus an optimum adaptation of the electron beam generator to the 
particular application can be accomplished in a simple and inexpensive 
manner.