Radiant energy – Radiant energy generation and sources
Patent
1982-02-08
1985-02-19
Smith, Alfred E.
Radiant energy
Radiant energy generation and sources
2504923, 313448, H01J 302, H01J 37063
Patent
active
045007918
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Technical Field
The invention relates to a high stability electron beam generator for processing material, comprising an electrically heated cathode, a perforated anode, and a control electrode lying at a potential which is more positive than the cathode and disposed between the cathode and the anode.
2. Underlying Prior Art
In the known electron beam generating system for processing material, the electron beam is generated and controlled by three electrodes, cathode, perforated anode and Wehnelt cylinder. Directly or indirectly heated H-needle, ribbon- or bolt-cathodes consisting of tungsten are employed as the cathode and cathodes consisting of lanthanhexaborate are also employed.
The electrons of the electron beam are emitted from the cathode due to the heating and are subsequently accelerated. For example, the cathode can be charged with a high negative voltage, whereas the anode lies at grounded potential. The electrodes are accelerated toward the anode in the electrical field generated in that manner, pass through the anode perforation and arrive in the field-free space.
In the previous systems, the third electrode, the Wehnelt or lattice electrode, serves for controlling the current of the beam. The function of the Wehnelt electrode is described, for example, in the publication M. Blocke, Zeitschrift fur angewandte Physik, Vol. 3, 1951, pp. 441 through 449, "Elementare Theorie der Elektronenstrahlerzeugung mit Trioden-systemen".
When the negative voltage of the Wehnelt electrode is increased beyond a specific value, then further electrons are incapable of leaving the cathode surface, i.e., there are no electrical field vectors which accelerate the electrons to the anode directed to the anode at the cathode surface. The emission is blocked. When the Wehnelt voltage is reduced, then the anode penetration coefficient increases. Given a decreasing Wehnelt voltage, larger and larger areas of the cathode are released for emission, whereby the emission current increases. Thus, the variable negative voltage of the Wehnelt cylinder in comparison to the cathode allows a control of the beam current.
A characteristic of these systems is described in greater detail below. It derives from the structural disposition of the Wehnelt cylinder and due to the prescribed Wehnelt voltage which is required for setting a desired beam current, a fixed beam geometry which can only be changed by means of changing the structural shape or the Wehnelt voltage. However, a change of the Wehnelt voltage again leads to a change of the beam current. This rigid dependency of the beam current upon the Wehnelt voltage and the beam shape fixed by the Wehnelt arrangement and Wehnelt voltage are disadvantageous.
Added thereto as a further disadvantage is that, in the standard operating mode, the cathode is operated in the space charge range, whereby the beam value lies below the value which would theoretically derive given operation of the cathode in the saturation range. Resulting therefrom is that the efficiency of the electron beam generator does not assume the optimally attainable value.
SUMMARY OF THE INVENTION
It is therefore the object of the present invention to create an electron beam generator which does not exhibit these disadvantages and which has a higher beam value in comparison to known electron beam generators.
Thus, the invention consists of an electron beam generating system with a heated cathode, a perforated anode, and an auxiliary electrode lying at a more negative potential than the cathode, and is characterized in that the beam current is determined by means of rating the active surface of the cathode and by means of the controlled heating of the cathode to a constant temperature.
An advantageous further development consists therein that the auxiliary electrode surrounds the cathode and lies at a slightly more negative, constant potential than the cathode. In an advantageous manner, the auxiliary electrode is designed as a perforated disk surrounding the cathode. According to an adv
REFERENCES:
patent: 3846660 (1974-11-01), Wolfe et al.
Reference Data for Radio Engineers, Fourth Edition, International Telephone and Telegraph Co., 1956, pp. 367-369.
Dr. -Ing. Rudolf Hell GmbH
Grigsby T. N.
Smith Alfred E.
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