Reversible periodic magnetic focusing system

Electric lamp and discharge devices: systems – Cathode ray tube circuits – Combined cathode ray tube and circuit element structure

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Details

313442, 315 537, 315 539, H01J 2308

Patent

active

044332700

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The present invention relates to vacuum tubes and, more particularly, to a reversible periodic magnetic focusing system.


REVIEW OF THE PRIOR ART

Superhigh frequency tubes, such as klystrons and travelling wave tubes find extensive application in different branches of the economy in many countries. The factors that hinder their application are their great weight and the necessity of using high voltage sources. The weight of such tubes and their anode voltage are largely determined by the weight of the focusing system and the perveance of the electron flow. Light-weight focusing systems capable of forming high-perveance electron flows are an indispensable condition for the provision of light, low voltage superhigh frequency tubes.
At present use is made of different types of focusing systems.
There are known magnetic focusing systems (cf. U.S. Pat. No. 3,475,644, Cl. 315-35, of Oct. 28, 1969) of the type that comprises a solenoid with pole shoes mounted on its end faces. As the solenoid is excited, a uniform magnetic field is produced between the pole shoes, which provides for the transportation of a high-perveance flow exiting from a gun.
Such focusing systems are disadvantageous in that they have a great weight and size and require a special power source.
There are known focusing systems which use a permanent magnet instead of a solenoid to produce a uniform magnetic field over the entire length of the system (cf. G. Merdinian and J. V. Lebacqs, "High Power, Permanent Magnet Focused, S-Band Klystron for Linear Accelerator Use" in Proc. 5th Int. Conf. on Hyperfrequency Tubes, Paris, France, Sept. 1964).
Such systems require no special power source, but suffer from a great weight and size.
There are known electrostatic focusing systems (cf. U.S. Pat. No. 3,436,588, Cl. 3155.39, of Apr. 1, 1969) comprising a plurality of single electrostatic lenses arranged between the resonators of the klystron. Such systems have a small weight and size and require no special power source.
However, electrostatic systems do not provide for a sufficiently strong focusing; the perveance of the electron flow focused by such systems is never higher than 1.multidot.10.sup.-6 A/B.sup.3/2.
There is known a reversible periodic magnetic focusing system (cf. FRG Pat. No. 1,190,708, Cl. 21 g 13/17, of December 1965) comprising a plurality of successively arranged pole shoes with a central hole for the passage of an electron flow. Permanent magnets are used to produce a uniform variable-polarity (reversible) magnetic field between the pole shoes.
The focusing of such a system is stronger than that of an electrostatic system; the latter system is also advantageous in that it makes it possible to reduce the weight of the magnet by (n+1) times, as compared to the system with a uniform magnetic field, where n is the number of field reversals.
However, reversible magnetic systems can only operate at a small perveance of the electron flow. This is due to the presence of a reversal zone in which the magnetic field is weak. The extension of this zone is commensurable with the diameter of the hole provided in the pole shoe. As a high-perveance electron flow passes through the reversal zone, it gets out of focus and its further formation is disturbed.


BRIEF DESCRIPTION OF THE INVENTION

It is an object of the present invention to increase the perveance of the electron flow formed by a reversible periodic magnetic focusing system.
The invention essentially aims at providing a reversible periodic magnetic focusing system which would reduce the extension of the reversal zone by several tens of times and would ensure the transportation of a high-perveance electron flow due to an improved pole shoe design.
The foregoing object is attained by providing a reversible periodic magnetic focusing system comprising a successive array of permanent magnets magnetized in the opposite sense, and magnetically soft pole shoes interposed between the permanent magnets, each pole shoe having a hole for the passage of an electron flow, the

REFERENCES:
patent: 2305884 (1942-12-01), Litton
patent: 3020440 (1962-02-01), Chang
patent: 3021447 (1962-02-01), Jepsen et al.
patent: 3172008 (1965-03-01), Schmidt
patent: 3237059 (1966-02-01), Meyerer
patent: 3329915 (1967-07-01), Meyerer
patent: 3665242 (1972-05-01), Dubravec

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