DE1057244B - Focussing device for the bundled guidance of an electron beam over a larger distance through a periodically alternating magnetic field, especially for traveling wave tubes - Google Patents

Description

In a traveling wave tube or a similar electron tube means are provided that a generate a magnetic field in the axial direction of the electron beam so that the diameter of the The beam remains constant on the relatively long way through the actual transmission space of the tube Value. As is known, this longitudinal field does not necessarily have to be homogeneous. It is - as is also known - in certain cases advantageous if the magnetic induction in axial Direction, i.e. in the direction of the beam, varies periodically, for example in a sinusoidal distribution. Decisive for the construction of a device in which the magnetic field is used in this way as an alternating field is built, is above all the point of view that this makes the traveling wave tube considerably more space-saving can be operated than was possible with the usual arrangements. Furthermore, if this field is generated permanently magnetically in a known manner, the weight of the arrangement on one Reduce a fraction of the weight when using an electromagnetic Focusing coil is necessary.

In a known focusing device, particularly suitable for traveling wave tubes, a periodically alternating magnetic field in the (axial) direction is generated by a rotationally symmetrical permanent magnet system, which consists of several ring-shaped permanent magnets arranged one behind the other in the direction of the beam, alternately polarized in opposite directions with ring-shaped permeable parts arranged between them have a pole shoe-like approach towards the system axis. In this device, the inevitable fact is to be expected that, for. B. in traveling wave tubes, the relationship between the magnetic induction in the axial direction of this alternating field and the penetration factor P of the electron beam, i.e. the dependence on P focusing device for the bundled guidance of an electron beam over a longer distance through a periodically alternating magnetic field, especially for traveling wave tubes

Applicant:
International standard
Electric Corporation,
New York, NY (V. St. A.)

Representative: Dipl.-Ing. H. Ciaessen, patent attorney,
Stuttgart-Zuffenhausen, Hellmuth-Hirth-Str. 42

Claimed priority: Japan October 4, 1954

Susumu Yasuda, Tokyo,
has been named as the inventor

as a function of the variable field strength B _max , except

neatly critical. This disadvantage is the useful manufacture of such an arrangement as Obstacle against.

The purpose of the invention is now to provide a means by means of which this critical Dependency can be removed magnetically. Namely, the disadvantage mentioned has an effect with traveling wave tubes and the usual operating voltages of a few IOOO V there from that as a result of insufficient focusing of such a tube from the electron beam the Electrode openings are taken. As a result, for example, the spiral electrode can burn out, whereby at least the service life of the tube suffers considerably and the useful electrical power is greatly reduced.

These difficulties with the known focusing device are thereby eliminated according to the invention fixed that the bundling field strength between adjacent pole shoe-like approaches by means of magnetic shunt effect is adjustable in that highly permeable to form the shunts Rings are used on a tubular, coaxially enclosing the permanent magnet system non-magnetic sleeve are placed coaxially to the permanent magnet system, so that they both individually, preferably by a screwing movement, and as a whole, preferably by moving the tubular sleeve, are displaceable in the axial direction with respect to the permanent magnet system.

The invention will now be explained in more detail on the basis of an exemplary embodiment and with reference to the drawings explained.

Fig. 1 shows the cross section through an embodiment of the invention;

FIG. 2 shows the dependency, known per se, between the axial magnetic induction B _max and the penetration factor P of the electron beam in the case of a traveling wave tube of the arrangement according to FIG. 1.

The focusing device shown in FIG. 1 encloses a traveling wave tube designated by 1.

90Ϊ 510/370

Claims (1)

In this case, permanent magnetic rings 2 magnetized in the direction of the tube axis are separated from one another by permeable pole disks 3 in a manner known per se. The ring magnets 2 face each other with poles of the same name and thus form an alternating field of approximately sinusoidal distribution along the tube axis. The dimensions of the pole disks are chosen so that an exclusively axially directed magnetic field is generated in the area of the tube axis. On the other hand, they also serve to render harmless any Ouer field components that may occur, which may be caused by material scatter in the magnetic rings, by means of a magnetic short circuit in the ring magnets. About this magnet assembly is a tubular cylinder 4 made of non-magnetic material, so z. B. made of brass, which is pushed in the axial direction and on its outer periphery in part with screw ao thread 5 is provided. According to the invention, ring-shaped components 6 of high permeability, which may consist of iron, for example, are attached to the cylinder 4. These rings produce the magnetic shunts, the effectiveness of which depends on their relative axial position to the magnetic field. The shunt rings 6 in the embodiment also have a thread on their inside so that the field strength of each individual section can be easily adjusted with their help. You can optionally approach the adjacent north or south pole of the ring magnet located in the interior of the sleeve 4 by turning from the center position shown. The strength of the field strength of the magnet arrangement, which extends in the axial direction, is thereby changed. Since the axial magnetic field should be as free as possible of any transverse components, it is necessary to center the individual ring magnets 2 as precisely as possible. In addition, the magnetic field strength at the circumference of each ring magnet should have the same size. These requirements can be adequately met by moving or rotating adjacent rings 6 before the arrangement is determined. In Fig. 2 , the measurement results are shown on an arrangement according to the invention. The penetration factor P, which is a measure of the quality of the focusing, is plotted as a function of the field strength B _max in the direction of the tube axis. If the focussing field along the tube is too strong, a profile of the penetration factor P is obtained according to curve a. This can now be improved with a changed field strength as a result of the displacement of the shunt rings 6 until curve b is reached. If another traveling wave tube with different electrical data is used, a different field strength setting will be necessary. In the event that, as in Fig. 1, the individual magnetic shunt rings 6 are arranged at a distance of half a spatial period of the alternating magnetic field in the direction, the field strength of the entire arrangement can be regulated in such a way that with a shift the non-magnetic sleeve 4 then a field strength maximum is reached when the shunt rings 6 are in the immediate vicinity of the pole disks 3 . The magnetic shunt is a minimum in this case, while it assumes a maximum value when the rings 6 assume approximately the position shown in FIG. 1, which corresponds to a minimum of the field strengths inside the tube. In this way, the spatial field strength distribution given by the arrangement is retained even in the case of regulation. However, it was assumed here that all ring magnets involved generate exactly the same magnetic field strengths, an assumption that does not apply in practice. Rather, as a result of the manufacturing variations, it must be expected that the individual partial magnets deviate from one another by up to about 5% with regard to their magnetization. With the arrangements known up to now, the desired correction of the field strength distribution of the alternating magnetic field cannot be achieved, a fact which calls into question the use of the known permanent magnet systems with a magnetic field alternating in the direction. With the invention, however, this difficulty can be eliminated in that the shunt rings are moved axially individually by a screwing movement and thus the field strength of the individual sections is experimentally brought to the required level. In this context, it should be noted that it is particularly advantageous for traveling wave tubes to set the once optimally adjusted focusing device in its position so that the magnetic shunt rings remain set on the non-magnetic sleeve 6 so that the difficulties caused by poor focus remain off . The invention, which is explained on the basis of the exemplary embodiment using a traveling wave tube can be used in principle with all arrangements that focus an electron beam have to do. Claim: Focusing means for bundled guide an electron beam over a greater W ^T egstrecke by a periodically alternating in the direction of magnetic field which is generated by a rotationally symmetrical permanent-magnet system behind each other from a plurality of in the beam direction, alternately in the opposite sense polarized annular permanent magnet having therebetween disposed annular permeable parts , which have a pole shoe-like approach to the system axis, there is, in particular for traveling wave tubes, characterized in that the bundling field strength between adjacent pole shoe-like approaches can be adjusted by means of a magnetic shunt effect that highly permeable rings are used to form the shunts, which are on a tubular, the permanent magnet system coaxially enclosing non-magnetic sleeve are placed coaxially to the permanent magnet system in such a way that they are both individually, preferably d can be displaced in the axial direction relative to the permanent magnet system by a screwing movement and also as a whole, preferably by displacing the tubular sleeve. Considered publications: Proceedings IRE, May 1954, p. 800 ff. Here: Sheet drawings © 909 510/370 5.