EP0004492A2 - Microwave tube containing a delay line cooled by a circulating fluid - Google Patents

Abstract

The invention relates to a delay line, for microwave tubes, cooled by fluid circulation. The cooling fluid circulates in channels (10), formed by the space between two sleeves, made of non-magnetic material and impervious to this fluid, having as axis the axis of the line. The first sheath (8), vacuum-tight produced in its internal volume, is brazed to the dielectric rods (2) and connects two adjacent rods in a straight line. The second cylindrical sheath (9) contains the first, to which it is brazed at various points, a focusing device by permanent magnets being mounted on this second sheath. The delay line according to the invention is used in microwave tubes.

Description

The present invention relates to a delay line used in a microwave tube and cooled by fluid circulation. It also relates to microwave tubes comprising such a line.

The microwave tubes to which the invention applies, such as progressive wave tubes or type O carcinotrons, have a delay line ensuring the interaction between an electron beam and an electromagnetic wave: in fact, the electromagnetic wave propagates on the delay line and its phase speed is made comparable to that of the electron beam which moves along the axis of the line.

The delay line can have various structures: helical, "ring and bar", "ring and loop" type, according to English terminology ...

The invention is particularly applicable to cases where the focusing of the electron beam throughout the interaction space with the wave electromagnetic is carried out by a magnetic field produced by permanent magnets. In fact, the invention aims to cool the delay line by fluid: it is the site of high frequency losses and, moreover, poor focusing of the electron beam can increase its heating. The problem which arises is that of the arrangement of the channels where the cooling fluid circulates. This arrangement is easier when the focusing magnetic field of the electron beam is produced by an electromagnet than when it is produced by larger, permanent magnets. As on the other hand, focusing by permanent magnets has great advantages in terms of weight and consumption in particular, it is important to have the cooling channels as best as possible around a delay line focused by permanent magnets.

• - les canaux de refroidissement sont montés sur une collerette encerclant le dispositif de focalisation par aimants permanents. Dans ce cas, l'efficacité du refroidissement est faible car la résistance thermique entre la ligne et les canaux de refroidissement est grande ;
• - les canaux de refroidissement sont montés, avant le dispositif de focalisation, sur une collerette en matériau amagnétique encerclant un fourreau cylindrique séparé de la ligne à retard par des baguettes en diélectrique : la résistance thermique entre la ligne et les canaux de refroidissement est donc beaucoup plus faible que dans la disposition précédente. Un autre problème se pose alors dû au dispositif de focalisation constitué d'une suite alternée, selon l'axe de la ligne, d'aimants permanents et de masses polaires, les faces de même nom des aimants étant en vis-à-vis. Dans cette disposition, le dispositif de focalisation enserre la collerette de refroidissement et son diamètre interne augmente. L'épaisseur des aimants étant maintenue constante pour des raisons de pas magnétique, l'augmentation de leur diamètre interne provoque l'accroissement du champ démagnétisant dans lequel ces aimants travaillent: dans certains cas, en particulier pour les fréquences élevées (bandes I et J par exemple), le champ coercitif du matériau qui constitue les aimants peut être atteint, même si on utilise du samarium- cobalt dont le champ coercitif est élevé. La focalisation du faisceau d'électrons n'est alors plus possible.

When focusing is carried out by permanent magnets, it is known to arrange the cooling channels in the following two ways:

• - the cooling channels are mounted on a collar encircling the focusing device by permanent magnets. In this case, the cooling efficiency is low because the thermal resistance between the line and the cooling channels is high;
• - the cooling channels are mounted, before the focusing device, on a flange made of non-magnetic material encircling a cylindrical sheath separated from the delay line by dielectric rods: the thermal resistance that between the line and the cooling channels is therefore much lower than in the previous arrangement. Another problem then arises due to the focusing device consisting of an alternating sequence, along the axis of the line, of permanent magnets and of polar masses, the faces of the same name of the magnets being opposite. In this arrangement, the focusing device encloses the cooling collar and its internal diameter increases. The thickness of the magnets being kept constant for reasons of magnetic pitch, the increase in their internal diameter causes an increase in the demagnetizing field in which these magnets work: in certain cases, in particular for high frequencies (bands I and J for example), the coercive field of the material which constitutes the magnets can be reached, even if samarium-cobalt is used whose coercive field is high. The focusing of the electron beam is then no longer possible.

According to the invention, the cooling fluid circulates in channels, formed by the space between two sleeves, impervious to this fluid, having as axis the axis of the delay line. The first sheath, in non-magnetic material, is in contact with the face of rods which is opposite to one face of these rods in contact with the delay line, these rods, in dielectric material, being parallel to the axis of the line and regularly distributed around its perimeter. The first sleeve has no contact with the delay line and seals the vacuum created in its internal volume. The second scabbard contains the first with which it is in contact at different points constituting the separation between the channels in which the cooling fluid circulates.

The arrangement of the cooling channels according to the invention ensures cooling of the delay line more efficient than that which is achieved by the known arrangements. It allows in particular the cooling of a delay line operating in band I, for which the known arrangement which has just been mentioned is not applicable since it does not make it possible to obtain the focusing field of the beam d 'electrons. The arrangement according to the invention does not lead, like the known arrangements, to a significant increase in the volume of the tube.

• - la figure 1 : des coupes transversale et longitudinale d'une ligne à retard, refroidie par circulation de fluide, de l'art antérieur ;
• - la figure 2 : une coupe transversale d'une ligne à retard, refroidie par circulation de fluide, de l'art antérieur ;
• - la figure 3 : une coupe transversale d'une ligne à retard, refroidie par circulation de fluide, selon l'invention ;
• - la figure 4 : une coupe longitudinale-d'une variante de ligne à retard, refroidie par circulation de fluide, selon l'invention.

Other objects, characteristics and results of the invention will emerge from the following description given by way of nonlimiting example and illustrated by the appended figures which represent:

• - Figure 1: transverse and longitudinal sections of a delay line, cooled by circulation of fluid, of the prior art;
• - Figure 2: a cross section of a delay line, cooled by fluid circulation, of the prior art;
• - Figure 3: a cross section of a delay line, cooled by fluid circulation, according to the invention;
• - Figure 4: a longitudinal section of a variant of the delay line, cooled by fluid circulation, according to the invention.

In the different figures, the same references designate the same elements.

In Figures 1a and 2 is shown, by way of example, a cross section of a delay line cooled by circulation of fluid, of the prior art, the electron beam being focused by permanent magnets. The delay line 1 which is represented has a circular section: it can be helical for example. Three rods, identified by 2, in dielectric material and good thermal conductor, such as alumina, quartz, boron nitride, glucine, are regularly distributed on the delay line. They are parallel to the axis of the line. It is known to braze these rods by one of their faces on the line in order to reduce the thermal resistance at the interface between the line and the rods. The face of these rods opposite to that which is brazed on the line is generally brazed to a cylindrical sheath 3 which is sealed, the vacuum being created inside this sheath, non-magnetic and good conductor of heat; this sheath can be made of copper. When it is metallic, this sheath is like the line connected to ground continuously.

Figure 1b shows a longitudinal section of a delay line, along AA 'of Figure 1a.

In FIG. 1, the focusing device by permanent magnets is adjusted on the cylindrical sheath 3. It is constituted by an alternating sequence along the axis of the line 1 of permanent magnets 4 and of polar masses 5, the faces of the same name of the magnets being opposite. A collar 6 made of a material which is a good conductor of heat, copper for example, encircles the focusing device; it is crossed by channels 7 where the cooling fluid which is generally a liquid circulates. As already mentioned, this arrangement of the cooling channels does not ensure effective cooling of the delay line because the thermal resistance between the line and the channels is high: the focusing device is generally not soldered on the sheath 3 and the thermal resistance of the focusing device is important.

In FIG. 2, the collar 6 supporting the cooling channels 7 is adjusted on the sheath 3. The collar and the channels must be made of magnetic material and good conductor of heat, copper for example. The focusing device, consisting of permanent magnets 4 and polar masses 5 encircles the flange 6. As has been said previously, this arrangement decreases, compared to the previous one, the thermal resistance between the line 1 and the channels 7; it therefore improves the cooling of the line, but it has the disadvantage of making it more difficult and sometimes impossible, the production of the focusing device by permanent magnets.

According to the invention, the cooling fluid of the delay line, circulates in channels formed by the space between two sheaths sealed to this fluid, having for axis the axis of the line. A first sheath plays the role filled in the arrangements previously described by the cylindrical sheath 3: it is non-magnetic and ensures the vacuum tightness achieved in its volume inside, it is in contact with the face of rods, of dielectric material, which is opposite to one face of these rods in contact with the delay line, these rods being parallel to the axis of the line and regularly distributed around its periphery ; this first sleeve has no contact with the delay line. The first sheath according to the invention is distinguished from the sheaths 3 known by its section which is not necessarily circular. The second sleeve contains the first with which it is in contact at different points constituting the separation between the channels in which the cooling fluid circulates.

The second sheath is generally a cylinder, made of non-magnetic material, on which is mounted a focusing device by permanent magnets. The circular section of this second sheath allows the use of permanent magnet washers, this shape of the magnets being necessary for the proper focusing of the electron beam.

FIG. 3 shows, by way of example, a cross section of a delay line, cooled by circulation of fluid according to the invention, the electron beam being focused by permanent magnets.

Let 1 be the delay line which can be helical and 2 rods regularly distributed, generally three in number, made of dielectric material and good conductor of heat.

The rods 2 can be brazed on the line by one of their faces and brazed by their face opposite to that which is brazed on the line to the first sheath 8. The contact between the rods 2 and the line 1 on the one hand, the sheath 8 on the other hand, can also be made by adjusting the sheath 8 on the rods.

In FIG. 3, where three dielectric rods are shown, the first sheath 8 covers the face of each rod opposite the face in contact with the line and then connects two adjacent rods in a straight line, it is therefore substantially triangular. The second sleeve 9 is cylindrical and contains the first with which it is in contact at different points.

The first sheath 8 and the second sheath 9 are made of non-magnetic material, for example copper. The technological realization of the assembly of the two sheaths represented by FIG. 3 can be as follows: two copper tubes, one circular, the other substantially triangular, are brazed simultaneously with the rods 2 and the line 1.

The contact between the two sleeves 8 and 9 can therefore be achieved by brazing, but also by adjusting the cylindrical sheath 9 on the first sheath 8.

The cooling fluid circulating in the channels 10 formed by the space between the sleeves 8 and 9 can be water. When the first sheath 8 is made of non-magnetic material, a good thermal conductor, but not metallic, the cooling fluid must be dielectric.

The focusing device consisting of permanent magnets 4 and polar masses 5 is adjusted on the cylindrical sheath 9.

The thermal resistance between the delay line 1 and the channels 10 where the cooling fluid circulates is obviously lower with the arrangement according to the invention than with the known arrangements. The brazing of the rods on the line and on the first sleeve contributes to reducing this thermal resistance. The cooling of the delay line according to the invention is therefore effective.

The first sheath 8 does not appreciably modify the microwave characteristics of the delay line as long as the helix-mass capacity remains low. It is known that the introduction between two dielectric rods of a large helix-mass capacity modifies the microwave characteristics and in particular reduces the dispersion of the delay line. If, in order to widen the high frequency band, a reduction in the dispersion of the delay line is desired, the distance d between the line and the wall of the first sheath 8, in the zone where it is not in contact with an electric rod, must be decreased. It should be noted that this reduction in the dispersion of the delay line is accompanied by a reduction in its efficiency, which is a drawback.

The arrangement of the cooling channels according to the invention increases only slightly (by the thickness of the first sleeve 8) the internal diameter of the focusing device shown in FIG. 1. Thus the drawbacks linked to the arrangement shown in the figure are avoided. Figure 2. The arrangement according to the invention of the cooling channels of a delay line makes it possible to reduce the bulk of the tube required by the arrangements of known cooling channels by 30 to 40%: this reduction in volume is significant, all the more so since these tubes are frequently airborne.

The cooling channels 10 are connected to circuits for supplying and discharging the cooling fluid. These connections can be made by piercing the focusing system. It is however more advantageous to place them between the flanges of the tube, next to the barrel which produces the electron beam and next to the collector which receives this beam.

In Figure 4 is shown a longitudinal section of an alternative delay line cooled by fluid circulation according to the invention.

In this variant, the second sleeve, the role of which is to seal the cooling fluid and to ensure, when the focusing is done by permanent magnets, to the line assembly, first sleeve, cooling channels, an envelope cylindrical which supports the focusing device, is modified. The second sheath, shown in Figure 4 where it is generally identified by 12, has the originality of containing the polar masses 5 of the focusing device by permanent magnets. The second sheath 12 is constituted by an alternating sequence along the axis of the delay line of cylinders made of non-magnetic material 11, for example of copper and cylinders made of magnetic material, welded end to end. The cylinders of magnetic material carry in their center a collar in ma magnetic material also and constitute the polar masses 5 of the focusing device. Washers of permanent magnets 4 are inserted between two successive flanges, the faces of the same name of the magnets being opposite.

The second sheath 12, like the second sheath 9, can be in contact with the first sheath 8 by brazing or simply by adjustment on the first sheath 8.

This variant has the advantage of reducing the internal diameter of the focusing device, therefore that of the permanent magnet washers 4: at high frequencies, bands I and J for example, we have seen that it is advantageous to reduce this as much as possible. diameter. This variant also has the advantage of further contributing to the reduction in volume of the microwave tube.

Claims (8)

1. Delay line, for microwave tubes, cooled by fluid circulation, ensuring the interaction between an electron beam and an electromagnetic wave propagating on the line, the electron beam being focused along the line axis by a focusing device, characterized in that the cooling fluid circulates in channels (10), constituted by the space between two sleeves, impervious to this fluid, having as axis the axis of the delay line (1) , the first sheath (8) of non-magnetic material being in contact with the face of rods (2) which is opposite to one face of these rods in contact with the delay line, these rods, of dielectric material, being parallel to the axis of the line and regularly distributed around its periphery, this first sheath having no contact with the delay line and ensuring the vacuum tightness produced in its internal volume, the second sheath containing the first with which it is in contact in different points constituting the separation between the channels (10) in which the cooling fluid circulates. 2. delay line, cooled by fluid circulation, according to claim 1, characterized in that the second sheath (9) is a cylinder, made of non-magnetic material, on which is mounted a focusing device by permanent magnets consisting of a alternating sequence along the axis of the line (1) of polar masses (5) and permanent magnets (4), the faces of the same name of the magnets being opposite. 3. delay line, cooled by fluid circulation, according to claim 1, characterized in that the second sheath (12) consists of an alternating series along the axis of the delay line (1) of cylinders made of non-magnetic material (11) and cylinders of magnetic material, welded end to end, the cylinders of magnetic material carrying in their middle a flange of magnetic material also and constituting the polar masses (5) of the focusing device by permanent magnets, this device also comprising permanent magnet washers (4) inserted between two successive flanges, the faces of the same name of the magnets being opposite. 4. delay line, cooled by fluid circulation, according to one of the preceding claims, characterized in that the contact between the rods (2) and the delay line (1) on the one hand, and the first sleeve ( 8) on the other hand is provided by a solder. 5. Delay line, cooled by fluid circulation, according to one of the preceding claims, characterized in that the contact between the first sleeve (8) and the second sleeve is provided by a solder. 6. Microwave tube comprising a delay line, ensuring the interaction between an electron beam and an electromagnetic wave propagating on the line, the electron beam being focused along the axis of the line by a focusing device, characterized in that this delay line is cooled by circulation of fluid according to one of the preceding claims. 7. Microwave tube according to claim 6, characterized in that the connections between the channels (10), where the coolant circulates, and the supply and discharge circuits of this fluid are made through the focusing device . 8. Microwave tube according to claim 6, characterized in that the connections between the channels (10), where the cooling fluid circulates, and the circuits for supplying and discharging this fluid, are made between the flanges of the tube, next to the barrel producing the electron beam and next to the collector receiving this beam.

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