JPS5851655B2 - multi-cavity klystron - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a multi-cavity type high-efficiency narrowband klystron in which the dimensions of the tube and the overall length in the tube axial direction are shortened.

The conventional technology for increasing the efficiency of multi-cavity klystrons is
There are two methods: one that utilizes the second harmonic crowding effect, and the other that reduces the influence of the supergroup effect generated by the interaction gap electric field in the cavity during the electron beam gathering.

One of the latter methods, as described in Japanese Patent Application No. 47-38897, is to reduce the drift tube immediately downstream of the pre-intermediate cavity that causes a supergroup effect on the electron beam, so that the plasma angle is within 90 degrees.
It is larger than other drift tubes, giving it enough length to recover the supergroup in the electron beam, and one more.
The first method is to eliminate the occurrence of supergroups using a cavity tuning method, as described in Japanese Patent Application No. 47-106800.

When these conventional technologies are applied to continuous wave output wideband klystrons for UHF-TV broadcasting and communications, the conversion efficiency at saturated output can be increased to 6.5% without increasing the total length of the tube.
A value of 0% or more can be easily achieved.

However, for multi-cavity klystrons with good frequency characteristics in a narrow band, this method did not necessarily provide the best efficiency.

One method for obtaining the second harmonic grouping effect is to install a post-intermediate cavity and a pre-intermediate cavity immediately upstream thereof, as described in Japanese Patent Application Laid-Open No. 46-5765 and Japanese Patent Application No. 46-24221. A drift tube with a reduced plasma angle of 120 degrees is placed between the cavity and the long drift tube to utilize the second harmonic component of the intermediate charge electric field generated in the electron beam. , Japanese Unexamined Patent Publication No. 46-5766, Patent Application No. 46-2
4222, there is a method of adding a second harmonic resonant cavity.

One of the problems with the conventional technology that uses the second harmonic crowding effect is that it requires the use of an unusually long drift tube with a reduced plasma angle of 120 degrees and a second harmonic resonant cavity, which requires the entire length of the tube. becomes too large.

The large overall length of multi-cavity klystrons not only increases the size of the tube application, but also makes it difficult to utilize permanent magnet focusing devices.

The importance of using a permanent magnet as a focusing device has recently been recognized from the perspective of overall efficiency improvement, as it allows the need for an electromagnetic power source.

Therefore, a method for obtaining the second harmonic grouping effect without increasing the total length of the pipe is desired.

An object of the present invention is to provide a method for generating a second harmonic grouping effect and achieving high efficiency in a narrowband klystron in which the total length of the tube is limited to a short length.

According to the invention, a multi-cavity klystron has an input cavity, one or more pre-intermediate cavities, and two or more post-cavity cavities located downstream of the pre-intermediate cavity along the beam path. It consists of a rear intermediate cavity, one output cavity as an output circuit means, and a plurality of drift tubes between each cavity, and a rear intermediate cavity one before counting from the output cavity. The length of the drift tube between the two preceding intermediate cavities is larger than the length of other drift tubes, and is configured such that the reduced plasma angle is from 70 degrees to 90 degrees. .

In addition, since the tube has a narrow band gain vs. frequency characteristic, the input cavity, pre-intermediate cavity, and output cavity are tuned to frequencies within ±0.5% of the tube's passband center frequency. The input cavity and the pre-intermediate cavity move to increase the tube's gain, while the post-intermediate cavity is tuned to a high frequency within +5% of the passband center frequency, increasing the tube's gain. Work to increase efficiency.

Since the gain is increased in the input cavity and the front intermediate cavity, the magnitude of the high frequency voltage generated in the interaction gap of the rear intermediate cavity can easily reach a value of 20% or more of the DC beam voltage. .

If the magnitude of the high-frequency voltage generated in the interaction gap is more than 20% of the DC beam voltage, the length of the subsequent drift tube will be reduced.In the plasma angle range of 70 degrees to 90 degrees, the space in the electron beam By using the second harmonic component of the charge electric field, it is possible to obtain a second harmonic clustering effect.

FIG. 1 shows a multi-cavity klystron according to an embodiment of the present invention.

A multi-cavity klystron 1 according to the present invention includes an electron gun assembly 2 for forming and emitting an electron beam 3, and a collector electrode 4 disposed at the end of a long beam path.

A semi-coaxial human powered cavity 5 is arranged at the upstream end of the electron beam 3, and the input cavity 5 is excited with high frequency energy via an input coupling means 6.

Further, the input cavity 5 is arranged so that its tuning frequency is adjusted to a frequency of 0.1% of the band center frequency by adjusting the tuning frequency variable means, for example, the tuning end plate 21.
It also includes an interaction gap 7 defined between the free ends of the semi-coaxial cavity, and the high frequency voltage v1 generated in this interaction gap 7 modulates the velocity of the electron beam 3.

The first drift tube 8, having a length of 48 degrees at a reduced plasma angle, surrounds the electron beam 3 in the downstream area of the input cavity 5, providing an area free of external high-frequency electromagnetic fields;
Within this area the electrons drift with a velocity determined by the magnitude of the velocity modulation imposed by the input cavity 5, so that a density modulation, ie electron crowding, occurs.

When this density-modulated electron beam 3 passes through the interaction gap 10, it induces a high-frequency current in the pre-intermediate cavity 9.

Now, if this front intermediate cavity 9 is tuned to +0.1% of the band center frequency by adjusting the tuning frequency variable means 22, the cavity impedance at the band center frequency will be a large value, and the front intermediate cavity 9 will be tuned to +0.1% of the band center frequency. Even if the high frequency current induced in the intermediate cavity 9 is minute, the amplitude of the high frequency voltage v2 generated in the interaction gap 10 can be increased.

This means that a high gain is obtained in the input cavity 5 and the pre-intermediate cavity 9.

Although the high frequency voltage V2 is delayed in phase by about 60 degrees compared to (1), it further modulates the velocity of the electron beam 3 concentrated within the first drift tube 80 area.

The second drift tube 11 provides a 40 degree drift space at a reduced plasma angle for the velocity modulation applied to the electron beam 3 by the high frequency voltage V2 to change into density modulation.

In the area of the second drift tube 110, the density-modulated electron beam 3 induces in the interaction gap 13 a high-frequency current with an amplitude of about 20% of the DC beam current in the first downstream intermediate cavity 12. do.

At this time, a high frequency voltage V3 generated in the interaction gap 13
The rear intermediate cavity 12 is adjusted to the center of the passband of the tube by adjusting the tuning frequency variable means 23 so that the amplitude of is 20% of the DC beam voltage and the phase is almost the same as 2. However, +1.5% is tuned to a much higher frequency.

The high frequency voltage (3) further strongly modulates the velocity of the focused electron beam in the area of the second drift tube.

Since the third drift tube 14 provides a long drift space of 80 degrees with a reduced plasma angle in the downstream area of the first post-intermediate cavity 12, a strongly velocity-modulated electron beam 3
In the process of density modulation in the space charge field, the second harmonic component of the space charge electric field becomes stronger, resulting in a second harmonic clustering effect.

The second harmonic crowding effect acts to direct the electrons left behind between the crowd centers toward the crowd center by velocity modulation due to the interaction gap electric field, and the velocity is modulated by the high frequency voltage V4 generated in the interaction gap 16. At this time, a very dense cluster is obtained in the fourth drift tube 17.

The 20th rear intermediate cavity 15 is tuned to a frequency that is +2.5% higher than the center of the passband of the tube by adjusting the tuning frequency variable means 24.

The length of the fourth drift tube 17 is chosen to be 32 degrees at the reduced plasma angle to maximize the aggregation of the electron beam 3 in the interaction gap 19 of the output cavity 1B.

The output cavity 18 is tuned to the passband center frequency of the tube by adjusting the tuning frequency variable means 25, and the output wave energy extracted from the electron beam 3 is transferred to the coupling means 20.
is sent to the load via.

7 at reduced plasma angle with reference to FIGS. 2 and 3.
We will describe in detail how the second harmonic clustering effect due to the space charge electric field in the electron beam can be obtained in the length of the drift tube from 0 degrees to 90 degrees.

FIG. 2 shows the magnitude of the high-frequency voltage IVI generated in the interaction gap of the cavity and the DC beam voltage V.

FIG. 3 is a diagram showing changes in the electron concentration in the electron beam in the tube axis direction, using the ratio IVI/Vo as a parameter.

Here, the magnitude of the fundamental wave component of the high-frequency current in the electron beam is 1■11 and the DC beam current I.

The degree of electron gathering is expressed using the ratio I111/Io, and the length in the tube axis direction is expressed by the reduced plasma angle θ (normalized drift length).

The magnitude of the high frequency voltage generated in the interaction gap of the cavity IV
When I is small and IVI/Vo=0.02, θ=
The maximum value of I 111/Io is obtained at 90 degrees.

l V I/V. When = 0°2, III/I
It can be seen that the maximum value of o is at θ=60 degrees, and as the magnitude of the high frequency voltage IVI increases, the point where the maximum value of l 111/Io is obtained shifts to the smaller θ.

FIG. 3 is an electronic phase diagram for viewing in detail the state of the cluster when IVIVo=0.2 in FIG.

As in Fig. 2, the horizontal axis represents the length in the tube axis direction as the normalized drift length θ, and the vertical axis represents the time when a representative electron arrives at a certain point on the tube axis. frequency phase ψ
(electronic phase).

The representative electrons, which were arranged at equal intervals between ψ = 0 and 360 degrees at θ = 0 degrees, form a cluster centered at ψ = 180 degrees, since they are each given a velocity determined by the high frequency voltage. The particles move in such a manner that a dense cluster is formed near θ=60 degrees.

Since the space charge force that repels the electrons gathered in high density acts on each other, this time from θ = 80 degrees to φ = 9
They begin to move in such a way that a cluster is formed with two centers at 0 degrees and 270 degrees.

Since there are two cluster centers between φ=O and 360 degrees, this is the cluster effect of the second harmonic due to the space charge force.

Normally, the magnitude of the high frequency voltage generated in the interaction gap of the trailing intermediate cavity is 20 to 30% of the DC beam voltage, so the magnitude of the high frequency voltage generated in the interaction gap of the trailing intermediate cavity is 20% to 30% of the DC beam voltage. The length of the drift tube between the shells is 70 at reduced plasma angle.
~90 degrees.

First, regarding the lower limit of 70 degrees, as can be seen from Fig. 3 and the above explanation, when + v I /vo = 0.2, the electron beams are concentrated at high density when the drift tube length θ is about 60 degrees. , after that, it begins to spread due to the repulsion of space charges and moves so that θ is centered at two places, 90 degrees and 270 degrees, but it takes a drift tube for the second harmonic to actually form at two places. requires a length of about 70 degrees, which is about 10 degrees longer than 60 degrees.

When the drift tube length exceeds 70 degrees, the concentration of second harmonics increases further, but when the drift tube length exceeds 90 degrees (
Then, the once-concentrated second harmonics begin to spread out, and eventually the second harmonics crowding effect weakens.

Therefore, the clustering effect of the second harmonic is caused by a drift pipe length of 70~
It works best in the 90' degree range.

Finally, using the results of a computer simulation of the large-signal operation of a multi-cavity klystron shown in FIG. 4, we will explain how electron beams cluster due to differences in the length distribution of the drift tube.

A value obtained by normalizing the magnitude of the high-frequency current fundamental wave component in the electron beam of the tube of the embodiment shown in Fig. 1 and a multi-cavity klystron of the conventional design with the same overall length by the DC beam current. is compared as a function of distance in the tube axis direction.

5, 9, 12, 12' in the figure. The position numbered 15.1B corresponds to the axial center position of the interaction gap in the similarly numbered cavity of FIG.

Curve 31 represents the function according to the conventional design, and curve 32 represents the function according to the embodiment of the invention shown in FIG.

This shows that if the third drift tube 14 is made longer than the second drift tube 11, the second harmonic grouping effect can be utilized, so that the conversion efficiency is improved by about 7%.

[Brief explanation of drawings]

FIG. 1 shows a schematic configuration of a multi-cavity klystron according to the present invention, and FIG. 2 shows the magnitude of the high-frequency voltage IVI generated in the interaction gap of the cavities and the DC beam voltage V. Figure 3 is a diagram showing the change in the fundamental wave component of the normalized high-frequency current of the electron beam in the tube axis direction, using the ratio IVI/Vo as a parameter.
Figure 4 is an electron phase diagram to see in detail the state of the clustering when = 0.2, and Figure 4 shows the normalized high-frequency current in the electron beam for comparison between the tube in Figure 1 and a conventionally designed tube. FIG. 3 is a diagram showing the magnitude of the fundamental wave component as a function of the distance in the tube axis direction. Note that 1 is a multi-cavity klystron, 3 is an electron beam, and 5 is a multi-cavity klystron.
is a semi-coaxial human powered cavity, 6 is an input cavity coupling means, 8 is a first drift tube, 9 is a front intermediate cavity, 11 is a second drift tube, and 12 is a first rear intermediate cavity. , 14 is a third drift tube, 15 is a second post intermediate cavity, 1T is a fourth drift tube, 18 is an output cavity, 20 is an output cavity coupling means, 21
．． 22゜23.24, 25 are input cavities, pre-intermediate cavities,
Respective tuning frequency variable means 31 and 32 for the first rear intermediate cavity, the second rear intermediate cavity, and the output cavity are the basics of the normalized high-frequency current in the electron beam in the conventional and the present invention, respectively. Indicates the size of the wave component.

Claims (1)

[Claims] 1. A multi-cavity klystron with a passband of a certain frequency width, including one input cavity with an interaction gap for velocity modulating the electron beam, and an input cavity downstream of said input cavity along the electron beam path. one or more pre-intermediate cavities disposed downstream of said pre-intermediate cavity along a beam path; and two or more post-intermediate cavities disposed downstream of said pre-intermediate cavity along a beam path; an output cavity disposed downstream of the intermediate cavity for extracting output wave energy from the density-modulated electron beam; and a plurality of drift tubes interposed between all the cavities. , the input cavity, the front intermediate cavity, and the output cap are all tuned to a frequency within ±0.5% of the passband center frequency, and the rear intermediate cavity is all tuned to a frequency within ±0.5% of the passband center frequency. %, and the length of one drift tube between said trailing intermediate cavities, with respect to said drift tube length defined by the length between interaction gap centers of each cavity. A multi-cavity klystron characterized in that the length of the drift tube is in the range of 70 degrees to 90 degrees expressed as a reduced plasma angle, and the length of the remaining drift tube is 70 degrees or less expressed as a reduced plasma angle.