JPS592137B2 - straight type klystron - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high performance linear klystron using a harmonic cavity as one of the cavities.

Several inventions have been made to obtain highly efficient linear klystrons.

For example, according to Japanese Patent Application Laid-Open No. 46-5765, with a configuration of only a fundamental wave cavity, the drift length between the gap center of the final intermediate cavity and the gap center of the intermediate cavity immediately upstream thereof is reduced by plasma wavelength λ, 1/4 times or more, 5/12 times or less, ideally 1/3 times, and the space charge force generated in the electron beam in this long drift tube is effectively used to focus the electron beam more strongly. There are some things that are really designed to improve efficiency.

Here, the reduced plasma wavelength λ should be 2πuo/ωg, right? be done.

Note that U is the DC velocity of the electron beam, ω. is the reduced plasma angular frequency.

Electron beam t-1 subjected to velocity modulation during small signal
- Maximum density modulation occurs at a point where the drift length is 1/4λ, beyond which the fundamental current component in the beam decreases.

And as the signal becomes larger, the point that produces the maximum of the fundamental current component will be much smaller than i/4 A y.

Therefore, in order to achieve high efficiency, it is necessary to use an unusually long drift tube of about 1/3 λ.

Therefore, the total length of the tube is longer than that conventionally used.

This means that pipe manufacturing equipment becomes larger, handling becomes more difficult, and
This results in an increase in the size of the entire device including the pipes, which is more inconvenient than the advantage of higher efficiency when viewed as a whole.

In addition, as described in Japanese Patent Publication No. 47-32386, there is also a proposal to use a second harmonic cavity in addition to the fundamental cavity to strongly concentrate the electron beam and improve efficiency. be.

However, according to this configuration, in the case of a cavity arrangement like the example described in the same publication, a total of five cavities, four fundamental wave cavities and one harmonic wave cavity, are used, and moreover, it is very narrow. Despite the band, the gain is very low at less than 20 dB.

Therefore, in order to obtain high efficiency and high gain with this configuration, it is considered that one or two cavities must actually be provided further upstream.

In this case, as the number of cavities increases, manufacturing and adjustment becomes extremely difficult, and the overall length of the tube is not much different from that using the long drift tube described above, resulting in similar problems.

The purpose of this invention is to provide a high-efficiency, high-gain tube in which the total length of the tube is much shorter than conventional ones by properly arranging the fundamental wave cavity and the harmonic cavity in a straight klystron. It is something to do.

The present invention will be explained in detail below with reference to the drawings.

The linear klystron in the present invention is a 5-cavity linear klystron with an electron gun section 11 that generates an electron beam.
, an interaction section 12 that converts the direct current energy of the electron beam into high-frequency energy, and a collector 3 that collects the spent electron beam, and further includes a focusing magnetic field surrounding the interaction section 12 to focus the electron beam. A generator (not shown) is provided.

The interaction part L is an input cavity 21 into which high frequency power is introduced.
, a pre-intermediate cavity 22 immediately downstream thereof in the electron beam stream n, and an output cavity 25 from which the high-frequency power is extracted.
It consists of a final stage intermediate cavity 24 immediately upstream of the ninth stage, and a second high frequency cavity 23 further in the middle.

The second harmonic cavity 23 is tuned around the second harmonic frequency corresponding to the center operating frequency f of this klystron, except that the cavity is tuned around the center operating frequency f 2 .

Therefore, these will be referred to as fundamental wave cavities, and each cavity has a drift tube gap within each of them.

Therefore, the second high frequency cavity 2 located third from the upstream
3, the gap center 23a is the intermediate cavity 22, 24 before and after it.
Arranged midway between the gap centers or shifted downstream from the midpoint.

In other words, the distance t 1 between the gap centers 22a, 23a, and 24a of these cavities is set to be equal to or smaller than t 2 .

Further, the tuning frequency of each cavity is set as follows.

Tuning frequency f of input cavity 21, immediately downstream cavity 22
f of the output cavity 25 and that of the output cavity 25 f is the center operating frequency f in the case of narrowband amplification.

In the case of broadband amplification, a staggered tuning method is used in which the frequency is slightly shifted up or down from f.

Therefore, the tuning frequency f of the second harmonic cavity 23 in the middle is set to a frequency slightly lower than the second harmonic frequency 2f, and the tuning frequency f of the second harmonic cavity 23 immediately downstream thereof is set to a frequency slightly lower than the operating frequency f. set to a high frequency.

The state of the electron beam in such an arrangement will be explained with reference to FIG.

FIG. 2 is a computer simulation of the large signal operation of the linear klystron shown in FIG. 1 using a disk model.

That is, this is a plot of the electron phase and the distance normalized by the reduced plasma wavelength along the beam path, and is equivalent to an ampoule gate diagram.

In this case, 24 electrons uniformly distributed over one period of the fundamental frequency are tracked.

The position of the gap center of each cavity of the interaction part is indicated on the horizontal axis.

First, a high-frequency electric field is generated in the cavity gap according to the high-frequency power introduced into the input cavity, and the electron beam is velocity-modulated according to this electric field.

Since there is no high-frequency electric field in the drift tube, the electrons are concentrated in response to the velocity modulation given by the manual cavity while running in the section between the cavities, that is, in the drift tube.

As a result, when the focused electron beam passes through the second cavity gap 22a, a high frequency electric field is generated therein, and the electron beam is further modulated and focused.

When the electron beam thus concentrated reaches the third cavity from upstream, that is, the harmonic cavity, the cavity is tuned to a frequency slightly lower than twice the operating frequency f of the tube, as described above. Because the electron beam is located midway between the front and rear intermediate cavities or downstream of the midway, the electron beams have been moving so as to converge at a certain phase, but this harmonic When passing through the gap in the wave cavity, the wave undergoes a sufficiently large velocity modulation, and after passing, it is divided into two groups, each of which converges in a different phase.

If you look at this as a whole, it will be subject to speed modulation that is more like being swarmed, but since this harmonic cavity is placed relatively downstream between the front and rear cavities, it will reach this harmonic cavity. Electrons that have already clustered well and are in a phase that has clustered well up to that point swarm a little, and electrons that are in a phase that is not clustered undergo velocity modulation due to the clustering.

As a result, when the electron beam reaches the fundamental wave cavity immediately downstream, the electron beam is very well concentrated and its velocity is also uniform.

This situation is the position of the fourth cavity in Figure 2.

24a, about 85% of the electrons exist almost uniformly in a range of about 0.4 times one period, and furthermore, the velocity is almost uniform, which means that all the slopes of the graph are almost parallel to the axis. It is clear from this.

In order to obtain high efficiency, it is necessary that the electron beam entering the output cavity is well-focused and has as uniform a velocity as possible, but in this invention, the fourth cavity, that is, the harmonic cavity. The cavity immediately downstream of is tuned to a higher frequency than the klystron's operating frequency f and thus serves to focus the electron beam more strongly.

In this way, the efficiency coefficient F=I/I at the position 25a of the output cavity achieves a high value of 1.7 or more, as shown in FIG.

Here ■ is the fundamental wave current component in the electron beam, ■.

is the DC beam current.

FIG. 3 is a plot of the efficiency coefficient of the invention, and it can be seen that it is 1.74 at the output cavity position.

Here, its superiority is obvious when compared with the prior art example (Japanese Patent Publication No. 47-32386) described above.

In other words, in this conventional example, a cavity tuned to the second harmonic is provided further upstream, and in that case, as mentioned above, the second harmonic cavity is effective unless the electron beam is concentrated considerably by the time it reaches there. does not work.

Therefore, if there is only one fundamental wave intermediate cavity installed upstream of this harmonic cavity, the electron beam must be concentrated considerably with just one cavity, so a large amount of high-frequency input power is required, and the gain of the tube is therefore reduced. It gets lower.

In order to obtain a sufficiently high gain for practical use, two or more fundamental wave cavities are required.

In contrast, in the present invention, there are five cavities, and the second harmonic cavity is installed third from the upstream, and the mutual positions and tuning frequencies of the cavities are set as described above.
A high gain of B or more can be achieved with a minimum number of cavities, and the total length of the tube can be shortened.

[Brief explanation of drawings]

Figure 1 is a schematic diagram showing an embodiment of the present invention, and Figure 2 is a plot of the electron phase and normalized distance in this invention, showing how the electrons cluster along the beam path. Figure 3 shows the efficiency coefficient F = I of this invention.
It is a characteristic diagram in which /I and normalized distance are plotted. 11...Electron gun section, 12...Interaction section, 13...Collector, 21...Manual cavity, 22...Front Intermediate cavity, 23...
・Second harmonic intermediate cavity, 24... Fundamental wave final stage intermediate cavity, 25... Output cavity, 21a to 25a.
・・・・・・Center of each cavity gap.

Claims (1)

[Scope of Claims] 1. A human powered cavity, an intermediate cavity having two fundamental wave cavities and one second harmonic cavity, and an output cavity,
The harmonic cavity is placed third from the upstream side of the electron beam, and the gap center position is placed in the middle between the gap centers of the front and rear intermediate cavities tuned to the fundamental wave, or downstream from the middle. A 5-cavity linear klystron featuring: 2 The tuning frequency f of the second harmonic cavity is the operating frequency f
The klystron according to claim 1, wherein the klystron is set at a frequency slightly lower than twice the frequency of the klystron. 3. The klystron according to claim 1, wherein the tuning frequency f of the fundamental wave cavity immediately downstream of the second harmonic cavity is set to a higher frequency than the operating frequency f.