JPH0361297B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to high power microwave electron tubes based on the principles of electron cyclotron masers, such as gyrrotrons, gyroklystrons and gyroscope traveling wave tubes.

So-called electron beam gyroscopes such as gyroscopes, gyroclystrons, and gyroscope traveling wave tubes generate high-power electromagnetic waves by utilizing the combination of the TE mode of a high-frequency circuit and the cyclotron mode of an electron beam. High frequency circuit is TE
It is a circular waveguide or cylindrical cavity in which modes are excited, and the electron gun forms a hollow beam in which the lateral beam energy is sufficiently larger than the beam energy in the tube axis direction, and the variation in lateral beam energy is small. A magnetron type is used. Frequency ω of TE mode of high frequency circuit
and the cycloton frequency ω _c of the electron beam are n
When the synchronization condition _ωnωc is satisfied, where ωnωc is an integer, a strong interaction occurs and a high-power electromagnetic wave is generated in the high-frequency circuit. This kind of interaction using the cyclotron motion of the electron beam allows the dimensions of the electron beam and high-frequency circuit to become large compared to the wavelength, and the current power of conventional traveling wave tubes and klystrons in the millimeter wave band can be increased. Density problems can be avoided.

According to the prototype results of the gyrrotron reported so far, a shot pulse output of 200 kW has been obtained in the 28 GHz band with a high efficiency of more than 30%, and the electron beam gyroscope device can be used as a large electron source in the millimeter wave to submillimeter wave band. Expectations are high from all quarters. In particular, the ability to generate large amounts of power with high efficiency in the millimeter wave band is attractive as a means of adding heat to plasma in fusion reactors. However, for plasma additional heat, the pulse width is 0.1
Long pulse operation or continuous wave operation of about ~10 seconds is required, and there are many technical problems that must be solved in order to realize such an electron beam gyro device, and active research is being carried out in various fields. being done.

The most important technical issue is the stabilization of the cathode temperature. As mentioned above, in the electron gun of an electron beam gyro device, in order to increase the lateral beam energy and reduce the variation in beam energy, the cathode is used in a temperature limited region, and the amount of electron radiation, that is, the beam current, is controlled by the cathode temperature. It's in control. Porous tungsten impregnated with barium is used as the cathode material for electron beam gyroscopes because of its mechanical machining accuracy and high current density, and the cathode temperature is selected to be around 850°C. There is. The heater power required to maintain this cathode temperature varies depending on the size of the cathode, but there are several
It is 10W.

In long pulse or continuous wave operation,
There is a serious problem that the cathode is heated by energy other than the heater power, and the cathode temperature rises too much, causing the beam current to increase rapidly and causing the electron beam gyroscope to run out of control.In extreme cases, the heater may break. Ta. Microwave Systems News Volume 7, a famous magazine published in the United States in November 1977
The article “Gyrotron-reborn” in the November issue, item 75
tubeis a millimeter powerhouse” (TF
Godlove, VLGranatstein) discloses a prior art technique in which an electromagnetic wave attenuator is provided between an electron gun and a high frequency circuit to prevent the cathode from being heated by high frequency power. However, even if the heating of the cathode by high-frequency power is prevented, when the pulse width of the beam voltage is expanded, the beam current suddenly increases, making it difficult to make long pulses or continuous wave operation of the electron beam gyro device. There is.

An object of the present invention is to realize long pulse or continuous wave operation of an electron beam gyro device by stabilizing the cathode temperature.

In this invention, ions ionized by an electron beam are accelerated toward an electron gun electrode with a negative potential.
This study focused on the fact that the kinetic energy lost during the collision is converted into heat, which increases the cathode temperature. That is,
A normal gyroscope device uses an ion pump to generate 10 ^-8 ~
A vacuum level of 10 ^-9 Torr is maintained, and it is known that the main component of the residual gas is hydrogen molecules.
Hydrogen molecules in such residual gas have energy
When bombarded with an electron beam of about 80 keV, ionized hydrogen ions are accelerated toward the electron gun electrode at a negative potential, and the impact energy reaches several tens of W in continuous wave operation. This is approximately the same energy as the heater power, and it was found that even if heating by high-frequency power was prevented, the cathode temperature would rise due to heating by this ion bombardment, making the operation of the electron beam gyro device unstable.

The electron beam gyro device of the present invention provides an ion barrier electrode between an electron gun and a high-frequency circuit, and by applying a voltage 200 to 500 V higher than that of the high-frequency circuit to this ion barrier electrode, electron ions drift toward the electron gun. In addition, by providing an ion drain electrode between the high frequency circuit and the collector electrode and applying a voltage 200 to 500 V lower than the high frequency circuit and collector electrode to this electrode, ionized ions can be prevented from entering the electron beam gyroscope. This prevents accumulation and prevents heating of the cathode due to ion bombardment.

Yet another advantage of the present invention is that the insulating gap created to provide the ion barrier electrode and the ion drain electrode acts as a so-called mode filter that absorbs unnecessary modes generated within the electron beam gyro device.

According to FIG. 1, an overall view of a gyrrotron 1 embodying the present invention is shown, and the figure shows an electron gun assembly 2, an ion barrier electrode 3, a high frequency circuit 4,
Ion drain electrode 5, collector 6 and output window 7
A structure in which the output waveguides 8 and 8 are aligned along the tube axis 16 is shown.

The electron gun assembly 2 is configured such that an electron gun electrode 11 including a ring-shaped cathode 12 and a heater 13 and a ring-shaped anode 14 are coaxial with respect to a tube axis 16 . As a typical value, a power of 10V, 5A is supplied to the heater 13 by the heater power supply 21, and a -
A beam voltage of 80 kV is applied, and the anode 14 has a -
An accelerating voltage of 54 kV is applied. Electron gun solenoid 9, energized by a suitable DC power source, generates a DC magnetic field along tube axis 16 passing through electron gun electrode 11 and anode 14. An electron beam having a hollow spiral motion is formed from the electron gun assembly 2 by the interaction of the DC voltage applied between the cathode 12 and the anode 14 and the DC magnetic field set by the electron gun solenoid 9. be ejected.

The hollow electron beam is accelerated into an ion barrier electrode 3 and a high frequency circuit 4. The main solenoid 10 generates a high intensity DC magnetic field along the high frequency circuit 4. The magnetic field strength is large enough to cause the hollow electron beam to spiral at a relativistic electron cyclotron frequency close to the millimeter wave operating frequency of tube 1.

The high frequency circuit 4 includes a cylindrical cavity 15 in its center that resonates in the TE ₀₂₁ mode at the operating frequency of the tube 1, and has a small diameter part on the electron gun side where the TE ₀₁ mode is cut off, and a cylindrical cavity 15 on the collector side. The diameter is made large so that the TE _po mode can propagate. By adjusting the main solenoid 10 so that the angular frequency of the cyclotron mode of the hollow electron beam is synchronized with the TE ₀₂₁ mode in the cylindrical cavity 15, there is a gap between the electron beam and the electromagnetic waves in the cylindrical cavity 15. A strong interaction occurs, and the kinetic energy of the electron beam is converted to electromagnetic wave energy, generating high-power electromagnetic waves. The details of the interaction between the hollow electron beam and the TE mode electromagnetic waves are described in the above-mentioned paper. The high-power electromagnetic waves generated inside the cylindrical cavity 15 are guided through the collector 6 and the output window 7 from the output waveguide 8 to an external load.

On the other hand, the hollow electron beam is diverged by the space charge force of the electrons themselves in the region of the collector 6 where the magnetic field from the main solenoid 10 disappears and is captured by the collector 6. At this time, most of the kinetic energy of the electron beam is consumed on the surface of the collector 6 as thermal energy. Therefore, the surface temperature of the collector 6 has reached about 400° C., and gas molecules are easily released from the surface of the collector 6. Gas molecules liberated from the high-temperature metal surface collide with a high-energy electron beam and become ionized.

The ionized ions are trapped inside the hollow electron beam whose potential is lowered by space charges and drift toward the lower potential in the tube axis direction. In the conventional gyrrotron, the potential distribution on the tube axis is like the curve 30 shown by the dotted line in FIG. It had the disadvantage of making it unstable. On the other hand, the gyrrotron 1 of the present invention is equipped with an ion barrier electrode 3 and an ion drain electrode 5, and has a bias power supply 23 and an ion drain electrode 5, respectively.
Since +300V and -300V are applied at 24, the potential distribution on the tube axis has a high potential area between the electron gun assembly 2 and the high frequency circuit 4, as shown by the solid line 31 in FIG. , a low potential portion is created between the high frequency circuit 4 and the collector 6. Therefore, the ions ionized inside the collector 6 are captured by the ion drain electrode 5 before entering the high frequency circuit 4, and the ions ionized inside the high frequency circuit 4 are bounced off by the high potential part of the ion barrier electrode 3 and ionized. Since it is captured by the drain electrode 5, the electron gun electrode 1
The ion bombardment described in No. 1 can be prevented, and the cathode temperature can be stabilized.

Furthermore, since the resonance mode of the cylindrical cavity 15 is TE ₀₂₁ , the high power electromagnetic waves generated inside propagate from the output waveguide 8 to the external load as TE ₀₂ mode, but due to mismatch in the external load or waveguide reaching the external load. Due to deformation of the tube, etc., the mode-resolved reflected waves return to the Gyrrotron 1. Among the mode-decomposed reflected waves,
Other than the TE _po mode component, there is a tube wall current component in the tube axis direction, so the insulating ceramic 17 between the electrodes
Absorption occurs at portions 18, 19, and 20 and is attenuated. Furthermore, since the inner diameter of the high frequency circuit 4 is made small so that the TE ₀₁ component is cut off between the cylindrical cavity 15 and the electron gun assembly 2, heating of the electron gun electrode 11 due to high frequency power can be prevented.

As described above, according to the gyrrotron of the present invention, it is possible to not only prevent heating of the cathode due to high frequency power but also to prevent the temperature rise of the cathode due to ion bombardment.
The cathode temperature can be stabilized during continuous operation.

The invention is capable of various modifications other than the embodiments described here. For example, the same effect can be expected by simply providing an ion drain electrode and an ion barrier electrode, respectively.

[Brief explanation of drawings]

FIG. 1 is an overall view of an embodiment of a gyrrotron embodying the present invention, and FIG. 2 is a curve diagram showing a comparison of the potential distribution on the tube axis in the gyrrotron according to the prior art and the embodiment shown in FIG. 1... Gyrotron, 2... Electron gun assembly,
3...Ion barrier, electrode, 4...High frequency circuit, 5
...Ion drain electrode, 6...Collector, 7...
... Output window, 8 ... Output waveguide, 9 ... Electron gun solenoid, 10 ... Main solenoid, 11 ... Electron gun electrode, 12 ... Cathode, 13 ... Heater, 14
... Anode, 15 ... Cylindrical cavity, 16 ... Tube shaft, 1
7, 18, 19, 20...Insulating ceramic, 21
... Heater power supply, 22 ... High voltage power supply, 23 ... Bias power supply for ion barrier, 24 ... Bias power supply for ion drain, 30, 31 ... Potential distribution curve on the tube axis.

Claims (1)

[Scope of Claims] 1. An electron gun assembly for forming and emitting an electron beam that performs a hollow spiral motion, a high frequency circuit that includes a circular waveguide or a cylindrical cavity along the hollow electron beam, and In an electron beam gyro device in which collectors for capturing are arranged and an output window and an output waveguide are attached to the tip of the collector, a bias is applied between the electron gun assembly and the high-frequency circuit to a positive potential with respect to the high-frequency circuit. 1. An electron beam gyro device, characterized in that the electrode is insulated. 2. An electron gun assembly that forms and emits an electron beam that performs a hollow spiral motion, a high frequency circuit that includes a circular waveguide or a cylindrical cavity along the hollow electron beam, and a collector that captures the electron beam are arranged. , an electron beam gyro device having an output window and an output waveguide attached to the tip of the collector, characterized in that an electrode is provided adjacent to the collector and negatively biased with respect to the collector, and the electrode is insulated. Electron beam gyro device. 3. An electron gun assembly that forms and emits an electron beam that performs a hollow spiral motion, a high frequency circuit that includes a circular waveguide or a cylindrical cavity along the hollow electron beam, and a collector that captures the electron beam are arranged. In an electron beam gyro device in which an output window and an output waveguide are attached to the tip of the collector, an electrode biased to a positive potential with respect to the high frequency circuit is provided between the electron gun assembly and the high frequency circuit, and the high frequency An electron beam gyro device characterized in that an electrode biased to a negative potential with respect to a high frequency circuit is provided between the circuit and the collector, and each of the electrodes is insulated.