RU2044361C1 - Microwave generator - Google Patents

Abstract

FIELD: relativistic microwave devices. SUBSTANCE: device has anode electrode having anode, diaphragm and drift tube, which are connected by galvanic charge. In addition device has cathode electrode, which is mounted inside anode, is coaxial to it and spaced from it. Diaphragm is mounted in parallel to face surface of cathode electrode. Magnetic field excitation system is positioned around perimeter of diaphragm on outer side of tube and spaced from it. In addition device has radiation output system, which is connected to drift tube. First claim of invention described design of magnetic field excitation system having one solenoid with ring from ferromagnetic material which is positioned in plane of diaphragm between solenoid and drift tube and spaced from latter. Second claim of invention describes design of magnetic field excitation system having two solenoids when both solenoids are mounted on equal distance from plane of diaphragm. EFFECT: increased efficiency of generation due to removal from interaction zone of non-phase electrons. 2 cl, 3 dwg

Description

 The invention relates to relativistic microwave electronics and can be used in the development of powerful generators of microwave radiation.

 Powerful microwave radiation generators based on systems with a virtual cathode (VC) are known as vircators and contain an anode electrode consisting of an anode, a diaphragm and a drift tube, a cathode electrode, an axial magnetic field excitation system, and a radiation output device (Grigoryev V. P. Zherlitsyn A.G. Koval T.V. Plasma Physics. 1990, v.16, N 11, p. 1353).

 The generation of microwave radiation in devices of this type is possible only if the VC is formed, that is, when the current in the diode exceeds a certain limiting current of the equipotential region (drift tube), and from the electron acceleration energy in the VC diode, formed in the drift tube, emits portions of charge in turn first forward, then backward.

 Electrons flying forward are called passing electrons. Their presence reduces the efficiency of the generator, since they, accelerating, carry away the energy of the field.

 Electrons returning back are called oscillating: trapped in the oscillatory motion between the real cathode of the accelerator diode and VC, they generate microwave radiation.

[i(t)-i_o]dt (1) где α некоторый коэффициент, зависящий от темпа накопления частиц в потенциальной яме "катод-ВК" и от доли энергии, затрачиваемой электроном на излучение в единицу времени;
t_o момент времени, когда ток в диоде достигнет значения предельного для трубы дрейфа тока i_o.Oscillating electrons in the gap gradually become larger than transit electrons, since the former accumulate in the interaction region, and the latter are immediately removed from it. This is the mechanism of phase separation, which determines a high generation efficiency: if the current in the diode changes with time according to the law ii (t) (Fig. 1a), then the generated power is found by integration
P (t)

[i (t) -i _o ] dt (1) where α is a certain coefficient depending on the rate of particle accumulation in the potential cathode-VC well and on the fraction of the energy spent by the electron on radiation per unit time;
t _{o the} point in time when the current in the diode reaches the limit value for the current drift pipe i _o .

 This dependence is shown in Fig. 1b of curve 1. In principle, there are no restrictions on the amount of generated power, including a mode where the generation power at some point in time exceeds the instantaneous beam power (power efficiency over 100%).

 However, this does not happen in the experiment, since at some point a generation disruption, a sharp power drop, spectrum enrichment and electron flux randomization occur, which is shown in curve 1b in Fig. 1b. This instability is the main drawback in vircators and manifests itself in almost all experiments ( Platt R. et al. Appl. Phys. Lett. 1989, v. 54, No. 13, p. 1215), [3] (Hwang CS et al. J. Appl. Phys. 1991, v. 69, No. 3, p. 1247) and others. The reason for this failure of generation is the accumulation in the VC region of a spatial charge of such magnitude that a breakdown occurs between the VC and the side walls second drift tube, which bypasses the VC.

 This instability does not develop in the reditron of the species of vircator (reflected electron discrimination tube reditron) (Davis H.A. et al. IEEE Trans. On Pl. Sc. 1988, v. PS-16, No. 2, p. 192). The reditron contains an anode electrode, which consists of a galvanically coupled and axially located anode, a diaphragm and a drift tube, a cathode electrode axially located inside the anode and separated by a gap, a diaphragm parallel to the end surface of which has a gap, a magnetic field excitation system in the form of a single solenoid, located along the perimeter of the diaphragm on the outside of the pipe with a gap relative to it, as well as a system for outputting radiation connected to the drift pipe. This generator is the closest in essence to the claimed one and is selected as a prototype for both versions of the proposed device.

 The lack of instability of the breakdown of oscillations in the reditron is due to the special structure of the diaphragm. It is known that the electrons reflected from the VC fly back along somewhat different paths than when moving to the VC. Thus, if we use a diaphragm with a thickness corresponding to the total absorption of electrons and with a circular slot opposite the cylindrical hollow cathode, then the electrons injected into the drift tube through the slot will bounce off the VC and be absorbed by the thick part of the diaphragm.

 This mechanism prevents the accumulation of oscillating electrons in the potential cathode-VC well or, what is the same, the growth of the space charge in the VC region.

 However, for the same reason, the generation power in the reditron cannot grow as in a conventional vircator, which is associated with the artificial suppression of the phase separation mode, that is, in the known reditron (see figv).

P (t) = β [i (t) -i _o ] (2) where β has the same meaning as the coefficient α in the vircator.

 The low generation efficiency is a disadvantage of the well-known reditron.

 For a reditron, the power generation efficiency is an important criterion for the possibility of its practical application. The technical problem is to increase the generation efficiency by at least two times in comparison with the known reditrons.

 The aim of the invention is to increase the efficiency of generation of microwave radiation in a reditron.

 The goal is achieved in that the reditron according to the first embodiment contains an anode electrode consisting of a galvanically connected and axially located anode, a diaphragm and a drift tube, an cathode electrode axially located inside the anode and separated from it by a gap, a diaphragm parallel to the end surface of which has a gap, an excitation system a magnetic field located along the perimeter of the diaphragm on the outside of the pipe with a gap relative to it, as well as a system for outputting radiation connected to the drift pipe, system ma excitation magnetic field is formed as a single coil with a ring of ferromagnetic material arranged in a diaphragm plane between the solenoid and the drift tube with a gap relative to the latter.

 According to a second embodiment of the invention, the reditron contains an anode electrode consisting of a galvanically connected and axially arranged anode, a diaphragm and a drift tube, an cathode electrode axially located inside the anode and separated from it by a gap, a diaphragm parallel to the end surface of which has a gap, a magnetic field excitation system, located along the perimeter of the diaphragm on the outside of the pipe with a gap relative to it, as well as a system for outputting radiation connected to the drift pipe, the system in excitation magnetic field is formed by two solenoids, both solenoid arranged equidistant on opposite sides of the plane of the diaphragm.

 The combination of two technical solutions in one application is due to the fact that these two options solve the same problem of increasing the efficiency of microwave radiation generation in a reditron by essentially the same way by creating a magnetic field configuration in the interaction region (between the cathode and VC) so that its field lines running parallel to the cathode electrode in the diode region along the system axis would intersect the anode in the diaphragm region, and the field lines in the drift pipe parallel to the system axis in the VC region would also intersect the drift pipe aperture diaphragm. This is structurally implemented in the proposed options by a specific implementation of the magnetic field excitation system.

 If we choose the magnitude of the magnetic field in homogeneous regions of the magnetic system so that the Larmor radius of the electrons accelerated in the diode is much larger, and the Larmor radius of the oscillating electrons, which have already spent their energy on microwave radiation and come out of synchronism with the microwave field, is much smaller than the anode of the cathode gap, then the electrons synchronous with the microwave field and having sufficient energy will continue to oscillate in the potential well, and the slow (soft) electrons will move along the lines of force of the magnetic field, settling on the walls ah drift tube and anode.

 Thus, there is an optimal magnetic field so that the aforementioned breakdown does not occur, since soft electrons that are no longer directly involved in the generation of microwave radiation would be removed from the interaction region, thereby reducing the space charge of the VC. Thus, the removal (discrimination) of only soft electrons, in contrast to the discrimination of all electrons in a known reditron, is a feature of the generation mode in the proposed reditron.

 The generation efficiency in the mode of discrimination of soft electrons will be higher than in the known vircator, due to elimination of the generation failure, as well as due to phase separation.

 It is quite difficult to write down any analytical expression for the magnitude of the required magnetic field; however, this magnitude can be easily selected experimentally.

 In FIG. 1 shows the above-mentioned qualitative time dependences of the current and power of microwave radiation; figure 2 presents an example of a technical implementation of a reditron with discrimination of soft electrons in the first embodiment; figure 3 presents examples of a technical solution of a reditron according to the second embodiment.

 In both cases, the reditron consists of an anode electrode consisting of galvanically coupled and axially arranged anode 1, diaphragm 2 made in the form of a metal mesh or thin foil, drift pipe 3 ending with a mouthpiece 4 and a radiation output window 5 axially located inside the anode and separated from it by the gap of the cathode electrode 6, parallel to the end surface of which the diaphragm is located with a gap, and a magnetic field excitation system located along the perimeter of the diaphragm on the outside of the pipe with a clearance relative to her. According to the first embodiment, the magnetic field excitation system is made in the form of a single solenoid 7 with a ring 9 of ferromagnetic material located in the plane of the diaphragm between the solenoid and the drift pipe with a gap relative to the latter.

 In this case, a magnetic field is created in such a configuration that the lines of force that run along the axis of the system parallel to the cathode electrode in the diode region intersect the anode in the diaphragm region, and the lines of force in the drift tube that run parallel to the axis of the system in the VC region also intersect the drift tube diaphragm area. The indicated configuration of the magnetic field lines is shown in FIG. 2 by arrows. The trajectories of the electrons are indicated there with a dashed line: A is the trajectory of an electron synchronous with the microwave field; B is the trajectory of a soft electron that has lost synchronism with the microwave field and is removed from the interaction region; In the trajectory of a passing electron, which is in antiphase with a microwave field.

 According to the second embodiment, the magnetic field excitation system consists of two solenoids 7, 8, both of which are placed at equal distances on opposite sides of the plane of the diaphragm, connected in series (Fig. 3a) or counter to each other (Fig. 3b). In this case, a magnetic field of the same configuration is created in the interaction region as in the first embodiment. In Fig. 3, the arrows also show the lines of force of the magnetic field, and the dotted lines show the corresponding electron paths.

 The indicated trajectories are realized when magnetic fields are very moderate for both versions, when synchronous electrons "do not feel" the magnetic field, and electrons that have lost synchronism due to radiation energy loss after crossing the potential well many times are removed from the interaction region, moving along the magnetic field lines .

 Consider the operation of a reditron with discrimination of soft electrons. When a high-voltage pulse is applied to the anode-cathode gap in the latter, as a result of explosive emission, a high-current electron beam, accelerating, rushes to the diaphragm 2, passing through it into the drift tube 3. When the electron current exceeds the limiting current for a given geometry of the drift tube and a given voltage in the diode, a VK 10 is formed in the drift tube, which alternately emits portions of electrons back and forth.

 Electrons flying forward are removed from the interaction space, settling on the drift tube in the region of the horn 4.

 Electrons returning back to the diaphragm are captured in oscillatory motion in a potential cathode-VC well. These oscillating electrons, accumulating in the interaction region, generate powerful microwave radiation. Radiating, oscillating electrons gradually lose their energy and go out of synchronism with the microwave field. As soon as the electron energy decreases to the value when the Larmor radius of the electron in this field becomes less than the cathode-anode gap, they are removed from the interaction space, settling on the anode 1 and the drift tube in the region of the diaphragm.

 Thus, in the reditron, the regime of discrimination of soft electrons that have come out of synchronism with the microwave field is implemented.

Here are the technical characteristics of one of the options for the proposed reditron:
Accelerating voltage in the diode, kV 500 Beam current, kA 50
The size of the gap of the anode-cathode, cm 3
Approximate field range in solenoids, kGf 0.5-5
The expected increase in the efficiency of generation of microwave radiation in power by 3-4 times compared with the prototype for both the first and second options.

 In addition to eliminating the stall and increasing the generation efficiency, discrimination of soft electrons exacerbates the spectrum of the generated microwave radiation, and also increases the pulse duration of the microwave radiation.

 The expected output parameters make it possible to use the proposed options for practical purposes, for example, for plasma heating in pulsed thermonuclear installations, as well as in long-distance transmission lines of electromagnetic energy.

Claims (2)

 1. REDITRON containing an anode electrode, which consists of a galvanically connected and axially located anode, a diaphragm and a drift tube, an cathode electrode axially located inside the anode and separated by a gap, a diaphragm parallel to the end surface of which has a gap, a magnetic field excitation system in the form one solenoid located along the perimeter of the diaphragm on the outside of the pipe with a gap relative to it, as well as a system for outputting radiation connected to the drift pipe, characterized by m, in the plane of the diaphragm between the solenoid and the drift tube with a gap relative to the latter is a ring of ferromagnetic material.  2. A reditron containing an anode electrode, which consists of a galvanically connected and axially located anode, a diaphragm and a drift tube, an cathode electrode axially located inside the anode and separated by a gap, a diaphragm parallel to the end surface of which has a gap, a magnetic field excitation system with one a solenoid located along the perimeter of the diaphragm on the outside of the pipe with a gap relative to it, as well as a system for outputting radiation connected to the drift pipe, characterized in that a second solenoid is introduced into the magnetic field excitation system, both of which are placed on opposite sides of the diaphragm plane.

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