Microwave vacuum amplifier
The microwave vacuum amplifier addresses the challenges of size and cost by employing a secondary emission discharge to enhance beam current and density, achieving low-voltage control and reduced dimensions.
Patent Information
- Authority / Receiving Office
- RU · RU
- Patent Type
- Patents
- Current Assignee / Owner
- AKTSIONERNOE OBSHCHESTVO NAUCHNO PROIZVODSTVENNOE PREDPRIYATIE ISTOK IMENI A I SHOKINA
- Filing Date
- 2025-12-22
- Publication Date
- 2026-07-10
AI Technical Summary
Existing microwave amplifiers, such as klystrons, require bulky magnetic systems for electron beam transport, leading to large dimensions and high costs, and suffer from limitations in frequency range, input signal amplitude range, and lack of low-voltage control.
A microwave vacuum amplifier design with input and output resonators, a grid-shaped input resonator wall, and a high accelerating voltage between resonators, utilizing a single-electrode secondary emission discharge to create a modulated electron beam for efficient energy transfer without a magnetic system, enabling low-voltage control and reduced size.
The design achieves reduced weight and size, increased power, and allows for low-voltage control of the output signal, overcoming limitations of existing amplifiers by using a secondary emission discharge to enhance beam current and density.
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Abstract
Description
[0001] The invention relates to the field of microwave radio electronics, namely to powerful amplifiers of microwave oscillations in the decimeter, centimeter and millimeter wavelength ranges.
[0002] Modern linear electron accelerators use powerful microwave sources, typically klystrons. They offer high output power and significant efficiency. However, due to the need to transport the electron beam over long distances (0.5-2 m), they require a bulky magnetic system, resulting in large dimensions and high cost.
[0003] Thus, reducing the weight, size, and cost of the amplifier is difficult due to the fundamental need to provide a magnetic field for electron beam transport. A powerful microwave signal amplifier is known - a klystrode [Patent US 4480210 D. H. Preist, M. B. Schrader], containing a hot-cathode electron gun, input and output cavity resonators connected to external transmission lines, and a collector. The cathode is part of the input resonator and forms a capacitive gap with the opposite wall of the resonator, made in the form of a grid; the input resonator is divided by DC by capacitive elements, so that a constant bias voltage from an external source is applied to the gap; a high accelerating voltage is applied between the cathode and the output resonator.When an input signal is applied, the cathode emits an electron beam, which is density-modulated by a high-frequency signal in the input resonator gap. The beam passes through the grid, is accelerated by the high voltage between the input and output resonators, and enters the output resonator, where it transfers energy to the output signal and then deposits in the collector. The disadvantages of this device include the need for a hot cathode heater, the long hot cathode readiness time, and the limited frequency range of ~1 GHz, due to the need to maintain a small grid-cathode gap.
[0004] A micropulse electron gun (Patent EP 0809271 A2) is known. It creates an electron beam modulated by a radio frequency signal and generated by a two-electrode secondary emission discharge (multipaktor) in a resonator gap into which RF power is supplied. One of the walls of the resonator is designed as a grid or has a hole through which the beam is released from the resonator and, as stated in the patent, after additional acceleration can be used to generate an amplified high-frequency signal. A disadvantage of this design is the narrow range of permissible input signal amplitudes, determined by the gap size and the operating frequency. Furthermore, this approach has not been implemented for microwave signal amplification.
[0005] A device for amplifying a high-frequency signal is known [C. Bates, G. deLhery, P. Fischer, J. Hartley "Multipactor Electron Gun For Millimeter Wave Tubes" 1981 International Electron Devices Meeting, 7-9 December 1981, Washington, DC, p. 339-343, DOI: 10.1109 / IЕОМ. 1981.190082], which has input and output microwave resonators, between which an accelerating voltage is applied, and microwave power is supplied to the input resonator, which excites a two-electrode secondary emission discharge in the resonator gap and creates a modulated electron beam. This beam is further accelerated by a constant voltage applied between the input and output resonators and passed through the output resonator, generating an output signal that is fed into an external circuit. Another disadvantage of this design is the narrow range of input signal amplitudes and the lack of low-voltage control of the output signal.
[0006] The closest to the proposed invention (prototype) is a microwave amplifier [F. Mako "Novel particle and radiation sources and advanced materials" AIP Conf. Proc. 1721, 050001 (2016) p. 050001-1-050001-16 doi:10.1063 / 1.4944023]. A klystron containing a micropulse electron gun as a source of a modulated beam and a toroidal output resonator traditional for klystrons, while the input resonator is connected to the signal source by external microwave lines, which ensures the supply of microwave power to the resonator and high-frequency modulation of the beam by the input signal, the beam is further accelerated in the section between the resonators and gives energy to the signal in the output resonator. The device does not have a hot cathode or magnetic system, which helps reduce its weight and dimensions and reduce the readiness time.
[0007] The disadvantages of the prototype amplifier are related to the lack of the ability to low-voltage pulse modulation of the output signal and the lack of low-voltage control of the operating mode and output power of the device, as well as the need to ensure small gaps in the input resonator when operating in short-wave ranges (millimeter and submillimeter).
[0008] The technical result of the proposed invention is the design of a new class of microwave vacuum amplifiers with the possibility of low-voltage control of the output signal, an increase in the power of the device, and a reduction in the weight and size parameters of the device.
[0009] The technical result is achieved by a microwave vacuum amplifier comprising input and output resonators, an energy input and output, and a collector; the input resonator is divided into two parts by capacitive elements; a constant bias voltage from an external source is applied between the parts of the input resonator; the wall of the input resonator facing the output resonator is formed as a grid made of a material with a high secondary emission coefficient, and a high accelerating voltage is applied between the part of the input resonator facing the output resonator and the output resonator. The grid and the opposite wall of the input resonator gap may have a spherical shape.
[0010] The essence of the technical solution is as follows. When high-frequency power and bias voltage are applied to the input resonator, the electron motion in the gap reverses: initially, electrons emitted by the grid at a specific phase of the high-frequency field move away from the grid in the gap. Then, when the phase (direction) of the high-frequency field changes, they return to the grid and create new secondary electrons. In the next period, the process repeats with a higher emitted current. The electron current rapidly increases until it reaches an equilibrium value, limited by the influence of space charge and the spread of initial velocities. Part of the returning electron bunch passes through the grid and is further accelerated in the section between the input and output resonators by the voltage applied to this section from the power source. This energy is transferred to the high-frequency signal in the output resonator, similar to a klystrode.The current and output power are highly dependent on the bias voltage, enabling low-voltage control of the output power. During the return motion of electrons in the input resonator gap, bunching of the electrons in the bunch occurs, compensating for the unbunching effect of the space charge field and the spread of the initial velocities of the secondary electrons, significantly increasing the beam current and the device's power. Since the device does not require an extended slow-wave structure, as in a TWT, or a set of resonators, as in a klystron, its size and weight are significantly reduced compared to existing vacuum microwave amplifiers.
[0011] The device's operating mode can be controlled using bias voltage, including complete shutdown. This allows for fine-tuning of operating parameters and also enables pulsed operation.
[0012] When the walls of the gap of the input resonator and the output resonator are spherical, the electron beam is compressed, which increases the gain of the device.
[0013] The invention is illustrated by drawings. Fig. 1 (a, b) shows the structural diagrams of a microwave vacuum amplifier, where
[0014] 1 - input resonator
[0015] 2 - output resonator
[0016] 3 - Energy input
[0017] 4 - Energy output
[0018] 5 - capacitive element
[0019] 6 - Bias source
[0020] 7 - power supply
[0021] 8 - collector
[0022] 9 - grid.
[0023] Fig. 2 shows the evolution of the coordinates of the particles in the gap, the field on the cathode and the emission current as a function of time during the development of the discharge (A - periods 1 and 2, B - periods 3 to 12, C - periods 25-30), where:
[0024] curve 1 - dependence of the field on the cathode on time;
[0025] curve 2 - dependence of the average emission current on time;
[0026] curve 3 - particle positions versus time.
[0027] Fig. 3 shows the dependence of the secondary emission coefficient of the PdBa alloy on the energy of primary electrons, which was used in the simulation.
[0028] The device (Fig. 1) operates as follows. When high-frequency power is supplied to the input resonator 1 through the power input 3 and a bias voltage from the bias source 6, an alternating electric field is created in the gap. Random, "seed" electrons existing in the gap are accelerated by this field in the direction from the grid 9 to the opposite wall of the input resonator gap. As they move, the field changes sign, and they return to the emitter with increased energy received from the high-frequency field. Here, they knock out a larger number of secondary electrons from the emitter. For electrons returning to the emitter in the correct phase (correct-phase), when the electric field again changes sign and becomes accelerating for secondary electrons, the secondary electrons are accelerated and again return to the emitter through a period of high-frequency oscillation. Those electrons that arrive at the grid in the wrong phase of the microwave field (out of phase) are removed from the gap.Thus, a single-electrode secondary-emission discharge is excited in the gap, resulting in the formation of a growing bunch of secondary electrons emitted by the grid. These electrons move in the gap during the high-frequency oscillation period and return to grid 9. The return motion of the bunch electrons leads to its additional grouping, which compensates for the influence of the space charge and allows for an increase in the current and current density of the beam. Some of the electrons pass through the grid, are further accelerated by high voltage from power source 7 applied between resonators 1 and 2, and enter output resonator 2, where they transfer energy to the output signal and then settle in collector 8. Microwave power is extracted from the output resonator through power output 4. The operating mode of the device can be controlled using the bias voltage from bias source 6, including complete shutdown.This allows for fine-tuning of operating parameters and ensures pulsed operation. The readiness time is determined by the discharge development time, which depends on the secondary emission coefficient and the device's operating frequency, and is measured in nanoseconds.
[0029] The microwave vacuum amplifier of the proposed design was simulated.
[0030] PdBa palladium-barium alloy was chosen as the mesh material. It has proven itself as a secondary emission material in M-type microwave devices and is capable of providing high secondary emission coefficient (SEC) values in the operating temperature range of 400-700°C.
[0031] Mesh material - Pd+1.5%Ba alloy with parameters σ max =2.7, E max=40-45 eV. The secondary emission coefficient of elastically reflected electrons is less than 1%, the secondary electron energy spread is <3 eV. The spread of emitted electrons by initial energies was modeled by dividing them into three groups with energies from 0 to 3 eV. The input gap size is d=0.1 mm, the bias voltage U0=-50 V, the microwave voltage across the gap is U1=182 V. With these parameters, the primary electron energy is E=80 eV, the secondary emission coefficient σ=1.75.
[0032] The initiation of a secondary-emission discharge is due to vacuum ionization, which is associated with the natural radioactivity of materials, the influence of cosmic radiation, and field emission from irremovable microprotrusions in the gap walls. The initial ionization was modeled by the emission from the cathode of a set of seed particles uniformly distributed during the first period of oscillations (with a total current of about 0.1 μA). The subsequent evolution of the particles is shown in Fig. 2 (a, b, c) (where the electric field at the cathode and the average emission current are also shown). The steady-state value of the average emission current density is 12 A / cm 2 It is worth noting the high quality of beam grouping: the relative amplitude of the first harmonic of the electron current at the output is 1.7.
[0033] The simulation results (Fig. 2) show that the proposed device design separates out-of-phase electrons and groups in-phase particles into a bunch. The process reaches a steady state within 25 periods (~1.25 ns). The average secondary emission current density reaches 12 A / cm 2 .
[0034] The dependence of the secondary emission coefficient of the PdBa alloy on the energy of primary electrons is shown in Fig. 3.
[0035] The maximum secondary emission coefficient of the PdBa alloy is σ=3.5 at E=200 eV, which allows the formation of an electron beam with an average secondary emission current density of 12 A / cm 2 , and provide the required gain and output power of the device.
[0036] The manufacture of the proposed microwave amplifier design involves the use of traditional technological operations and is performed on standard metalworking equipment.
Claims
1. A microwave vacuum amplifier comprising input and output resonators, an energy input and output, and a collector, characterized in that the input resonator is divided into two parts by capacitive elements; a constant bias voltage from an external source is applied between the parts of the input resonator; wherein the wall of the input resonator facing the output resonator is made in the form of a grid made of a material with a high secondary emission coefficient, and an accelerating voltage is applied between the part of the input resonator facing the output resonator and the output resonator.
2. A microwave vacuum amplifier according to claim 1, characterized in that the grid and the wall of the input resonator gap opposite it have a spherical shape.