Method for inhibiting dielectric window breakdown under dual-frequency high-power microwaves

Abstract

The invention discloses a method for inhibiting dielectric window breakdown under double-frequency high-power microwaves, and belongs to the field of high-power microwaves. An external magnetic field B parallel to the dielectric window and perpendicular to a deposition electric field Edc and a high-power microwave electric field Erf on the surface of the dielectric window at the same time is applied to the vacuum side of the dielectric window, the magnetic field meets # imgabs0 #, so that energy obtained by electrons through cyclotron resonance is higher than a second cross point of a secondary yield curve, upper and lower boundaries of a sensitive curve are reduced, and the sensitivity is improved. Secondary electron multiplication is suppressed due to a lower upper boundary; wherein Omega is rotation frequency, and Omega 1 and Omega 2 respectively represent angular frequencies of two microwave components of the double-frequency high-power microwave Erf. Under the double-frequency microwave electric field, when the external magnetic field is parallel to the dielectric window and is perpendicular to the Edc and the Erf at the same time, the condition of being higher than the upper boundary can be met, the multiplication restraining effect is achieved, due to mutual modulation of the external magnetic field and the microwave electric field, along with rising of the field intensity of the double-frequency microwave electric field, the upper boundary of a sensitive curve is relatively stable and low, and multiplication is restrained.

Description

Technical Field

[0001] The present invention belongs to the field of high-power microwaves, and particularly relates to a method for suppressing dielectric window breakdown under dual-frequency high-power microwaves. Background Art

[0002] High-power microwave (HPM) technology has important applications in modern radar, electronic countermeasure, and directed energy weapons. As a key component of the HPM system, the dielectric window undertakes the core functions of isolating the external environment from the vacuum cavity and transmitting microwave energy. With the arduous efforts of scholars from various countries, the quality factor of vacuum HPM source devices has increased from 1 GW(GHz) in the 1970s 2 to 104 GW(GHz) at the beginning of the 21st century 2 , the output power has reached several GW or even more than 10 GW, and the power flow density is as high as several hundred MW / cm 2 . However, with the continuous increase of the required HPM power index, dielectric window breakdown on the vacuum side is extremely likely to be induced. Dielectric window breakdown affects the normal operation of HPM devices and is becoming a prominent bottleneck in the development of HPM. Dielectric window breakdown is the combined action of various physical phenomena such as seed electrons, secondary electron multiplication, particle bombardment, and energy deposition. Suppressing secondary electron multiplication on the dielectric window can effectively suppress dielectric window breakdown.

[0003] The research on dielectric window breakdown can be traced back to the early 1960s. However, currently, the existing research on HPM dielectric window breakdown mainly focuses on single-frequency signals. Chang Chao et al. in China proposed methods such as using a serrated dielectric window surface and applying an external magnetic field to suppress dielectric window breakdown and achieved certain results. They also found that applying an external resonant magnetic field can effectively suppress secondary electron multiplication and thus effectively increase the breakdown threshold of the dielectric window. Compared with single-frequency high-power microwaves, dual-frequency high-power microwaves can more effectively improve the overall efficiency of energy transmission and provide more stable performance, especially in applications such as electronic countermeasure and aerospace communication. The application prospects of dual-frequency high-power microwaves make the research in this field become increasingly important. In a dual-frequency signal, the coupling between two different frequency components brings a more complex mechanism to dielectric window breakdown. Under the nonlinear physical process of dielectric window breakdown, the coupling between the frequency components of dual-frequency HPM will bring harmonic phenomena such as frequency doubling, sum frequency, and difference frequency, as well as harmonic resonance phenomena. These phenomena will have a huge impact on the dielectric window breakdown threshold and breakdown mode.

[0004] At present, the research on dual-frequency HPM dielectric windows is still relatively scarce. The existing single-frequency HPM breakdown suppression schemes cannot be directly applied to dual-frequency HPM breakdown suppression because the parameter selection in the commonly used surface grooving and external magnetic field suppression schemes in single-frequency research is usually based on the microwave frequency. For example, the selection of the magnitude of the external magnetic field usually depends on the relative relationship between the cyclotron frequency and the microwave frequency. Therefore, referring to the external magnetic field suppression scheme in single-frequency research, this patent conducts research on the breakdown of the dielectric window of dual-frequency high-power microwaves and proposes to apply a magnetic field that meets the requirements to achieve the suppression of dielectric window breakdown, which has important theoretical significance and practical application value. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to make up for the defects in the technology of suppressing the breakdown of the dielectric window under dual-frequency high-power microwaves, and to propose a method for suppressing the breakdown of the dielectric window under dual-frequency high-power microwaves.

[0006] The technical solution of the present invention is as follows: A method for suppressing the breakdown of a dielectric window under dual-frequency high-power microwaves, and the method is: applying an external magnetic field B parallel to the dielectric window and perpendicular to the deposition electric field E on the vacuum side of the dielectric window, and dc the high-power microwave electric field E rf such that the energy obtained by electrons through cyclotron resonance is higher than the second intersection point of the secondary yield curve, reducing the upper and lower boundaries of the sensitivity curve, and the lower upper boundary results in the suppression of secondary electron multiplication; where Ω is the cyclotron frequency, and ω1 and ω2 respectively represent the angular frequencies of the two microwave components of the dual-frequency high-power microwave E rf .

[0007] Furthermore, the external magnetic field B = Ωm / e, where m is the electron mass and e is the electric charge.

[0008] Furthermore, the external magnetic field B = 0.1T.

[0009] Furthermore, where ω1 and ω2 satisfy:

[0010] E rf = E[sin(ω1t + θ1) + sin(ω2t + θ2)]

[0011] where E is the magnitude of the electric field strength, and θ1 and θ2 respectively represent the phase angles of the two microwave components of the dual-frequency high-power microwave E rf . When the present invention applies an external magnetic field parallel to the dielectric window and perpendicular to E dc and E rf under the dual-frequency microwave electric field, it can meet the condition of being higher than the upper boundary and achieve the effect of suppressing multiplication. Due to the mutual modulation of the external magnetic field and the microwave electric field, as the field strength of the dual-frequency microwave electric field increases, the upper boundary of the sensitivity curve is relatively stable and low, and the multiplication is suppressed.​ Description of the Drawings

[0012] Figure 1 It is a classic curve showing the variation of the secondary electron yield with the electron impact energy.

[0013] Figure 2 Figures (1)-(4) show diagrams of the case without a magnetic field and three ways of applying an external magnetic field.

[0014] Figure 3 It shows the secondary electron multiplication sensitivity curves when no external magnetic field is applied and when three external magnetic fields with different directions are respectively applied. Detailed Implementation Manner

[0015] The average number of secondary electrons generated by each primary electron is called the secondary electron yield δ, which is a function of the impact energy E i of the primary electron and the angle ξ at which the primary electron impacts the surface of the dielectric window. As Figure 1 shown, the secondary electron yield curve has two crossover points E1 and E2, which are called the first and second crossover points. When the impact energy falls between the two crossover points, δ > 1 and secondary electron multiplication occurs; when E i < E1 and E i > E2, δ < 1 and secondary electron multiplication is suppressed. The relationship between the secondary electron yield, the impact energy, and the impact angle is described by the Vaughan empirical formula:

[0016] δ = δ(E i ) = δ max (we 1-w ) k ,

[0017]

[0018] E i and ξ are expressed as:

[0019]

[0020] δ max is the maximum value of the yield, E max is the electron impact energy at which the yield is maximum. When w < 1, k = 0.62; when k > 0.25, w > 1. E max0 and δ max0 are the corresponding parameters when the impact angle is 0, and k sis the surface smoothness coefficient, taking 1. The first and second intersection points in the secondary electron yield curve correspond to the lower and upper boundaries in the multiplication sensitivity curve respectively. When it is lower than the upper boundary and higher than the lower boundary, δ>1, and secondary electron multiplication occurs; when it is lower than the lower boundary and higher than the upper boundary, δ<1, and secondary electron multiplication is suppressed. By applying an external magnetic field that meets the conditions, electron cyclotron resonance causes the electron impact energy to increase, and the upper and lower boundaries of the sensitivity curve decrease, so that the multiplication effect can be suppressed by exceeding the upper boundary even in a lower microwave electric field environment.

[0021] E rf = E[sin(ω1t + θ1) + sin(ω2t + θ2)]

[0022] u x 、u y 、u z are the velocity components of the electron along the x, y, and z directions respectively, m is the electron mass, and E dc is the deposited electric field on the surface of the dielectric window, and E rf is the high-power microwave electric field, B is the external magnetic field, Ω is the cyclotron frequency, and T is the electron flight time. B rf / B≈eE / mΩc. When eE / mΩ << c, B rf is ignored; Next, the dynamic equations of electrons with three external magnetic fields in different directions and without applying an external magnetic field are listed respectively:

[0023] (1) No additional magnetic field is applied;

[0024]

[0025] u z (t) = u z (0)

[0026]

[0027] (2) The external magnetic field is parallel to E dc ;

[0028]

[0029] (3) The external magnetic field is parallel to E rf and the surface of the dielectric window;

[0030]

[0031] (4) The external magnetic field is parallel to the dielectric window and perpendicular to E dc and E rf at the same time; All the following symbols will be explained in Chinese;

[0032]

[0033] It can be analyzed from the kinetic theory that when the external magnetic field is parallel to E dc , the electron flight time is determined by the change of E dc . Compared with the first case without magnetic field, electrons can obtain energy from the dual-frequency microwave field through electron cyclotron. To obtain higher energy, a longer flight time is required. Therefore, compared with the case without magnetic field, when an external magnetic field parallel to E dc is applied, the sensitivity curve needs to be changed by a sufficiently small E dc . When the external magnetic field is parallel to E rf and the surface of the dielectric window, the cyclotron motion of electrons cannot obtain energy from the dual-frequency microwave field, and the sensitivity curve does not change compared with the case without magnetic field. Only in the fourth case, the electron motion time is modulated by the external magnetic field and the dual-frequency microwave electric field. When Ω = ω1 ~ ω2, the electrons are accelerated by cyclotron resonance to obtain higher energy, and both the upper and lower boundaries will decrease. The external magnetic field can be taken to satisfy Numerically calculate the change of the sensitivity curve and plot the multiplication sensitivity curves in all cases as shown in Figure 3 . It can be seen from Figure 3 that the numerical results are consistent with the theoretical results. When the external magnetic field is parallel to the dielectric window and perpendicular to E dc and E rf at the same time, the upper boundary of the sensitivity curve decreases significantly, and it is even lower than the lower boundary and its upper boundary in other cases. Therefore, under the dual-frequency microwave electric field, when the external magnetic field is parallel to the dielectric window and perpendicular to E dc and E rf at the same time, it can meet the condition of being higher than the upper boundary and achieve the effect of suppressing multiplication. Due to the mutual modulation of the external magnetic field and the microwave electric field, as the field strength of the dual-frequency microwave electric field increases, the upper boundary of the sensitivity curve is relatively stable and low, and multiplication is suppressed.

Claims

1. A method for suppressing dielectric window breakdown under dual-frequency high-power microwaves, the method comprising: applying a deposition electric field E parallel to the dielectric window and perpendicular to the dielectric window surface on the vacuum side of the dielectric window. dc and high power microwave electric field E rf The external magnetic field B satisfies The energy obtained by the electron through cyclotron resonance is higher than the second intersection point of the secondary yield curve, and the upper and lower boundaries of the sensitivity curve are reduced. The lower upper boundary leads to the suppression of secondary electron multiplication; wherein, Ω is the cyclotron frequency, ω1 and ω2 represent the dual-frequency high-power microwave E rf The angular frequencies of the two microwave components.

2. A method for suppressing dielectric window breakdown under dual-frequency high-power microwaves as claimed in claim 1, characterized in that: External magnetic field B = Ωm / e, m is the mass of the electron, and e is the charge.

3. The method for suppressing dielectric window breakdown under dual-frequency high-power microwaves according to claim 1, characterized in that: External magnetic field B=0.1T.

4. The method for suppressing dielectric window breakdown under dual-frequency high-power microwaves according to claim 1, characterized in that: Where ω1 and ω2 satisfy: E rf =E[sin(ω1t+θ1)+sin(ω2t+θ2)] Where E is the electric field strength, θ1 and θ2 represent the dual-frequency high-power microwave E rf The phase angle of the two microwave components.

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