阅读说明：本技术 一种铁电阴极测试系统及方法 (Ferroelectric cathode test system and method ) 是由 王新霞 王党树 于 2020-04-15 设计创作，主要内容包括：本发明公开了一种铁电阴极测试系统及方法,涉及铁电阴极,其中的一种铁电阴极测试系统,包括高压脉冲电源、真空室、发射电流测试电路、样品电压测试电路；所述高压脉冲电源分别连接真空室的一端和样品电压测试电路；所述发射电流测试电路连接真空室的另一端；所述样品电压测试电路连接示波器。本发明通过共点接地、屏蔽、双端匹配、线路连接以及设备布置等方式,妥善地解决了铁电阴极测试系统的电磁干扰问题。(The invention discloses a ferroelectric cathode test system and a method, relating to a ferroelectric cathode, wherein the ferroelectric cathode test system comprises a high-voltage pulse power supply, a vacuum chamber, an emission current test circuit and a sample voltage test circuit; the high-voltage pulse power supply is respectively connected with one end of the vacuum chamber and the sample voltage testing circuit; the emission current test circuit is connected with the other end of the vacuum chamber; and the sample voltage testing circuit is connected with the oscilloscope. The invention properly solves the problem of electromagnetic interference of the ferroelectric cathode test system by means of common point grounding, shielding, double-end matching, line connection, equipment arrangement and the like.)

1. A ferroelectric cathode test system is characterized by comprising a high-voltage pulse power supply, a vacuum chamber, an emission current test circuit and a sample voltage test circuit;

the high-voltage pulse power supply is respectively connected with one end of the vacuum chamber and the sample voltage testing circuit;

the emission current test circuit is connected with the other end of the vacuum chamber;

and the sample voltage testing circuit is connected with the oscilloscope.

2. A ferroelectric cathode test system as in claim 1, wherein the sample voltage test circuit comprises resistors R0, R01, R1, R2, R3, R4, double shielded through-axis cable Z, an attenuator;

after the resistors R0 and R01 are connected in series, one end of the resistor R0 is connected with a high-voltage pulse power supply, and one end of the resistor R01 is connected with the ground;

after the resistors R1 and R2 are connected in series, one end of the resistor R1 is connected with a high-voltage pulse power supply, and one end of the resistor R2 is connected with the ground;

one end of the resistor R3 is connected between the resistors R1 and R2, and the other end of the resistor R3 is connected with one end of the double-shielded through-axis cable Z;

one end of the attenuator is connected with the other end of the double-shielding through-axis cable Z, and the other end of the attenuator is connected with an oscilloscope;

the resistor R4 is connected between one end of the attenuator and the ground, and the double-shielding through-axis cable Z and the attenuator are connected with the sample voltage testing circuit in common.

3. A ferroelectric cathode test system as in claim 1, wherein the emission current test circuit comprises a dc power supply, a dc blocking capacitor C1, a rogowski coil K, resistors R5, R6;

the direct current power supply is respectively connected with a graphite collector FC and a resistor R5;

one end of the resistor R5 is connected with a direct current power supply, and the other end of the resistor R5 is respectively connected with a graphite collector FC;

one end of the Rogowski coil K is connected with the resistor R5, and the other end of the Rogowski coil K is connected with the capacitor C1;

one end of the resistor R6 is connected with the capacitor C1, and the other end is connected with the ground.

4. A ferroelectric cathode test method is characterized by comprising the following steps:

s1, providing a vacuum environment for testing by a vacuum chamber, inhibiting the interference of internal high-frequency electromagnetic radiation on external equipment by an electromagnetic shielding chamber in the vacuum chamber, shielding the interference of external electromagnetic radiation on an internal circuit, and establishing a low-resistance path between a grid and the ground to prevent the personal safety from being endangered by high-voltage discharge;

s2, selecting an oil diffusion pump as a main pump to obtain high vacuum in the test, wherein the vacuum environment is obtained through the cooperative work of a backing pump and the main pump;

s3, measuring the connection and arrangement method of the equipment;

and S4, anti-interference method.

5. A ferroelectric cathode test method as in claim 4, wherein said steps are performed in the same manner as described above

S3 includes:

position of voltage divider and test article: the voltage divider is directly connected to the high-voltage end of the test article through a high-voltage lead wire, and is not connected to the output end of the impulse voltage generator or directly connected to a connecting wire between the generator and the test article, so that the inductive voltage drop on the connecting wire is avoided being included in measurement;

grounding of the test equipment: connecting the oscillograph and the voltage divider by red copper braided belts with the width of 2cm and the thickness of 1.5mm, so that the transient current in the cable sheath is weakened to reduce the electromagnetic interference; the grounding end of the impulse voltage generator is connected with the red copper braided belt directly in order to reduce the impedance of the grounding when the current passing through the grounding end of the impulse voltage generator is larger;

a concentrated grounding electrode is arranged close to the voltage divider, and the voltage divider and a grounding end of a test article adopt a copper foil broadband of 2cm and 0.2mm in thickness to be connected with the grounding electrode; the voltage divider is directly connected with the grounding end of the sample to be grounded and form a loop; the impedance of the grounding loop is reduced as much as possible so as to reduce the measurement error caused by the impedance voltage drop of the loop;

end matching of the measuring cable: matching measures are adopted at the connection parts of the two ends of the measuring cable and the voltage divider and the measuring instrument so as to prevent wave oscillation caused by multiple reflections in the cable; a matching mode of matching two ends is adopted in the test;

the oscilloscope is externally connected with an attenuator: an attenuator is used at a measuring cable terminal, and an attenuator with 20dB and 3GHz bandwidth is selected;

a vacuum chamber lead: the vacuum chamber is designed to adopt a coaxial structure, the upper end and the lower end of the vacuum chamber are led out by copper bars, the upper end is a high-voltage electrode, and the lower end is a collector; a double-layer shielding cover is manufactured by adopting a PVC sleeve and a copper sheet with the thickness of 0.2 mm; the high-voltage lead is led out from the copper bar of the inner layer of the shielding sleeve by a BNC connector, and the shielding cover outer skin is grounded; shielding the collector by using a double-layer shielding cover by adopting the same method, and leading out an emission current signal wire from a copper bar connected with graphite from the inner layer through a BNC joint; meanwhile, a direct-current bias lead of the collector is led out by connecting a BNC connector in series with a resistor of 5M omega.

6. A ferroelectric cathode test method as in claim 4, wherein said steps are performed in the same manner as described above

S3 includes:

s31, reducing the transient current in the cable sheath;

s32, shielding of the oscilloscope;

and S33, isolation of the power supply.

7. A ferroelectric cathode test method as in claim 6, wherein said steps are performed in the same manner as described above

S31 includes:

the voltage divider is arranged at a place close to the concentrated grounding electrode and is connected with the concentrated grounding electrode by the shortest connecting line, and the grounding connecting line adopts a wider copper strip or aluminum strip;

a metal plate or a metal belt with larger laying width from the voltage divider to the oscilloscope is used as a grounding connecting line, and a measuring cable is laid along the grounding connecting line and is close to the ground, so that the area of a loop formed by a cable sheath and the grounding connecting line is reduced as much as possible;

the length of the measuring cable is as short as possible;

the measuring cable adopts a wiring mode with two matched ends;

the measured voltage signal transmitted in the coaxial cable is improved, so that the proportion of common mode interference is reduced, namely the signal-to-noise ratio of a cable transmission link is improved, and the influence of the interference on measurement is reduced; the oscilloscope is connected with the measuring cable through the external 20dB attenuator, so that a measured voltage signal transmitted in the measuring cable takes a higher level, the signal-to-noise ratio is improved, and the influence of interference is reduced.

Technical Field

The invention relates to a ferroelectric cathode, in particular to a ferroelectric cathode testing system and a method.

Background

At present, a ferroelectric cathode is a novel electron emission cathode which obtains a pulsed electron beam from the surface of a ferroelectric material under external excitation (rapid temperature rise, mechanical pressure, laser pulse, high voltage pulse, and the like). Compared with the traditional cathode technology, the ferroelectric cathode has the advantages of high emission current density, excellent electron beam, normal-temperature emission, no poisoning and the like. The advantages make the ferroelectric cathode have potential application value in the high current electron beam cathode technology.

For a high-current ferroelectric cathode material, electron emission current and emission current density are key indexes for researching electron emission performance of the ferroelectric cathode material. The excitation voltage and the emission current waveform have important reference values for researching an electron emission mechanism. However, due to the influence of ground current coupling and other electromagnetic interference on the test signal, it is not easy to measure the real emission current signal.

Disclosure of Invention

The invention mainly aims to provide a system and a method for testing a ferroelectric cathode.

According to one aspect of the invention, a ferroelectric cathode test system is provided, which comprises a high-voltage pulse power supply, a vacuum chamber, an emission current test circuit and a sample voltage test circuit;

the high-voltage pulse power supply is respectively connected with one end of the vacuum chamber and the sample voltage testing circuit;

the emission current test circuit is connected with the other end of the vacuum chamber;

and the sample voltage testing circuit is connected with the oscilloscope.

Further, the sample voltage testing circuit comprises resistors R0, R01, R1, R2, R3, R4, a double-shielded through-axis cable Z and an attenuator;

after the resistors R0 and R01 are connected in series, one end of the resistor R0 is connected with a high-voltage pulse power supply, and one end of the resistor R01 is connected with the ground;

after the resistors R1 and R2 are connected in series, one end of the resistor R1 is connected with a high-voltage pulse power supply, and one end of the resistor R2 is connected with the ground;

one end of the resistor R3 is connected between the resistors R1 and R2, and the other end of the resistor R3 is connected with one end of the double-shielded through-axis cable Z;

one end of the attenuator is connected with the other end of the double-shielding through-axis cable Z, and the other end of the attenuator is connected with an oscilloscope;

the resistor R4 is connected between one end of the attenuator and the ground, and the double-shielding through-axis cable Z and the attenuator are connected with the sample voltage testing circuit in common.

Furthermore, the emission current test circuit comprises a direct current power supply, a blocking capacitor C1, a Rogowski coil K, and resistors R5 and R6;

the direct current power supply is respectively connected with a graphite collector FC and a resistor R5;

one end of the resistor R5 is connected with a direct current power supply, and the other end of the resistor R5 is respectively connected with a graphite collector FC;

one end of the Rogowski coil K is connected with the resistor R5, and the other end of the Rogowski coil K is connected with the capacitor C1;

one end of the resistor R6 is connected with the capacitor C1, and the other end is connected with the ground.

According to yet another aspect of the present invention, there is provided a ferroelectric cathode testing method comprising the steps of:

s1, providing a vacuum environment for testing by a vacuum chamber, inhibiting the interference of internal high-frequency electromagnetic radiation on external equipment by an electromagnetic shielding chamber in the vacuum chamber, shielding the interference of external electromagnetic radiation on an internal circuit, and establishing a low-resistance path between a grid and the ground to prevent the personal safety from being endangered by high-voltage discharge;

s2, selecting an oil diffusion pump as a main pump to obtain high vacuum in the test, wherein the vacuum environment is obtained through the cooperative work of a backing pump and the main pump;

s3, measuring the connection and arrangement method of the equipment;

and S4, anti-interference method.

Further, the step S3 includes:

position of voltage divider and test article: the voltage divider is directly connected to the high-voltage end of the test article through a high-voltage lead wire, and is not connected to the output end of the impulse voltage generator or directly connected to a connecting wire between the generator and the test article, so that the inductive voltage drop on the connecting wire is avoided being included in measurement;

grounding of the test equipment: connecting the oscillograph and the voltage divider by red copper braided belts with the width of 2cm and the thickness of 1.5mm, so that the transient current in the cable sheath is weakened to reduce the electromagnetic interference; the grounding end of the impulse voltage generator is connected with the red copper braided belt directly in order to reduce the impedance of the grounding when the current passing through the grounding end of the impulse voltage generator is larger;

a concentrated grounding electrode is arranged close to the voltage divider, and the voltage divider and a grounding end of a test article adopt a copper foil broadband of 2cm and 0.2mm in thickness to be connected with the grounding electrode; the voltage divider is directly connected with the grounding end of the sample to be grounded and form a loop; the impedance of the grounding loop is reduced as much as possible so as to reduce the measurement error caused by the impedance voltage drop of the loop;

end matching of the measuring cable: matching measures are adopted at the connection parts of the two ends of the measuring cable and the voltage divider and the measuring instrument so as to prevent wave oscillation caused by multiple reflections in the cable; a matching mode of matching two ends is adopted in the test;

the oscilloscope is externally connected with an attenuator: an attenuator is used at a measuring cable terminal, and an attenuator with 20dB and 3GHz bandwidth is selected;

a vacuum chamber lead: the vacuum chamber is designed to adopt a coaxial structure, the upper end and the lower end of the vacuum chamber are led out by copper bars, the upper end is a high-voltage electrode, and the lower end is a collector; a double-layer shielding cover is manufactured by adopting a PVC sleeve and a copper sheet with the thickness of 0.2 mm; the high-voltage lead is led out from the copper bar of the inner layer of the shielding sleeve by a BNC connector, and the shielding cover outer skin is grounded; shielding the collector by using a double-layer shielding cover by adopting the same method, and leading out an emission current signal wire from a copper bar connected with graphite from the inner layer through a BNC joint; meanwhile, a direct-current bias lead of the collector is led out by connecting a BNC connector in series with a resistor of 5M omega.

Further, the step S3 includes:

s31, reducing the transient current in the cable sheath;

s32, shielding of the oscilloscope;

and S33, isolation of the power supply.

Further, the step S31 includes:

the voltage divider is arranged at a place close to the concentrated grounding electrode and is connected with the concentrated grounding electrode by the shortest connecting line, and the grounding connecting line adopts a wider copper strip or aluminum strip;

a metal plate or a metal belt with larger laying width from the voltage divider to the oscilloscope is used as a grounding connecting line, and a measuring cable is laid along the grounding connecting line and is close to the ground, so that the area of a loop formed by a cable sheath and the grounding connecting line is reduced as much as possible;

the length of the measuring cable is as short as possible;

the measuring cable adopts a wiring mode with two matched ends;

the measured voltage signal transmitted in the coaxial cable is improved, so that the proportion of common mode interference is reduced, namely the signal-to-noise ratio of a cable transmission link is improved, and the influence of the interference on measurement is reduced; the oscilloscope is connected with the measuring cable through the external 20dB attenuator, so that a measured voltage signal transmitted in the measuring cable takes a higher level, the signal-to-noise ratio is improved, and the influence of interference is reduced.

The invention has the advantages that:

the invention properly solves the problem of electromagnetic interference of the ferroelectric cathode test system by means of common point grounding, shielding, double-end matching, line connection, equipment arrangement and the like.

The vacuum chamber cavity structure has good electromagnetic interference resistance; acquiring low vacuum degree by adopting a mechanical pump and a diffusion pump; the amplitude of the output voltage of the pulse source is large, and the pulse rising time is short; designing an electromagnetic compatibility type resistance voltage divider to be combined with a 20dB attenuator to form a voltage test circuit; the current testing part adopts the Rogowski coil and the coupling capacitor, so that the electromagnetic interference shielding capability is strong, and the testing sensitivity is high.

In addition to the objects, features and advantages described above, other objects, features and advantages of the present invention are also provided. The present invention will be described in further detail below with reference to the drawings.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the invention and not to limit the invention.

FIG. 1 is a schematic diagram of a ferroelectric cathode test system according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of a sample voltage test circuit according to an embodiment of the present invention;

FIG. 3 is a cross-sectional view of a vacuum chamber of an embodiment of the present invention;

FIG. 4 is a schematic diagram of an improved voltage divider structure according to an embodiment of the present invention;

FIG. 5 is a schematic diagram of an improved voltage divider circuit according to an embodiment of the present invention;

FIG. 6 is a waveform of a pulse voltage measured by the improved voltage divider circuit according to an embodiment of the present invention;

fig. 7 is a schematic diagram of a transmit current test circuit of an embodiment of the present invention.

Reference numerals:

1 is a stainless steel vacuum chamber, 2 is polytetrafluoroethylene, 3 is a tray, 4 is a bracket, 5 is high-purity graphite, 6 is a copper electrode, 7 is a spring, 8 is a ceramic sample, and 9 is a shielding wire mesh;

the matching resistor 51 is a matching resistor 52, a high-voltage arm resistor 53 is a low-voltage arm resistor, a copper foil cylinder 54, a BNC connector 55, a stainless steel shielding box 56 and a vacuum cavity 57.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

According to one aspect of the present invention, a ferroelectric cathode test system is provided.

Referring to fig. 1, as shown in fig. 1, a ferroelectric cathode testing system includes a high voltage pulse power supply, a vacuum chamber, an emission current testing circuit, and a sample voltage testing circuit;

the high-voltage pulse power supply is respectively connected with one end of the vacuum chamber and the sample voltage testing circuit;

the emission current test circuit is connected with the other end of the vacuum chamber;

and the sample voltage testing circuit is connected with the oscilloscope.

The invention properly solves the problem of electromagnetic interference of the ferroelectric cathode test system by means of common point grounding, shielding, double-end matching, line connection, equipment arrangement and the like.

The vacuum chamber cavity structure has good electromagnetic interference resistance; acquiring low vacuum degree by adopting a mechanical pump and a diffusion pump; the amplitude of the output voltage of the pulse source is large, and the pulse rising time is short; designing an electromagnetic compatibility type resistance voltage divider to be combined with a 20dB attenuator to form a voltage test circuit; the current testing part adopts the Rogowski coil and the coupling capacitor, so that the electromagnetic interference shielding capability is strong, and the testing sensitivity is high.

Referring to fig. 2, as shown in fig. 2, the sample voltage test circuit includes resistors R0, R01, R1, R2, R3, R4, a double-shielded through-axis cable Z, and an attenuator;

after the resistors R0 and R01 are connected in series, one end of the resistor R0 is connected with a high-voltage pulse power supply, and one end of the resistor R01 is connected with the ground;

after the resistors R1 and R2 are connected in series, one end of the resistor R1 is connected with a high-voltage pulse power supply, and one end of the resistor R2 is connected with the ground;

one end of the resistor R3 is connected between the resistors R1 and R2, and the other end of the resistor R3 is connected with one end of the double-shielded through-axis cable Z;

one end of the attenuator is connected with the other end of the double-shielding through-axis cable Z, and the other end of the attenuator is connected with an oscilloscope;

the resistor R4 is connected between one end of the attenuator and the ground, and the double-shielding through-axis cable Z and the attenuator are connected with the sample voltage testing circuit in common.

R0＝47.8Ω R01＝6.9Ω R1＝792.4Ω R2＝48.7Ω R3=0.2Ω R4=50Ω Z=48.9Ω。

Referring to fig. 7, as shown in fig. 7, the emission current test circuit includes a direct current power supply (0-5 kV), a blocking capacitor C1, a rogowski coil K, and resistors R5, R6;

the direct current power supply is respectively connected with a graphite collector FC and a resistor R5;

one end of the resistor R5 is connected with a direct current power supply, and the other end of the resistor R5 is respectively connected with a graphite collector FC;

one end of the Rogowski coil K is connected with the resistor R5, and the other end of the Rogowski coil K is connected with the capacitor C1;

one end of the resistor R6 is connected with the capacitor C1, and the other end is connected with the ground.

Outer diameter of vacuum chamber and thickness of vacuum chamber wall

According to the electromagnetic field radiation principle, the induction electromagnetic field is inversely proportional to the square of the distance, and the radiation electromagnetic field is inversely proportional to the distance, so that the larger the shielding distance is, the larger the attenuation amplitude of the electromagnetic field intensity is, in other words, the shielding effect is improved, the shielding distance is better in principle, under the condition of permission, the horizontal shielding distance can be selected from 20cm to 30cm, under the general condition that the vertical shielding distance can be selected from 50cm to 60 cm., when the good high-frequency electrical contact performance and the good radio-frequency grounding of the shielding body are ensured, the shielding distance can be reduced to 10cm to 20 cm., the increase of the distance is beneficial to the improvement of the shielding effect and the experiment operation (ferroelectric samples are frequently required to be taken and replaced), however, the overlarge distance is not beneficial to vacuum pumping, and the grounding resistance of the grid is increased.

Considering the wall thickness of the vacuum chamber, the penetration depth of the high-frequency electromagnetic wave radiated in the experiment to the stainless steel is very small, and is only a few hundredths of millimeters, so the design of the thickness of the vacuum chamber can reduce the grounding resistance of the grid by thickening on the premise of meeting the pressure resistance strength required in the experiment under the vacuum degree.

Selecting a vacuum chamber cavity structure and materials:

the cavity structure is designed into a cylindrical coaxial structure with an upper part and a lower part, namely, an excitation pulse source is introduced from the top end of the cavity, and an electron emission signal is led out from the bottom (as shown in figure 3), so that the purpose of reducing electromagnetic interference is mainly achieved. Because the top end of the cavity is grounded, the central axis of the cavity and the wall of the cavity form a loop, and current in opposite directions flows through the central axis and the wall of the cavity, so that the space magnetic field is weakened to a certain extent.

In the aspect of selecting cavity materials, considering the problems of grid grounding, electromagnetic compatibility of the whole experiment platform and the like in the experiment, metal is selected as a vacuum chamber manufacturing material. Metals have high mechanical strength, are not easily broken, and have low saturated vapor pressure, so the choice of the vacuum chamber material between metals is mainly due to its airtightness and outgassing rate. The metal materials commonly used for manufacturing the vacuum container include carbon steel, stainless steel, alloy steel, stainless clad steel, copper, aluminum, gold, and the like. The choice between copper and stainless steel is a major consideration depending on the requirements of the actual process.

TABLE 1 Normal temperature outgassing rates for stainless steels and copper

Referring to the above table, the stainless steel surface outgassing rate is low at room temperature, the gas permeation rate to stainless steel is small, and the vacuum performance is superior to copper. The stainless steel has good chemical stability, corrosion resistance, high temperature stability and good mechanical strength, and is a better material for a vacuum system. Copper has good heat conductivity and electrical conductivity, good vacuum performance, high plasticity and impact toughness at low temperature, and easy processing. However, copper is easy to rust when exposed to air for a long time, and the vacuum performance and the mechanical strength of the copper are inferior to those of stainless steel, and the price of the copper is higher than that of the stainless steel. Stainless steel is selected to be superior to copper in terms of vacuum performance, mechanical performance, corrosion resistance, price ratio and the like of the material. Therefore, the cavity material is determined to be stainless steel, and the chemical formula is 1Cr18Ni9 Ti. On one hand, the stainless steel material has better electrical conductivity and higher mechanical strength, and is easy to be processed into various shapes. In addition, polytetrafluoroethylene is uniformly adopted as an insulating material in the design of the cavity, and the design is also based on the consideration of both insulating property and mechanical strength.

(4) Selection of vacuum cavity insulating lining

According to the practical requirement of the experiment, the vacuum cavity insulating lining is selected mainly considering the aspects of good insulating property, good vacuum property, corrosion resistance, good temperature stability and the like, and compared with polytetrafluoroethylene, the polyethylene and polyvinyl chloride applied to a vacuum system are narrow in the use range, generally-40-60 ℃, and poor in mechanical property when the temperature is higher than 60 ℃, the Polytetrafluoroethylene (PTFE) has the advantages that ① tissues are compact, the air permeability is low, the air release amount is small if the temperature is not high in vacuum, the air release rate is increased rapidly when the temperature is increased to 200-300 ℃, toxic gaseous fluorine is released after decomposition at 400 ℃, ② has excellent electric insulating property, the resistivity is as high as 1 × 1017 ohm cm, is not influenced by the working environment, the temperature and the frequency, has good arc resistance, ③ has good dielectric property, the dielectric strength is 60kV/mm, the dielectric loss angle is small, and the tangent angle is 1MHz,the composite material is less than or equal to 2.5 × 10-4, ④ has good low-temperature resistance, can be used for a long time at the temperature of-250-260 ℃, ⑤ has very good chemical stability and corrosion resistance, and ⑥ polytetrafluoroethylene is insoluble in any organic solvent, does not absorb water and is not soaked.

(5) Ferroelectric cathode sample support structure

The support structure for the sample comprises a sample tray and a support. Considering that samples with different sizes, thicknesses, shapes and electrode structures (grounded gate electrodes) need to be replaced in experiments, the tray for placing the samples in the cavity is of a detachable structure. Making multiple sets of sample trays with emission apertures ofAnd for samples with different size characteristics, only the corresponding tray needs to be replaced.

In order to reduce the grid ground resistance, the sample tray position is as low as possible, considering the adjustment of the collector height, where the tray height is designed to be 30 mm. The support is welded on the wall of the vacuum chamber, the tray and the support are tightly lapped by three screws, and the contact surface between the sample tray and the support frame is kept clean. The connecting part needs to keep certain contact pressure, and is fastened by screws, and the fastening distance of the screws is small enough; the contact surface is machined to a regular, rough surface, which is better than smooth machining.

(6) Electrode connection

Based on the consideration of conductivity, a copper connecting rod is selected as a connecting passage of an excitation pulse source and a sample back electrode in an experiment. To ensure good and reliable electrical contact between the tie-bar and the back electrode, a threaded structure was initially used. However, if the sample is thin, the sample is susceptible to chipping during tightening of the threads. In order to ensure the soft connection between the connecting rod and the sample back electrode while ensuring good electric contact, a soft spring with smaller elastic coefficient is arranged in the improved connecting rod. In order to reduce the inductive interference, a thicker connecting rod is structurally selected.

(7) Collector electrode

In the aspect of designing the electron collector, graphite is selected as a collector material. Graphite is selected instead of a common metal material (such as copper) as an anode material for collecting electrons, because graphite is inert in chemical property at normal temperature, has good heat resistance and is not easy to oxidize, solid compounds are not formed on the surface at high temperature like metal, but CO and CO2 are generated and volatilized, and graphite has thermal conductivity not inferior to that of metal and better electrical conductivity. In addition, the metal texture is harder than graphite, and after electrons fly from the emitter, the electrons touch the surface of copper metal, most of the electrons are absorbed by copper, and part of the electrons are refracted secondarily and are ejected from a copper collector like an elastic ball. The graphite collector is soft and loose in texture and good in conductivity, so that the graphite collector is more suitable for collecting electrons.

The designed graphite is planar truncated cone graphite with D =45mm, and the height of the graphite is thinner in order to reduce the resistance of the graphite, and 15mm is selected. The graphite electrode is connected with the copper bar at the bottom end of the cavity through threads, and the transmitting signal is guided out of the cavity. The height of the graphite, and thus the anode-cathode distance, can be varied by rotating the threads.

Fig. 4 shows a cross-sectional view of the vacuum chamber of the electron emission system. The air extraction holes on the side surfaces are of a larger size of phi 100mm, and the purpose is to improve the air extraction speed.

The vacuum of the electron emission system is obtained by the cooperative work of a backing pump (mechanical pump) and a main pump (diffusion pump).

The system adopts a TK-150 diffusion pump, and the heating power is 1.2 KW. The diffusion pump consists of a pump shell, a pump core, an evaporating pot, a heater, a cooling water pipe (sleeve) and the like. The pump casing of the pump is made into a convex cavity between the first-stage nozzle and the second-stage nozzle, so that the pumping speed is increased conveniently. The pump casing is mainly used for installing a pump core, isolating atmosphere and condensing oil steam, and the inner surface of the pump casing is polished. The pump core consists of several stages of nozzles and several steam pipes and is fixed inside the pump casing with central pull rod.

Selecting a high-voltage pulse power supply:

the pulse source used in the experiment was shanghai tribasicModel ENS-24XA high frequency noise simulator manufactured by electronics industry limited. ENS-24XA can provide rectangular pulse with maximum output amplitude of 2.2kV and pulse width of 50 ns-1 mu s, and the rise time of the rectangular pulse isThe pulse polarity may be positive or negative.

And (3) voltage testing:

the ceramic coated electrode can be seen as a capacitor in the circuit. In the experiment, the voltage on two sides of the ceramic needs to be measured, and a resistance type voltage divider needs to be adopted for measurement due to higher excitation voltage. The voltage divider type selects a resistive voltage divider, and fig. 2 is a test circuit diagram.

In fig. 2, R0 and R01 are matching dummy resistors for reducing stray capacitance between resistors and between the resistors and ground, R1 is a high-voltage arm resistor, R2 is a low-voltage arm resistor, and an oscilloscope records voltages on both sides of the low-voltage arm. The coaxial cable and the attenuator are attached to the digital oscilloscope probe.

Design and determination of partial pressure ratio

Any resistor has certain stray inductance, certain stray capacitance exists between the resistors and between the resistor and the ground, and leads are inevitable in the voltage divider and the measuring loop. Thus, designing a resistive divider with nanosecond response time must take into account the effect of the distributed parameters on the response time of the resistive divider.

The 10% -90% rise time of the output waveform of the resistor voltage divider considering the distributed stray parameters is as follows:

（1）

where R is the total resistance of the voltage divider and C is the total capacitance to ground of the voltage divider. I.e. the rise time of the resistor divider is proportional to the product of the total resistance and the total capacitance to ground. Therefore, to reduce the rise time of the voltage divider, the capacitance to ground and the total resistance of the voltage divider should be reduced as much as possible. The stray inductance of the resistor is required to be small, the oscillation of the measured waveform is reduced, and the requirements must be metFor low-voltage arm resistor, the stray inductance to the ground is also required to be small, and the requirement must be met. The inductance of the non-inductive resistor is close to the magnitude of 0.1 muH-0.1 mH. The capacitance to ground of the whole voltage divider is generally 1-hundreds of PF magnitude, and the capacitance to ground of the coaxial cable is generally 100 PF/m. Therefore, for the first-stage resistor divider, the low-voltage arm resistor cannot be too small, and the voltage dividing ratio cannot be too large.

According to the analysis, the high-voltage arm, the low-voltage arm and the matching resistor of the resistor divider are designed based on the characteristics of the experiment, as shown in fig. 2. The theoretical voltage division ratio of the voltage divider is calculated

（2）

Correction of the voltage division ratio, estimated as 2% attenuation of the surge voltage peak per 100m cable, isCan be modified into

（3）

Wherein the content of the first and second substances,to measure the cable length, the unit m.

（4）

The designed voltage divider is placed in the circuit shown in fig. 2, the pulse source outputs different voltages, the oscilloscope records the voltages at two sides of the low-voltage arm, and the output terminal is connected to the oscilloscope through the 20dB attenuator. The actual voltage division ratio of the circuit was measured and the measured value was slightly below the theoretical value, and table 2 gives the experimental results. The partial pressure ratios used in the following experiments were all the partial pressure ratios measured in table 2.

TABLE 2 divider ratio measurement (terminated with a 20dB attenuator)

An electromagnetic compatibility voltage divider architecture is presented. The high-voltage arm, the low-voltage arm and the matching resistor of the voltage divider are ceramic non-inductive resistors made of the same material and by the same process, the low-voltage arm and the matching resistor are arranged in a coaxial structure, and the core wire of the BNC joint is superposed with the axis of the cylindrical resistor, so that the current direction of the axis is opposite to that of the resistor body. And put into a metal cylinder made of a copper foil 0.2mm thick with intermediate insulation. The top end of the cylinder is connected to common ground with the shield can to reduce the inductive effect. The whole voltage divider is put into a shielding box made of stainless steel. Fig. 5 is a schematic diagram of the improved voltage divider, and fig. 6 is a waveform of the pulse voltage measured by the voltage divider. As can be seen, the pulse voltage waveform measured by the improved voltage divider is greatly improved.

The structure of the non-inductive resistor network coaxial shunt is characterized in that:

a) the resistor arrangement and the interface design both adopt coaxial structures, the symmetry is good, and the metal drum is adopted outside, so that the influence of distribution parameters can be reduced, and stray magnetic fields can be shielded. Signals are connected into the oscilloscope through the coaxial cable, so that the fidelity is good;

b) the connecting part between the resistors is made of brass, the surface of the connecting part is plated with silver, the conductivity is good, and the resistors and the lead wires are connected by welding tin; the high-voltage input end is connected with the pulse source output cable by adopting a BNC connector, and the low-voltage arm output end is connected with the double-shielded coaxial cable by adopting a BNC connector.

c) The voltage divider is placed in a shielding box made of stainless steel so as to avoid the interference of electromagnetic radiation generated by impact voltage and the like on an external measuring instrument and a signal wire.

Ross (Rogowski) coils are widely used for measurement of transient high frequency signals. The Ross coil method is also called hollow coil method, and has the advantages of wide measuring range, wide response frequency, no electric connection with the measured loop, small volume, convenient installation, etc.

As shown in FIG. 7, the current testing circuit comprises a DC power supply (0-5 kV), a blocking capacitor, a Rogowski coil and a resistor. The entire test circuit was placed in an aluminum shield box. Under experimental conditions, the potential of the gate is zero and the potential of the collector is also zero before the electrons reach, so that the emitted electrons have a distribution between the collector and the gate. Moreover, the initial velocity of the self-emitted electrons is limited and satisfies a distribution, and an extraction electric field is added to extract more electrons. A high DC voltage is applied to the graphite collector FC to apply an extraction electric field to the emitted electrons and improve the current distribution between electrodes.

The graphite collector FC is used for collecting electrons, the graphite electrode is connected with a copper bar at the bottom end of the cavity through threads, and an emission signal is guided out of the cavity.

In fig. 3, the 5M Ω resistance is relatively large for the emission current, approximately open circuit, which separates the emission current from the dc high voltage source. The capacitance must be selected such that:

(1) the transmitted current signal cannot be distorted, i.e. because ofWhile the lost part must be negligibly small; the output impedance of the Rogowski coil is 50 omega, and the transmitting current is measured by an electromagnetic induction method; the coupling capacitor is used for filtering and eliminating interference signals, and the capacitive reactance is required to be very small; satisfies the formula:

(2) c is too large and tends to oscillate, which also distorts the signal. Therefore, C should not be too large. It should satisfy:

l is the inductance of the Rogowski coil,C _{equivalence of}Is the equivalent capacitance in parallel with the oscilloscope, and BW is the bandwidth of the oscilloscope.

When the oscillation frequency is larger than the bandwidth of the oscilloscope, the oscilloscope does not show oscillation. The coupling capacitor in this experiment was a 100nF polypropylene noninductive capacitor.

Selection of measuring devices

(1) Oscilloscope

A TDS724C model dual channel digital storage oscilloscope manufactured by Tektronix corporation. The bandwidth is 500M, and the highest sampling rate is 1G/s. For TDS724C, the relationship between rise time and bandwidth satisfies:，。

(2) rogowski coil

The Ross coil used in the experiment was the model 6585 Ross coil Pearson Current Generator MODE L6585, manufactured by Pearson corporation.

(a) The electromagnetic interference shielding device has very strong electromagnetic interference shielding capability;

(b) the universality is strong, a standard BNC connector is adopted, and the output impedance is 50 omega;

(c) the bandwidth range is large, 400 Hz-250 MHz, and all rising edges which are not faster than 1.5ns can be detected;

(d) the current signal with the peak value not exceeding 500A and the root mean square not exceeding 10A can be detected;

(e) the test sensitivity of the coil is 1V/A1%。

(3) Measuring cable

In order to ensure better waveform transmission performance and anti-interference performance, a double-shielding high-frequency coaxial cable is selected as the measuring cable. The length of the measuring wire should be as short as possibleTo reduce the attenuation deformation of the measured waveform in the measuring cable and reduce the electromagnetic interference formed in the measuring cable. The length of the measuring cable used in the experiment was 1 m. The inner diameter a =1.38mm and the outer diameter b =4.62mm of the coaxial cable, and an insulating medium polytetrafluoroethyleneThereby calculating the cable impedance.

（5）

(4) High-voltage lead wire

The high-voltage lead wire adopts a wire which has low inductance, low resistance and larger sectional area and is formed by connecting a plurality of uniformly split wires in parallel. The electric field around the individual wires is reduced to avoid corona effects on the performance of the measurement system and the high voltage leads are as short as possible. A red copper braided belt with the length of 12cm, the width of 2cm and the thickness of 1.5mm is selected as a high-voltage lead.

According to yet another aspect of the present invention, there is provided a ferroelectric cathode testing method comprising the steps of:

s1, providing a vacuum environment for testing by a vacuum chamber, inhibiting the interference of internal high-frequency electromagnetic radiation on external equipment by an electromagnetic shielding chamber in the vacuum chamber, shielding the interference of external electromagnetic radiation on an internal circuit, and establishing a low-resistance path between a grid and the ground to prevent the personal safety from being endangered by high-voltage discharge;

s2, selecting an oil diffusion pump as a main pump to obtain high vacuum in the test, wherein the vacuum environment is obtained by the cooperative work of a backing pump (mechanical pump) and the main pump (diffusion pump);

s3, measuring the connection and arrangement method of the equipment;

and S4, anti-interference method.

The step S3 includes:

position of voltage divider and sample: the voltage divider is directly connected to the high-voltage end of the test object by a high-voltage lead wire, and is not connected to the output end of the surge voltage generator or directly connected to a connecting wire between the generator and the test object, so that the inductive voltage drop on the connecting wire is not included in measurement.

Grounding of the test equipment: the oscillograph and the voltage divider are connected with each other by red copper braided belts with the width of 2cm and the thickness of 1.5mm, so that the transient current in the cable sheath is weakened, and the electromagnetic interference is reduced. The impulse voltage generator ground end has larger current passing through, and is directly connected to the red copper braided belt in order to reduce the impedance of the ground.

A concentrated grounding electrode is arranged close to the voltage divider, and the voltage divider and a grounding end of a test article adopt a copper foil broadband of 2cm and 0.2mm in thickness to be connected with the grounding electrode. The voltage divider is directly connected with the grounding end of the sample (common ground) and forms a loop by itself. And the impedance of the grounding loop is reduced as much as possible so as to reduce the measurement error caused by the impedance voltage drop of the loop.

End matching of the measuring cable: matching measures are adopted at the joints of the two ends of the measuring cable and the voltage divider and the measuring instrument so as to prevent wave oscillation caused by multiple reflections in the cable. And a matching mode of matching two ends is adopted in the experiment.

The oscilloscope is externally connected with an attenuator: in order to make the measured voltage signal transmitted in the measuring cable take a higher level so as to improve the signal-to-noise ratio and reduce the influence of interference, an attenuator is used at the terminal of the measuring cable. On the other hand, the voltage divider ratio can be improved by using the voltage divider, and the oscilloscope is connected with the measuring cable through the external attenuator. In the experiment, an attenuator with 20dB and a bandwidth of 3GHz is selected.

A vacuum chamber lead: the design of the vacuum chamber adopts a coaxial structure. The upper end and the lower end are led out by copper bars, the upper end is a high-voltage electrode, and the lower end is a collector. In order to shield the electromagnetic radiation of the high-voltage pole, a double-layer shielding cover is manufactured by adopting a PVC sleeve and a copper sheet with the thickness of 0.2 mm. The high-voltage lead is led out from the copper bar of the inner layer of the shielding sleeve by the BNC connector, and the outer skin of the shielding cover is grounded. In the same way, the collector is shielded by a double-layer shielding cover, and a transmitting current signal wire is led out from a copper bar connected with graphite from the inner layer through a BNC joint. Meanwhile, a direct-current bias lead of the collector is led out by connecting a BNC connector in series with a resistor of 5M omega.

There are three main sources of electromagnetic interference: measuring transient current flowing in the cable and the sheath of the trigger signal cable; space electromagnetic wave radiation generated during gap discharge; interference and potential introduced by the oscilloscope power line. Corresponding anti-interference measures are required for the three interference sources.

The step S3 includes:

s31, reducing the transient current in the cable sheath;

s32, shielding of the oscilloscope;

and S33, isolation of the power supply.

The step S31 includes:

measuring electromagnetic interference caused by transient currents in the cable sheath is commonly referred to as common mode interference. In actual measurement, compared with interference caused by other sources, the interference is often the most serious and must be fully considered. To reduce the common mode interference level, the following measures are taken.

The voltage divider is arranged at a place close to the concentrated grounding electrode and is connected with the concentrated grounding electrode by the shortest connecting line, and the grounding connecting line adopts a wider copper strip or aluminum strip;

a metal plate or a metal belt with larger laying width from the voltage divider to the oscilloscope is used as a grounding connecting line, and a measuring cable is laid along the grounding connecting line and is close to the ground, so that the area of a loop formed by a cable sheath and the grounding connecting line is reduced as much as possible;

the length of the measuring cable is as short as possible;

the measuring cable adopts a wiring mode with two matched ends;

the measured voltage signal transmitted in the coaxial cable is improved, so that the proportion of common mode interference is reduced, namely the signal-to-noise ratio of a cable transmission link is improved, and the influence of the interference on measurement is reduced; the oscilloscope is connected with the measuring cable through the external 20dB attenuator, so that a measured voltage signal transmitted in the measuring cable takes a higher level, the signal-to-noise ratio is improved, and the influence of interference is reduced.

The invention provides a corresponding solution to the problem of electromagnetic interference which may be encountered in the emission of a ferroelectric cathode. On the basis, various main electromagnetic interference control means are integrated, and the built test system is repeatedly debugged and improved through structural design, grounding, shielding, impedance matching, line connection, equipment arrangement and other modes, so that the electromagnetic interference problems are properly solved, and a satisfactory test result is obtained.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.