CN109270374B - Method for monitoring safe work of convoluted traveling wave - Google Patents
Method for monitoring safe work of convoluted traveling wave Download PDFInfo
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Abstract
The invention discloses a method for monitoring the safe operation of a gyrotron traveling wave tube, which comprises the following steps: s1, constructing a convoluted traveling wave tube model based on complex plasma formation and evolution; s2, setting a parameter range of the gyrotron traveling wave tube during normal work; s3, continuously inputting the electron beam and the external magnetic field into the gyrotron traveling wave tube model, and judging whether the working parameters are in the parameter range during normal working, if so, continuously outputting microwaves by the gyrotron traveling wave tube model, and if not, entering the step S4; s4, temporarily stopping inputting the electron beam and the external magnetic field into the gyrotron traveling wave tube model until the working parameters return to the parameter range in normal working, continuing to work the gyrotron traveling wave tube model, and continuously outputting microwaves. Aiming at the problem of poor continuous working reliability of the current gyrotron traveling wave tube, the invention establishes a gyrotron traveling wave tube model and provides effective improvement guidance for the continuous working reliability of the gyrotron traveling wave tube.
Description
Technical Field
The invention belongs to the technical field of plasma analysis, and particularly relates to a method for monitoring the safe work of a gyrotron traveling wave tube.
Background
The gyrotron traveling wave tube is difficult to stably and reliably work for a long time due to the reasons of material outgassing and the like in high working and continuous wave states, and after the gyrotron traveling wave tube continuously works for 6-7 hours, a device enters a failure high-frequency period. At present, the factors for limiting the stable and reliable work of the gyrotron traveling wave tube are not completely clear internationally, so that the engineering practicability of the gyrotron traveling wave tube is greatly reduced.
Through a large number of high-power experimental researches in a laboratory, it is concluded that residual gas impact ionization is the most important factor affecting stable operation of a device, as shown in fig. 1, as the vacuum degree is reduced, residual gas impact ionization is aggravated, and the device operation will face the following problems: ripple waves in working current pulses, noise floor improvement of devices, frequency spectrum stray, power fluctuation, pulse waveform abnormity, pulse waveform collapse, breakdown ignition, output window burst and the like.
As shown in fig. 2, the reason why the above problem occurs is that: the device is inevitably operated in a small-cross-section, high-voltage and large-current environment to provide an effective interaction high-frequency structure and sufficient direct-current conversion power in order to meet the requirement of millimeter-wave high-power output, and the small-scale, high-power, high-voltage and large-current operating environment causes large power loss of the device per unit area, high electric field intensity and high current density. Along with the increase of the power loss density, the working temperature of the inner wall of the device rises, the contained deep gas diffuses outwards, the surface gas is also desorbed, the quantity of residual gas in the device is increased, and the vacuum degree is reduced; the device works in a high-voltage and high-current state, a large number of electrons are accelerated by an external electric field and collide with residual gas, and ionization is generated after collision because the kinetic energy of the electrons is greater than the ionization energy of the residual gas; the ionized electrons are continuously accelerated by an external electric field to generate an avalanche breakdown phenomenon, so that a large amount of ionization occurs.
Particularly, under the action of a 'magnetic mirror' formed by a rising magnetic field of the transition section, part of stray electrons with higher transverse speed can reside in the adiabatic compression area to reciprocate, so that the ionization probability of residual gas is increased; a large amount of protons and electrons are detonated to the cathode and the anode surface to cause local temperature rise and surface gas desorption, and the vacuum degree is further deteriorated; electrons formed by ionization can also form synchronous radiation under the action of a high-frequency field, so that the noise floor of the device is improved, the parasitic mode oscillation starting threshold is reduced, and the occurrence of stray frequency spectrum is caused; if continuous ionization appears, still can cause the breakdown "strike sparks" of device, if the device protection is untimely, the breakdown energy will last to be used in weak links such as body output window, causes the output window to damage.
In summary, the output power of the high-power millimeter wave device operating under high voltage and large current is increased, the vacuum degree is reduced, and the residual gas is ionized, so that the performance of the device is reduced and even the device is damaged.
The traditional high-power vacuum device wave injection interaction transduction analysis model is always established under the assumption of 'absolute vacuum', namely only the interaction between emitted electron beams and electromagnetic waves is considered, the assumption is reasonable under the condition that the device works under the conditions of lower duty ratio and short pulse, so that the traditional plasma analysis method is widely applied to the development stage of a performance sample tube, the traditional plasma analysis method is mainly used for describing the physical process of impact ionization, and the system does not consider the bombardment effect of 'stray' charges on the inner wall of the device after the impact ionization and the problem of cycle deterioration of vacuum degree caused by the bombardment ionization under the action of a strong electromagnetic field, and the influence of the change of the electron beam phase space distribution after the impact ionization on the wave injection interaction.
Disclosure of Invention
Aiming at the defects in the prior art, the method for monitoring the safe work of the gyrotron traveling wave tube solves the problem that the gyrotron traveling wave tube can not work stably and efficiently for a long time in the prior art.
In order to achieve the purpose of the invention, the invention adopts the technical scheme that: a method for monitoring the safe operation of a gyrotron traveling wave tube comprises the following steps:
s1, constructing a convoluted traveling wave tube model based on complex plasma formation and evolution;
s2, setting a parameter range of the gyrotron traveling wave tube during normal work;
s3, continuously inputting the electron beam and the external magnetic field into the cyclotron traveling wave tube model, judging whether the working parameters of the cyclotron traveling wave tube model are within the parameter range during normal working, if so, continuously outputting microwaves by the cyclotron traveling wave tube model, and finishing monitoring until the output microwaves reach the set target working parameters and duration; if not, go to step S4;
s4, temporarily stopping inputting the electron beam and the external magnetic field into the cyclotron traveling wave tube model, simultaneously vacuumizing and cooling the cyclotron traveling wave tube, improving the environment in the tube under the condition of not changing the material of the tube wall until the working parameters return to the parameter range in normal working, enabling the cyclotron traveling wave tube model to continuously work, and continuously outputting microwaves; and when the output microwaves reach the set target working parameters and duration, finishing the monitoring.
Further, in step S1, the gyrotron traveling wave tube model includes a trajectory analysis module, a collision analysis module, a tube internal air pressure dynamic analysis module, and an electromagnetic field analysis module;
the trajectory analysis module is used for quantitatively giving charge trajectories and velocity distributions before and after collision, providing charge phase space distribution conditions for collision probability analysis, air pressure dynamic analysis and wave injection interaction, and evaluating the bombardment effect of stray electrons on the wall of the device; the track analysis module is coupled with the collision analysis module, the air pressure dynamic analysis module and the electromagnetic field analysis module;
the collision analysis module is used for quantitatively giving collision occurrence probability, collision position, charge speed and track change after collision scattering and new charge distribution after ionization; the collision analysis module is respectively coupled with the track analysis module and the in-pipe air pressure dynamic analysis module;
the in-tube air pressure dynamic analysis module is used for quantitatively analyzing the collision probability of the charges and the residual gas in the cyclotron traveling wave tube model; the in-pipe air pressure dynamic analysis module is coupled with the track analysis module;
the electromagnetic field analysis module is used for analyzing the influence of the new space charge phase space distribution generated after impact ionization on the wave injection interaction; the electromagnetic field analysis module is coupled with the collision analysis module.
Further, the analysis process of the trajectory analysis module specifically includes:
a1, determining the phase space of each macro charge according to the emitted electron beam, the electromagnetic field in the cyclotron traveling wave tube, the current time step of each electron and charge and the distribution of the new charge determined by the collision analysis module;
a2, determining the electromagnetic field force borne by the macro charge according to the position of the macro charge in the gyrotron traveling wave tube, and obtaining the speed of the next time step of the macro charge according to a macro charge motion equation;
a3, obtaining the position of the next time step according to the macro charge motion equation, and determining the bombardment effect of stray electrons on the wall of the gyrotron traveling wave tube according to the motion trail of the position;
the macro charge motion equation is as follows:
wherein the content of the first and second substances,is the charged particle momentum;
t is time;
e is the amount of charge;
is the electric field strength;
is the charged particle motion velocity;
is magnetic induction intensity;
the macro charge trajectory equation is:
wherein the content of the first and second substances,is the spatial position vector of the charged particles.
Further, the analysis process of the collision analysis module specifically includes:
b1, taking the time step of each macro charge as the increment of the time used by each round of calculation; circularly calculating the collision probability of macro charge changing along with the time evolution;
b2, according to the macro-charge movement speed and the position obtained by the trajectory analysis module and the gas collision cross section and the gas space density obtained by the gas pressure dynamic analysis module in the pipe, circularly calculating the collision probability p of each macro-charge changing along with the time evolutioni；
B3, generating a random number q of 0-1 for each macro particle in the interaction spaceiAnd with a collision probability piThe comparison is carried out in such a way that,
if q isi>piIf no collision occurs, the macro-ions keep the original motion state;
if q isi<piIf so, collision occurs, and collision ionization analysis and collision scattering analysis are carried out;
the collision probability p of each macro chargeiComprises the following steps:
in the formula, σ (E)0) Is a gas collision cross section;
viis the macro charge movement speed;
Δ t is the time length of the movement before the collision of the macro charge;
is the gas space density.
Further, the analysis process of the in-tube air pressure dynamic analysis module specifically comprises:
c1, determining the distribution of the dissipation power formed by the stray electrons bombarding the wall of the gyrotron traveling wave tube according to the trace analysis result of the macro charges obtained by the trace analysis module;
c2, determining the local temperature rise of the gyrotron traveling wave tube by taking the dissipated power as a heat source, and measuring the wall temperature of the tube;
c3, determining the material air-out rate of the gyrotron traveling wave tube according to the local temperature rise of the gyrotron traveling wave tube;
c4, calculating the gas space density according to the gas output rate of the material and an ideal gas state equation;
the ideal gas state equation is:
in the formula (I), the compound is shown in the specification,is the gas pressure;
is the gas space density;
k is Boltzmann constant;
t is the temperature in the cyclotron traveling wave tube.
Further, the analysis process of the electromagnetic field analysis module specifically includes:
d1, determining the state of the electron beam after ionization according to the trajectory analysis module and the collision analysis module;
the state of the electron beam comprises a trajectory and a velocity distribution of the electron beam;
d2, determining the influence degree of the electron beam on the wave-filling interaction process according to the quality and quantity change of the electron beam;
and D3, obtaining the influence of the collision effect on the wave-filling interaction by combining the wave-filling interaction equation according to the trajectory and the velocity distribution of the electron beam.
Further, the parameter range of the step S2 when the gyrotron traveling wave tube normally works includes:
gas space density: greater than 5 Pa;
tube wall temperature: less than 400 degrees Celsius;
dissipated power per unit area of tube wall: less than 1KW/cm2。
The invention has the beneficial effects that: the method for monitoring the safe working of the gyrotron traveling wave tube, provided by the invention, aims at the problem that the continuous working reliability of the current gyrotron traveling wave tube is poor, a mechanism formed by complex plasmas is taken as a main body, and subjects such as gas analysis dynamics, material physics, relativistic electronics and the like are combined, so that a gyrotron traveling wave tube model is established, and effective improvement guidance is provided for the continuous working reliability of the gyrotron traveling wave tube.
Drawings
Fig. 1 is a schematic diagram illustrating an influence of residual gas of a gyrotron traveling wave tube on device performance according to an embodiment of the present invention.
Fig. 2 is a schematic diagram of impact ionization analysis under impact under millimeter wave high-power operation in the embodiment provided by the invention.
Fig. 3 is a flowchart illustrating an implementation of a method for monitoring the safe operation of a gyrotron traveling wave tube according to an embodiment of the present invention.
Fig. 4 is a graph comparing the trajectory of the incident electron beam after impact ionization with the change in velocity in the embodiment of the present invention.
FIG. 5 is a comparison graph of the effect of vacuum degree in the electron gun region of the middle cyclotron traveling wave tube on the trajectory dispersion of the electron beam.
FIG. 6 is a graph comparing the effect of vacuum in electron gun region of a middle cyclotron traveling wave tube on electron beam energy dispersion.
FIG. 7 is a graph comparing the effect of vacuum in the electron gun region of a middle cyclotron traveling wave tube on the speed dispersion of electron beams.
FIG. 8 is a comparison graph of the effect of vacuum degree in the electron gun region of the middle cyclotron traveling wave tube on the fluctuation of electron beam current.
FIG. 9 is a graph comparing the ionization effect of vacuum in the high frequency region of the gyrotron traveling wave tube on the interaction in the embodiment of the present invention.
FIG. 10 is a graph comparing the effect of vacuum level in the high frequency region of the gyrotron traveling wave tube on the energy dispersion of the interaction in the embodiment of the present invention.
FIG. 11 is a graph comparing the effect of vacuum level in the high frequency region of the gyrotron traveling wave tube on the interaction power in the embodiment of the present invention.
FIG. 12 is a graph comparing the effect of vacuum in the high frequency region of a gyrotron traveling wave tube on the spectral spurious effect of interaction in the embodiment of the present invention.
Detailed Description
The following description of the embodiments of the present invention is provided to facilitate the understanding of the present invention by those skilled in the art, but it should be understood that the present invention is not limited to the scope of the embodiments, and it will be apparent to those skilled in the art that various changes may be made without departing from the spirit and scope of the invention as defined and defined in the appended claims, and all matters produced by the invention using the inventive concept are protected.
As shown in fig. 3, a method for monitoring the safe operation of a gyrotron traveling wave tube is characterized by comprising the following steps:
s1, constructing a convoluted traveling wave tube model based on complex plasma formation and evolution;
in step S1, the gyrotron traveling wave tube model includes a trajectory analysis module, a collision analysis module, a tube internal air pressure dynamic analysis module, and an electromagnetic field analysis module;
the trajectory analysis module is used for quantitatively giving charge trajectories and velocity distributions before and after collision, providing charge phase space distribution conditions for collision probability analysis, air pressure dynamic analysis and wave injection interaction, and evaluating the bombardment effect of stray electrons on the wall of the device; the track analysis module is coupled with the collision analysis module, the air pressure dynamic analysis module and the electromagnetic field analysis module;
the collision analysis module is used for quantitatively giving collision occurrence probability, collision position, charge speed and track change after collision scattering and new charge distribution after ionization; the collision analysis module is respectively coupled with the track analysis module and the in-pipe air pressure dynamic analysis module;
the in-tube air pressure dynamic analysis module is used for quantitatively analyzing the collision probability of the charges and the residual gas in the cyclotron traveling wave tube model; the in-pipe air pressure dynamic analysis module is coupled with the track analysis module;
the electromagnetic field analysis module is used for analyzing the influence of the new space charge phase space distribution generated after impact ionization on the wave injection interaction; the electromagnetic field analysis module is coupled with the collision analysis module.
In the trajectory analysis module, a macro charge motion equation and a trajectory equation are used as a basis, the space macro charge after impact ionization is considered to be composed of two parts, macro electrons and ionization macro charge are emitted, the ionized macro charge is required to be superposed into the trajectory analysis module and the electromagnetic field analysis module which are calculated in the next step in each step, and the analysis process specifically comprises the following steps:
a1, determining the phase space of each macro charge according to the emitted electron beam, the electromagnetic field in the cyclotron traveling wave tube, the current time step of each electron and charge and the distribution of the new charge determined by the collision analysis module;
a2, determining the electromagnetic field force borne by the macro charge according to the position of the macro charge in the gyrotron traveling wave tube, and obtaining the speed of the next time step of the macro charge according to a macro charge motion equation;
a3, obtaining the position of the next time step according to the macro charge motion equation, and determining the bombardment effect of stray electrons on the wall of the gyrotron traveling wave tube according to the motion trail of the position;
the macro charge motion equation is as follows:
wherein the content of the first and second substances,is the charged particle momentum;
t is time;
e is the amount of charge;
is the electric field strength;
is the charged particle motion velocity;
is magnetic induction intensity;
the macro charge trajectory equation is:
wherein the content of the first and second substances,is the spatial position vector of the charged particles.
In the collision analysis module, firstly, the collision probability in the whole interaction space is analyzed, and the collision probability formula of the incident macro charges in the interaction space is determined, and the collision probability formula shows that the higher the gas space density is, the higher the collision probability is. Generating a random number between 0 and 1 for each macro particle in the space on the basis, wherein if the random number is smaller than the ionization probability, the macro particles collide with the residual gas, and when the incident charge energy is larger than the ionization energy of the residual gas, ionization occurs; if the random number is greater than the collision probability, no collision or ionization occurs. When collision occurs, incident electrons are scattered, the speed and the motion track of the incident electrons are changed due to scattering, and the change rule meets the energy conservation and momentum conservation principle. The analysis process specifically comprises the following steps:
b1, taking the time step of each macro charge as the increment of the time used by each round of calculation; circularly calculating the collision probability of macro charge changing along with the time evolution;
b2 macro obtained by the trajectory analysis moduleThe charge movement speed, the position and the gas space density of the gas collision section obtained by the gas pressure dynamic analysis module in the tube are circularly calculated, and the collision probability p of each macro charge changing along with the time evolution is calculatedi；
B3, generating a random number q of 0-1 for each macro particle in the interaction spaceiAnd with a collision probability piThe comparison is carried out in such a way that,
if q isi>piIf no collision occurs, the macro-ions keep the original motion state;
if q isi<piIf so, collision occurs, and collision ionization analysis and collision scattering analysis are carried out;
the collision probability p of each macro chargeiComprises the following steps:
in the formula, σ (E)0) Is a gas collision cross section;
viis the macro charge movement speed;
Δ t is the time length of the movement before the collision of the macro charge;
is the gas space density.
It should be further noted that, because the occurrence of impact ionization changes the trajectory of incident electrons and generates ionized charges, the motion trajectory and speed of these charges will be influenced by the electromagnetic field and impact effect, and the motion trajectory is no longer the cyclotron motion along the fixed magnetic lines, but the "jump" motion between different magnetic lines due to impact scattering and random ionization. This type of electron is called "stray" charge, where positive ions ionized in the center of the electron gun bombard the porous cathode structure, and some "electrons" ionized at the high frequency edge bombard the porous loaded ceramic structure along the outer magnetic lines, all of which cause the temperature of these materials to rise, the gas out rate to increase, the vacuum degree of the device to decrease, and the probability of residual gas impact ionization to increase.
In the above-mentioned in-tube gas pressure dynamic analysis module, the analysis module can quantitatively analyze the collision probability of the charge and the residual gasThe gas space density must be clearAnd the ideal gas state equation:it is known that the density of the gas space is constant at a constant temperatureWith gas pressureProportional relation is formed; the analysis process specifically comprises the following steps:
c1, determining the distribution of the dissipation power formed by the stray electrons bombarding the wall of the gyrotron traveling wave tube according to the trace analysis result of the macro charges obtained by the trace analysis module;
c2, determining the local temperature rise of the gyrotron traveling wave tube by taking the dissipated power as a heat source, and measuring the wall temperature of the tube;
c3, determining the material air-out rate of the gyrotron traveling wave tube according to the local temperature rise of the gyrotron traveling wave tube;
c4, calculating the gas space density according to the gas output rate of the material and an ideal gas state equation;
the ideal gas state equation is:
in the formula (I), the compound is shown in the specification,is the gas pressure;
is the gas space density;
k is Boltzmann constant;
t is the temperature in the cyclotron traveling wave tube.
In the electromagnetic field analysis module, the analysis method can adopt a wave injection interaction analysis method under 'absolute vacuum', but the influence of an ionization term needs to be superposed in the wave injection interaction analysis process, so that the active term of the active MAXWELL equation is composed of two parts when the active MAXWELL equation is solved: 1) the cathode emits an electron beam; 2) ionizing the charge. Due to the randomness of the ionization process, the analysis process is more complex, so that the analysis needs to be hierarchically decomposed. The analysis process specifically comprises the following steps:
d1, determining the state of the electron beam after ionization according to the trajectory analysis module and the collision analysis module; wherein the state of the electron beam comprises the trajectory and the velocity distribution of the electron beam; compared with the non-collision ionization state, the electron beam is influenced by collision and ionization of residual gas besides the action of an external static field in the motion process, the disturbance of the part can cause the quality and quantity change of the electron beam, and the quality change comes from the change of the trajectory and the speed of the electron beam after the electron beam collides with the residual gas; and the change in the number of electron beams results from ionization of the residual gas to create a new source of ionizing charge.
D2, determining the influence degree of the electron beams on the wave injection interaction process according to the quality and quantity changes of the electron beams; when the high-frequency field of the interaction is comparable to the external magnetic field, the interaction process is very complex, for simplifying analysis, the amplitude of the high-frequency field generated in the interaction process can be assumed to be far smaller than the amplitude of the external magnetic field (small signal approximation), the modulation of the electron beam by the high-frequency field is ignored at the moment, only the collision effect of the static field and the residual gas is considered, at the moment, the motion track and the velocity distribution of the electron beam can be obtained according to the electron motion and collision theory, as shown in fig. 4, the motion track of the emitted electron beam is not changed greatly due to the action of the external magnetic field after collision, and the velocity dispersion is increased; and the ionization charge appears, and the ionization corresponds to different motion tracks and speeds at different positions. In FIG. 4, (a) and (c) are10-7Pa under light ionization conditions, (b) and (d) are at 10-6Obtained under the condition of moderate ionization of Pa; under the action of the applied magnetic field, the trajectory of the emitted electron beam does not change much as shown in (a) and (b), and the velocity dispersion increases as shown in (c) and (d).
D3, according to the trajectory and the velocity distribution of the electron beam, combining the wave-injection interaction equation, and approximately obtaining the influence of the collision effect on the wave-injection interaction.
S2, setting a parameter range of the gyrotron traveling wave tube during normal work;
the parameter ranges of the step S2 when the gyrotron traveling wave tube normally works include:
gas space density: greater than 5 Pa;
tube wall temperature: less than 400 degrees Celsius;
dissipated power per unit area of tube wall: less than 1KW/cm2。
S3, continuously inputting the electron beam and the external magnetic field into the gyrotron traveling wave tube model, and judging whether the working parameters are in the parameter range during normal working, if so, continuously outputting the microwaves by the gyrotron traveling wave tube model until the output microwaves reach the set target working parameters and duration, finishing the monitoring, and if not, entering the step S4;
s4, temporarily stopping inputting the electron beam and the external magnetic field into the cyclotron traveling wave tube model, simultaneously vacuumizing and cooling the cyclotron traveling wave tube, improving the environment in the tube under the condition of not changing the material of the tube wall until the working parameters return to the parameter range in normal working, enabling the cyclotron traveling wave tube model to continuously work, and continuously outputting microwaves; and when the output microwaves reach the set target working parameters and duration, finishing the monitoring.
In one embodiment of the present invention, during the analysis process of the electromagnetic field analysis module, a large amount of simulation calculation is needed to realize the simulation of the device interaction process after considering the residual gas impact ionization. The simulation process can be effectively connected with corresponding theoretical analysis and experimental verification in series, and is the core of a whole set of physical model, so that the simulation process needs to be deeply researched; meanwhile, the simulation process involves the temperature change and the air pressure dynamic change of the inner wall of the device, and the change period of the physical processes is thousands of times of that of the time-varying high-frequency field, so that long-time simulation is needed for completely analyzing the interaction process of residual gas impact ionization. Two analysis methods are provided below, namely, the rapid analysis can be carried out for a long time and the accurate analysis can also be carried out for a limited time, wherein the rapid analysis is used for analyzing the wave injection interaction under the consideration of the coupling of multiple physical fields, and the influence of quasi-periodic change of external conditions on the impact ionization and the wave injection interaction of residual gas can be effectively revealed; the accurate analysis method is used for accurately analyzing the residual gas impact ionization and the wave injection interaction in a limited period so as to verify the accuracy of rapid analysis. The two methods are combined with each other, so that the simulation precision is effectively guaranteed, and the effective simulation of the complex physical process of multiple physical fields is realized.
Method one (rapid analysis): similar to the small signal analysis of the wave injection interaction, firstly, the wave injection coupling is cut off, the undisturbed trajectory of the electron beam and the excitation of a high-frequency field cold field are respectively analyzed, the collision of residual gas is introduced in the analysis process, only the influence of the collision and the ionization on emitted electrons and ionized electrons is considered, the excitation of the high-frequency field of the electron beam is ignored, the motion process and the collision process only consider the static field action, so that the steady-state process is adopted, the distribution of the electron beam in the space can be described by using a steady-state distribution function, once the collision and the ionization processes reach a steady state, the formed distribution function can be taken as an initial distribution function to be introduced into a wave injection interaction equation, and the influence of the ionization on the interaction is analyzed.
Unlike PIC analysis, which divides each step of time into two phases, impact ionization and interaction, small signal analysis divides the whole interaction process into impact ionization and interaction processes. The effect of residual gas ionization on the interaction was gradually revealed using a successive approximation method. The method can effectively reflect the physical nature of the influence of the ionization process on the interaction.
Method two (precision analysis): the impact of ionization on interaction is analyzed by adding an ionization module in a 'traditional' PIC analysis method by directly utilizing a PIC simulation analysis model added with an impact ionization module. This analytical method divides the interaction process into two regions: region 1 beam interaction region, region 2 ionization collision region: the electron beam in the area 1 is only acted by an electromagnetic field and is not impacted by residual gas; in region 2 the electron beam is subjected only to collision forces with the residual gas. By partitioning the interaction, the interaction can be partitioned into electromagnetic interaction processes and collision interaction processes at each time step. Firstly, judging collision probability according to residual gas atmosphere and air pressure, incident electron density and a corresponding collision section; then randomly selecting corresponding macro electrons in the interaction region by utilizing the probability to participate in the collision process, analyzing the scattering process of the macro electrons by utilizing an energy and momentum conservation and collision scattering angle empirical formula, and analyzing the ionization process of the residual gas by utilizing an ionization model; and (4) carrying out finite difference-based MAXWELL equation solving on the collided macro electrons and the ionized charges together with the non-collided macro electrons, and carrying out modulation of electron beams and excitation analysis of a high-frequency field. The analysis process does not strictly distinguish the emitted electrons from the ionized electrons, but incorporates them into the injection wave interaction solving process, and the analysis method has the advantages of being more consistent with the actual physical process and having the defect of needing a large amount of calculation time and resources.
In one embodiment provided by the present invention, fig. 5 to 12 analyze ionization problems of a device under different vacuum degrees through quantitative simulation, and give reasons and consequences of influence of ionization of residual gas on device performance:
1) under mild ionizationThe lower device only generates a small amount of ionization charges, and the influence of the ionization charges on the operation of the emitted electron beam, the quality of the emitted electron beam and the interaction of the injected wave can be ignored;
2) moderate ionizationThe generated ionization charge is comparable to the density of the main electron beam, which can cause the quality reduction of the main electron beam, the reduction of the interaction efficiency of the injection wave, the accumulation and boosting noise of the stray charge, the oscillation starting of the parasitic mode and the spectrum impurityProblems such as scattering;
3) severe ionizationThe ionization charge density is larger than the emission charge density, so that the dispersion of the scattering speed of main electron beams is greatly increased due to collision, the main electron beams cannot be synchronized with a high-frequency field, the main electron beams and the high-frequency field cannot be effectively transduced, the device cannot output power, a large amount of stray charges intensively bombard the cathode and the attenuation material of the device, the vacuum degree is sharply reduced, the device is broken down and ignited, and the device cannot normally work. By establishing a scattering and ionization model, the ionization problem of different regions under different vacuum degrees can be accurately and quantitatively analyzed.
As shown in FIG. 5, (a) is 10-7Pa under mild ionization, (b) is 10-6Pa under mild ionization, (c) is 10-5Pa, and from (a), (b), and (c), it is known that the trace dispersion increases with the increase in the degree of ionization;
as shown in FIG. 6, (a) is 10-7Pa under mild ionization, (b) is 10-6Pa under mild ionization, (c) is 10-5Pa, and from (a), (b), and (c), it is known that the energy dispersion increases with the increase in the degree of ionization;
in FIG. 7, (a) is 10-7Pa under mild ionization, (b) is 10-6Pa under mild ionization, (c) is 10-5Pa, and from (a), (b), and (c), it is known that the velocity dispersion increases with the increase in the degree of ionization;
in FIG. 8, (a) is 10-7Pa under mild ionization, (b) is 10-6Pa under mild ionization, (c) is 10-5Pa, and (a), (b), and (c) show that the current fluctuation increases with the increase of the ionization degree;
in FIG. 9, (a) is 10-7Pa under mild ionization, (b) is 10-6Pa under mild ionization, (c) is 10-5Pa, and (a), (b), and (c) shows that as the degree of ionization increases,ionization aggravates trajectory confusion;
in FIG. 10, (a) is 10-7Pa under mild ionization, (b) is 10-6Pa under mild ionization, (c) is 10-5Pa, and the energy dispersion is increased and stray electrons absorb energy along with the increase of the ionization degree;
as shown in FIG. 11, (a) is 10-7Pa under mild ionization, (b) is 10-6Pa under mild ionization, (c) is 10-5Pa, and the power reduction fluctuation is increased along with the increase of the ionization degree according to (a), (b) and (c);
in FIG. 12, (a) is 10-7Pa under mild ionization, (b) is 10-6Pa under mild ionization, (c) is 10-5Pa, and (a), (b), and (c) show that the spectral spurious increases with increasing ionization level.
The invention has the beneficial effects that: the method for monitoring the safe working of the gyrotron traveling wave tube, provided by the invention, aims at the problem that the continuous working reliability of the current gyrotron traveling wave tube is poor, takes a mechanism formed by complex plasmas as a theme, combines the fields of gas analysis dynamics, material physics, relativistic electronics and the like, establishes a gyrotron traveling wave tube model, and provides effective improvement guidance for the continuous working reliability of the gyrotron traveling wave tube.
Claims (6)
1. A method for monitoring the safe operation of a gyrotron traveling wave tube is characterized by comprising the following steps:
s1, constructing a convoluted traveling wave tube model based on complex plasma formation and evolution;
s2, setting a parameter range of the gyrotron traveling wave tube during normal work;
s3, continuously inputting the electron beam and the external magnetic field into the cyclotron traveling wave tube model, judging whether the working parameters of the cyclotron traveling wave tube model are within the parameter range during normal working, if so, continuously outputting microwaves by the cyclotron traveling wave tube model, and finishing monitoring until the output microwaves reach the set target working parameters and duration; if not, go to step S4;
s4, temporarily stopping inputting the electron beam and the external magnetic field into the cyclotron traveling wave tube model, simultaneously vacuumizing and cooling the cyclotron traveling wave tube, improving the environment in the tube under the condition of not changing the material of the tube wall until the working parameters return to the parameter range in normal working, enabling the cyclotron traveling wave tube model to continuously work, and continuously outputting microwaves; when the output microwave reaches the set target working parameters and duration, the monitoring is finished;
in step S1, the gyrotron traveling wave tube model includes a trajectory analysis module, a collision analysis module, a tube internal air pressure dynamic analysis module, and an electromagnetic field analysis module;
the trajectory analysis module is used for quantitatively giving charge trajectories and velocity distributions before and after collision, providing charge phase space distribution conditions for collision probability analysis, air pressure dynamic analysis and wave injection interaction, and evaluating the bombardment effect of stray electrons on the wall of the device; the track analysis module is coupled with the collision analysis module, the air pressure dynamic analysis module and the electromagnetic field analysis module;
the collision analysis module is used for quantitatively giving collision occurrence probability, collision position, charge speed and track change after collision scattering and new charge distribution after ionization; the collision analysis module is respectively coupled with the track analysis module and the in-pipe air pressure dynamic analysis module;
the in-tube air pressure dynamic analysis module is used for quantitatively analyzing the collision probability of the charges and the residual gas in the cyclotron traveling wave tube model; the in-pipe air pressure dynamic analysis module is coupled with the track analysis module;
the electromagnetic field analysis module is used for analyzing the influence of the new space charge phase space distribution generated after impact ionization on the wave injection interaction; the electromagnetic field analysis module is coupled with the collision analysis module.
2. The method for monitoring the safe operation of a gyrotron traveling wave tube according to claim 1, wherein the analysis process of the trajectory analysis module specifically comprises:
a1, determining the phase space of each macro charge according to the emitted electron beam, the electromagnetic field in the cyclotron traveling wave tube, the current time step of each electron and charge and the distribution of the new charge determined by the collision analysis module;
a2, determining the electromagnetic field force borne by the macro charge according to the position of the macro charge in the gyrotron traveling wave tube, and obtaining the speed of the next time step of the macro charge according to a macro charge motion equation;
a3, obtaining the position of the next time step according to the macro charge motion equation, and determining the bombardment effect of stray electrons on the wall of the gyrotron traveling wave tube according to the motion trail of the position;
the macro charge motion equation is as follows:
wherein the content of the first and second substances,is the charged particle momentum;
t is time;
e is the amount of charge;
is the electric field strength;
is the charged particle motion velocity;
is magnetic induction intensity;
the macro charge trajectory equation is:
wherein the content of the first and second substances,is the spatial position vector of the charged particles.
3. The method for monitoring the safe operation of a gyrotron traveling wave tube according to claim 2, wherein the analysis process of the collision analysis module is specifically as follows:
b1, taking the time step of each macro charge as the increment of the time used by each round of calculation; circularly calculating the collision probability of macro charge changing along with the time evolution;
b2, according to the macro-charge movement speed and the position obtained by the trajectory analysis module and the gas collision cross section and the gas space density obtained by the gas pressure dynamic analysis module in the pipe, circularly calculating the collision probability p of each macro-charge changing along with the time evolutioni；
B3, generating a random number q of 0-1 for each macro particle in the interaction spaceiAnd with a collision probability piThe comparison is carried out in such a way that,
if q isi>piIf the macro particles are not collided, the macro particles keep the original motion state;
if q isi<piIf so, collision occurs, and collision ionization analysis and collision scattering analysis are carried out;
the collision probability p of each macro chargeiComprises the following steps:
in the formula, σ (E)0) Is a gas collision cross section;
viis the macro charge movement speed;
Δ t is the time length of the movement before the collision of the macro charge;
is the gas space density.
4. The method for monitoring the safe operation of a gyrotron traveling wave tube according to claim 3, wherein the analysis process of the in-tube air pressure dynamic analysis module specifically comprises:
c1, determining the distribution of the dissipation power formed by the stray electrons bombarding the wall of the gyrotron traveling wave tube according to the trace analysis result of the macro charges obtained by the trace analysis module;
c2, determining the local temperature rise of the gyrotron traveling wave tube by taking the dissipated power as a heat source, and measuring the wall temperature of the tube;
c3, determining the material air-out rate of the gyrotron traveling wave tube according to the local temperature rise of the gyrotron traveling wave tube;
c4, calculating the gas space density according to the gas output rate of the material and an ideal gas state equation;
the ideal gas state equation is:
in the formula (I), the compound is shown in the specification,is the gas pressure;
is the gas space density;
k is Boltzmann constant;
t is the temperature in the cyclotron traveling wave tube.
5. The method for monitoring the safe operation of the gyrotron traveling wave tube according to claim 4, wherein the analysis process of the electromagnetic field analysis module specifically comprises:
d1, determining the state of the electron beam after ionization according to the trajectory analysis module and the collision analysis module;
the state of the electron beam comprises a trajectory and a velocity distribution of the electron beam;
d2, determining the influence degree of the electron beam on the wave-filling interaction process according to the quality and quantity change of the electron beam;
and D3, obtaining the influence of the collision effect on the wave-filling interaction by combining the wave-filling interaction equation according to the trajectory and the velocity distribution of the electron beam.
6. The method for monitoring the safe operation of the gyrotron traveling wave tube according to claim 5, wherein the parameter ranges of the step S2 during the normal operation of the gyrotron traveling wave tube comprise:
gas space density: greater than 5 Pa;
tube wall temperature: less than 400 degrees Celsius;
dissipated power per unit area of tube wall: less than 1KW/cm2。
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