A heating method without working fluid cathode

Abstract

This application belongs to the field of space electric propulsion, specifically relating to a heating method for a propellantless cathode. The method employs constant-pressure and constant-power modes to heat the propellantless cathode, dividing the heating process into multiple stages. The heating voltage is calculated based on the desired power for each stage, and heating is carried out for a corresponding period. After completing the multi-stage constant-pressure heating, the method switches to constant-power heating mode, adjusting the propellantless cathode heating voltage to equal the set rated heating power. This method effectively reduces the thermal instability of the propellantless cathode heating and enhances its performance. In constant-power heating mode, because the input heating power remains constant, the temperature of the propellantless cathode eventually stabilizes over time due to the zeroth law of thermodynamics, i.e., the law of thermal equilibrium, thereby reducing thermal instability and noise caused by the thermal performance of the propellantless cathode.

Description

Technical Field

[0001] This application belongs to the field of space electric propulsion, specifically relating to a heating method for a cathode without a working fluid. Background Technology

[0002] In space gravitational wave detection missions, propellantless cathodes rely on surface electric fields and thermionic emission from materials to directly release electrons into the thruster's ion plume for neutralization. In miniaturized propulsion systems, propellantless thermionic emission cathodes, in addition to meeting the thruster's ion plume neutralization requirements, also need to maintain stable operation when working with the thruster in gravitational wave detection projects. This would enable high-precision neutralization of the positive charge plume ejected by the thruster and reduce thrust noise, preventing the introduction of significant noise into the thrust system that could affect the thruster's normal operation.

[0003] For the cathode, the key component for emitting electrons is the emitter, which is a material with a low work function (work function) on its surface, making it easier for electrons to escape from the material surface. Based on the thermionic emission characteristics of metallic materials, taking tungsten wire as an example, the emission current density on the surface of tungsten wire will increase tenfold if the temperature is increased by about 100 degrees. Therefore, even a small change in temperature has a significant impact on the emitting material. Since gravitational wave detection missions have extremely high precision requirements for the propulsion system, the cathode itself needs to be stable. However, the integration of the heating component (hot wire) and the emitter in a cathode without a working fluid makes the instability problem during cathode heating particularly prominent. Therefore, measures need to be taken to suppress the temperature drift and thermal instability of the emitter during the cathode heating process. Summary of the Invention

[0004] To address the problem of thermal instability in the heating process of a cathode without a working fluid in the existing technology, a heating method for a cathode without a working fluid is proposed.

[0005] A heating method for a cathode without a working fluid includes:

[0006] Step 1: Measure the cold resistance of the cathode hot wire without working fluid as the initial resistance value; set the rated heating power of the cathode without working fluid, divide the stage according to the set rated heating power, and obtain a total of N stages, and set a desired power and a heating time for each stage.

[0007] Step 2: Calculate the heating voltage for each stage based on the initial resistance and the expected power for each stage, and heat the cathode without working medium according to the heating voltage and heating time for each stage until the heating time corresponding to the heating voltage of the Nth stage is reached, then proceed to Step 3.

[0008] Step 3: Obtain the actual heating voltage and actual heating current of the working medium-free cathode, and calculate the actual heating power based on the actual heating voltage and actual heating current. If the actual heating power is not equal to the set rated heating power, adjust the heating voltage of the working medium-free cathode so that the adjusted heating power of the working medium-free cathode is equal to the set rated heating power.

[0009] The beneficial effects of this application are as follows: This application provides a method for heating a cathode without a working medium. The heating voltage for each stage is calculated based on the initial resistance and the desired power for each stage. The cathode without a working medium is then heated according to the heating voltage and heating time for each stage, until the heating time corresponding to the heating voltage of the Nth stage is reached. Afterward, the heating power is adjusted via feedback.

[0010] Step 3: Obtain the actual heating voltage and actual heating current of the working medium-free cathode, and calculate the actual heating power based on the actual heating voltage and actual heating current. If the actual heating power is not equal to the set rated heating power, adjust the heating voltage of the working medium-free cathode so that the adjusted heating power of the working medium-free cathode is equal to the set rated heating power.

[0011] The beneficial effects of this application are as follows: The heating method for a working-fluid cathode of this application employs constant pressure mode and constant power mode to heat the working-fluid cathode. The heating process is divided into multiple stages, and the heating voltage is calculated according to the expected power of each stage. The cathode is heated for a period of time under the corresponding heating conditions. After the constant pressure heating of multiple stages is completed, the method switches to constant power heating mode. The heating voltage of the working-fluid cathode is adjusted so that the adjusted heating power of the working-fluid cathode is equal to the set rated heating power. This method can effectively reduce the thermal instability of the working-fluid cathode heating and enhance the working performance of the cathode. In the constant power heating mode, since the input heating power is always a constant value, the temperature of the working-fluid cathode will eventually stabilize over time due to the zeroth law of thermodynamics, namely the law of thermal equilibrium, thereby reducing the thermal instability and noise caused by the thermal performance of the working-fluid cathode. Attached Figure Description

[0012] Figure 1 A flowchart illustrating a heating method for a cathode without a working fluid, as described in a specific embodiment of this application;

[0013] Figure 2 The curve showing the change in resistance of the tungsten wire versus temperature in a specific embodiment of this application;

[0014] Figure 3 The curve showing the change of ceramic thermal conductivity with temperature in a specific embodiment of this application;

[0015] Figure 4 Temperature drift of the emitter temperature measured by the thermometer in the constant current heating mode according to the specific embodiment of this application;

[0016] Figure 5 A schematic diagram illustrating the principle of the constant current heating mode of the emitter in a specific embodiment of this application;

[0017] Figure 6 Temperature drift of the emitter temperature measured by the thermometer in the constant pressure heating mode according to the specific embodiment of this application;

[0018] Figure 7 A schematic diagram illustrating the principle of the constant pressure heating mode of the emitter in a specific embodiment of this application;

[0019] Figure 8 A comparison diagram of emitter temperature fluctuation amplitude in constant voltage mode and constant current mode in a specific embodiment of this application;

[0020] Figure 9 A comparison of the fluctuation amplitude of the current value in the circuit at different frequencies after Fourier transform when heating the cathode in constant current mode, constant voltage mode and constant power mode, respectively, for specific embodiments of this application.

[0021] Figure 10 The current value in the circuit after Fourier transform is shown in the embodiment of this application when the cathode is heated in constant voltage mode, and the fluctuation amplitude at different frequencies is shown. Detailed Implementation

[0022] Specific Implementation Method 1: The following will refer to the appendix of the embodiments of the present invention. Figure 1 To be continued Figure 9 This description explains the embodiments of the present invention, providing a clear and complete description of the technical solutions in these embodiments:

[0023] A heating method for a cathode without a working fluid includes:

[0024] Step 1: Measure the cold resistance of the cathode hot wire without working fluid as the initial resistance value; set the rated heating power of the cathode without working fluid, divide the stage according to the set rated heating power, and obtain a total of N stages, and set a desired power and a heating time for each stage.

[0025] Step 2: Calculate the heating voltage for each stage based on the initial resistance and the expected power for each stage, and heat the cathode without working medium according to the heating voltage and heating time for each stage until the heating time corresponding to the heating voltage of the Nth stage is reached, then proceed to Step 3.

[0026] Step 3: Obtain the actual heating voltage and actual heating current of the working medium-free cathode, and calculate the actual heating power based on the actual heating voltage and actual heating current. If the actual heating power is not equal to the set rated heating power, adjust the heating voltage of the working medium-free cathode so that the adjusted heating power of the working medium-free cathode is equal to the set rated heating power.

[0027] Specifically, the present application discloses a heating method for a non-working-medium cathode, which includes an emitter, a heating wire, a cathode cylinder shell, and a filling ceramic. The emitter is disposed outside one end of the cathode cylinder shell, the filling ceramic is disposed inside the cathode cylinder shell, and the heating wire is disposed inside the filling ceramic near the emitter. The heating wire is used to generate heat and heat the emitter after being energized, and the emitter is used to generate electrons after being heated.

[0028] In the design of a heat cathode without a working fluid, the ability of a metallic emitter to emit electrons is described by the following equation:

[0029] In the formula, j e Thermoemission current density, in A·m -2 A is the thermal emission constant, which is 1204000 A·m. -2 ·K -2 ;k B The value is Boltzmann's constant, which is 1.38 J·K. -1 T is the temperature of the metallic material, in Kelvin; D is the thermionic emission current correction factor; W f Let be the surface work function (work function) of the emitter material, representing the minimum energy at which an electron leaves the material surface; exp(·) represents an exponential function.

[0030] As can be seen from the above formula, as the temperature of the cathode emitter without working fluid increases, the emission current density will increase rapidly.

[0031] Due to its operating characteristics, the working fluidless cathode has a high degree of integration between its heating components and emitter elements. The heating wire, filling ceramic, and metal cylindrical shell made of insulating tantalum are all integrated into a very small component. This integration means that the resistance of the heating wire and the heat transfer within the ceramic and metal cylindrical shell structures have a significant impact on its temperature. This makes the temperature change and the alteration of material properties due to temperature variations non-negligible, and these two factors interact, leading to instability. For example, the resistivity of the heating wire changes with temperature, causing the resistance to rise from 2.5Ω at cold to 4.5Ω at 950℃. This resistance, in turn, affects the heating effect and the emitter temperature, resulting in temperature instability. Based on this instability mechanism, an improved heating method is proposed to suppress the thermal instability of the cathode.

[0032] Furthermore, the method of calculating the heating voltage corresponding to each stage based on the initial resistance and the expected power corresponding to each stage, and heating the cathode without working fluid based on the heating voltage and heating time corresponding to each stage, until the heating time corresponding to the heating voltage of the Nth stage is reached, includes:

[0033] Step 21: Set the stage number as i, let i = 1; calculate the heating voltage corresponding to the first stage based on the initial resistance and the expected power corresponding to the first stage; heat the cathode without working fluid according to the heating voltage and heating time corresponding to the first stage; and after heating is completed, proceed to Step 22.

[0034] Step 22: Let i = i + 1, obtain the current heating voltage and current of the cathode without working medium, and calculate the current heating resistance of the cathode without working medium based on the current heating voltage and current of the cathode without working medium;

[0035] Steps 2 and 3: Calculate the heating voltage corresponding to the i-th stage based on the current heating resistance of the cathode without working fluid and the expected power corresponding to the i-th stage; heat the cathode without working fluid according to the heating voltage and heating time corresponding to the i-th stage, and after heating is completed, proceed to step 2 and 4.

[0036] Step 24: Determine if stage number i is equal to N. If yes, proceed to step 3; otherwise, proceed to step 22.

[0037] Specifically, in order to improve the thermal stability of the non-working medium cathode, a constant pressure heating mode is adopted in each stage when heating the non-working medium cathode. The heating voltage corresponding to the i-th stage is calculated based on the current heating resistance of the non-working medium cathode and the expected power corresponding to the i-th stage. The non-working medium cathode is then heated for a corresponding time based on the calculated heating voltage, so that the resistance of the heating wire of the non-working medium cathode remains stable.

[0038] As attached Figure 2 As shown, the heater of the cathode emitter without a working fluid, also known as the heating wire, is made of a tungsten-rhenium alloy. Increased temperature leads to increased atomic vibrations, resulting in increased resistivity (resistance per unit length and cross-sectional area). Therefore, during heating, the resistance of the heating wire increases with rising temperature. In contrast, the thermal conductivity of ceramics decreases with increasing temperature; that is, higher temperatures result in slower heat transfer and better insulation. (See attached diagram.) Figure 3 As shown;

[0039] Therefore, for different heating methods, the interaction between temperature and material properties exists through the following mechanism:

[0040] like Figure 4 and Figure 5 As shown, in the existing technology, constant current heating mode is used for cathodes without working fluid. When constant current heating is used, as the temperature rises, the resistance of the hot wire increases while the heating current remains unchanged, which inevitably leads to an increase in the voltage across its terminals, thus increasing the total heating power. For the filled ceramic, this will reduce its thermal conductivity, that is, increase its thermal insulation performance. Both of these effects will lead to an increase in the temperature of the hot wire and the ceramic. The increase in temperature, in turn, further increases the resistance of the hot wire and the thermal insulation performance of the ceramic. Therefore, constant current heating has two positive feedback mechanisms, which leads to unstable temperature drift during heating and operation, that is, thermal instability. The interaction between material and electrical properties makes this temperature drift more drastic. Therefore, measures need to be taken to suppress this temperature change.

[0041] like Figure 6 and Figure 7 As shown, when heating a cathode without a working medium using constant voltage heating mode, the increase in the resistance of the heating wire under constant voltage leads to a decrease in its current, thus reducing the heating power of the heating wire. If the effect of ceramic insulation is not considered, the temperature of the heating wire will decrease, and the resistance will decrease accordingly, leading to an increase in heating current and heating power. This is a negative feedback mechanism. Therefore, regarding the interaction between temperature and the characteristics of the heating wire material, switching to constant voltage heating results in the interaction between the characteristics of the heating wire and the heating power supply in constant voltage mode, making the temperature of the heating wire tend to stabilize. This is beneficial for stable temperature control. Even if the interaction between the thermal conductivity of the ceramic and temperature introduces unstable positive feedback, making the temperature still unstable, switching to constant voltage heating will reduce the degree of temperature drift.

[0042] Furthermore, the calculation method for the heating voltage corresponding to the first stage, based on the initial resistance and the expected power corresponding to the first stage, is as follows: U1 = (W set_1 *R1) 0.5 Where U1 is the heating voltage corresponding to the first stage, R1 is the initial resistance, and W... set_1 This represents the expected power for the first stage.

[0043] Furthermore, the current heating resistance of the cathode without working fluid is calculated based on the current heating voltage and current of the cathode without working fluid, and the current heating resistance is set to R. i The method is as follows; U instant I is the current heating voltage of the cathode without working fluid. instant This is the current heating current for the cathode without a working fluid.

[0044] Furthermore, the method for calculating the heating voltage corresponding to the i-th stage based on the current heating resistance of the cathode without working fluid and the expected power corresponding to the i-th stage includes:

[0045] U i =(W set_i *R i ) 0.5 Among them, U i R is the heating voltage corresponding to the i-th stage. i Let W be the current heating resistance in stage i. set_i Let be the expected power corresponding to the i-th stage.

[0046] Furthermore, the expected power corresponding to the Nth stage is equal to the set rated heating power.

[0047] Specifically, the constant-power heating mode means that regardless of changes in the resistance of the hot wire or the thermal conductivity of the ceramic, the heating power supply provides energy to the entire integrated launcher structure at a constant power. Regardless of changes in the thermal conductivity of the ceramic over time, as long as the heating power input to the cathode and the background environment (space or vacuum chamber) where the cathode dissipates heat are a stable thermodynamic system, the entire system will eventually stabilize over time due to the zeroth law of thermodynamics. Therefore, by adopting a constant-power heating method, the positive feedback mechanism in the material-induced thermal feedback mechanism no longer exists. This is a more stable heating mechanism for the overall structural characteristics, reducing cathode temperature drift and performance changes, thereby reducing cathode performance drift and helping to reduce thrust noise in the thrust system.

[0048] For an integrated emitter structure with hot filament heating, there is only one source of energy input, namely the heating power supply. The main forms of heat loss are thermal radiation and thermal conduction. Under a certain power input, as the temperature of the emitter structure gradually increases, the heat transferred in the form of thermal radiation will become faster and faster. The rate of heat conduction is related to the temperature difference and the thermal conductivity of the structure. Under constant power input, the two will eventually reach a dynamic balance between heat loss and heat transfer. If there is no large external disturbance, the thermal equilibrium state will be maintained at a stable value.

[0049] Specific implementation: When heating a cathode without a working fluid, first measure the cold resistance of the hot wire, that is, the resistance when no power is applied, as the initial resistance value. Based on the performance of the emitter and the application scenario of the cathode, set the rated heating power according to the emission current capability of the cathode required by the mission. Based on this power and the thermal stress that the internal structure can withstand (stress inside the material caused by the different thermal expansion coefficients of different materials), divide the heating power into several stages, and set a heating time corresponding to each stage, so that the heating power of the cathode stays in a certain stage for a certain period of time. For example, to heat the cathode to the rated heating power of 11W, it is divided into 8 stages according to the characteristics of the cathode without a working fluid. The expected power of the first stage is 0.5W, the expected power of the second stage is 1W, the expected power of the third stage is 3W, the expected power of the fourth stage is 5W, the expected power of the fifth stage is 7W, the expected power of the sixth stage is 9W, the expected power of the seventh stage is 10W, and the expected power of the eighth stage is 11W, and the heating time of each stage is greater than ten minutes.

[0050] When heating a cathode without a working medium, the heating voltage is adjusted to achieve the desired power at each stage and the heating time is set accordingly. Once the rated heating power is reached, the cathode enters normal operating mode. At this point, it is desirable for the cathode to stabilize at a certain operating point to further improve the stability of the cathode operation. Therefore, constant power feedback control is used to adjust the heating voltage. Using constant power control can further improve the thermal stability of the cathode without a working medium.

[0051] like Figure 8 As shown, the electrical signal collected from temperature fluctuations can be decomposed into fluctuations of different frequencies and their amplitudes through Fourier transform. The vertical axis of the figure represents the amplitude of temperature fluctuations. It can be seen that the constant pressure heating mode has the best performance in the low frequency range (10). -2 Up to 10 0 The fluctuation amplitude (within the frequency range) is indeed significantly lower than the temperature fluctuation noise amplitude of the constant current heating mode;

[0052] The cathode was heated using constant current, constant voltage, and constant power modes, respectively. The cathode was operated in conjunction with a thruster under constant operating conditions. A small resistor was connected in series in each mode, and the voltage across the resistor was measured to calculate the current in the circuit. The current values ​​in the circuit were collected, and the amplitude of fluctuations at different frequencies was compared using Fourier transform. The comparison results are shown in the attached figure. Figure 9As shown; when the thruster's operating state remains unchanged, it is approximately assumed that the fluctuation of the cathode's own emission current is reflected in the fluctuation of the contact electrode current. After unifying the vertical axis, from left to right, the vertical axis decomposition amplitude comparisons are shown for constant voltage heating mode, constant current heating mode, and constant power heating mode. Data without feedback control to suppress fluctuations in an open-loop configuration are used for comparison. It can be seen that the final amplitude of the constant voltage heating mode is below the red line, while that of the constant current mode is above the red line. Therefore, the stability of the constant voltage heating mode compared to the constant current mode is also evident under the condition of thruster coupled operation. Compared to the constant power mode, the amplitude is lower at 10... -4 Up to 10 0 The decrease in noise amplitude at logarithmic amplitude is more pronounced in the frequency band.

[0053] As attached Figure 10 As shown, in constant voltage heating mode, because the power supply needs to quickly respond and regulate the current value, it will be within 10... 3 Up to 10 4 The introduction of high-frequency noise between higher frequency bands is reflected in the increase in amplitude at the red box.

[0054] However, this noise is actually in the high frequency range relative to the low frequency band of interest (on the order of 0.01Hz-1Hz), specifically in the range of 1kHz-10kHz. Noise in such a high frequency range will not actually affect the measurements in the main detection frequency band of gravitational wave detection. Therefore, for gravitational wave detection projects, this improvement in heating method is meaningful and effective in improving system stability and reducing measurement noise.

[0055] Specific Embodiment Two: A computer device includes a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that the processor executes the computer program to implement the steps of a heating method for a working fluid-free cathode as described in Specific Embodiment One.

[0056] Specific Embodiment Three: A computer-readable storage medium storing a computer program thereon, characterized in that, when the computer program is executed by a processor, it implements the steps of a heating method for a working fluid-free cathode as described in Specific Embodiment One.

[0057] While the invention has been described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the invention. Therefore, it should be understood that many modifications can be made to the exemplary embodiments, and other arrangements can be designed without departing from the spirit and scope of the invention as defined by the appended claims. It should be understood that different dependent claims and features described herein can be combined in ways different from those described in the original claims. It is also understood that features described in conjunction with individual embodiments can be used in other described embodiments.

Claims

1. A heating method for a cathode without a working fluid, characterized in that, include: Step 1: Measure the cold resistance of the cathode hot wire without working fluid as the initial resistance value; Set the rated heating power of the cathode without working fluid, and divide it into stages according to the set rated heating power, resulting in a total of N stages. Each stage is set to correspond to a desired power and a heating time. Step 2: Calculate the heating voltage for each stage based on the initial resistance and the expected power for each stage, and heat the cathode without working medium according to the heating voltage and heating time for each stage until the heating time corresponding to the heating voltage of the Nth stage is reached, then proceed to Step 3. Step 3: Obtain the actual heating voltage and actual heating current of the working medium-free cathode, and calculate the actual heating power based on the actual heating voltage and actual heating current. If the actual heating power is not equal to the set rated heating power, adjust the heating voltage of the working medium-free cathode so that the adjusted heating power of the working medium-free cathode is equal to the set rated heating power. The method for calculating the heating voltage for each stage based on the initial resistance and the expected power for each stage, and then heating the cathode without working fluid based on the heating voltage and heating time for each stage, until the heating time corresponding to the heating voltage for the Nth stage is reached, includes: Step 21: Set the stage number as i, let i=1; calculate the heating voltage corresponding to the first stage based on the initial resistance and the expected power corresponding to the first stage; heat the cathode without working fluid according to the heating voltage and heating time corresponding to the first stage; and after heating is completed, proceed to Step 22. Step 22: Let i = i + 1, obtain the current heating voltage and current of the cathode without working medium, and calculate the current heating resistance of the cathode without working medium based on the current heating voltage and current of the cathode without working medium; Steps 2 and 3: Calculate the heating voltage corresponding to the i-th stage based on the current heating resistance of the cathode without working fluid and the expected power corresponding to the i-th stage; heat the cathode without working fluid according to the heating voltage and heating time corresponding to the i-th stage, and after heating is completed, proceed to step 2 and 4. Step 24: Determine if stage number i is equal to N. If yes, proceed to step 3; otherwise, proceed to step 22.

2. The heating method for a working fluid-free cathode according to claim 1, characterized in that: The calculation method for the heating voltage corresponding to the first stage, based on the initial resistance and the expected power corresponding to the first stage, is as follows: ;in, This is the heating voltage corresponding to the first stage. This is the initial resistance value. This represents the expected power for the first stage.

3. The heating method for a cathode without working fluid according to claim 2, characterized in that: Calculate the current heating resistance of the cathode without working fluid based on the current heating voltage and current of the cathode without working fluid, and let the current heating resistance be . The method is as follows; ;in The current heating voltage of the cathode without working fluid. This is the current heating current for the cathode without a working fluid.

4. The heating method for a working fluid-free cathode according to claim 3, characterized in that: The methods for calculating the heating voltage corresponding to stage i based on the current heating resistance of the cathode without working fluid and the expected power corresponding to stage i include: ;in, Let be the heating voltage corresponding to the i-th stage. Let be the current heating resistance in stage i. Let be the expected power corresponding to the i-th stage.

5. The heating method for a working fluid-free cathode according to claim 1, characterized in that: The expected power for the Nth stage is equal to the set rated heating power.

6. A computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the steps of a heating method for a non-working-fluid cathode as described in any one of claims 1 to 5.

7. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steps of a heating method for a non-working-fluid cathode as described in any one of claims 1 to 5.

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