A method for evaluating the vacuum life of a two-point variable-temperature Dewar with a low coverage model

Abstract

The present invention discloses a method for evaluating the vacuum life of a two-point variable-temperature Dewar with a low coverage model. First, the desorption rate equation under low coverage is used as the Dewar outgassing rate model, and the overall outgassing rate change trend of the Dewar is obtained through the pumping speed of the ion pump and the vacuum in the exhaust system. Then, the method of two-point variable temperature at the end of exhaust is used to eliminate the influence of coverage, and the overall outgassing activation energy of the Dewar is obtained. Finally, the initial outgassing rate and the relationship between the outgassing rate and time at the storage temperature are obtained using the outgassing activation energy. The vacuum life of the Dewar is evaluated according to the Dewar volume and the cut-off vacuum. The present invention is a non-destructive testing and evaluation method, which will not damage the performance of the detector, is convenient to implement, and provides a non-destructive testing and evaluation method for the vacuum life of small-batch and diversified Dewars.

Description

Technical Field

[0001] The present invention belongs to the field of integrated packaging of cryogenic infrared detectors, and specifically relates to a method for evaluating the vacuum life of a two-point variable-temperature Dewar with a low coverage model. It is applicable to the evaluation of the vacuum life of cryogenic vacuum-packaged Dewars. Background Art

[0002] With the development of infrared detection requirements towards long wavelengths and high sensitivity, infrared detectors can only operate at deep low temperatures, and a certain degree of vacuum must be maintained inside the infrared detector Dewar to maintain operation. The change in the Dewar vacuum degree will affect the maintenance cost, optoelectronic performance, and service life of the entire detector. That is, the vacuum life is an important technical indicator of the infrared detector Dewar. The vacuum life of an infrared detector Dewar is generally obtained using empirical formulas or Arrhenius accelerated life model tests. However, the new application requirements of infrared detectors make the Dewars diverse, and various new types of ceramic and organic materials have also begun to be used in Dewars, making the previous life calculations and empirical data of Dewars no longer applicable, and it has become difficult to estimate the life of new Dewars. Therefore, there is an urgent need for a method for estimating the vacuum life of small-batch and diverse Dewars.

[0003] Chinese Patent CN110529728A, an apparatus and method for on-line detecting the life of an infrared focal plane detector Dewar bottle, obtains the Dewar vacuum life by applying the principles of rarefied gas physics and vacuum technology. However, no calculation method is given when there are temperature changes during storage and exhaust gas monitoring. If the storage temperature changes, the life becomes unpredictable.

[0004] Since the main source of gas inside the Dewar is the outgassing of materials inside the Dewar. The outgassing rate during Dewar exhaust can reflect the overall outgassing level and its trend of the Dewar caused by the materials used and the technological process. The storage temperature is usually inconsistent with the exhaust temperature and is generally lower than the exhaust temperature. The present invention is not only convenient to implement, applicable to various new types of small-batch and diverse Dewars, but also applicable to the prediction of the vacuum life at different storage temperatures. Summary of the Invention

[0005] The present invention proposes a method for evaluating the vacuum life of a two-point variable-temperature Dewar with a low coverage model. It solves the problem of estimating the life of new Dewars using new ceramic and organic packaging materials. The advantage of this vacuum life detection and evaluation method is that it will not damage the detector performance, is convenient to implement, and provides a non-destructive detection and evaluation method for the vacuum life of small-batch and diverse Dewars.

[0006] The present invention is achieved by, for example Figure 1Implementation of the principle block diagram for the two-point variable temperature Dewar vacuum life evaluation method for the low coverage model shown. In view of the gas emission mechanism and the long-time exhaust characteristics of the infrared detector Dewar assembly, the first-order desorption rate equation that meets the low coverage condition is used as the gas emission model, where the coverage refers to the ratio of the actual gas adsorption amount of the material inside the Dewar to the maximum adsorption amount. The Dewar gas emission rate model is as follows:

[0007]

[0008] In the formula, T is the temperature, t is the time, R is the gas constant, E d is the desorption activation energy, σ is the gas adsorption amount, τ 0 is the vibration period of the adsorbed molecules perpendicular to the surface.

[0009] The Dewar vacuum life evaluation method is as follows

[0010] (1) By the method of rapid two-point variable temperature, the gas emission rates q 1 and q 2 at the same coverage under different temperatures T 1 and T 2 are obtained, and the gas desorption activation energy E d of the whole Dewar is obtained.

[0011]

[0012] (2) The storage temperature after the Dewar is sealed is T 0 , and using the first-order desorption rate equation that meets the low coverage condition and the above desorption activation energy E d , the initial gas emission rate q 0 of the Dewar storage is obtained.

[0013]

[0014] In the formula, T 3 and q 3 are the temperature and gas emission rate before the Dewar is sealed.

[0015] (3) Using the first-order desorption rate equation that meets the low coverage condition and the above desorption activation energy E d , the initial gas emission rate q 0 of the Dewar, the relationship between the gas emission rate q of the Dewar and time t during storage is obtained.

[0016]

[0017] In the above formulas, the units are as follows: temperature T, K; time t, s; desorption activation energy E d , J / mol; τ 0 is about 10 - 13s; gas outlet rate q, Pa.m 3 / s. According to the actual Dewar volume, the vacuum life is cut off at vacuum and the vacuum life is calculated.

[0018] The present invention uses a Dewar exhaust system to obtain the Dewar gas outlet rate. The exhaust system is as follows Figure 2 As shown, it includes a mechanical pump 1, a molecular pump 2, an ion pump 5, a vacuum chamber 4, a first vacuum valve 3, a second vacuum valve 6, a third vacuum valve 8, and a vacuum gauge 7. The test method for obtaining the dewar outgassing rate using the vacuum exhaust system is as follows:

[0019] (1) Connect the Dewar sample 10 to the exhaust system through the Dewar connecting pipe 9, open the mechanical pump 1 and the molecular pump 2 and the first vacuum valve 3, the second vacuum valve 6, and the third vacuum valve 8 to exhaust the vacuum chamber 4 and the Dewar sample 10 at a low temperature below 100°C.

[0020] (2) After the vacuum reaches 10E-4Pa, close the vacuum valve 3 and continue to exhaust using the ion pump 5 at a pumping speed of S 0 , the exhaust temperature is T 1 , and monitor and record the vacuum degree of vacuum gauge 7.

[0021] (3) Close the third vacuum valve 8 and read the vacuum gauge 7 to obtain the base vacuum degree P. m .

[0022] (4) Open the third vacuum valve 8. When the exhaust time exceeds 3 days and the reading of the vacuum gauge 7 reaches the Dewar sealing condition, the exhaust is completed and the vacuum degree P is recorded. 1 . Change the temperature to T within half an hour 2 , record the vacuum degree P of vacuum gauge 7 2 .

[0023] (5) Temperature T 1 At the end of exhaust, the Dewar gas output rate q 1 For S 0 (P 1 -P m ), becomes T 2 Post-Dewar gas outflow rate q 2 For S 0 (P 2 -P m ). Considering the accuracy of the system, it is generally recommended to 2 Greater than T 1 .

[0024] (6) Gas outflow rate q when Dewar seal is in place 3 =q 2 , Dewar temperature T 3 =T 2 .

[0025] According to the Dewar storage temperature T 0 The initial outgassing rate of the Dewar is obtained according to the formula (3), and then the relationship between the outgassing rate and time is obtained according to the formula (4). Finally, according to the actual volume of the Dewar and the ultimate vacuum of 0.1 Pa, the vacuum life of the Dewar can be obtained.

[0026] The advantages of the present invention are as follows:

[0027] 1. The vacuum life of the Dewar is obtained through the data obtained by the Dewar exhaust system before clamping, without adding test equipment and test process, which is convenient to implement.

[0028] 2. This method will not damage the performance of the detector and is a non-destructive testing and evaluation method.

[0029] 3. This method does not require a large number of samples and can be used for the vacuum life detection and evaluation of small batches and diverse Dewars.

[0030] 4. The actual outgassing rate data of each measured Dewar is tested, and the true state Dewar life data of each Dewar can be obtained.

[0031] 5. This method obtains the outgassing activation energy of the Dewar, and the vacuum life of the Dewar at different storage temperatures can be calculated. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is the principle block diagram of the two-temperature variable Dewar vacuum life evaluation method for low coverage model;

[0033] Figure 2 is the principle block diagram of the Dewar exhaust system;

[0034] 1 - Mechanical pump

[0035] 2 - Molecular pump

[0036] 3 - First vacuum valve

[0037] 4 - Connection cavity

[0038] 5 - Ion pump

[0039] 6 - Second vacuum valve

[0040] 7 - Vacuum gauge

[0041] 8 - Third vacuum valve

[0042] 9 - Dewar connection pipeline

[0043] 10 - Dewar DETAILED DESCRIPTION OF THE INVENTION

[0044] In order to make the above objects, features and advantages of the present invention more obvious and understandable, the following uses a new type of infrared detector Dewar as a sample to make a detailed description of the specific implementation manner of the present invention.

[0045] The internal volume V of the novel infrared detector Dewar used is V = 1.94E-4 m 3 . To extend the vacuum life, two getters are installed in the Dewar.

[0046] Install the Dewar at Figure 1 Position 10. Turn on the mechanical pump 1, the molecular pump 2, the first vacuum valve 3, the second vacuum valve 6, and the third vacuum valve 8 to evacuate the vacuum chamber 4 and the Dewar sample 10. After the vacuum reaches 10E-4 Pa, close the valve 3, and the ion pump continues to evacuate. The temperature of the Dewar during evacuation is 70 °C. The pumping speed S0 of the ion pump is 320 l / s. Close the first vacuum valve 3 and the third vacuum valve 8 to obtain the base vacuum of 3.30E-8 Pa, that is, the base gas flow rate is 1.05E-8 Pa·m 3 / s. After 12 days of evacuation, the vacuum degree is 2.18E-7 Pa, that is, the total gas flow rate is 6.96E-8 Pa·m 3 / s. Subtract the base gas flow rate to obtain the outgassing rate of the Dewar of 5.91E-8 Pa·m 3 / s. After the evacuation is completed, quickly heat up to 80 °C, and the vacuum degree is 1.04E-6 Pa. Using the same method, the outgassing rate of the Dewar is calculated to be 3.24E-7 Pa·m 3 / s. According to Equation 2, the activation energy of the Dewar outgassing is 161 KJ / mol. Then immediately activate the getter and activate the Dewar. The Dewar is stored at room temperature of 23 °C. According to Equation 3, the initial outgassing rate of the Dewar can be obtained as 7.56E-12 Pa·m 3 / s. According to the working principle of the getter used in the Dewar and the analysis results of the residual gas in the Dewar, its gas absorption capacity is set to 98%. Using Equation 4 and the volume of the Dewar and the vacuum life cutoff vacuum of 0.1 Pa, the vacuum life of this Dewar is obtained as about 4 years (1485 days).

[0047] The above completes the implementation of a method for evaluating the vacuum life of a two-point variable-temperature Dewar with a low coverage model.

Claims

1. A method for evaluating the vacuum life of a two - point variable - temperature Dewar with a low - coverage model, characterized in that it includes the following steps: 1) Using the first-order desorption rate equation that satisfies the low coverage condition, by means of the method of rapid two-point temperature change, the outgassing rates q 1 and T 2 at the same coverage and q 1 and q 2 are obtained, and the gas desorption activation energy E d of the whole Dewar is obtained as follows: where R is the gas constant; 2) The storage temperature after Dewar sealing is T 0 , using the first-order desorption rate equation that meets the low coverage condition and the above desorption activation energy E d , the initial outgassing rate q of Dewar storage is obtained 0 : where T 3 and q 3 are the temperature and outgassing rate before Dewar sealing; 3) Use the first - stage desorption rate equation that meets the low - coverage condition and the above desorption activation energy E d and the initial outgassing rate q of the Dewar 0 , to obtain the relationship between the outgassing rate q of the Dewar and time t during storage: where τ 0 is the vibration period of the adsorbed molecules perpendicular to the surface. Based on the actual Dewar volume and the final vacuum, the vacuum lifetime of the Dewar is calculated.

2. According to the method for evaluating the vacuum life of a two - point variable - temperature Dewar with a low - coverage model described in claim 1, characterized in that the Dewar outgassing rate test method is as follows: The vacuum exhaust system used to obtain the Dewar outgassing rate includes a mechanical pump (1), a molecular pump (2), an ion pump (5), a vacuum chamber (4), a first vacuum valve (3), a second vacuum valve (6), a third vacuum valve (8), and a vacuum gauge (7); The specific steps of the Dewar outgassing rate test method are as follows: 1) Connect the Dewar sample to the exhaust system with a Dewar connection pipe, and turn on the mechanical pump (1), the molecular pump (2), the first vacuum valve (3), the second vacuum valve (6), and the third vacuum valve (8) to perform low - temperature exhaust below 100 °C on the vacuum chamber (4) and the Dewar sample; 2) After the vacuum reaches 10E-4 Pa, close a vacuum valve (3), and continue exhausting using an ion pump (5) with a pumping speed of S 0 , and the exhaust temperature is T 1 , and monitor and record the vacuum degree of the vacuum gauge (7); 3) Close the third vacuum valve (8) and obtain the base vacuum degree P from the reading of the vacuum gauge (7). m ; 4) Open the third vacuum valve (8). When the exhaust time exceeds 3 days and the reading of the vacuum gauge (7) reaches the Dewar sealing condition, the exhaust ends, and record the vacuum degree P. 1 ; Change the temperature to T within half an hour. 2 , Record the vacuum degree P of the vacuum gauge (7). 2 , Seal the Dewar within half an hour. 5) Temperature T 1 The outgassing rate q of the Dewar at the end of exhaust 1 is S 0 (P 1 - P m ), becomes T 2 After that, the outgassing rate q of the Dewar 2 is S 0 (P 2 - P m ); Considering the test accuracy of the system, it is generally recommended that T 2 be greater than T 1 ; 6) Dewar outgassing rate q when sealed 3 =q 2 , Dewar temperature T 3 =T 2 .

Images