Cold atom ultra-high vacuum mixed gas partial pressure measuring device and method

Abstract

The application discloses a device and method for measuring partial pressure of mixed gas in ultra-high vacuum based on cold atom technology. The application is based on the theory that the regularity attenuation of the cold atoms trapped in the potential well caused by the particle collision of the background gas can be used to reverse the density of the gas particles, and the characteristics that the velocity thermal average collision cross section of different gas particles and cold atoms has a certain and independent change trend with the depth of the potential well. A multivariate linear regression equation set of total collision loss rate about mixed gas density under different well depth conditions is constructed to analyze the change of the total loss rate of the cold atom group under different well depth conditions, so that the type and density of each component in the mixed gas are separated, and the partial pressure of each component is determined. The method avoids the measurement uncertainty caused by the effects brought by the ionization process of the traditional mass spectrometer, and has the advantages of no calibration, no disturbance to the measurement environment, high accuracy, reproducibility at different times and different places and the like based on the basic physical characteristics of the cold atoms.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of vacuum measurement, in particular to a cold atom ultra-high vacuum mixed gas partial pressure measuring device and method. BACKGROUND

[0002] Partial pressure measurement refers to comprehensively determining the composition of gas components in a mixed gas and the partial pressure of each component. With the rapid development of modern vacuum measurement technology, the importance of partial pressure measurement is becoming more and more prominent. First, in the measurement of vacuum degree in ultra-high / vacuum, the calibration coefficient of air or N2 is usually used to obtain the vacuum degree, but this may cause an order of magnitude error due to the uncertainty of the measured gas composition; second, in the diagnosis of a vacuum system, the main gas components and their proportions in the system can be used to determine whether the system leaks, whether the vacuum cavity adsorbs stray gas, whether the pump backflows, and the like, so as to optimize the system purposefully; in addition, partial pressure measurement is increasingly important in the field of high-end manufacturing technology. A small amount of sulfur and chlorine in an electric vacuum device can cause poisoning of an oxide cathode, the density of oxygen and water vapor in a coating chamber in semiconductor production needs to be strictly controlled, and the partial pressure of hydrogen in high-purity gas production needs to be strictly controlled to prevent explosion, and the like.

[0003] At present, most partial pressure vacuum gauges are ionization type, and mass spectrometry, as a main means of partial pressure measurement, is widely used in scientific research and industrial production. The principle is that the gas is ionized under the action of a high-energy electron stream, the ions are separated in space or time according to their different mass-to-charge ratios in an electromagnetic field, and the gas composition and proportion in the system are determined by measuring the intensity of the ion spectrum peak. However, the traditional mass spectrometer has the following defects:

[0004] 1) Most mass spectrometers belong to the ionization type, and any measurement instrument based on ionization technology will introduce measurement uncertainty due to the influence of the best ionization probability, ion mass discrimination, soft X-ray collection, mass spectrometry resolution, and the like;

[0005] 2) In the quantitative analysis and calculation of partial pressure, the N2 sensitivity and the relative sensitivity of different gases are generally required, so the N2 sensitivity needs to be calibrated periodically;

[0006] 3) The use of a mass spectrometer can only determine the proportion of different gas components in a mixed gas, and the specific partial pressure value needs to be calculated after being accurately measured by a total pressure vacuum gauge. However, different vacuum gauges will introduce additional uncertainties to different degrees. For example, in an ultra-high (10 -6 Pa to 10 -9 Pa) / extreme (below 10 -9 Pa) vacuum environment, an ionization gauge is usually used, which is affected by ESD, secondary electrons, space charge effect, and the like;

[0007] 4) Most importantly, one of the basic assumptions of mass spectrometer partial pressure measurement, the same mass-to-charge ratio between ions independent of each other without interference, the same mass-to-charge ratio of ion flow can be linearly superimposed. But this basic assumption is often not true when the vacuum degree is too large. SUMMARY

[0008] Therefore, the application provides a cold atom ultrahigh vacuum mixed gas partial pressure measuring device and method. According to the characteristics that the velocity thermal average collision cross section of cold atoms and neutral particles is only related to the potential well depth and the type of neutral particles, by studying the total loss rate change of cold atoms with different potential well depths under the collision of different particles of mixed gas, the type of particles of mixed gas and its partial pressure can be determined. The method can effectively avoid the defects of traditional mass spectrometers, and has better accuracy, stability and reproducibility in different time and space.

[0009] The device for measuring ultrahigh vacuum mixed gas partial pressure based on cold atom technology provided by the application comprises a cold atom unit and a vacuum system unit. The cold atom unit comprises an alkali metal atom source, a permanent magnet 2D-MOT, a differential tube and a 3D-MOT connected in sequence. Different well depths are arranged in the 3D-MOT, and the number of well depths is greater than the number of gas types in the mixed gas to be measured.

[0010] The vacuum system unit comprises a pumping system and a pressure stabilizing chamber. The pressure stabilizing chamber is connected with the 3D-MOT and used for introducing the mixed gas to be measured into the 3D-MOT. The pumping system is used for pumping the 3D-MOT and the pressure stabilizing chamber to an ultrahigh vacuum.

[0011] Preferably, the alkali metal atom source generates Li, Rb, Cs or other alkali metal atoms.

[0012] Preferably, the well depths have low mutual influence.

[0013] Preferably, the pumping system comprises a non-evaporable getter pump, a first molecular pump, a second molecular pump, a dry pump and an ionization gauge. The non-evaporable getter pump is connected with the 3D-MOT through a first valve. The dry pump and the second molecular pump are connected in sequence, and then connected with the first molecular pump through a third valve, and then connected with the 3D-MOT through a second valve. The ionization gauge is used for monitoring whether the pressure in the 3D-MOT is stable. The pressure stabilizing chamber is connected with the 3D-MOT through a fourth valve. The mixed gas to be measured is introduced into the pressure stabilizing chamber through a fifth valve.

[0014] The application further provides a measuring method using the above device, comprising the following steps.

[0015] Step 1, start the pumping system, and pump the 3D-MOT (4) and the pressure stabilizing chamber (14) to an ultrahigh vacuum.

[0016] Step 2, the test gas is introduced into the pressure stabilization chamber (14), and after the pressure is stabilized, the 3D-MOT is introduced;

[0017] Step 3, the alkali metal atom source (1) is heated to generate a hot atom beam, the hot atom beam is collimated by the permanent magnet 2D-MOT, pre-cooled, transferred to the 3D-MOT (4) through the differential tube (3), and trapped as a cold atom group;

[0018] Step 4, the loss rate Γ(U) of the cold atoms under the current 3D-MOT trap depth condition is measured;

[0019] The 3D-MOT trap depth is changed, and steps 3-4 are repeated to measure the loss rate Γ(U) of the cold atoms under different 3D-MOT trap depths U j j );

[0020] Step 5, a multivariate linear regression equation set is constructed The density of the i-th gas particle in the test mixed gas is solved; wherein, U j is the trap depth set in the j-th measurement; Γ(U j ) is the loss rate of the cold atoms under the trap depth U j condition in the j-th measurement; i is the i-th gas particle in the test mixed gas; <σ loss (U j )v> i is the velocity-averaged collision loss cross section of the i-th gas particle in the test mixed gas after collision with the cold atoms under the trap depth U j ; n i is the density of the i-th gas particle in the test mixed gas to be solved;

[0021] Step 6, based on the ideal gas state equation, the partial pressure of each component gas in the test mixed gas is obtained according to the density of each gas particle solved in step 5.

[0022] Preferably, the step 4 further comprises: constructing an MT, transferring the cold atom group trapped by the 3D-MOT into the MT and cooling the trapping; measuring the loss rate Γ(U) of the cold atoms under different MT trap depth conditions by changing the MT trap depth; wherein, the number of 3D-MOT trap depths and MT trap depths is greater than the number of gas species in the test mixed gas;

[0023] A multivariate linear regression equation set is constructed by combining the loss rates of the cold atoms under different 3D-MOT trap depth conditions and the loss rates under different MT trap depth conditions.

[0024] Preferably, the combination of 3D-MOT deep potential well and MT shallow potential well is adopted.

[0025] Preferably, the number of 3D-MOT trap depths is greater than the number of MT trap depths.​

[0026] Preferably, the gas extraction system comprises a non-evaporable getter pump, a first molecular pump, a second molecular pump, a dry pump and an ionization gauge; the non-evaporable getter pump is connected with the 3D-MOT through a first valve; the dry pump and the second molecular pump are connected in sequence, and the first molecular pump is connected with the dry pump through a third valve, and the second valve is connected with the 3D-MOT through the second valve; the ionization gauge is used for monitoring whether the pressure in the 3D-MOT is stable; the pressure stabilization chamber is connected with the 3D-MOT through a fourth valve; and the mixed gas to be measured is introduced into the pressure stabilization chamber through a fifth valve.

[0027] In the step 1, the fifth valve is closed, the first valve, the second valve, the third valve and the fourth valve are opened, and the dry pump, the first molecular pump and the second molecular pump are sequentially opened to continuously extract the gas from the 3D-MOT and the pressure stabilization chamber; the 3D-MOT, the pressure stabilization chamber, the first valve, the second valve, the third valve and the fourth valve are baked and degassed; meanwhile, the non-evaporable getter pump is started to activate the program for high-temperature baking and heat preservation for a certain period of time, and then the activation is completed, and the second valve is closed; the 3D-MOT, the pressure stabilization chamber, the first valve, the second valve, the third valve and the fourth valve are continuously baked and heat preserved, and then cooled, and the baking is stopped when the temperature is cooled to room temperature; then, the second valve is opened, and the activated non-evaporable getter pump is used to extract the 3D-MOT and the pressure stabilization chamber to an ultra-high vacuum -9 below 10 Pa.

[0028] Advantages:

[0029] (1) The method of the present application is based on the collision theory of neutral particles and cold atoms, and does not depend on ionization technology, avoiding the measurement uncertainty introduced by various effects in the ionization process and ion collection process. The coefficient <σ loss (U j )v i in the multivariate linear regression equation is a parameter based on the physical properties of cold atoms, and only related to the potential well depth and the type of collision system, so the pressure measurement based on cold atom technology has the advantages of no need for calibration of equipment, high accuracy, reproducibility at different times and different places. The final result of the quantitative analysis of the pressure measurement based on the cold atom technology is the partial density of different components in the mixed gas rather than only the proportion of each component, and then the density is converted into partial pressure according to the ideal gas state equation P=nk B T, so there is no need for additional total pressure gauge to assist in measurement, thereby further reducing the introduction of measurement uncertainty.

[0030] (2) The scheme of the present application adopts the combination of 3D-MOT potential well and MT potential well, i.e. the combination of deep and shallow potential wells, so that a larger range of well depth conditions can be obtained, thereby improving the measurement accuracy of the partial pressure of the mixed gas. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 This is a schematic diagram of the device for measuring the partial pressure of ultra-high vacuum mixed gas based on cold atom technology according to the present invention.

[0032] Among them, 1—alkali metal atom source, 2—permanent magnet 2D-MOT, 3—differential tube, 4—3D-MOT, 5—ionization vacuum gauge, 6—first valve, 7—non-evaporative getter pump, 8—second valve, 9—first molecular pump, 10—third valve, 11—second molecular pump, 12—dry pump, 13—fourth valve, 14—ultra-high vacuum stabilizing chamber, 15—fifth valve. Detailed Implementation

[0033] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0034] This invention provides a device and method for measuring the partial pressure of a cold atom-containing ultra-high vacuum mixed gas. Based on the theory that the gas particle density can be deduced from the regular decay of trapped cold atoms in a potential well due to collisions with background gas particles, and the characteristic that the velocity-average collision cross-section between different gas particles and cold atoms exhibits a definite and independent variation trend with the potential well depth, a multivariate linear regression equation system is proposed to construct the total collision loss rate with respect to the partial density of the mixed gas under different well depths. This system analyzes the change in the total loss rate of cold atom clusters under different well depths, thereby separating the types and densities of each component in the mixed gas and determining the partial pressure of each component. This method avoids the measurement uncertainties caused by the numerous effects of ionization processes in traditional mass spectrometers. Furthermore, based on the fundamental physical properties of cold atoms, it possesses unique advantages such as requiring no calibration, being undisturbed by the measurement environment, high accuracy, and reproducibility across different times and locations.

[0035] like Figure 1 As shown, the ultra-high vacuum mixed gas partial pressure measuring device based on cold atom technology of the present invention mainly consists of two parts: a cold atom unit and a vacuum system unit.

[0036] The main function of the cold atom unit is to load cold atoms and monitor their loss under different trap depths. Its main structure consists of a sequentially connected alkali metal atom source 1, a permanent magnet two-dimensional magneto-optical trap (2D-MOT) 2, a differential tube 3, and a three-dimensional magneto-optical trap (3D-MOT) 4. The alkali metal atom source 1 generates cold atoms, which can typically be Li, Rb, or Cs atoms. Ideally, a suitable atom emission channel design can effectively reduce the influence of stray gases on the measurement environment. The vacuum level of the permanent magnet 2D-MOT 2 is typically 10⁻⁶. -6Pa, for pre-cooling of cold atoms; preferably, the spatial position of permanent magnet is precisely adjusted to effectively improve the loading speed of atoms. The differential tube 3 is used to generate a high differential degree of vacuum between the permanent magnets 2D-MOT 2 and 3D-MOT 4, which can greatly weaken the influence of stray gas on the 3D-MOT 4. The vacuum degree of the 3D-MOT 4 is 10 -9 -10 -10 Pa, different trap depths are set in the 3D-MOT 4, the number of trap depths is greater than the number of gas species of the mixed gas to be measured, and the mixed gas to be measured collides with cold atoms in the 3D-MOT 4; preferably, maintaining the temperature of each part of the cavity constant can effectively avoid the thermal effusion effect of the mixed gas to be measured.

[0037] The main function of the vacuum system unit is to extract the background gas pressure in the 3D-MOT cavity to an extremely high vacuum below 10 - 9 Pa, and then introduce the mixed gas to be measured, including an ionization gauge 5, a first valve 6, a non-evaporable getter pump 7, a second valve 8, a first molecular pump 9, a third valve 10, a second molecular pump 11, a dry pump 12, a fourth valve 13, an ultra-high vacuum pressure stabilization chamber 14, and a fifth valve 15. The ultra-high vacuum pressure stabilization chamber 14 is connected with the 3D-MOT cavity 4 through the fourth valve 13; the non-evaporable getter pump 7 is connected with the 3D-MOT cavity 4 through the first valve 6; the first molecular pump 9 is connected with the 3D-MOT cavity 4 through the second valve 8; the second molecular pump 11 and the dry pump 12 are used as the front stage pump of the first molecular pump 10, and are connected with the first molecular pump 9 through the third valve 10; the mixed gas to be measured is introduced into the ultra-high vacuum pressure stabilization chamber 14 through the fifth valve 15; the ionization gauge 5 is used to monitor whether the pressure in the 3D-MOT cavity 4 is stable, and does not need to accurately measure the vacuum degree of the 3D-MOT cavity 4.

[0038] The principle of measuring the partial pressure of the mixed gas by the device is as follows:

[0039] The cold atoms trapped in the potential well are lost by colliding with neutral particles of each component of the mixed gas, and the density of each component particle can be inversely calculated by measuring the loss rule of the cold atoms in the well. Combined with the Dalton partial pressure law The partial pressure of each component of the mixed gas is determined by the following formula:

[0040]

[0041] Wherein, i represents the particle species in the mixed gas, U is the trap depth of the potential well, [Γ loss (U)] irepresents the loss rate caused by the collision between cold atoms in the potential well and the ith type of particles in the mixed gas, the number of cold atoms decays exponentially with time, and the formula is expressed as N(t)=N0 exp[-Γ loss (U)t], where N0 represents the initial loading number of cold atoms, N(t) represents the number of cold atoms changing with time, and thus [Γ loss (U)] i This parameter has a value. <σ loss (U)v> i represents the velocity thermal average collision loss cross section of the ith type of collision system in the mixed gas, also known as the loss rate coefficient, which is only related to the potential well depth U under the same collision system. <…> represents the thermal average value of a certain parameter. σ loss (U) is the collision cross section, which is a basic property of atoms. v is the relative speed of the collision system. <σ loss (U)v> can be calculated according to the semi-classical theory, starting from the conservation of momentum and energy, combining the Van der Waals interaction potential and the partial wave phase shift approximation theory, and the formula is as follows:

[0042]

[0043] where κ and ζ are fixed coefficients, κ=12.88 and ζ=0.3755; m cold is the mass of the cold atom; m i and T i respectively represent the mass and temperature of the ith type of particles in the mixed gas to be measured; μ=m cold ·m i / (m cold +m i ) represents the reduced mass; is the Van der Waals length, is the Van der Waals energy, C6 is the diffusion coefficient, and x6, E6 are different for different collision systems; U is the potential well depth of the trapped cold atom; k B is the Boltzmann constant; is the reduced Planck constant. As can be seen from equation (2), <σ loss (U)v> is only related to the diffusion coefficient C6, the mass and temperature m i and T of the particles in the mixed gas to be measured, the mass m cold of the cold atom, and the potential well depth U.

[0044] Therefore, the same collision system has a certain <σ loss v> under the condition of a fixed well depth U, that is, a certain <σ loss(U)v>the trend of the potential well depth U, and the <σ loss (U)v>the trend of the potential well depth U, and the <σ

[0045] According to the above theory, in the quantitative analysis of the mixed gas partial pressure measurement based on the cold atom technology, a correction can be made to the following multivariate linear regression equation,

[0046]

[0047] In the formula, U j represents the set well depth in the jth measurement; Γ(U j ) is the total loss rate of the mixed gas at a certain well depth U j under the condition of the jth measurement; i represents the particle species in the mixed gas; <σ loss (U j )v> i is the velocity thermal average collision loss cross section of the ith particle at the well depth U j ; n i represents the density of different components in the mixed gas, which is the final result to be solved and determined in the partial pressure measurement.

[0048] Therefore, by measuring the total loss rate Γ(U) under different well depth conditions, the component species and partial pressure of the mixed gas can be obtained.

[0049] The measurement method based on the above measurement device is as follows:

[0050] Step 1, the 3D-MOT cavity, the ultra-high vacuum stable chamber is pumped to 10 -9 Pa:

[0051] Close the fifth valve 15, open the first valve 6, the second valve 8, the third valve 10, the fourth valve 13, open the dry pump 12, the first molecular pump 9, the second molecular pump 11 in turn to continuously pump the 3D-MOT cavity 4 and the ultra-high vacuum stable chamber 14; and bake out the 3D-MOT cavity 4, the ultra-high vacuum stable chamber 14, the first valve 6, the second valve 8, the third valve 10, the fourth valve 13; at the same time, control the non-evaporable getter pump 7 to start the activation program to perform high temperature baking and keep warm for a certain time, then complete the activation, close the second valve 8; continuously bake and keep warm the 3D-MOT cavity 4, the ultra-high vacuum stable chamber 14, the first valve 6, the second valve 8, the third valve 10, the fourth valve 13, and then cool down at a certain cooling rate, stop baking when cooled to room temperature; then, open the second valve 8, use the activated non-evaporable getter pump 7 to pump the 3D-MOT cavity 4 and the ultra-high vacuum stable chamber 14 to an ultra-high vacuum 10 -9Pa or less;

[0052] Step 2, pass the gas to be measured into the 3D-MOT cavity:

[0053] Close the fourth valve 13, open the fifth valve 15, pass the mixed gas to be measured into the ultra-high vacuum pressure stabilization chamber 14, after the pressure is stabilized, sequentially close the fifth valve 15, the first valve 6 and the second valve 8, open the fourth valve 13 to pass the gas to be measured into the 3D-MOT cavity 4, and monitor the pressure stabilization in the 3D-MOT cavity 4 with the ionization vacuum gauge 5, and then close the fourth valve 13 after the pressure reaches equilibrium;

[0054] Step 3, load the cold atoms into the 3D-MOT:

[0055] Heat the alkali metal atom source 1 to generate a hot atom beam, collimate and pre-cool in the permanent magnet 2D-MOT 2, transfer the pre-cooled atom beam to the 3D-MOT 4 through the differential tube 3 under the action of the push beam and trap it as a cold atom group, and then close the alkali metal atom source 1 after the loading of the 3D-MOT 4 is completed;

[0056] Step 4, obtain the loss rate Γ(U) under different MOT trap depth conditions:

[0057] Measure the potential well depth of the MOT, and record the number of atoms in the cold atom group with the fluorescence technique, and simultaneously calculate the corresponding loss rate; adjust the MOT laser intensity, the amount of detuning and the magnetic field gradient to change the MOT trap depth, repeat steps 3 and 4 for several cycles, and record the loss rate Γ(U) under different trap depth conditions;

[0058] Step 5, use the multivariate linear regression equation set to solve the component types and partial pressures in the mixed gas:

[0059] Based on the loss rates Γ(U) under different trap depth conditions U j j ), and the certain known velocity-thermal average collision loss cross sections <σ loss (U j )v> i of different gas particles under different trap depth conditions U j , a multivariate linear regression equation set as formula (3) is constructed.

[0060] For the convenience of operation, formula (3) is written in matrix form as follows:

[0061]

[0062] To ensure that the equation set has a solution, it is required that j≥i, that is, the measurement times (the total number of selected trap depths) j is not less than the number of components i of the mixed gas; and each group of trap depth conditions (such as U​j＝a ) Loss rate coefficient <σ loss (U j＝a v> i The vectors are not related, that is, the row vectors of the matrix in formula (4) are not related, otherwise it is equivalent to increasing the number of meaningless experiments, and even it may make the equation have no unique solution or unique minimum norm least square solution.

[0063] By solving equation (4), the density n i of each type of gas particle in the mixed gas to be detected can be obtained.

[0064] Step 6, based on the ideal gas state equation P=nk B T, the partial pressure of each component gas in the mixed gas to be detected can be obtained according to the density of each gas particle solved in step 5.

[0065] In order to obtain a larger range of trap depth conditions, in step 4, a combination of MOT trap depth and MT trap depth is used, that is, steps 41 and 42 are also included:

[0066] Step 41, constructing MT, transferring the cold atoms trapped by MOT to MT and cooling the trapped atoms:

[0067] On the basis of completing the loading of cold atoms in MOT in step 3, the laser frequency is tuned to transfer all the atomic states in the cold atom group loaded into MOT to a single magnetic trap bound state; the magnetic field gradient is increased to establish a magnetic trap while the pumping light is turned off;

[0068] Step 42, obtaining the loss rate Γ(U) of MT trap depth condition:

[0069] Set the MT potential well depth, after the cold atoms evolve in the MT for a certain time, turn on the MOT to count the remaining number of cold atoms, obtain a point on the atomic decay curve N(t)=N0 exp[-Γ loss t], set different collision times and cycle steps 41 and 42 multiple times, obtain the remaining number of cold atoms after the cold atoms evolve in the MT for different times, draw the atomic decay curve, and obtain the loss rate Γ(U) under the MT trap depth condition; adjust the MT magnetic field gradient, cycle steps 41 and 42 several times, and record the loss rates Γ(U) under different MT trap depth conditions.

[0070] Based on the combination of the loss rates Γ(U) under different MT trap depth conditions and the loss rates Γ(U) under different 3D-MOT trap depth conditions, equation (4) is solved.

[0071] In order to make the selected range of the trap depth condition of the measuring process large enough, the deep potential well (magnetic optical trap) and the shallow potential well (magnetic trap or optical dipole trap) are adopted in the selection of the potential well, and the deep and shallow potential wells can be converted by adjusting the parameters of the magnetic optical trap device; however, the operation procedure of the loss rate of the cold atoms in the different trap depth conditions in the MT is more complex than that in the MOT, and the adjustable range of the MT trap depth is smaller, so the number of the equations constructed in the MOT is more than that in the MT; in addition, several groups of trap depth conditions can be selected in the deep and shallow potential wells for the experiment; or the experiments can be carried out in the respective potential wells respectively, and then the experiments are verified with each other, so as to improve the measurement accuracy.

[0072] Embodiment 1

[0073] Firstly, the 3D-MOT cavity and the ultra-high vacuum pressure stabilization chamber are vacuumized to 10 -9 Pa by using a baking and pumping system, the mixed gas (containing He, Ar and N2 particles) to be measured is introduced into the ultra-high vacuum pressure stabilization chamber, and then introduced into the 3D-MOT cavity after pressure stabilization; secondly, the cold atom species is selected as Li atom, the MOT laser intensity, the detuning amount and the magnetic field gradient are adjusted, three known different trap depths U1, U2 and U3 are set, the MT magnetic field gradient is adjusted, one known MT trap depth U4 is set, and the velocity thermal average collision loss cross section <σ loss (U j )v i of the i-th particle under the j-th trap depth is determined according to the formula (2) and the experimental verification; then the loss curves of the Li cold atoms under the conditions of the different MOT trap depths U1, U2, U3 and the MT trap depth U4 are measured by the experiment, and the loss rates Γ(U1), Γ(U2), Γ(U3) and Γ(U4) under the respective trap depth conditions are obtained; finally, the following multivariable linear regression equation group is established:

[0074]

[0075] The least norm least square solution of the equation is solved, and the proportions of He, Ar and N2 in the mixed gas are obtained n Ar .

[0076] To sum up, the above is only a preferred embodiment of the present application, and is not used to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A device for measuring the partial pressure of a cold atom ultra-high vacuum mixed gas, characterized in that, The cold atom unit and the vacuum system unit are included; the cold atom unit includes sequentially connected alkali metal atom source (1), permanent magnet two-dimensional magnetic optical trap (2), differential tube (3) and three-dimensional magnetic optical trap (4); different trap depths are arranged in the three-dimensional magnetic optical trap (4), and the number of trap depths is greater than the number of gas species in the mixed gas to be detected; The vacuum system unit includes a pumping system and a pressure stabilizing chamber (14), wherein the pressure stabilizing chamber (14) is connected with the three-dimensional magnetic optical trap (4) and used for introducing the mixed gas to be detected into the three-dimensional magnetic optical trap (4); the pumping system is used for pumping the three-dimensional magnetic optical trap (4) and the pressure stabilizing chamber (14) to an extremely high vacuum; The pumping system includes a non-evaporable getter pump (7), a first molecular pump (9), a second molecular pump (11), a dry pump (12) and an ionization gauge (5); the non-evaporable getter pump (7) is connected with the three-dimensional magnetic optical trap (4) through a first valve (6); the dry pump (12) and the second molecular pump (11) are sequentially connected, and then connected with the first molecular pump (9) through a third valve (10), and then connected with the three-dimensional magnetic optical trap (4) through a second valve (8); the ionization gauge (5) is used for monitoring whether the pressure in the three-dimensional magnetic optical trap (4) is stable; the pressure stabilizing chamber (14) is connected with the three-dimensional magnetic optical trap (4) through a fourth valve (13); the mixed gas to be detected is introduced into the pressure stabilizing chamber (14) through a fifth valve (15).

2. The apparatus of claim 1, wherein, The alkali metal atom source (1) adopts Li, Rb or Cs atom.

3. The apparatus of claim 1, wherein, The trap depths have low mutualities.

4. A measuring method using the cold atom ultrahigh vacuum mixed gas partial pressure measuring apparatus according to any one of claims 1 to 3, characterized by, It includes: Step 1, start the pumping system, and pump the three-dimensional magnetic optical trap (4) and the pressure stabilizing chamber (14) to an extremely high vacuum; Step 2, introduce the mixed gas to be detected into the pressure stabilizing chamber (14), and then introduce into the three-dimensional magnetic optical trap after the pressure is stable; Step 3, heat the alkali metal atom source (1) to generate a hot atom beam, collimate and pre-cool the hot atom beam through the permanent magnet two-dimensional magnetic optical trap, and then transfer the hot atom beam to the three-dimensional magnetic optical trap (4) through the differential tube (3) and trap the cold atom group in the three-dimensional magnetic optical trap (4); Step 4, measure the loss rate Γ(U) of the cold atom under the current three-dimensional magnetic optical trap trap depth condition; Construct a magnetic trap, transfer the cold atom trapped in the three-dimensional magnetic optical trap to the magnetic trap and cool and trap it, and obtain the loss rate Γ(U) of the magnetic trap trap depth condition; Change the three-dimensional magnetic optical trap trap depth and the magnetic trap trap depth, and repeat steps 3-4 to measure the combination of the loss rates of the cold atom under different three-dimensional magnetic optical trap trap depth conditions and different magnetic trap trap depth conditions; wherein the number of the three-dimensional magnetic optical trap trap depth and the magnetic trap trap depth is greater than the number of gas species in the mixed gas to be detected; Step 5, constructing a multivariate linear regression equation set Solving the density of the i-th type of gas particles in the mixed gas to be measured; wherein, U j is the set trap depth at the j-th measurement; Γ(U j ) is the loss rate of cold atoms at the trap depth U j under the j-th measurement; i is the i-th type of gas particles in the mixed gas to be measured; <σ loss (U j )v> i is the velocity thermal average collision loss cross section of the i-th type of gas particles in the mixed gas to be measured after collision with cold atoms at the trap depth U j ; n i is the density of the i-th type of gas particles in the mixed gas to be measured to be solved. Step 6, according to the density of each gas particle solved in step 5, based on the ideal gas state equation, the partial pressure of each component gas in the mixed gas to be detected is obtained.

5. The method of claim 4, wherein, The combination of three-dimensional magnetic optical trap deep potential well and magnetic trap shallow potential well is adopted.

6. The method of any one of claims 4-5, characterized in that, The number of three-dimensional magnetic optical trap depths is greater than the number of magnetic trap depths.

7. The method of any one of claims 4 to 5, characterized in that, In the step 1, the fifth valve (15) is closed, the first valve (6), the second valve (8), the third valve (10) and the fourth valve (13) are opened, the dry pump (12), the first molecular pump (9) and the second molecular pump (11) are opened in sequence to continuously pump the three-dimensional magnetic optical trap (4) and the pressure stabilization chamber (14); the three-dimensional magnetic optical trap (4), the pressure stabilization chamber (14), the first valve (6), the second valve (8), the third valve (10) and the fourth valve (13) are baked and degassed; at the same time, the non-evaporable getter pump (7) is controlled to start the activation program to perform high-temperature baking and keep warm for a certain time to complete the activation, and the second valve (8) is closed; the three-dimensional magnetic optical trap (4), the pressure stabilization chamber (14), the first valve (6), the second valve (8), the third valve (10) and the fourth valve (13) are continuously baked and kept warm, and then cooled, and the baking is stopped after cooling to room temperature; then, the second valve (8) is opened, and the activated non-evaporable getter pump (7) is used to pump the three-dimensional magnetic optical trap (4) and the pressure stabilization chamber (14) to an ultra-high vacuum 10 -9 Pa or below.

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