阅读说明：本技术 适用于负氢粒子束的中性化气体靶单元及系统设计方法 (Neutral gas target unit suitable for negative hydrogen particle beams and system design method ) 是由 闫逸花 王忠明 王迪 王茂成 刘卧龙 王敏文 杨业 吕伟 陈伟 于 2020-04-08 设计创作，主要内容包括：本发明属于粒子束中性化气体靶单元及配套真空差分系统设计方法,为解决需在加速器系统上获得中性粒子束时,能实现最大中性化效率的气体靶单元计算方法及经验公式不足,现有的真空差分系统设计繁琐的问题,提供一种适用于负氢粒子束的中性化气体靶单元及系统设计方法,中性化气体靶单元设计方法能够快速给出在采用几种常用气体时的气体靶质量厚度、平均压强、平均长度和气体靶内径等关键参数,并依据上述参数,结合加速器实际,快速构建出一组适宜的配套真空差分系统核心元件,根据中性化气体靶单元与加速器束线真空压差等级,确定差分等级、第n级差分比、第n级差分管流导、第n级差分管内径及长度,完成气体中性化系统的初步设计。(The invention belongs to a particle beam neutral gas target unit and a matched vacuum differential system design method, and aims to solve the problems that a gas target unit calculation method and an empirical formula which can realize the maximum neutralization efficiency when neutral particle beams are obtained on an accelerator system are insufficient, and the design of the conventional vacuum differential system is complicated And (4) finishing the primary design of the gas neutralization system by the flow guide of the nth stage differential pipe and the inner diameter and the length of the nth stage differential pipe.)

1. The design method of the neutral gas target unit suitable for the negative hydrogen particle beam is characterized by comprising the following steps of:

s1, determining the total stripping section sigma of the negative hydrogen ions_t

The total stripping cross section sigma of the negative hydrogen ions is calculated according to the following formula_t

Wherein i represents a target chamber gas species; e is hydrogen ion energy; β (E) is the relativistic velocity of the corresponding hydrogen ion; epsilon₀Is the static energy of a hydrogen atom,. epsilon₀＝938.27MeV；Ψ(E)_iAs a generalized total cross-section, Ψ (E)_iThe values are as follows:

wherein the content of the first and second substances,the generalized total section corresponding to the hydrogen gas in the target chamber is shown;the generalized total section corresponding to helium gas in the target chamber is shown;the generalized total section corresponding to the nitrogen gas in the target chamber is shown;the generalized total section corresponding to oxygen gas in the target chamber is shown;general expression of argon gas as target chamber gasA cross section;

s2, determining the negative hydrogen ion stripping section ratio eta₀₁(i)

Negative hydrogen ion stripping cross-sectional ratio eta corresponding to each target chamber gas type₀₁(i) Respectively as follows:

η₀₁(H₂)＝0.295；η₀₁(He)＝0.345；η₀₁(N₂)＝0.380；η₀₁(O₂)＝0.381；η₀₁(Ar)＝0.413；

s3, calculating the mass thickness chi of the neutralized gas target

Calculating the mass thickness chi of the neutral gas target according to the following formula

S4, determining the average pressure P of the neutralization gas target unit₀And an average length L₀

Set mean pressure P₀And an average length L₀Substituting any of the values in (1) to calculate another value as:

L₀P₀＝χRT/N_A

wherein R is an ideal gas constant, T is a gas temperature, and dimensions are K and N_AIs Afugardro constant;

s5, determining the inner diameter D of the neutralized gas target

Inner diameter D ═ r of gas target_beam+2 mm; wherein r is_beamIs the beam spot inner diameter;

s6, according to the neutral gas target mass thickness chi obtained in the step S4 and the average pressure P determined in the step S4₀And an average length L₀And S5, processing and manufacturing the determined gas target inner diameter D to obtain the corresponding gas target unit.

2. The method of claim 1, wherein the method comprises: in step S4, the set average pressure P₀And an average length L₀Any one of (1) to (2)The value being in particular the set mean pressure P₀。

3. The method of claim 2, wherein the method comprises: the mean pressure P₀The value of (A) is 0.1-10 Pa.

4. The design method of the neutralization system suitable for the negative hydrogen particle beam is characterized by comprising the following steps of:

s1, designing a neutralization gas target unit

Use of the method for designing a neutral gas target unit according to any one of claims 1 to 3, to design a corresponding gas target unit, i.e. having an internal gas of i and a pressure of P₀Length of L₀A hollow cylinder with an inner diameter D;

s2, determining the pressure difference level M between the neutralization gas target unit and the vacuum pressure of the beam line

According to the vacuum pressure P of the beam line_accAnd average pressure P of the neutral gas target unit₀Obtaining a differential pressure grade M;

s3, determining a vacuum differential level N and an nth level differential ratio lambda_n

Selecting a vacuum differential grade N according to the differential pressure grade M obtained in the step S2, and determining the number of differential tubes, wherein the number of differential tubes is equal to the vacuum differential grade N; according to the pressure P of the nth stage differential pipe_nAnd the pressure P of the preceding stage_n-1The magnitude of the phase difference is determined, and the nth order difference ratio lambda is determined_n(ii) a Wherein n is the number of differential tube stages;

s4, determining the nth stage differential pipe conductance C_n

According to the nth order difference ratio lambda_nConfirmation of nth stage differential conductance C_n；

S5, determining the inner diameter d of the differential pipe_nAnd differential tube length L_n

The nth stage differential pipe conductance C obtained according to the step S4_nDetermining the inner diameter d of the differential pipe_nAnd differential tube length L_n；

And S6, processing and manufacturing according to the parameters obtained in the steps S1 to S5 to obtain the corresponding neutralization system.

5. The method of claim 4, wherein the method further comprises: in step S2, specifically, the step,

the differential pressure level M is calculated according to the following formula:

6. the method of claim 4 or 5, wherein: in the step S3, in the step S,

selecting a vacuum differential level N according to the differential pressure level M obtained in step S2, specifically,

when M is 2, N is 1

When M is 3, N is 2

When M is 4, N is 2 or 3

When M is 5, N is 2, N is 3 or N is 4

When M is 6, N is 2 or N is 3 or N is 4 or N is 5;

the gas pressure P at the later stage of the differential pipe according to the nth stage_nAnd the pressure P of the preceding stage_n-1The magnitude of the phase difference is determined, and the nth order difference ratio lambda is determined_nIn particular to a method for preparing a high-performance nano-silver alloy,

the nth stage differential pipe has a rear stage air pressure P_nPressure P of earlier stage_n-1Lower by 1 order of magnitude, λ_n＝0.1；

The nth stage differential pipe has a rear stage air pressure P_nPressure P of earlier stage_n-12 orders of magnitude lower, λ_n＝0.01；

The nth stage differential pipe has a rear stage air pressure P_nPressure P of earlier stage_n-1Lower by 3 orders of magnitude, λ_n＝0.001。

7. The method of claim 6, wherein the method further comprises: in step S4, specifically, the step,

when lambda is_nWhen not equal to 0.1, C_n40L/s; when lambda is_nWhen not greater than 0.01, C_n10L/s; when lambda is_nWhen not equal to 0.001, C_n＝1L/s。

8. The method according to claim 7, wherein the method further comprises: in step S5, the differential pipe inner diameter d_nHas a value range of r_beam≤d_nLess than or equal to 40 mm; differential tube length L_nHas a value range of 0 to L_n≤150mm。

9. The method of claim 8, wherein the method further comprises: in step S5, specifically, the step,

C_nwhen 1L/s, d_n＝6mm,L_n＝18mm

Or d_n＝8mm,L_n＝50mm

Or d_n＝10mm,L_n＝110mm

C_nWhen 10L/s, d_n＝15mm,L_n＝18mm

Or d_n＝20mm,L_n＝67mm

Or d_n＝25mm,L_n＝145mm

C_nWhen equal to 40L/s, d_n＝25mm,L_n＝10mm

Or d_n＝32.5mm,L_n＝53mm

Or d_n＝40mm,L_n＝130mm。

Technical Field

The invention belongs to a neutral gas target unit of a particle beam and a system design method, and particularly relates to a neutral gas target unit suitable for a negative hydrogen particle beam and a system design method.

Background

Neutral hydrogen atomic beams are not charged, can be prevented from being influenced by a magnetic field environment under a suitable vacuum condition to realize remote transmission, and have the advantages that charged particle beams are incomparable; in addition, the neutral atom beam obtained based on the accelerator can provide a good platform for developing atomic energy level research, thereby playing an important role in relevant basic research. The generation of neutral beams generally requires driving a negative ion beam through a solid or gaseous medium to achieve charge state conversion by charge exchange with a target material and ionization resolution. The bound energy of the trapped electrons outside the negative hydrogen ion nucleus is 0.754eV, the bound energy of the ground state electrons is 13.6eV, when the mass thickness of the target medium is large enough, both the trapped electrons and the ground state electrons are lost, and the total stripping efficiency of not less than 95% can be realized. However, how to control the parameters of the target chamber medium so that the negative hydrogen ions lose only one electron and further ionization of hydrogen atoms is reduced as much as possible is the key point for achieving the neutralization to the maximum extent. In order to realize the maximum neutralization efficiency, the parameters of the gas target chamber need to be accurately controlled, and in this respect, the early-stage related theoretical research and referenceable test conclusion are less, which is not enough to directly guide the design of the neutralization target chamber; in addition, the introduction of the gas target can bring extra air load to an accelerator vacuum system, so one set of differential vacuum system must be synchronously introduced, the matching of a neutral gas target chamber and the accelerator vacuum system is realized, the vacuum design process is often tedious and time-consuming, a researcher needs to invest a great deal of energy to establish one set of basic model, repeated iteration needs to be carried out in combination with the accelerator actually, the time and the labor cost are higher, a set of method with strong operability is urgently needed, the preliminary design steps are simplified, an alternative scheme is provided for the final actual engineering design, and the complexity of the overall design is reduced.

Disclosure of Invention

The invention mainly aims to solve the technical problems that a set of matched vacuum differential system needs to be built for solving the matching problem with an accelerator vacuum system when a gas neutralization system suitable for a negative hydrogen beam needs to be designed, an empirical formula and a conclusion are not available for reference, and the initial design of a neutralization target unit capable of realizing the maximum neutralization efficiency is not enough to be guided, and the neutral gas target unit needs to be practically applied, but the design of the vacuum differential system is complicated, and the cost of manpower and time required to be invested is high, so that the initial design method of the neutralization gas target unit suitable for the negative hydrogen beam and the matched vacuum system is provided.

In order to achieve the purpose, the invention provides the following technical scheme:

the design method of the neutral gas target unit suitable for the negative hydrogen particle beam is characterized by comprising the following steps of:

s1, determining the total stripping section sigma of the negative hydrogen ions_t

The total stripping cross section sigma of the negative hydrogen ions is calculated according to the following formula_t

Wherein i represents a target chamber gas species; e is hydrogen ion energy; β (E) is the relativistic velocity of the corresponding hydrogen ion; epsilon₀Is the static energy of a hydrogen atom,. epsilon₀938.27 MeV; general cross section psi (E)_iThe values are as follows:

wherein the content of the first and second substances,the generalized total section corresponding to the hydrogen gas in the target chamber is shown;the generalized total section corresponding to helium gas in the target chamber is shown;the generalized total section corresponding to the nitrogen gas in the target chamber is shown;the generalized total section corresponding to oxygen gas in the target chamber is shown;the generalized total section corresponding to argon gas as the gas of the target chamber is shown;

s2, determining the negative hydrogen ion stripping section ratio eta₀₁(i)

Negative hydrogen ion stripping cross-sectional ratio eta corresponding to each target chamber gas type₀₁(i) Respectively as follows:

η₀₁(H₂)＝0.295；η₀₁(He)＝0.345；η₀₁(N₂)＝0.380；η₀₁(O₂)＝0.381；η₀₁(Ar)＝0.413；

s3, calculating the mass thickness chi of the neutralized gas target

Calculating the mass thickness chi of the neutral gas target according to the following formula

S4, determining the average pressure P of the neutralization gas target unit₀And an average length L₀

Set mean pressure P₀And an average length L₀Substituting any of the values in (1) to calculate another value as:

L₀P₀＝χRT/N_A

wherein R is an ideal gas constant, T is a gas temperature, and dimensions are K and N_AIs Afugardro constant;

s5, determining the inner diameter D of the neutralized gas target

Inner diameter D ═ r of gas target_beam+2 mm; wherein r is_beamIs the beam spot inner diameter;

s6, obtaining the gas target mass thickness chi obtained in the step S3 and the average pressure P determined in the step S4₀And an average length L₀And determining the inner diameter D of the gas target determined in the step S5, namely determining the key geometric dimension and the internal vacuum degree of the neutralization gas target unit.

Further, in step S4, the set average pressure P₀And an average length L₀Is specifically the set average pressure P₀。

Further, the mean pressure P₀The value of (A) is 0.1-10 Pa.

The design method of the neutralization system suitable for the negative hydrogen particle beams is characterized by comprising the following steps:

s1, designing a neutralization gas target unit

Designing to obtain a corresponding neutral gas target unit by adopting the design method of the neutral gas target unit;

s2, determining the differential pressure level M between the vacuum degrees of the neutralization gas target unit and the beam line

According to the vacuum pressure P of the beam line_accAnd average pressure P of the gas target unit₀Obtaining a differential pressure grade M;

s3, determining a vacuum differential level N and an nth level differential ratio lambda_n

Selecting a vacuum differential grade N according to the differential pressure grade M obtained in the step S2, and determining the number of differential tubes, wherein the number of differential tubes is equal to the vacuum differential grade N; according to the pressure P of the nth stage differential pipe_nAnd the pressure P of the preceding stage_n-1The magnitude of the phase difference is determined, and the nth order difference ratio lambda is determined_n(ii) a Wherein n is the number of differential tube stages;

s4, determining the nth stage differential pipe conductance C_n

According to the nth order difference ratio lambda_nConfirmation of nth stage differential conductance C_n；

S5, determining the inner diameter d of the differential pipe_nAnd differential tube length L_n

The nth stage differential pipe conductance C obtained according to the step S4_nDetermining the inner diameter d of the differential pipe by using a vacuum pipeline flow conductance calculation method and combining the beam spots of the accelerator and the spatial layout_nAnd differential tube length L_n；

And S6, designing and obtaining a corresponding gas neutralization system according to the parameters obtained from the step S1 to the step S5.

Further, in step S2, specifically,

and calculating the differential pressure grade M between the neutral gas target unit and the vacuum pressure of the beam line according to the following formula:

further, in step S3,

the vacuum differential level N is confirmed according to the differential pressure level M obtained in step S2, specifically,

when M is 2, N is 1

When M is 3, N is 2

When M is 4, N is 2 or 3

When M is 5, N is 2, N is 3 or N is 4

When M is 6, N is 2 or 3 or N is 4 or 5.

The gas pressure P at the later stage of the differential pipe according to the nth stage_nAnd the pressure P of the preceding stage_n-1The magnitude of the phase difference is specifically that the pressure P of the next stage of the nth stage of the differential tube_nPressure P of earlier stage_n-1Lower by 1 order of magnitude, λ_n＝0.1；

The nth stage differential pipe has a rear stage air pressure P_nPressure P of earlier stage_n-12 orders of magnitude lower, λ_n＝0.01；

The nth stage differential pipe has a rear stage air pressure P_nPressure P of earlier stage_n-1Lower by 3 orders of magnitude, λ_n＝0.001。

Further, in step S4, specifically,

when lambda is_nWhen not equal to 0.1, C_n40L/s; when lambda is_nWhen not greater than 0.01, C_n10L/s; when lambda is_nWhen not equal to 0.001, C_n＝1L/s。

Further, in step S5, the differential pipe inner diameter d_nHas a value range of r_beam≤d_nLess than or equal to 40 mm; differential tube length L_nHas a value range of 0 to L_n≤150mm。

Further, in step S5, specifically,

C_nwhen 1L/s, d_n＝6mm,L_n＝18mm

Or d_n＝8mm,L_n＝50mm

Or d_n＝10mm,L_n＝110mm

C_nWhen 10L/s, d_n＝15mm,L_n＝18mm

Or d_n＝20mm,L_n＝67mm

Or d_n＝25mm,L_n＝145mm

C_nWhen equal to 40L/s, d_n＝25mm,L_n＝10mm

Or d_n＝32.5mm,L_n＝53mm

Or d_n＝40mm,L_n＝130mm。

Compared with the prior art, the invention has the beneficial effects that:

1. the invention can quickly realize the design of key parameters of the gas neutralization target chamber which are suitable for negative hydrogen particles with different energies and can realize the maximum neutralization efficiency, the mass thickness, the average pressure, the average length and the inner diameter of the gas target, and can quickly construct a group of core elements of the vacuum differential system according to the key parameters and by combining the actual situation of an accelerator, thereby greatly simplifying the fussy calculation process in the early stage of the design of the neutralization target chamber and bringing great convenience for the scheme design of the neutralization target chamber.

2. In the design of the average pressure and the average length of the neutralizing gas target unit, the average pressure value is given, and the average length is calculated, so that the average pressure is generally selected in a narrow range, and the design is simpler and more convenient.

3. The average pressure is 0.1-10Pa, so that the method is more suitable for actual use conditions and more accurate in calculation.

4. According to the design method of the matched vacuum differential system when the negative hydrogen particle beam neutralization gas target unit is matched with the accelerator system, on the basis of the design of the gas target unit, the preliminary parameters of the vacuum differential system are further confirmed and obtained through a simple method, the vacuum pressure difference grade between the neutralization gas target unit and a beam line, the number of differential tubes, the nth-level differential ratio, the nth-level differential tube conductance and the nth-level differential tube inner diameter and length are sequentially obtained, and finally all key parameters of the matched vacuum differential system (namely a group of differential tube sequences) are obtained, so that the preliminary design of the gas neutralization system is completed. The initial design process of the gas neutralization system is greatly simplified, a plurality of different alternative schemes can be quickly formed by the method, the accelerator is combined for actual further screening, great convenience is brought to the design of the gas neutralization system, and the method has popularization and practicability.

5. In the present invention, only r_beam≤d_nLess than or equal to 40mm and less than or equal to 0L_nThe inner diameter and the length of the differential pipe are selected within the range of less than or equal to 150mm, the sizes of the actual beam spot, the pipeline, the magnet aperture and the like of the accelerator are fitted, the vacuum differential system cannot occupy too much space along the beam direction, and the physical beam line of the accelerator is prevented from being designed too complicated.

Drawings

FIG. 1 is a schematic flow chart of an embodiment of the method for designing a neutral gas target unit for a negative hydrogen particle beam according to the present invention;

FIG. 2 is a schematic flow chart of an embodiment of the present invention for designing a neutralization system for a negative hydrogen particle beam;

Detailed Description

The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention and the accompanying drawings, and it is obvious that the described embodiments do not limit the present invention.

The invention provides a set of gas target unit parameter formulas capable of realizing the maximization of the neutralization efficiency by combining the practical application of the accelerator aiming at the difficult problems of the key parameter design of the neutralization gas target chamber and the design of a matched differential vacuum system, establishes a set of differential vacuum system design method for the transitional connection of the gas target unit and the vacuum system of the accelerator, forms a set of clear gas neutralization system design flow by the vacuum ratio modulization of each level, has the advantages of convenient operation, accurate and reliable result and the like, and has good application value in the design of the gas neutralization target chamber in the accelerator system and the matched vacuum differential system scheme.

Referring to fig. 1, firstly, a method for designing a neutralizing gas target unit suitable for a negative hydrogen particle beam includes the following steps:

1) the relationship between the maximum neutralization efficiency and the mass thickness and the peeling cross section of the gas target is calculated.

Let sigma_-10Is H^-→H⁰Peeling cross section of (a)_-11Is H^-→H⁺Peeling cross section of (a)₀₁Is H⁰→H⁺The section dimension of the peel section of (2) is cm²(ii) a Let N^-Is H^-Particle number ratio, N⁰Is H⁰Particle number ratio, N⁺Is H⁺The particle number proportion is a dimensionless unit; let chi be the mass thickness of the gas target and measure the molecules/cm²(ii) a The relationship between the particle number ratio and the peeling cross section and the gas target mass thickness χ is shown as follows:

N⁺＝1-N^--N⁰；

let H^-→H⁰The neutralization efficiency of (a) is K:

when K is maximized, let the gas target mass thickness be χ, then χ can be solved by solving dN⁰Where/dx is 0:

let sigma_tIs H^-Peeling total cross section: sigma_t＝σ_-10+σ_-11；

When the target chamber gas is i, σ₀₁And σ_tHas a ratio of [. eta ]₀₁(i)：

The gas target mass thickness χ can be simplified as represented by equation (1):

2) solving for sigma_t＝σ_-10+σ_-11。

Let H^-Energy is E, dimension is MeV; beta (E) is the relativistic velocity, epsilon, of the corresponding hydrogen ion₀Is the static energy of hydrogen atoms, thenε₀＝938.27MeV；σ_tThe change with the particle energy E is approximately proportional to 1/beta²Let the general section Ψ (E)_i＝σ_tβ²(E) In a specific gas psi (E)_iIs approximated by a constant, σ_tCan be calculated by equation (2):

wherein:

when E is>Ψ (E) at 20MeV_iApproximately 10MeV ≦ E<The 20MeV interval value, but an energy correction factor needs to be introduced in the accurate calculation, and the correction method is out of the discussion range of the method.

3) Solving negative hydrogen ion stripping section ratio eta₀₁(i)

Coefficient of proportionality eta₀₁(i)＝σ₀₁/σ_-10+σ_-11For a negative hydrogen beam, this value is approximately constant in a specific gas, and in a common gas the values are taken as follows:

η₀₁(H₂)＝0.295(E≤20MeV)；η₀₁(He)＝0.345(E≤20MeV)；η₀₁(N₂)＝0.380(E≤20MeV)；η₀₁(O₂)＝0.381(E≤20MeV)；η₀₁(Ar)＝0.413(E≤20MeV)；

when E is>20MeV, η₀₁(i) The above values can still be referred to for approximate calculation, but accurate calculation requires introduction of energy correction factors, and the correction method is out of the scope of the method.

4) Calculating the average pressure P of the gas target unit₀And an average length L₀

Average length of gas target unit is L₀Dimension is cm; mean pressure of P₀Dimension is Pa; n is a radical of_AIs Afuga de Ro constant, N_A＝6.022×10²³(ii) a R is ideal gas constant, R is 8.314472J mol^-1K^-1(ii) a T is the gas temperature and the dimension is K; l can be obtained from the ideal gas state equation₀And P₀The relationship is shown in formula (3):

L₀P₀＝χRT/N_A (3)

sigma calculated by equation (2)_tAnd eta obtained by calculation in step (3)₀₁(i) Substituting formula (1) to obtain χ, substituting formula (3) with χ, and setting P₀、L₀Either one of the two values can be used to obtain the other value. As a preferred option, the mean pressure P can be set₀Find the average length L₀。

5) Selecting gas target inner diameter D

Let the beam spot have an inner diameter of r_beam(r_beamNo more than 20mm), the inner diameter D of the gas target is r_beam+2 mm; when the inner diameter of the beam spot is too large, the size of the gas neutralization target chamber is correspondingly increased, and larger gas load is introduced into a common accelerator system, so that the structure of a matched differential system is more complex and more complicatedThe structure is more lengthy and the applicability is lower, so the method is preferably applicable under the condition that the beam spot size is not more than 20mm, and accords with the practical condition of an accelerator.

6) According to the mass thickness chi and the average pressure P of the gas target obtained above₀Average length L₀And designing the inner diameter D of the gas target to obtain a corresponding gas target unit.

The invention also provides a method for calculating the parameters of a differential vacuum transition system between the neutralization gas target and the accelerator vacuum system, namely a method for designing a gas neutralization system suitable for negative hydrogen particle beams, which comprises the following steps:

referring to FIG. 2, the design method of the neutralized gas target unit is adopted to design a corresponding gas target unit, and then the design method is carried out according to the following method,

1) calculating the vacuum pressure difference level M between the gas target chamber and the beam line

P₀Is the average pressure, P, of the gas target unit_accCalculating the pressure difference grade M according to the formula (5) as the vacuum pressure of the beam line, wherein M is a positive integer and is more than or equal to 2 and less than or equal to 6;

2) selecting vacuum differential grade N and nth grade differential ratio lambda_n

N is less than or equal to M-1 and also represents the number of differential tubes; n is not more than N and is a positive integer; the pressure of the front stage of the nth stage differential pipe is P_n-1The rear stage air pressure is P_n；

λ_nSetting three stages of 0.1, 0.01 and 0.001.

λ_n0.1: the pressure P of the ith stage differential pipe_nPressure P of earlier stage_n-1Lower by 1 order of magnitude;

λ_n0.01: the pressure P of the ith stage differential pipe_nPressure P of earlier stage_n-12 orders of magnitude lower;

λ_n0.001, the pressure P of the i-th stage differential pipe_nPressure P of earlier stage_n-1Lower by 3 orders of magnitude;

wherein the content of the first and second substances,

then:

when M is 2, N is 1(λ)₁＝0.01)

When M is 3, N is 2(λ)₁＝0.01,λ₂＝0.1)

When M is 4, N is 2(λ)₁＝0.01,λ₂＝0.01)

N＝3(λ₁＝0.01,λ₂＝0.1,λ₃＝0.1)

When M is 5, N is 2(λ)₁＝0.001,λ₂＝0.01)

N＝3(λ₁＝0.01,λ₂＝0.01,λ₃＝0.1)

N＝4(λ₁＝0.01,λ₂＝0.1,λ₃＝0.1,λ₄＝0.1)

When M is 6, N is 2(λ)₁＝0.001,λ₂＝0.001)

N＝3(λ₁＝0.01,λ₂＝0.01,λ₃＝0.01)

N＝4(λ₁＝0.01,λ₂＝0.01,λ₃＝0.1,λ₄＝0.1)

N＝5(λ₁＝0.01,λ₂＝λ₃＝λ₄＝λ₅＝0.1)

Average pressure P of gas target unit₀Will be greater than the beam line vacuum P_accIs several orders of magnitude higher, if M is 6, it represents P₀Ratio P_accThe vacuum degree is 6 orders of magnitude higher.

P is realized step by utilizing a vacuum differential system_accAnd P₀A step transition between them.

If the vacuum differential level N is 3, it means that the vacuum drop is realized step by step through three steps, and finally the vacuum drop and P are realized_accIs connected with the transition of (2).

3) Selecting nth stage differential pipe flow guide C_n

λ_nWhen not equal to 0.1, C_n＝40L/s

λ_nWhen not greater than 0.01, C_n＝10L/s

λ_nWhen not equal to 0.001, C_n＝1L/s。

4) Differential pipe inner diameter d_nAnd length L_nSelecting

By using a vacuum pipeline conductance calculation method and combining the beam spot of an accelerator and the actual situation of spatial layout, the method suggests only in r_beam≤d_n≤40mm,0≤L_nThe selection is carried out within the range of less than or equal to 150mm, so that the differential system does not occupy excessive space in the beam direction, and the over-complex beam design is avoided. The differential pipeline conductance is sensitive to size parameters, the initial design and use requirements can be basically met by adopting the following combination through calculation, and the selected size meets the actual application requirements of the accelerator.

C_nWhen 1L/s, d_n＝6mm,L_n＝18mm

Or d_n＝8mm,L_n＝50mm

Or d_n＝10mm,L_n＝110mm

C_nWhen 10L/s, d_n＝15mm,L_n＝18mm

Or d_n＝20mm,L_n＝67mm

Or d_n＝25mm,L_n＝145mm

C_nWhen equal to 40L/s, d_n＝25mm,L_n＝10mm

Or d_n＝32.5mm,L_n＝53mm

Or d_n＝40mm,L_n＝130mm。

5) Designing and obtaining a corresponding negative hydrogen particle beam neutralization gas target unit matched vacuum differential system according to the parameters obtained in the steps 1) to 4), namely, sequentially arranging N differential tubes on the extension line of the central axis of the neutralization gas target unit on two sides of the neutralization gas target unit at proper intervals according to the sequence of 1, 2, … … and N and the actual beam line.

As further illustrated by an example as follows:

a200 MeV proton application device (XipAF) is combined with the beam line condition of a 7MeV negative hydrogen injector, and a set of neutralization target chamber is designed according to the method, and the specific implementation steps are as follows:

1) solving the total stripping section sigma of negative hydrogen ions_t

Negative hydrogen ion energy E is 7MeV, and the gas of the neutralization target chamber is Ar;

σ_t＝1.35×10¹⁶cm²；

2) solving negative hydrogen ion stripping section ratio eta₀₁(i)

η₀₁(Ar)≈0.413；

3) Solving the gas target mass thickness χ

T20 deg.C, x 1.148X 10¹⁶cm^-2

4) Calculating the average pressure P of the gas target unit₀And length L₀Wherein P is more than or equal to 0.1Pa and less than or equal to 10Pa

L₀P₀＝4.05×10^-15χ；

Selection of P₀1 Pa; then L is₀＝45cm；

5) Selecting gas target inner diameter D

Inner diameter of beam spot is r_beam8 mm; inner diameter D ═ r of gas target_beam+2＝10mm；

6) Calculating the vacuum pressure difference level M between the gas target chamber and the beam line

Neutral target chamber vacuum P₀1 Pa; wire harness vacuum P_acc1E-5 Pa; then

7) Selecting vacuum differential grade N and nth grade differential ratio lambda_n

Selecting N-3 (lambda)₁＝0.01,λ₂＝0.01,λ₃＝0.1)；

8) Selecting nth stage differential pipe flow guide C_n

λ₁＝0.01，C₁＝10L/s；

λ₂＝0.01，C₂＝10L/s；

λ₃＝0.1，C₃＝40L/s；

9) Differential pipe inner diameter d_n(r_beam≤d_nLess than or equal to 40mm) and length L_n(0≤L_nLess than or equal to 150mm) selection

d₁＝15mm,L₁＝18mm；

d₂＝15mm,L₂＝18mm；

d₃＝25mm,L₃＝10mm。

Based on the parameters of the neutralized gas target chamber and the differential tube, the composition of a 7MeV negative hydrogen neutralization system of the version is determined by combining the actual situation of a 7MeV negative hydrogen beam line of a 200MeV proton device, MathCAD is used for simulation calculation, the differential effect of each level is expected to accord with the theoretical value, the pumping speed of a matched vacuum pump is reasonable, the requirement can be met by adopting a common commercial vacuum pump, and the design scheme is reasonable and feasible.

The above description is only an embodiment of the present invention, and is not intended to limit the scope of the present invention, and all equivalent structural changes made by using the contents of the present specification and the drawings, or applied directly or indirectly to other related technical fields, are included in the scope of the present invention.