Vacuum pump U12 Low temperature pump UIVac cryo-u12hsp

Low temperature pump, also known as low-temperature vacuum pump, cold pump, or condenser pump. The cold source of a cryogenic pump can be a cryogenic liquid (liquid nitrogen or liquid helium) or a cryogenic refrigeration unit. Here is an introduction to the refrigeration model of the cryogenic pump. This type of cryogenic pump produces refrigeration at two temperature levels, cooling two low-temperature surfaces respectively, and the extracted gas is cooled on the low-temperature surfaces.

1. Low temperature pump is

The real container is equipped with an extremely low temperature surface, which captures the gas in the container and exhausts it through condensation and adsorption.
Due to the minimal use of mechanical moving parts and the absence of oil, a clean high vacuum can be achieved.
In order for the low-temperature pump to effectively exhaust, the vapor pressure during condensation and the adsorption equilibrium pressure during adsorption must be below 10-8 Pa.
Figure 1 shows the vapor pressure of each gas. For gases with lower vapor pressure than nitrogen, when cooled to below 20K on an extremely low temperature surface (low temperature surface or low temperature baffle), their vapor pressure is below 10-8Pa. Gases with high vapor pressure such as hydrogen, helium, neon, etc. cannot be discharged through condensation at 20K, so they can be discharged through adsorbents below 20K.
In this way, the cryogenic pump can exhaust all gases to achieve ultra-high vacuum.

Figure 1. Vapor pressure of various gases

The method of forming a frozen surface usually uses a small helium freezer with a closed cycle. The cryogenic pump uses a small helium freezer, which does not require regular refrigerant supply like the storage type cryogenic pump. With simple operation, it can obtain clean ultra-high vacuum and can operate continuously for a long time and stably.

2. Operating principle and structure of cryogenic pump

Taking CRYO-U8H as an example to illustrate the structure of a cryogenic pump.
The refrigeration unit of the low-temperature pump is a two-stage type, with the first stage having a larger refrigeration capacity and can cool to 80K or lower, and the second stage having a smaller refrigeration capacity and can cool to 10 to 12K.
The 15K baffle (1) (condensing plate) and the 15K baffle (2) (adsorption plate) are installed on the second section of the freezer. The 80K baffle and the 80K shielding bucket are installed on the first section with higher refrigeration capacity to prevent thermal radiation (radiation) at room temperature. In addition, to prevent the adsorbent surface from not being covered, the adsorbent is installed on the inside of the baffle where concentrated gases cannot enter.

Figure 2. CRYO-U8H

The main exhaust gases of cryogenic pumps are (1) to (3).

(1) Air (N2, O2): residual gas after rough pumping by vacuum equipment

(2) Release gas 1 H2O: the main component of gas released from glass, plastic, and ceramics adsorbed on the surface of a vacuum container (the largest part in ordinary vacuum equipment)

2 H2: Diffusion and release of molten metal (especially aluminum) inside the metal wall of the vacuum container (due to ultra-high and vacuum issues) at high temperatures (such as evaporation and sputtering)

3 CO、CO2、
CH4, CnHm: dirt on the wall of vacuum equipment

(3) Importing gas 4 Ar: sputtering equipment

5 H2: Ion implantation

6 O2: Oxide

7 Other

According to the steam pressure gauge, if the temperature of water vapor (H2O) is below 130K, the steam pressure will be below 10-8Pa. Gases such as nitrogen (N2), oxygen (O2), carbon monoxide (CO), argon (Ar), etc. cannot condense at 80K due to their high steam pressure and need to be condensed and discharged through the outer surface of the baffle (1) below 20K.

Gases with higher vapor pressures, such as helium (He), hydrogen (H2), neon (Ne), etc., do not condense at temperatures between 10-20K. Therefore, they are adsorbed and vented using adsorbents installed inside the 15K baffle (1) (condenser plate). The adsorbent is installed in the 15K baffle (2) (adsorption plate). In order to prevent the adsorbent surface from not being covered, the adsorbent is installed on the inside of the baffle where concentrated gases cannot enter.
The outer surfaces of the 80K shielding bucket, 80K baffle, and 15K baffle (1) are mirror surfaces that can reflect radiant heat at room temperature. The inner surface of the 80K shielding bucket has been blackened to prevent room temperature radiation from reflecting on the 80K shielding inner surface and entering the 15K baffle. To ensure the normal operation of the low-temperature pump, the temperature of the 80K shielded bucket and 80K baffle must be below 130K, and the temperature of the 15K baffle must be below 20K.

In order to confirm these temperatures, CA thermocouples were installed on the 80K baffle, and hydrogen vapor pressure thermometers (H2VP) and MB type low-temperature thermocouple thermometers were installed on the 15K baffle. The standard electromotive force of CA thermocouple 130K is -5.5mV

3. Regeneration and safety valve of low-temperature pump

Oil diffusion pumps and turbo molecular pumps release compressed exhaust gas outside the pump, but cryogenic pumps store it in a 15K baffle through condensation and adsorption, so it must be released and regenerated regularly.
Regeneration refers to raising the temperature of a cryogenic pump to room temperature and returning the condensed or adsorbed gas to its gaseous state. When a large amount of gas is stored in a sealed state at low temperature, the interior of the low-temperature pump may become high-pressure gas during regeneration, so a safety valve needs to be installed on the low-temperature pump.
The working pressure of the safety valve is set to 20kPa (gauge pressure).
The use of safety valves is for safety reasons, therefore do not close the safety valves or use them for other purposes.
Also, do not use it as a gas release valve during the regeneration process. When the safety valve is working, dust and other particles in the blowing gas adhere to the surface of the o-ring, which can cause leakage.

4. Low temperature pump system

The low-temperature pump system is basically composed of

《1》 Low temperature pump unit (including refrigeration unit)
《2》 Compressor unit
《3》 Two hoses

Composition, connected as shown in Figure 3. The start-up of the low-temperature pump (the low-temperature pump cannot be started at atmospheric pressure) and the regeneration require a rough pump (to be prepared by the customer).

Figure 3. Low temperature pump system

Performance of Low Temperature Pump

The main performance of a cryogenic pump includes: (1) cooling characteristics, (2) exhaust speed, (3) exhaust capacity, (4) maximum flow rate, (5) cross pressure, (6) ultimate pressure, (7) thermal load capacity, etc.
Jiang will explain these projects below.

1. Cool down characteristics

Due to the inability of the cryogenic pump to start at atmospheric pressure, a rough pump is required. When using a rotary pump for rough pumping, ULVAC Cryo's 40Pa low-temperature pump will not cause oil vapor reflux. All gases remaining in the pump are adsorbed by the adsorbent inside the low-temperature pump. The cooling time is affected by the following factors.

Table 1. Factors affecting cooling time

Due to

Cooldown

1.

2. Prolonged high pump temperature

3. The composition of residual gas after rough pumping is dry (dried inside the pump) and prolonged

Reduced moisture content

4. The pollution of the pump has been prolonged

The cooling time is affected by the regeneration method. When nitrogen is used to blow or heat the belt to increase the temperature, the moisture will decrease and become dry, making vacuum insulation difficult to achieve, resulting in longer cooling time. Additionally, please note that even minor leaks can lead to prolonged cooling time or inability to cool down (please pay special attention to leaks caused by safety valves). In addition, the cooling rate in the 60Hz region is 10-15% faster than that in the 50Hz region. Usually, the cooling time is defined as the time required for the temperature of the 15K baffle to be lower than 20K, as shown in Table 4-2.

2. Exhaust velocity characteristics

2-1. Exhaust performance for water

If the temperature of the freezing surface is below 150K, the probability of condensation of water on the freezing surface is almost 1. Usually, the temperature during the 80K shielded bucket and 80K operation of a cryogenic pump is below 130K (usually around 80K), so the exhaust velocity of the cryogenic pump relative to water is equal to the ideal exhaust velocity of the 80K shielded bucket diameter. The ideal exhaust velocity per unit area of gas with molecular weight M is s=62.5/M1/2 (L/s/cm2) (20 ℃) for water, and the ideal exhaust velocity for M=18 is s=14.7 (L/s/cm2). The suction area of the 80K shielded bucket is A (cm2), and the exhaust velocity S of the low-temperature pump for water is S=s · A (L/s).

For example, the suction port area of the Type 8 low-temperature pump and 80K shielded bucket is about 275cm2, and the exhaust speed for water is 4000L/s. Perform the same calculation for gases (e.g. CO2, NH4) condensed and discharged in an 80K baffle. The exhaust velocity calculation of CRYO-U8H for CO2 shows that the exhaust velocity for water is 4000L/s, and the molecular weight of CO2 is 44, SCO2=SH2O X ( 18 / 44 )1/2=2560 L/s。

Table 2. Exhaust velocity of low-temperature pump for water

caliber

model

Exhaust velocity (L/s)

6 U6H 2100

8 U8H,U8H-U,U8HSP 4000

10 U10PU 6900

12 U12H,U12H-K2,U12HSP 9500

16 U16,U16P 16000

20 U20P 29000

22 U22H 39000

30 U30H 70000

2-2. Exhaust characteristics of Ar and N2 (condensable gases)

Gases with relatively high vapor pressure, such as N2, Ar, CO, and O2, are not condensed by 80K baffles or shields, but rather condensed and discharged at temperatures below 20K.
If the freezing surface temperature is below 20K, the probability of capturing condensed gases by the freezing surface is 1. In addition, due to the constant conduction from the inlet to the low-temperature baffle in the molecular flow area, the exhaust velocity of the low-temperature pump in the molecular flow area is constant.

The exhaust velocity value of the low-temperature pump in the product manual is the exhaust velocity of nitrogen gas in the molecular flow area. The exhaust velocity of condensed gas with unexpected molecular weight M for nitrogen can be calculated using the following formula.

SM=SN2×(28／M)1/ 2（L/s） ・・・・・・・(1)
SN

2: Exhaust velocity of nitrogen gas (L/s)

For example, the exhaust velocity of CRYO-U8H for argon gas can be calculated from Table 6-3 with SN2=1700 (L/s) and the molecular weight of argon gas M=40 using this formula
Sar=1700X(28/40)1 / 2=1400L/s

Figure 1. Exhaust velocity of CRYO-U for nitrogen gas

model

Exhaust velocity (L/s)

U6H 750

U8H/U8H-U/U8HSP 1700

U10P 2300

U12H 4000

U12HSP 4100

U16/U16P 5000

U20P 10000

U22H 17000

U30H 28000

Table 3. Exhaust velocities of various low-temperature pumps for nitrogen gas (product manual values)

When the airflow changes from molecular flow to intermediate flow (transition flow), the conductivity is proportional to the pressure, resulting in an increase in exhaust velocity. However, as the heat input to the cryogenic pump increases with pressure, when the heat load exceeds the refrigeration capacity of the chiller, the exhaust limit of the cryogenic pump will be reached. ULVAC Cryo defines the flow rate at which the temperature of the low-temperature baffle reaches 20K as the maximum flow rate based on this heat load (point ○ in Figure 6-1). Although the maximum flow rate increases with the strengthening of refrigeration capacity, the thermal conductivity of the condensation layer is also limited due to the stronger refrigeration capacity, resulting in temperature gradients in the thickness direction. If the surface temperature of the condensation layer exceeds the limit, the gas will not condense, so the exhaust velocity becomes 0, which becomes the physical exhaust limit.

2-3. Exhaust velocities for H2, He, Ne (non condensable gases)

H2, He, and Ne are the gases with the highest vapor pressure. At around 20K, they are also known as non condensable gases because their vapor pressure is too high to be discharged through condensation. Since these gases cannot be discharged through condensation, they are discharged by adsorption with adsorbents cooled to below 20K. When adsorbents adsorb non condensable gases, they become saturated, resulting in a gradual decrease in exhaust velocity. When the exhaust speed drops to 80% of the initial value, the amount of gas emitted at this time is defined as the exhaust volume (described later).
In non condensable gases, hydrogen is an important component of exhaust gases and also an important gas for applications. Therefore, after detailed research, the pattern has been determined. There are few examples of neon gas usage, so the data is scarce. In addition, helium is the most difficult gas to adsorb and can only be expelled by 1/100 to 1/1000 of argon gas, so it is not recommended to use a cryogenic pump for exhaust.

model
CRYO-U

Exhaust velocity
(L/s)

maximum flow
(Pa・L/s)

Exhaust flow rate
(Pa・L)

-U6H 1100 1.1×102 3.1×105

-U8H 2700 2.4×102 1.0×106

-U8HSP 3200 2.4×102 1.0×106

-U10PU 3600 1.5×102 6.7×105

-U12H 6000 4.1×102 9.8×105

-U12HSP 6000 4.1×102 1.6×106

-U16 10000 4.1×102 2.4×106

-U16P 10000 4.5×102 2.4×106

-U20P 18000 5.0×102 4.6×106

-U22H 25000 1.3×103 8.5×106

-U30H 43000 7.4×102 1.5×107

Table 4. Exhaust characteristics of CRYO-U for hydrogen

Figure 2. Discharge velocity of CRYO-U for hydrogen

3. Exhaust capacity of low-temperature pump

3-1. Exhaust capacity for solidified gases

The gases discharged through condensation are (1) gases (mainly water) discharged through 80K shielded drums or 80K baffles, and (2) gases (nitrogen, argon, oxygen, etc.) discharged through 15K baffles.

(1) Exhaust capacity for water
When water condenses on the 80K baffle and the thickness of ice increases, the conductivity of the 80K baffle decreases, and the exhaust velocity of the gas condensed and adsorbed through the 15K baffle also decreases. Due to the need for regeneration, the amount of water discharged at this time is the exhaust capacity, and there is no clear definition of the exhaust capacity for water. However, the values in the table below can serve as a rough guide for the exhaust limits of water. (Note that the unit of displacement is g (grams))

model

Exhaust capacity (g)

CRYO-U6H 40

CRYO-U8H,U8H-U 90

CRYO-U10PU 170

CRYO-U12H 260

CRYO-U16,U16P 500

CRYO-U20P 1000

CRYO-U22H 1400

Table 5. Discharge Capacity of Low Temperature Pump for Water (Reference)

(1) The situation where there is a lot of water

Plastic

Glass

Ceramics

(2) Attention points for regeneration when there is a lot of water

When the temperature rises, ice melts

Do not freeze water during rough pumping

Remove water from the pump

Check the performance of the rotary pump (pay attention to oil emulsification)

(2) Exhaust capacity for argon gas

The challenge in the gas discharged by condensation through a 15K condenser plate is the exhaust capacity of argon gas in the sputtering process. The thickness of the condensed argon gas layer on the outer surface of the 15K baffle increases, causing it to touch the higher temperature 80K baffle and 80K shielding bucket, or the temperature gradient of the argon gas layer itself increases, resulting in an increase in the surface temperature of the argon gas. In such cases, condensation will no longer be possible. At this point, the amount of argon gas discharged is the exhaust capacity. ULVAC Cryo defines the discharge capacity of argon gas as the amount of argon gas discharged when the main valve is closed and the pressure does not drop below 1.3X10-4Pa 5 minutes after the main valve is closed. Figure 6-3 shows the pressure value of CRYO-U12HSP after continuously introducing 200CCM of argon gas and stopping the introduction for 5 minutes. When the exhaust volume exceeds 4.3 × 108Pa · L, the pressure suddenly recovers, resulting in an exhaust volume of 4.3 × 108Pa · L. Table 6-6 shows the argon emission capacity of each model of cryogenic pump.

Figure 3. Pressure recovery of CRYO-U12HSP (measurement example)

Model CRYO-

Exhaust capacity (Pa · L)

-U6H 5.6×107

-U8H,U8H-U 1.0×108

-U8HSP 2.5×108

-U10PU 1.0×108

-U12H 2.1×108

-U12HSP 4.3×108

-U16,U16P 4.3×108

-U20P 5.8×108

-U22H 8.1×108

-U30H 7.8×108

3-2. Exhaust capacity for non condensable gases

Hydrogen, helium, neon, and other gases that cannot be condensed and discharged at around 10K are adsorbed and discharged by the adsorbent inside the 15K baffle. Therefore, as the adsorption amount increases, it will approach a saturated state, (1) the exhaust velocity decreases, (2) the adsorption equilibrium pressure increases, and the exhaust performance gradually decreases, ultimately making it impossible to exhaust. ULVAC Cryo defines the exhaust capacity of hydrogen as the amount of hydrogen adsorbed until the exhaust velocity of hydrogen is reduced to 80% of the initial exhaust velocity. In order for the adsorbent to exert its predetermined adsorption capacity, it is necessary to clean the adsorbent. The pollution caused by adsorbents is

(1) When adsorbing condensing gases (mainly air)
(2) When adsorbing moisture
(3) When adsorbing oil vapor

When these substances are adsorbed in large quantities, their ability to adsorb hydrogen gas will decrease. Air and moisture can be removed by regenerating the low-temperature pump, but once oil vapor is adsorbed, it cannot be removed again. At this time, the 15K baffle (2) (adsorption plate) must be replaced. In order to maintain the adsorption performance of the cryogenic pump for hydrogen, it is necessary to absolutely avoid the reflux of oil vapor into the cryogenic pump.
Figure 4 shows the relationship between the exhaust velocity of hydrogen gas and the exhaust capacity of hydrogen gas, where S is the exhaust velocity and C is the exhaust capacity. Please refer to Figure 4 for the exhaust speed and exhaust capacity of various models.

Figure 4. Relationship between exhaust velocity and exhaust capacity for hydrogen gas

4. Thermal load and maximum flow rate of low-temperature pump

The thermal load of the cryogenic pump is radiation heat and gas load (gas heat conduction, condensation heat), and the following equations are given respectively.

σ

Boltzmann constant 5.67 × 10-12 W/cm2/K4

eAV

: Average radiation rate

T1

: Low temperature surface temperature (K)

T2

: Temperature of high temperature surface (K)

A

Heating surface area (cm2)

A1: Inner A2: Outer

γ

Specific heat ratio of gas

ａ0

: Average coefficient of thermal adaptation

Ｐ

Pressure (Pa)

M

: Molecular weight

T1

Temperature of pressure P measurement point (K)

T2

: Low temperature surface temperature (K)

A: Heating surface area (cm2)

The average thermal fitness coefficient a0 equation (A1<A2)



Adaptation coefficients a1, a2 (approximate values)

γ

Condensation heat (adsorption heat for H2, He, Ne) (W/Pa · L/s)

Tc

: Low temperature surface temperature (K)

Tg

Temperature of gas (K)

S

Exhaust velocity of low-temperature pump (L/s) SP: (Pa · L/s)

P

Pressure (Torr)

Cp

Average specific heat of gas (W/(Pa · L/s)/K)

The heat load of section 1 of the freezer is radiation heat and gas conduction heat, and unless continuously used within the range of 10-1Pa, most of it is usually radiation heat. The cooling capacity of section 2 of the freezer is affected by the heat load of section 1. If the heat load of section 1 increases, the cooling capacity of section 2 will decrease, and the maximum flow rate will also decrease.
Therefore, when the amount of gas introduced into the low-temperature pump is large, please keep the low-temperature pump clean (reduce radiant heat) and minimize thermal overload caused by thermal radiation. Usually, for large cryogenic pumps, the heating surface area is larger and there will be more heat radiation, thus requiring a refrigeration unit with greater cooling capacity. The maximum flow rate of a cryogenic pump is defined as the flow rate at which the temperature of the cryogenic pump reaches 20K due to condensation heat (or adsorption heat) when standard radiation heat is applied. If the diameter of the pump is the same, the greater the refrigeration capacity or exhaust speed of the freezer, the greater the maximum flow rate. For example, the CRYO-U16 and U16P have the same diameter and exhaust velocity. The refrigeration unit (R50) of U16P has a greater cooling capacity than the refrigeration unit (R20) of U16, resulting in a higher maximum flow rate.
The maximum working pressure Pmax of the cryogenic pump is obtained by dividing the maximum flow rate Qmax by the exhaust velocity Smax at that time. (Pmax=Qmax/Smax)。 For argon gas, Pmax is about 10-1Pa, which is an intermediate flow. Table 7 shows the maximum flow rates for various models.

Maximum flow rate of low-temperature pump

argon
（Pa・ L/s）

hydrogen
（Pa・ L/s）

CRYO-U6H

1.1×103 1.1×102

CRYO-U8H,U8H-U,U8HSP

1.2×103 2.4×102

CRYO-U10PU

8.0×102 1.5×102

CRYO-U12H,U12HSP

2.0×103 4.1×102

CRYO-U16

1.4×103 4.1×102

CRYO-U16P

1.6×103 4.5×102

CRYO-U20P

1.1×103 5.0×102

CRYO-U22H

4.1×103 1.3×103

CRYO-U30H

2.7×103 7.4×102

5. Cross over pressure

The cross pressure is the pressure of the vacuum tank when the main valve is opened and switched to the low-temperature pump during rough pumping (rough pressure). The maximum allowable rough pumping pressure at this time is the maximum allowable cross pressure. At the moment when the main valve opens, the gas in the vacuum chamber flows into the low-temperature pump. If the amount of gas exceeds the limit, the low-temperature pump cannot restore its exhaust capacity again, the temperature will rise, and all the already exhausted gas will be released. The maximum allowable cross pressure is calculated by dividing the maximum gas intake that can be processed by the volume of the vacuum chamber.

The maximum gas intake that can be processed is the limit value for restoring exhaust performance (usually the temperature of the low-temperature baffle exceeds 20K). Usually for safety reasons, the limit of rough pumping pressure is 1/2 of the maximum allowable cross pressure obtained from formula (1). In addition, if you want to improve the safety factor, you can set the maximum allowable cross temperature to the value when the temperature of the low-temperature pump baffle does not exceed 20K. The maximum gas suction capacity that can be processed will vary with the heat load on the cryogenic pump and the amount of condensed gas in the cryogenic pump.

Table 6-8 provides a reference for the maximum gas intake (relative to air) that various models can handle. For example, for U8H, the maximum allowable cross pressure Pmax of a vacuum container with a volume of 100L is the maximum suction gas volume that can be processed, which is 133000Pa · L, Pmax ≤ 133000Pa · L/100L=1330Pa, and rough suction is below 1330Pa. Usually, the safety factor is 2 or more, which means the rough suction pressure is set to 665Pa. To ensure that it does not exceed 20K and can handle a maximum suction gas volume of 20000Pa, P=20000/100=200Pa. When the volume of the vacuum container is large and the rough pumping pressure is below 40Pa, measures must be taken to prevent oil vapor reflux. Install larger pumps or increase the number of pumps to achieve a rough machining pressure of 40Pa or higher.

6. Arrival

The pressure reached by the low-temperature pump without gas flow is, and the vapor pressure and condensation coefficient of various gases at the low-temperature surface temperature of the condensing gas (assuming 1) are obtained by substituting them into the following formula.

Pg=Ps(Tg/Ts)1/2

Ts

Low temperature surface temperature 10-20K

Ps

Gas vapor pressure at temperature Ts (hydrogen as adsorption equilibrium pressure) (Pa)

Tg

Gas temperature~300K

The gas with the highest vapor pressure in condensed gases is nitrogen. For nitrogen, the pressure is reached when the low-temperature surface temperature is 10-20K, as shown in Figure 6. Usually, in the absence of load, the baffle of the low-temperature pump is 10-12K and the vapor pressure is~10-21Pa, which can be ignored in practical use. The ultimate pressure of non condensable gas hydrogen is determined by the adsorption equilibrium pressure. As shown in Figure 6-7, the activated carbon used in the cryogenic pump has a very large hydrogen adsorption capacity, and when operating in ultra-high vacuum, the adsorption equilibrium pressure Pa of hydrogen can also be ignored due to the very small exhaust volume of hydrogen. For example, the hydrogen adsorption capacity of U8H (SH2O=2700 L/s) running continuously for one month at 1.3X10-8Pa is Q=1.3 × 10-8x2700 × 30x24 × 3600=91 Pa. Therefore, the maximum pressure of the cryogenic pump is determined by the amount of gas introduced into the cryogenic pump and the exhaust speed. Usually, the ultimate pressure of a cryogenic pump unit is measured by the minimum gas inflow of the cryogenic pump when a blind flange is used on the pump. In addition, the maximum pressure will vary greatly depending on the specifications of the low-temperature pump (standard specifications and ultra-high vacuum specifications), rough pumping pressure, whether it is baked, etc. The maximum pressure for 12 hours of operation is usually (1-4) X10-6Pa with O-RING, rough drawing of 40Pa, and no baking. Figure 6-7 shows the measurement of residual gas composition with and without baking. In addition, Table 6-9 shows the reference values for the ultimate pressure of a single cryogenic pump. Under ultra-high vacuum baking conditions, a vacuum of 10-10TPa can be obtained. The ultimate pressure of the device depends on the amount of gas released by the device (P=Q/S).

Figure 6. Ultimate pressure determined by vapor pressure

Adsorption temperature curve of activated carbon for hydrogen gas

Ultimate pressure of cryogenic pump (reference)

specification

Rough extraction pressure (Pa)

bake

Limit (Pa)

standard

40
40 None
(100～150℃)×(3～10h) (1～4)×10-6
(1～4)×10-7

超高真空

10-2～10-3
10-2～10-4
10-2~10-3 None
(200～220℃)×(3～8h)
(200-220 ℃) × about 20 hours 10-8
10-9
10-10

[Basic Knowledge of Low Temperature Pump 5]

The structure and freezing principle of a freezer

The structure and freezing principle of a freezer
1. Freezing principle (for general explanation)

Figure 1. Freezing principle

The representative refrigeration cycle used for cryogenic pumps is
(1) Gifford McMahon cycle (G-M cycle)
(2) Modified Solvay cycle (M-Solvay cycle)

2. The refrigeration cycle used by the cryogenic pump
Taking CRYO-U8H as an example to illustrate the structure of a cryogenic pump.
The refrigeration unit of the low-temperature pump is a two-stage type, with the first stage having a larger refrigeration capacity and can cool to 80K or lower, and the second stage having a smaller refrigeration capacity and can cool to 10 to 12K.
The 15K baffle (1) (condensing plate) and the 15K baffle (2) (adsorption plate) are installed on the second section of the freezer. The 80K baffle and the 80K shielding bucket are installed on the first section with higher refrigeration capacity to prevent thermal radiation (radiation) at room temperature.

Figure 2-2 shows the operating principle and P-V diagram of the G-M cycle (the relationship between the pressure P and volume V of the expansion chamber).

2-1. G-M cycle
The G-M cycle is a refrigeration cycle developed by Gifford in the late 1950s, with the displacement device driven by mechanical drive and utilizing the pressure difference of the operating gas. The G-M cycle is very efficient, but the driving speed may be relatively slow. In addition, the internal seals used have a light load, making it a highly reliable refrigeration cycle. Here, we will explain the refrigeration cycle driven by the mechanical compressor used in ULVAC Cryo.

The A converter is located at the bottom of the cylinder. At this point, the low-pressure valve is closed and the high-pressure valve is open.

↓

(a) The room temperature and low temperature parts of the cylinder are filled with high-pressure gas.

↓

The interior of cylinder B becomes high-pressure.

↓

(b) The displacement device is pulled up, and the helium gas at room temperature is cooled by the accumulator while the low-temperature part is filled.

↓

The area of the low-temperature part is the largest. At this point, the high-pressure valve is closed and the low-pressure valve is open.

↓

(c) The high-pressure gas in the low-temperature pump section is released through the accumulator. At this point, due to Simon's expansion, the gas problem decreases, resulting in low temperature.

↓

D Low temperature section pressure.

↓

(d) The displacement device is pressed and cooled, and the helium gas is cooled by the accumulator while being transferred to the room temperature section.

↓

Return A and complete one loop.

As such, the ideal G-M cycle P-V curve is square, and if one cycle has a period of t seconds, the ideal freezing capacity would be

Q ideal is obtained by the following formula
Q ideal =W/t

The actual freezer is a two-stage structure that can achieve extremely low temperatures below 15K. In addition, in order to simplify the structure, the cold storage device is built inside the displacement device and integrated with it. The seals of section 1 and section 2 have no pressure difference, and the load on the seals is very light, with a long service life and high reliability.

CRYO-U series low-temperature pumpCRYO-U12HSPCRYO-U16CRYO-U16F

UIVaccryo-u12hsp

standard specifications

Wide Variety of Models, ranging from 6' diameter to 30' diameter.

Purpose:

Vacuum coating, surface analysis, semiconductor processing, sputtering coating, ion implantation, etc.

advantage:

Create an extremely pure vacuum environment that other vacuum pumps cannot create, capable of expelling all types of gases without the need for liquid helium, resulting in low operating costs. It can be installed in any direction, with a compact and lightweight design, simple operation, and a much higher exhaust speed than ion pumps, turbo molecular pumps, etc.

CRYO-U12HSP