1. Vacuum Technology and Components for Cryogenics
Spring School and Educational Courses at Fethiye
April 2016
Vacuum Technology and Components
for Cryogenics
Yasuharu Kamioka Ph.D
ColdTech Associates
2016
Cryogenics and Superconductivity Society of Japan

2. Vacuum and Low Temperature
Deep relation of Vacuum technology and Cryogenics
1. Vacuum insulation is essential for cryogenics
2. Evacuation is required in case of replacement of gases
3. Lower temperature by evacuation of cryogen
4. Circulation of He-3 and depression of 1K pot of
Dilution refrigerator

3. Use of Vacuum
Force of vacuum : Suction, Transfer > 300Torr (10kPa) Thermal insulation : below molecular flow region < 10-4Torr (10-2Pa) Clean surface : Solid state physics < 10-7Torr (10-5Pa) Removing obstacles : Ion, Cluster molecules, Particle physics < 10-8Torr (10-6Pa)
P= 10-6 torr, lifetime ~ 4 sec
10-8 torr ~ 6 min
10-10 torr, ~ 11 hr

4. Region of vacuum and pump, gauge
Two ranges according to molecular density (intermolecular collisions) Viscous flow range : bulk of molecules moving together, just as ordinary gas ・Vacuum pump : Diaphragm pump, Rotary pump, Kinney pump, Roots pump ・Vacuum gauge : Bourdon gauge, Diaphragm gauge, Pirani gauge Molecular flow range : each molecule moving any direction ・ Vacuum pump : Roots pump, Ejector pump, Diffusion pump, Turbo-molecular pump, Cryopump, Ion pump ・Vacuum gauge : Penning Gauge, B-A gauge (Ionization gauge)

5. Vacuum components

6. Vacuum pumps
Cryopump

7. Rotary vane pump / Kinney Vacuum pump

8. Diaphragm pump

9. Sorption pump Suction Safety valve Molecular sieve Net LN Dewar

10. Scroll pump

11. Roots pump

12. Diffusion pump and Ejector pump
Vapor

13. Turbo-molecular pump

14. Cryopump

15. Vacuum pump set A set of Turbo-molecular pump and Rotary pump
A set of Roots pump and Kinney pump

16. Vacuum pump
Pumping speed and pressure

17. Ultimate pressure
Ultimate pressure : Depending on the pumping speed, the out gas rate and the pumping capacity 　 Torr　 (Pa)
　　The lowest pressure after evacuation.
　Ultimate pressure of a pump : depending on a type of pump
　Pumping speed : Pumping speed of vacuum pumping system
　Out gas rate : Greatly depending on materials, it’s surface condition and related on the materials and cleanliness of evacuation system
Working pressure of pump
EUHV UHV HV MV LV
Rotary pump
Roots pump
Turbo-molecular pump
Steam ejector pump
Oil ejector pump
Oil diffusion ejector pump
Oil diffusion pump
Hg ejector pump
Hg diffusion pump
Sorption pump
Sputter ion pump
Getter pump(Troom)
Getter pump(TLN)
Cryopump
Working pressure (Torr)

18. Vacuum gauge He leak detector Diaphragm gauge Pirani gauge
Penning gauge
B-A gauge
(Ionization gauge)

19. Vacuum gauge
　Ranges of gauges

20. Vacuum piping
Piping connectors and valves

21. Vacuum components

22. Vacuum pump set High vacuum pump set RP : Rotary pump
TMP: Turbo-molecular pump
OME :Oil mist trap
Low out gas materials must be selected for piping such as stainless steel, copper, ceramics, viton.

23. Viscous flow and Molecular flow
Mean free path :
Viscous flow and Molecular flow
　　　　 k×T mean free path 　L=　 　　
　　　　　　　　　　　　　　20.5×p×π×d2
k：Boltzmann constant　T：temperature p：pressure　d：molecular diameter
Mean free path
P = 10-3 torr,　 　 ~ 5 cm
10-6 torr, ~ 50 m
10-10 torr, ~ 500 km
Viscous flow：bulk of molecules moving together
pressure：high
Molecular flow：each molecule moving any direction
Pressure：low L1
L1 < L2 L2

24. Three factors of vacuum evacuation and Leak / Out gas
　Conductance : the rate of flow per unit difference of pressure 　　
m3/sec
　Pump speed : the rate of evacuation volume
　 　　　 m3/sec
　Ultimate pressure : the attainable pressure.
depending on pump speed and the rate of out gas
Torr　 (Pa)
　Leak : Torr・liter/sec　(atm・CC/sec, Pa・m3/sec)
　Out gas : Torr・liter/sec　(atm・CC/sec, Pa・m3/sec)

25. Conductance　①
Quantity of gas : pressure × volume Pa・m3 Gas flow rate Q： pressure × volume ／time Pa・m3 /sec Conductance C：Q=C(P1-P2) m3 /sec Conductance of viscous flow range πa4 proportional to 4th power of a C= Pav 8ηL Conductance of molecular flow range proportional to 3rd power of a 4a3 a3 C = (2πRT/M)1/2= 30.5× (T/M) 1/2 3L L
Flow in a tube : Inner diameter a Length L, pressure difference P1-P2, average pressure Pav =(P1-P2) /2

26. Conductance ② C = C1 + C2 + C3 + ・・・・+ C n C C
Total conductance of elements
in series
　 = ・・・ 　　　
C C C C C n
　in parallel
　　 C = C1 + C2 + C3 + ・・・・+ C n C C

27. Conductance ③ Ca = Cv+ Cm Short tubes Ca 3L Ca = ×K×C 8a
　Clausing’s factor : K
　 L
　 Ca = ×K×C
　 a
Transition range of viscous and molecular flow
　Ca = Cv+ Cm

28. Conductance　④

29. Pumping speed Pumping speed : the rate of evacuation volume at point X
m3/sec
Pump speed : pumping speed of pump Sp
Pumping speed of a system : total pumping speed
consist of pump, valve, piping etc. S =
S Sp C
The total pumping speed S is dominated
by the smallest value of C and Sp.
C is very important. S C Sp

30. Calculation of evacuation time ①
Rough evacuation time：determined by the volume and pumping speed S 　　t 　sec
t = 2.3×τ×logK　　　　　τ=V/S, K=P1/P2
initial pressure：P1　　final pressure：P2
　　Chamber volume:0.5m3
Diffusion pump:0.7m3/sec, Rotary pump:0.01m3/sec
Rotary pump：798sec
Diffusion pump：76sec
Total：874sec
(14min. 34sec)
圧力範囲(Pa)
logK
S (m3/sec)
τ (sec)
t (sec)
105  103 2
8.3 x 10-3 60
276
103  102 1
6.6 x 10-3 76
175
102  10
3.3 x 10-3
151
347
圧力範囲(Pa)
logK
S (m3/sec)
τ (sec)
t (sec)
10  1 1
0.02 25 58
1  0.1
0.1 5 12
0.1  0.01
0.3
1.7 4
0.01  0.001
0.7 2

31. Calculation of evacuation time ②
Rough pumping
Out gas :
water
Evacuation of cryostat
Out gas:
H, N, CO2
High vacuum
Attainable pressure
Evacuation time in high vacuum ： below 10-1Pa(10-3Torr), evacuation time changes by out gassing.
out gassing is depending on materials and surface treatment.

32. Baking Baking : heating of vacuum system during evacuation
by high vacuum pump　　　　
Reducing evacuation time
　　　　 Keeping vacuum pressure after cut off
Evacuate the system keeping heat the whole system
about 120℃.
　　　　Mean adsorbing time of adsorbed gas：t
　　　　　t=t0・exp(Ed/RT)　　　t0 ：10-13sec
Ed: activation energy of desorption gas
　　　　　　In the case of Ed : 3.1× 103j/mol,
t=10-3sec at 20℃, 10-6sec at120℃.
　　Most part of out gas is water.
　　Baking box : 120℃　evacuation time 30days

33. Thermal insulation vacuum
Pressure should be below10-3Pa（10-5Torr）
In order to keep high vacuum in insulation vacuum, it is very important to know surface condition of materials in the vacuum.
Without evacuation for many years
　　　　Cryogenic dewar, bucket type cryostat, transfer tube
Evacuation before use or once per several times
　　　　Cryostat which can’t be baked :
　　　　　　Cryostat with a SCM, He liquefier, Fusion reactor,
Cryostat with a cryocooler

34. Insulation vacuum is the same as UHV
Keep HV
Reduce out gas
How to reduce out gas
Use low out gas materials : Stainless steel, Steel, Aluminum alloy, Titan, etc.
Surface area : without large surface area
Organic material like FRP : select materials and use clear background materials 　
G10-FRP, polyester, Teflon, Viton
Stock of materials : stock in dry space without grease, water
　　　　　　　　in desiccator, in vacuum, in dry nitrogen gas
Aluminized film, spacer etc. : stock in dry air/nitrogen
Treatment of materials before use : removing grease/dirt
clean with acetone　　
Handling of materials : don’t use bare hands, wash tools with acetone,
use polyethylene glove
Welding : weld from inside, don’t weld both side

35. Residual out gas in vacuum system