Vacuum Technology
Pumpdown and Vacuum Pumps Dr. Philip D. Rack Assistant Professor Department of Materials Science and Engineering University of Tennessee 603 Dougherty Engineering Building Knoxville, TN 37931-2200 Phone: (865) 974-5344 Fax (865) 974-4115 Email:
[email protected]
Dr. Philip D. Rack
Page 1
Vacuum Technology
Conductances • Series conductances 1 1 1 = + CT C1 C2
C2
C1
• Parallel conductances C1
CT = C1 + C2
C2
Dr. Philip D. Rack
Page 2
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Vacuum Technology
Pumpdown Procedure • 1.Start-up
Chamber
– Turn on pumps – Open foreline valve
• 2.Close foreline valve • 3.Open roughing valve • 4. Rough chamber ~100mtorr • 5.Close roughing valve • 6.Open foreline valve • 7.Open high-vac valve
Vent valve
High-vac Valve
N2
Roughing valve
High-Vac Pump Mechanical Pump
Foreline Valve Page 3
Dr. Philip D. Rack
Vacuum Technology
Venting Procedure • 1.Close high-vac valve • 2.Open vent valve • Why N2 or Ar for venting chamber??
Chamber Vent valve
High-vac Valve
N2
Roughing valve
High-Vac Pump Mechanical Pump
Foreline Valve Dr. Philip D. Rack
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Vacuum Technology
Pressure Curves • Pressure versus time
Chamber
−S t P = P0 exp eff V where : 1 1 1 = + S eff S p CT V = Volume
Vent valve
N2 C1 High-vac Valve
Ignores Sources of Gas in a vacuum (Vaporization, Thermal Desorption, Diffusion Permeation, Backstreaming, Leaks)
Roughing valve
High-Vac Pump
C3 C2
Mechanical Pump
Foreline Valve Page 5
Dr. Philip D. Rack
Vacuum Technology
System Pumpdown • Roughing chamber – Use Viscous flow equations
Chamber
1 1 1 1 = + + S eff S p ( MP) C2 C3
Vent valve
N2
Conductance
10000000 Conductance
100000
C1 High-vac Valve
1000 10 0.1 1
S(eff)
10
100
1000
10000
time (s)
Roughing valve
High-Vac C3 Pump
C2
Dr. Philip D. Rack
Mechanical Pump
Page 6
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Vacuum Technology
System Pumpdown
Pressure (Pa)
100000 10000 1000 100
100mTorr
10 1 0.1 0
1000
2000
3000
4000
Time (s)
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Dr. Philip D. Rack
Vacuum Technology
System Pumpdown • High Vac Pumping – Use molecular flow equations
Chamber
1 1 1 = + S eff S p ( HVP ) C1
Vent valve
N2 C1
10
Pressure (Torr)
0.1 0 0.001
5
10
15 V=1m3 Seff = 1m3/s
20
25
High-vac Valve
1E-05 1E-07
Roughing valve
High-Vac C3 Pump
1E-09
C2
1E-11
Mechanical Pump
Time (s)
Dr. Philip D. Rack
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Vacuum Technology
Real Systems • Pressure limits in vacuum systems − S eff t QO QD QK + P = P0 exp + + V S eff S eff S eff – 1st term -- time dependence of pressure that is due to the gas in the chamber volume (exp(-t)) – 2nd term -- pressure due to outgassing (~ t-1) – 3rd term -- pressure due to diffusion (~ t1/2 and later exp(-Dt)) – 4th term -- pressure due to permeation (constant)
Pressure (Torr) 103 10 10-1 10-3 10-5 10-7 10-9 10-11 10-13
Volume ~ exp(-t) Outgassing ~ t-1 Diffusion ~ t-1/2 Permeation
101103 105 107 109 101110131015 1017
Time (s) Dr. Philip D. Rack
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Vacuum Technology
Classificatoins • Pressure Ranges – 760 torr - 1x10-3 torr (essentially viscous flow roughing pumps – 10 torr - 10-5 torr (transition flow range) - high throughput pumps – 10-3 torr - 10-12 torr (molecular flow) - high vacuum pumps
Dr. Philip D. Rack
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Vacuum Technology
Classifications • Pumping Action – Entrainment pumps • Positive displacement – Rotary Vane – Rotary Piston – Roots Blower
• Momentum transfer – Turbomolecular – Diffusion
– Capture pumps • Cryosorption • Ion sublimation • Titanium Sublimation Pumps Dr. Philip D. Rack
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Vacuum Technology
Mechanical Pumps Single Stage Rotary Vane
Dr. Philip D. Rack
• Gas enters through suction chamber (A) • Compressed by rotor (3) and vane (5) • Expelled through discharge valve (8) • 500-2000 rpm • Single stage pumps • Sp ~ 10-200 m3/hour • Ultimate pressures ~ 1.4Pa (~10mtorr)
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Vacuum Technology
Mechanical Pumps Double Stage Rotary Vane • • • •
Dr. Philip D. Rack
500-2000 rpm Single stage pumps Sp ~ 10-200 m3/hour Ultimate pressures ~ 1.5x10-2Pa (~100µtorr)
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Vacuum Technology
Mechanical Pumps • Pumping speed of single versus double stage rotary vane (sp ~ 30m3/hour)
Gas ballast introduces gas out exit port to keep gases from condensing (ie water, acetone…) Dr. Philip D. Rack
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Vacuum Technology
Mechanical Pumps Rotary Piston Pump
• Gas is drawn in during 1st revolution (A) • After 1st revolution, that volume of gas is isolated from the inlet (B) • During second revolution the gas is compressed and ejected • ~40-600rpm • Sp~30-1500 m3/hour • Ultimate pressure ~ 10mtorr
Dr. Philip D. Rack
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Vacuum Technology
Mechanical Pumps • Rotary vane and Rotary Piston Pump Issues – Due to close tolerances (
