Page 1. Pumpdown and Vacuum Pumps. Dr. Philip D. Rack. Assistant Professor.
Department of Materials Science and Engineering. University of Tennessee.
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
1
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
Page 4
2
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
3
Vacuum Technology
System Pumpdown
Pressure (Pa)
100000 10000 1000 100
100mTorr
10 1 0.1 0
1000
2000
3000
4000
Time (s)
Page 7
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
Page 8
4
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
Page 9
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
Page 10
5
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
Page 11
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)
Page 12
6
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)
Page 13
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
Page 14
7
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
Page 15
Vacuum Technology
Mechanical Pumps • Rotary vane and Rotary Piston Pump Issues – Due to close tolerances (
