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Overview of Vacuum Systems

Overview of Vacuum Systems. Tejas Deshpande 24 July, 2014. Outline. Introduction Pumps Positive displacement pumps Momentum transfer pumps Entrapment pumps Pressure gauges Vacuum seals Manipulation and motion under vacuum. Introduction. Introduction: definitions.

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Overview of Vacuum Systems

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  1. Overview of Vacuum Systems Tejas Deshpande 24 July, 2014

  2. Outline • Introduction • Pumps • Positive displacement pumps • Momentum transfer pumps • Entrapment pumps • Pressure gauges • Vacuum seals • Manipulation and motion under vacuum

  3. Introduction

  4. Introduction: definitions Kinetic Theory of Gases • Ideal gas equation • Velocity of molecules hitting chamber walls

  5. Introduction: definitions Pumping • Rate of mass flow • Mass “conductance” http://fisica.ufpr.br/sharipov/tubefm.html

  6. Introduction: definitions Pumping • Pump capacity & effective pumping speed • Rate of evacuation • Example: Pfeiffer Hena-25 pump + cylindrical chamber • Finite C with a hose

  7. Introduction: definitions Pumping • Conductance of KF 40 hose (L = 10", D= 2.165") [1] [1]http://www.vacuumlab.com/Articles/Knowing%20Eff%20Pump%20Speed.pdf

  8. Positive displacement pumps Rotary vane pumps • Principle of operation

  9. Positive displacement pumps Scroll pumps • Principle of operation

  10. Positive displacement pumps Diaphragm pumps • Principle of operation

  11. Positive displacement pumps Roots “blower” • Principle of operation

  12. Momentum transfer pumps Diffusion pumps • Air diffuses to vapor stream • Baffles condense vapor • Oil backstreaming problem

  13. Momentum transfer pumps Turbomolecular pumps • Principle of a molecular “drag” pump • Mechanically similar to rotary pump • Good compression ratio • Poor pumping speed • Turbo pump

  14. Momentum transfer pumps Turbomolecular pumps • Principle of operation

  15. Entrapment pumps Ion pumps • Penning cell • Magnetic field acts as electron trap  cyclotron orbits • Ions deposit on Cathode

  16. Entrapment pumps Titanium sublimation pumps • Titanium as evaporatable “getter” material • Chemical sorption • 40-50 Ampere current evaporates Ti

  17. Pressure gauges Liquid Manometers • Simplest U-tube manometer • Atmospheric pressure = 1 bar The Diaphragm Manometer • Capacitive sensor • AC vs. DC • DC  capacitance bridge • AC  resonant circuit tuned to diaphragm vibration

  18. Pressure gauges Thermal Conductivity Gauges • Convection of heat through the gas • Other heat losses • Radiation ~ T4 • Solid conduction • Operating conditions • Free molecular flow • > 10-3torr

  19. Pressure gauges Ion Gauge • Measurement of ion current • Gauge sensitivity • Bayard-Alpert gauge • Collector potential: -10 V • Grid potential: 180 V • Cathode filament: 30 V • Screen: 0 (ground)

  20. Vacuum Seals O-ring seal • Elastomers, Viton-A, Polyimide • Quick and reusable • Limited baking range (< 250 °C) ConFlat flange seal • “Leak-tight” (< 10-12 Pa m3s-1) • Metal gaskets (typically copper) • Bakable to 450 °C • Not reusable

  21. Manipulation and motion under vacuum Metal bellows • Mechanical feedthroughs • Bakable to 450 °C • Limited linear/angular stroke Continuous rotation • Speeds up to 2000 RPM • High torque  bellows • Low torque  magnets

  22. Manipulation and motion under vacuum Gate Valve • Large bore • Sample transfer Right-angled valve • Small bore • Air evacuation

  23. Manipulation and motion under vacuum Transfer arm • Significantly greater stroke than bellow-sealed manipulator • Magnetic power transmission

  24. Summary • Introduction • Pumps • Positive displacement pumps • Momentum transfer pumps • Entrapment pumps • Pressure gauges • Vacuum seals • Manipulation and motion under vacuum

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