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Overview of Vacuum Systems Tejas Deshpande 24 July, 2014.

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Presentation on theme: "Overview of Vacuum Systems Tejas Deshpande 24 July, 2014."— Presentation transcript:

1 Overview of Vacuum Systems Tejas Deshpande 24 July, 2014

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

3 Introduction

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

5 Pumping Rate of mass flow Mass “conductance” Introduction: definitions

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

7 Pumping Conductance of KF 40 hose (L = 10", D = 2.165") Introduction: definitions [1] [1]

8 Rotary vane pumps Principle of operation Positive displacement pumps

9 Scroll pumps Principle of operation Positive displacement pumps

10 Diaphragm pumps Positive displacement pumps Principle of operation

11 Roots “blower” Positive displacement pumps Principle of operation

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

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

14 Turbomolecular pumps Momentum transfer pumps Principle of operation

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

16 Titanium sublimation pumps Titanium as evaporatable “getter” material Chemical sorption Ampere current evaporates Ti Entrapment pumps

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

18 Thermal Conductivity Gauges Convection of heat through the gas Pressure gauges Other heat losses Radiation ~ T 4 Solid conduction Operating conditions Free molecular flow > torr

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

20 O-ring seal Elastomers, Viton-A, Polyimide Quick and reusable Limited baking range (< 250 °C) Vacuum Seals ConFlat flange seal “Leak-tight” (< Pa m 3 s -1 ) Metal gaskets (typically copper) Bakable to 450 °C Not reusable

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

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

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

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


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