overview of vacuum systems

Overview of Vacuum SystemsTejas Deshpande24 July, 2014

• Introduction

• Pumps

• Positive displacement pumps

• Momentum transfer pumps

• Entrapment pumps

• Pressure gauges

• Vacuum seals

• Manipulation and motion under vacuum

Outline

Introduction

Introduction: definitionsKinetic Theory of Gases

• Ideal gas equation

• Velocity of molecules hitting chamber walls

Pumping

• Rate of mass flow

• Mass “conductance”

Introduction: definitions

http://fisica.ufpr.br/sharipov/tubefm.html

Pumping

• Pump capacity & effective pumping speed

Introduction: definitions

• Rate of evacuation

• Example: Pfeiffer Hena-25 pump + cylindrical chamber

• Finite C with a hose

Pumping

• Conductance of KF 40 hose (L = 10", D = 2.165")

Introduction: definitions

[1] http://www.vacuumlab.com/Articles/Knowing%20Eff%20Pump%20Speed.pdf

[1]

Rotary vane pumps

• Principle of operation

Positive displacement pumps

Scroll pumps

• Principle of operation

Positive displacement pumps

Diaphragm pumps

Positive displacement pumps

• Principle of operation

Roots “blower”

Positive displacement pumps

• Principle of operation

Diffusion pumps

• Air diffuses to vapor stream

• Baffles condense vapor

• Oil backstreaming problem

Momentum transfer pumps

Turbomolecular pumps

• Principle of a molecular “drag” pump

• Mechanically similar to rotary pump

• Good compression ratio

• Poor pumping speed

• Turbo pump

Momentum transfer pumps

Turbomolecular pumps

Momentum transfer pumps

• Principle of operation

Ion pumps

• Penning cell

• Magnetic field acts as electron trap cyclotron orbits

• Ions deposit on Cathode

Entrapment pumps

Titanium sublimation pumps

• Titanium as evaporatable “getter” material

• Chemical sorption

• 40-50 Ampere current evaporates Ti

Entrapment pumps

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

Thermal Conductivity Gauges

• Convection of heat through the gas

Pressure gauges

• Other heat losses

• Radiation ~ T4

• Solid conduction

• Operating conditions

• Free molecular flow

• > 10-3 torr

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)

O-ring seal

• Elastomers, Viton-A, Polyimide

• Quick and reusable

• Limited baking range (< 250 °C)

Vacuum Seals

ConFlat flange seal

• “Leak-tight” (< 10-12 Pa m3s-1)

• Metal gaskets (typically copper)

• Bakable to 450 °C

• Not reusable

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

Gate Valve

Manipulation and motion under vacuum

Right-angled valve

• Large bore

• Sample transfer

• Small bore

• Air evacuation

Transfer arm

Manipulation and motion under vacuum

• Significantly greater stroke than bellow-sealed manipulator

• Magnetic power transmission

• Introduction

• Pumps

• Positive displacement pumps

• Momentum transfer pumps

• Entrapment pumps

• Pressure gauges

• Vacuum seals

• Manipulation and motion under vacuum

Summary