Instrumental Presentation I Turbomolecular pump Jyotirmoy Ghosh - - PowerPoint PPT Presentation

Jyotirmoy Ghosh 06-02-16

1

Instrumental Presentation I Turbomolecular pump

Why is vacuum needed?

Contamination (usually water) Clean surface Atmosphere (High)Vacuum

To provide a clean surface

Pressure Ranges

Vacuum Low Vacuum High Vacuum Ultra High Vacuum Extreme High Vacuum Pressure (mbar) >1013-10 -3 (mbar) 10 -3 -10 -8 (mbar) 10 -8 -10 -12 (mbar) 10 -12 -10 -14 (mbar)

4

Introduction

A Vacuum pump is a device that removes gas molecules from a sealed volume in

• rder to leave behind a partial empty space. The first vacuum pump was invented in

1650 by Otto von Guericke, and was preceded by the suction pump, which dates to antiquity. Basically, there are three different types of vacuum pumps, which are explained in details as below:-

• Positive Displacement Vacuum Pumps
• Momentum Transfer Vacuum Pumps
• Entrapment Pumps

Sliding Vane Rotary Pump Molecular Drag Pump

Turbomolecular Pump

Fluid Entrainment Pump VACUUM PUMPS Reciprocating Displacement Pump Gas Transfer Vacuum Pump Drag Pump Entrapment Vacuum Pump Positive Displacement Vacuum Pump Kinetic Vacuum Pump Rotary Pump Diaphragm Pump Piston Pump Liquid Ring Pump Rotary Piston Pump Rotary Plunger Pump Roots Pump Multiple Vane Rotary Pump Dry Pump Adsorption Pump Cryopump Getter Pump Getter Ion Pump Sputter Ion Pump Evaporation Ion Pump Bulk Getter Pump Cold Trap Ion Transfer Pump Gaseous Ring Pump Turbine Pump Axial Flow Pump Radial Flow Pump Ejector Pump Liquid Jet Pump Gas Jet Pump Vapor Jet Pump Diffusion Pump Diffusion Ejector Pump Self Purifying Diffusion Pump Fractionating Diffusion Pump Condenser Sublimation Pump 5

Difgerent types of pumps

6

T urbomolecular pump (TMP)

• TMP is a momentum transfer pump it works on the principle that gas molecules

can be given momentum in a desired direction by repeated collision with a moving solid surface.

• In a TMP, a rapidly spinning fan rotor or blade 'hits' gas molecules from the inlet
• f the pump towards the exhaust in order to create or maintain a vacuum.
• The blade surface is rough, so no reflection will occur and it is thick and stable for

high pressure operation.

• The blade surface looks down, most of the scattered molecules will leave it

downwards and for high flow rates the blades are at 45° and close to the axis.

• TMP cannot work if it is exhausted directly to atm pressure, less than 10-2 mbar

exhaust pressure is required for its function. Till now there is no TMP which can work directly to atm.

• Pressure Range: 10-6 to 10-12 mbar (UHV Region)

7

History and development of T urbomolecular pump

The turbomolecular pump was invented in 1958 by Becker, based on the older molecular drag pumps developed by Gaede in 1913, Holweck in 1923 and Siegbahn in 1944. Considerable development has taken place since 1958 when the first pumps were made.

• Early pumps were dependent on oil or grease lubricated bearings, but the demand

for flexibility and greater cleanliness, we saw the development and introduction of ceramic ball-bearings.

• These bearings are lubricated for life and have lower mass, giving lower radial

forces which reduces running temperature and increases bearing life.

• Magnetic bearings using high-field permanent magnets have also been developed.
• To improve further the cleanliness of a system, the conventional oil-sealed rotary

vane backing pump is replaced with a ‘dry pump’ or ‘Diaphragm pump’.

T urbomolecular pump (TMP)

ROTOR BLADES HIGH PUMPING SPEED HIGH COMPRESSION EXHAUST HIGH FREQ. MOTOR INLET FLANGE STATOR BLADES BEARING BEARING

Turbomolecular Pump

10

T urbomolecular pump (TMP)

Rotor - stator assembly

11

Pumping speed of T urbomolecular pump

Volumetric flow rate, S=A.v A=Area, v=velocity Throughput, Q=P.S P=Pressure Conductance, C=Q/(P2-P1) Conductance should be very large for high vacuum, ideally it should be infinite. The pumping speed of a TMP depends on 4 basic parameters: 1. The diameter of the rotor and the blade height, which determines the entrance area. 2. The peripheral rotational velocity. 3. The blade angle of the rotor. 4. The blade spacing ratio. [i.e., the distance between blades divided by the width]

12

Compression ratio

Compression ratio for different gases, Compression ratio=Outlet pressure/Inlet pressure

13

General operating instructions

• In spite of the relatively large gap between the pump rotor and the stator, the pumps

should be protected against foreign objects entering through the intake port. It is for this reason that the pump should never be operated without the supplied wire-mesh splinter guard.

• In a radioactive environment standard TMP can be used without hazard at dose rates
• f from 104 to 105 rad. Since the semiconductors used inside the electronic

frequency converters can tolerate a dose rate of only about 105 rad.

• Roughing (backing) pumps are required for the operation of TMP. Depending on

the size of the chamber to be evacuated, the TMP and backing pumps may be switched on simultaneously.

Thank you