Exploring Vacuum Technology in Physics Lab

1. PHYSICS 225, 2ND YEAR LAB VACUUM TECHNOLOGY G.F. West Thurs, Jan. 12

2. INTRODUCTION • Humans work in a gaseous environment. • Although less dense than solids or liquids, the normal gas environment greatly influences much physics. • Often, to do interesting and important physics, one must get rid of it.

3. WHAT IS A VACUUM ? • The absence of appreciable matter (i.e., atoms, molecules, ions, particles), usually as gas. • How do we measure the amount of gas? • As mechanical pressure on container walls or neighbouring gas. • Pressure = Force /unit area = N/m2= Pa (SIU); = bars (cgs) = psi (USA/Imperial); = Atm (Chem); = mmHg = Torr (traditional physics);

4. KINETIC THEORY OF GASSES (The colliding billiard ball model ) • Gas atoms have a range of velocities, increasing with temperature. • Gas molecules therefore have appreciable energy and momentum. • Pressure is the cumulative result of the momentum changes in collisions. • Collision likelihood is usually expressed as “mean free path” (average distance molecules move between collisions).

5. LEVELS OF VACUUM Air at 273 K, molecular Vrms~ 485 m/s Pressure (V HV UHV UHV ) • Atm, 1.0 1/760 - - - - • kPa, 101.3 0.13, 0.13Pa - - - • psi, 14.7 0.02 - - - - • Torr, 760 1 1e-3 1e-6 1e-9 1e-12 Mean Free Path, at 273 K, mol radius 0.3 nm; • m ~1e-7,~7e-5,~7e-2, ~7e+1,~7e+4, ~7e+7

6. VACUUM PUMPS • Mechanical; with valves, vanes, diaphrams (Roughing pumps, forepumps). • Entrainment principle • Diffusion pumps, • Turbomolecular pumps. • Entrapment principle • Cryopumps, • ionpumps (gettering) • TI sputtering • molecular sieves (zeolites and other synthetic microporous compounds)

7. PROBLEMS WITH PUMPING • Need for a forepump. • Contamination of vacuum by backflow. • Gas selectivity. • Need for regeneration. • Virtual leaks. • Speed, ease of cycling to lab conditions.

8. VAPOUR PRESSURE

9. MULTI-PUMP SYSTEM

10. ROTARY VANE FORE PUMP

11. DIFFUSION PUMPS

12. TURBO-MOLECULAR PUMPS

13. TURBO-MOLECULARPUMP

14. ION PUMP

15. ION VACUUM GAUGE

16. THE VACUUM ENCLOSURE • Materials: - (Glass & stainless steel predominate.) • Requirements:- • Chemically inert • Cleanable • Bakeable • Strong • Workable, (e.g., machineable)

17. TYPICAL VACUUM SYSTEM • Forepump • Main vacuum pump with cooling. • Gate valve,(to allow pump turn off). • Vacuum gauges, if not intrinsic to pumps. • Cold trap(s) (Liquid air). • Sample inlets, if required. • View & manipulation ports, experiment area. • Bakeout system.

18. VACUUM SYSTEM COMPONENTS • Older systems mainly were hand fabricated from glass by artisanal glassblowing. • New systems mainly are constructed from commercially manufactured stainless steel components using (e.g.,):- • Bolted flange connections • Thin metal seals • Glass- to-metal sealed electrical connections • Bellows connected or in-vac bakeable manipulators • Special window glasses for radiation entry/exit

19. VACUUM COMPONENTS

20. USES OF VACUUM TECHNOLOGY Some examples:- • Semiconductor lithography and surface coating. • Analytical inst’s; e.g., spectrometers, microscopes. • Particle accelerators, HEP • Space simulation • Nanotechnoloy • Surface physics. • Gas lasers. • Manufacturing of special materials.