vacuum technology part ii of the “what exactly do we have down there?” series
Post on 19-Dec-2015
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TRANSCRIPT
How does one achieve vacuum?
• Pumping – Two types– Transfer – relies on moving molecules from
low to high pressure regions
– Trapping – makes use of chemistry to trap or bury gas particles
Diffusion Pumps
• Rely on jets of boiling fluid (usually silicone oil) to force air particles out of the region being evacuated. Cold traps prevent back streaming.
Kurt J. Lesker Vacuum Technology
Turbomolecular Pumps
• Similar in design to a jet engine. Alternating rotor and stator blade assemblies turn at 20,000-90,000 rpm to force out molecules. Requires a region of low or medium vacuum behind and in front of pump.
Pfeiffer Vacuum GmbH
Ion pumps
• Main components– Array of parallel
stainless tubes– Various charged
surfaces– Titanium or tantalum
coated surfaces
• Trap molecules with varying speeds via chemical reactions
Varian Scientific Instrumentation, Inc.
Cryopumps
• Similar in principle to the ion pump but uses a cryogenically cooled surface of activated charcoal or zeolites to condense and trap gas molecules.
Kurt J. Lesker Vacuum Technology
Measuring the vacuum• Ion gauges – Similar in principle to
the triode ion pump– An array of surfaces are held at
different potential (collector – grounded, grid ~100V, W or Ir filament ~30V)
– Filament emits electrons which circle the grid, bombard with gas molecules to create ions, which are subsequently accelerated toward the collector.
– A variation known as a cold cathode uses an electron plasma in crossed E and B fields of ~5kV and 2kG respectively
MDC Vacuum, Inc.