In this space, visitors are invited to post any comments, questions, or skeptical observations about Philo T. Farnsworth's contributions to the field of Nuclear Fusion research.
Subject: Re: Vacuum Alternatives
Date: May 14, 3:03 am
Poster: Dave Cooper
On May 14, 3:03 am, Dave Cooper wrote:
No need to apologize for being a novice experimenter Pat, we all are always such in some ways.. however much experience we may have.
Regarding vacuum pumps (mechanical ones)... many older manuals refer to them as "compressors". That is, they compress very low density gases to slightly above atmospheric density and then release to the atmosphere. To pump down to 0.1 micron pressure, this requires a 10 million to one compression ratio. Most piston type compressors have compression ratios of less than 30. The older type refrigeration compressors are very nice very rough roughing pumps but usually cannot get below a few Torr presure.
As to the heating concept, you can estimate the ultimate pressure by remembering the ideal gas law equation of state.. PV = NRT where P is pressure, V is volume, N is the number of moles of gas, R is the universal Gas constant.. and T is temperature in Kelvins. Without doing any serious math, you can see that a temperature change of 10 to one will give a pressure change of a similar amount. Since the T is absolute temperature, a 10 to one increase would take room temps to 3000 K , way above the melting temp of the chamber itself.
Cooling works much more effectively (Cryo pumping) because the gases are entirely liquified.. except for the helium.. which is present at a few ppm in std atmospheres. So a good cryo system can drop the pressure by about 1 million times.. rather quickly... but as has been noted .. the cryopump must be regenerated... warmed up ... to let the condensed gases leave.
I like you idea of the microwave gas-dyanmic pumping but it probably is more costly than plain ole rough pump and a diffusion, ion or turbo pump.