No diffusion pump I have used (oil or mercury) ionized and accelerated the vaporized fluid. You may be thinking of an ion pump, which works differently (http://en.wikipedia.org/wiki/Vacuum_pump).

As nasaspook said, oil diffusion pumps do contaminate a system, but nothing like a mercury diffusion pump did, even with a liquid nitrogen cooled trap.

John

The system I refer to employed the 'electro-spray' (q.v.) model (not to be confused with the 'Mass Spec.' technique of similar nomenclature)...

Best regards
HP

 

As nasaspook said, oil diffusion pumps do contaminate a system, but nothing like a mercury diffusion pump did, even with a liquid nitrogen cooled trap.

John

Hmmm... Perhaps we are indeed talking 'apples and oranges'... But now I'm curious (a good thing)

Best regards
HP

 

It so happens that my brother-in-law operates one of the world's leading microscopy/visualization labs. Everything he does requires incredibly good vacuum and as a result he uses some of the best equipment in the world, and the manufacturers of this equipment come to him to test the latest advances. He achieves orders of magnitude better vacuum than can be obtained anywhere else.

Sorry, sounds like bragging now that I read what I just wrote.

 

We stopped using diffusion pumps 20 years ago, much too messy. Instead of clean bits of metal exploding you have an oil film on every part of a machine from the pressure shockwave in the vacuum chamber.

I always thought the pump oil smelled a little bit like popcorn. One of the first things you noticed when you went into any plasma lab.

 

Hello,

We use several types of turbo pumps in our mass spectrometers.
Here are some types that I could find on the web:
http://www.pchemlabs.com/product.asp?pid=3119
And the split flow turbo pump:
http://www.fergutec.com/shop/pfeiffer-tmh-261-250-030-split-flow-turbomolecular-vacuum-pump/

Bertus

 

I always thought the pump oil smelled a little bit like popcorn. One of the first things you noticed when you went into any plasma lab.

That's because it's the same stuff they pass off as butter in the theater.

 

The first part shows the general location of the pump chamber before the accel tube, the second part shows the far end after the acceleration tube with bits from the other end.

Sorry about the shaky cam from the Netbook used to video this.

The pictures show metal dust in the chamber from the exploded pump that needs to be completely cleaned out.

 

A less frequent occurrence with the (IMO generally superior) Hg systems -- albeit nastier from a HAZMAT standpoint

Best regards
HP

There are degrees of nasty. We had a system that generated p+ ions, kicked them up to about 40kev into a magnesium vapor cell charge exchanger for p- ions into a 1.5 Mev Tandtron. A large turbo is installed on the top , when that thing blows you have a Phosphorus Magnesium toxic fire that's almost impossible extinguish unless you have a special Class D. Had it happen a few times but I'm not on the HAZMAT team so I could watch it burn while they put it out.

Similar system: