Fusion Message Board

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: micro-maze amazement
Date: Jul 02, 12:53 pm
Poster: Richard Hull

On Jul 02, 12:53 pm, Richard Hull wrote:


I just finally got around to hooking up my Micro-Maze trap by Kurt Lesker Co. ( I have had it for 5 months) It is beyond belief!

Here's th' skinny:

This puppy cost a boodle and at $348.00 it ain't for the faint of heart or out of work. Nevertheless, I had seen Tom Ligon's unit in action and decided to try one myself.

In the current Lesker catalog they give self aggrandizing and glowing reviews with charts and such about how this thing can hit 10e-4 torr with a regular oil mechanical pump. I never saw Tom's do that, but did note it lowered his base pressure when using his alcatel direct drive unit.

I followed their procedures for pre-installation and bakeout like a good little nazi and it paid off, big time!

The key is to have two top quality bellows valves handy (right!) I picked up two KF-25 NorCal valves in USED condition from Duniway for a mere $370.00. (more than the darned trap!!!) I slapped them on each side of the trap and stuck it in the foreline to the chamber. I opened the valve nearest to the pump and closed the valve to the fusor chamber side. I next fired up the built in heater. I monitored the temp with a K type thermocouple meter and let it hit 300 degrees C. (over 500 Deg F).

It is important to run your pump from the moment the heater starts to heat. It must be run with the gas ballast wide open and filler cap off. (choke choke)...Can you say oil mist and bluba-bluba noise. After 1-2hours of this, the oil looked like sewage through the site glass. The trap's fine imbedded molecular seive material was divesting itself of all manner of atmospheric stuff it picked up since manufacture.

The oil started to clear in about the third hour and in the fourth was back to normal. This was the sign bakeout is near completion. After the fifth hour, I sealed off the gas ballast and unplugged the heater to let the micromaze cool. Again, while still under full running pump action.

Next it is important to valve off the pump side once totally cooled. Now the mechanical pump can be turned off. You must never ever open either end of the micromaze to air ever again!! It won't ruin it, but you will have the 5 hour oil mist adventure to do all over again. Lesker's vacuum gurus ssid it well.........." if the proper proceedures are not fully followed, a trap can dirty up a vacuum system much worse than if no trap is used."

After allowing my poor overworked pump a cool down period, turned it back on and let it run just one minute to clean and vacuum out the gum rubber line up to the first valve. I then opened the valve nearest the pump and let the pump again run for about two minutes to insure deep vacuum inside the mircomaze. Finally the valve to the chamber side of the micromaze was opened. In the short time it took the valve to thread all the way open, the darned TC gauge indicated 20 microns!!!! within 1 minute I had totally zero'd (back pegged) the instrument!! I was prepared, and had installed a KF-25 "T" with a capacitance manometer on it. this ultimately bottomed out at 8e10-5 torr!!!! I then started the glow clean mode. This took the system down to 3e10-5 torr!!! wow! This rivaled a moderate diffusion pump and I was only using a mechanical pump. This is the deepest I have ever had my system! The mircomaze is all they said it was. Thanks Kurt Lesker!!!

Prior to this, with long pump sessions and lots of glow cleaning, I might hit .5 micron (very rare)

The pump, by itself would not take the chamber deeper than about 3 microns and that is a very good pump!

The bulk of the garbage removed by the trap are things not removed, but actually often placed in a chamber by mechanical pumps. These are, oil based volatile hydrocarbons, and water vapor, the two biggest polluters in all the vacuum world.

Lesker notes that the micromaze can be recycled indefinitely. I have yet to get a handle on the bakeout schedule, but they note that the trap is good to go until you can't hit base pressure at all or it takes much longer to reach it. I would imagine that if you don't open the fusor itself to air, there will be no real pollutants to foul the pump other than the oil and mositure back feed from the small line from the pump itself, and this is only significant at the instant of startup.

Oh, I almost forgot, Always valve off the chamber and then the pump line valves before shutting off the mechanical pump. Ony then can you raise the pump line to air or dry nitrogen.

I am very pleased with this new addition to my vacuum system.

Richarad Hull