IEC-9000 Mark II

[KJNW]

Well, after a year of running a very large bell jar, we have taken the plunge on a major upgrade. This is our new chamber, and as you can see from the photo's we have followed the yellow brick road in design principal, but we did manage to add a couple of "bay windows" to the experience. We also have created a 1.6 MFD capacitor at 35 KV to take a 2,000 volt ripple down to about 200 volts at 30 KVDC. You can see the capacitor bank in the second picture. 16 teenagers are dragging the whole works to Microsoft on May 9th again this year to do their "science fair", and then we have a second presentation at WSU on May the 19th. We also will be presenting at some summer camps, but in one instance, they are going to load the busses, and come to our place to see the glow.

Overall, the chamber made a huge difference in the vacuum numbers, and we are able to pump down to 7 microns on the mechanical pump alone, but we also have a cold trap with LN2, and a diffusion pump which can take us down to 10 -4 somewhere. Our shortfall is that we don't have a vacuum sensor that goes below 1 micron. For the first time we need one, so I am going to be doing some looking around, and would love to hear any suggestions you all might have. The last picture is "first light" on the new chamber, and we did manage to see a few neutrons, but all is not dialed in yet. Robert is busy tanning his face while looking in the side port. It has a quick lock system that allows us to putz with our inner grid without breaking the copper seals on our chamber.

We will send some better pics once w get back from WSU.
Carl G.

[Richard Hull]

This is now truly fabulous! You now have a very safe and far more professional looking setup. This will continue to turn heads and also function far better in the long haul. You should have a lot less difficulties than with the bell jar.

In addition, the more professional observers will automatically give it more credence as it looks capable of doing the job claimed of it. In this case, looks will not be deceiving, but intriguing.

Watch out for X-radiation from those big glass ports!

Nice pix, too!

Richard Hull

[KJNW]

Thank you, Richard. The team will enjoy hearing that coming from you.

[clarkmcc]

If I may, where did you purchase the high voltage feed through?

[Doug Coulter]

Quite a few of my friends are using the Pfeiffer PKR-251 (sometimes you can find these cheap on ebay or other places) for full range vacuum measurement. They cover STP down to about 8e-9 mbar, with a log/analog output.

We use a divide by two (resistors) on our standard data aq device to get in range for that, and do the antilog math when we plot the pressure. Works a charm, very reliable gage. It does read differently on different gases - they provide a cal chart for say D vs air vs argon etc to handle that one.
(anyone who needs one, pm me) The ion gage part of the PKR-251 has quite a magnetic field, so we put it as far from the "active area" as we can.

As an aside, you might do even better without an outer grid such as I see here. Just screen off the holes in the cross with SS screen and it's close enough to a circle to work, though the screens will get kind of hot. I do this in mine also to keep EMI in the thing from blasting out of the viewport. You simply cut the screen about half an inch larger in diameter than the hole it's going to fill, and bend it back 1/4" all around for a nice tight spring fit. We get our SS screen from McMaster as well as local metal scrap yards (much less expensive if you can find it).

On the viewport - electron etc bombardment will eventually hurt the glass. We solved that one by getting a slightly smaller piece of round 3/8" thick pyrex (McMaster) that we clip in on the inside of the viewport, which also attenuates X rays somewhat, but we follow that with a really thick chunk of lead glass on the outside of everything that really stops them and allows real time eyeball views far better than you can get with a camera.

On the other hand, due to Paschen's law, and where we run on the curve, a long path or two down one or more of the cross arms can help you run lower pressures/higher voltages without space charge limiting the "focus". It's worth playing with for certain.

[Rich Feldman]

Carl Greninger wrote:
> We also have created a 1.6 MFD capacitor at 35 KV to take a 2,000 volt ripple down to about 200 volts at 30 KVDC. You can see the capacitor bank in the second picture.

Beautiful work you got there.

Just remember, the spacing between exposed HV surfaces is much more critical now.
There's lots more stored energy, and none of the current limiting that may be intrinsic to your HV supply. If that cap bank discharged suddenly through air, it would make one hell of a bang!
To get an idea, you might make it spark on purpose at lower voltages.
Even that might constitute electrical abuse of your capacitors.

-Rich

[Richard Hull]

A ballast resistor must be in the line after the capacitors. In other words, it must be between the capaciotrs and the fusor HV terminal. Finally, 2000 volts of ripple is no big deal. There is no law that says their can't be a lot of ripple, just so long as there are no negative bias reversals of the DC system.

Richard Hull