Fusor construction questions

[Joshua Turbyfill]

Should I turn off my backing pump when its still connected to the pumped down chamber and then open it up to atmosphere once its off or do I open it up to atmosphere and then turn it off? I've been doing the latter but after a couple times the pump now hums for a couple of seconds after I turn it on before it starts pumping down so I don't know if I may have damaged it. Funny enough its now pumping far lower than before.

[Dennis P Brown]

For oil vane pumps, open to atmosphere isn't a big deal for short periods. Some (minor) amount of oil will be lost via misting. However, this isn't unlike a bleed air vent to remove trapped water vapor from a pump. Since your vacuum quality improved, that is/was a likely issue. So, you might want to preform that (the bleed valve for that purpose) from time to time.

[Richard Hull]

Good vacuum practice is all about valves....Good valves. A valve should isolate the mechanical pump from the for line. bleed valve might be between the pump foreline valve to obviate the suck back issue.
Close the big foreline valve first. turn off the mechanical pump and immediately open the bleed valve to let the pump up to air. then immediately close the bleed valve. It is important to never let the working mechanical pump draw in outside air, unless you have to let your entire system up to air. (as in repairs, changes or additions to the vacuum system). Once you have a good system down to vacuum keep it there, via valving. when shutting down only let the mechanical pump up to air.

Richard Hull

[Joshua Turbyfill]

Im somewhat confused.

My shutdown procedure is:

1. Turn off turbo pump and wait for it to stop spinning
2. Close ball valve and then open turbo's bleed valve to put chamber back to atmosphere
3. Open KF16 connection to let air into the backing pump and immediately after turnoff backing pump

I read somewhere that you dont want to turn off the backing pump when the inlet is at vacuum because it will suck oil into the chamber.

Is this setup & procedure good or is it flawed?

Thanks

[Dennis P Brown]

That method is fine.

One point: Unless you need to access the fusor, keeping it under vacuum (ball valve closed; turbo off) is a good idea. Far less water vapor introduced into the fusor chamber.

[Richard Hull]

If you are planning to do fusion. You will need a superlative bellows high vacuum valve between the turbo and your chamber. your procedure is great. once the ball valve is closed you must then turn off the mechanical pump and within seconds open the KF fitting to air to avoid suck back. then refit the KF fitting. your HV line is still under vacuum and your mechanical pump is up to air. This is how I do it. suck back is not instantaneous.

Question........did you ever look at the FAQ in the vacuum forum that was so very important that I labeled it number one? You will note two valves are demanded at minimum for a successful fusor system. You cannot control a system without a valve between the turbo or diff pump and the fusor.

viewtopic.php?f=25&t=9291

Richard Hull

[Joshua Turbyfill]

I didn't want to have to a buy an 8" conflat gate valve as those run over $1000. Is fusion totally impossible without one? I do have the turbo throttled down to 20% power if that helps any.

[Richard Hull]

You will have extreme issues it you turbo has an 8" throat. I assume you have an 8" conflat flange on your fusor chamber as well. I find it difficult to imagine a worse situation for gobbling up Deuterium at a prodigious rate.
Richard Hull

[Joshua Turbyfill]

Yeah it blows through the deuterium that it took the PEM cell an hour to make in about 30 seconds.

I do have a 2.75" bellows valve and a 2.75" conflat 5 way cross. So I could essentially build a 2.75" fusor and connect it to the main chamber via said bellows valve.

fusor2_diagram.png (16.67 KiB) Viewed 5396 times

Will this work or could I just lay a plate of aluminum on top of the turbo's inlet shield to block gas?

[Richard Hull]

A good bit better. An 8" throat on a turbo pump means it is a very serious pump and very aggressive devourer of air or deuterium.

Richard Hull

[Joshua Turbyfill]

Okay I'll build that then. I read in one of the faq's that arcing can be an issue. I have a thick copper wire wrapped around the main 8" cross which goes straight to ground on a wall outlet. Is there any risk of arcing destroying any of the equipment (Turbo, turbo controller, vacuum gauge, etc)? Also is there anything else I need to know before operating a 2.75" fusor?

Currently I've got a table about 12' from the fusor which has the variac for voltage control, a laptop for neutron monitoring, and a big screen showing 4 different cameras mounted on the reactor. I was intending to remotely operate it. Since the needle valve which admits deuterium and the bellows valve are manually operated, will I need to run the fusor standing next to it?

[Richard Hull]

Wrap no bare wire around the cross for a Ground!! A proper ground is a copper tab or solder lug with a hole the size of one of the bolt threads placed under the bolt head and torqued down as part of a flange within the cross end plates. A wire is then secured to the copper lug mechanically and then soldered to it. This and this alone, is now a proper ground connection to the chamber. It may then be taken to a star point ground and the star point then connected to the mains ground.

The star point ground is explain in the power wsupply forum FAQ's.

Richard Hull

[Joshua Turbyfill]

I'll change that then. Heres the new fusor. What do yall think?

[Richard Hull]

Beautiful and very impressive. We look forward to reports on operation.

Richard Hull

[ian_krase]

Looks pretty impressive.

Have never seen a fusor wearing a crucifix before, even if I did pray the rosary during pumpdown.

[Dennis P Brown]

I see you have two possible fusors chambers (a large diameter, and small); nice economy on pumping systems. Very professional system. If the cross is silver, are you trying activation, maybe?

[Rich Feldman]

I applaud the wireless connection of probe to HV feedthrough terminal. Did you modify the probe to read negative kV?

[Joshua Turbyfill]

Thanks guys. Haha no its not for activation I just thought it would be a nice touch.

Yeah so the big chamber I'll use as a demo fusor since its big and looks pretty cool with the turbo in the background.

For the probe I think someone told me to open it up and take the two wires on the inside and just swap which terminal they go to. That did the job.