Help to improve fusor

[Cristiano_Machado]

Hello,

I would like to share the latest result from our fusor and ask for some advice.

Today we could get a stable run at:
v: 25000 V
a: 1,5 mA
P: 40 mTorr
time: 180 s
Three bubble (the big one is a failure in the dosimeter).

Before test

Before test dosimeter

After test

After test - 3 bubbles

In our first and second runs (2 weeks ago) we could get 3.0 mA, with almost the same pressure and voltage, but know it didn't happen. Any idea what may be the problem?

We are using the precipitator HVPS, and we noted that if we try to increase the voltage too fast, then the current go crazy. We had 2 corona discharges because of that, and we could not identify where they happened. We had to abort 2 runs because of this.

Other problems we are trying to improve are in our vacuum and gas system. The throttle valve is too sensitive and hard to get a stable pressure and when we open the deuterium (open and close very fast the cylinder!) it starts to leak into the chamber, even with the microvalve and the control valve closed.

To control the pressure inside the chamber during the runs, we have to open the throttle valve and keep controlling the microvalve all the time. Two alternatives I read in the faqs and from other fusioneers are: using of hypodermic tubing or use one more valve. Any suggestion to improve the system and make it more stable?

We want to improve the efficiency and operability of the fusor to post a good video on youtube and try some activation.

Cristiano

[Mark Rowley]

Good to see you working towards improving your system!

"We had 2 corona discharges because of that, and we could not identify where they happened..."
What does this mean? Are you referring to flashover arcing on the outside of the system or within the chamber? If outside, then I can almost guarantee it's one of three places (or all).

--If your power supply is not submerged in oil, arcing is common under the flyback transformers where the wire enters the epoxy. Remedy is to submerge in oil. However, if you arced to the point of causing a carbon track, you may need to get another supply.

--Your HV feedline to the feedthru on the fusor is laying or placed too close to a common ground. Depending on the type of wire, insulation can easily break down and arc. I would not trust the small diameter HV wire on the power supply to maintain it's dielectric strength. Route it far away from anything it can "sense" as a ground...including wood. In my case everything is routed in air and if not, it is against thick acrylic plastic.

--Your HV feedthru insulator is a top location for flashover arcing. Early on I suffered this problem and had to resort to submerging it in oil (Carl Willis design from several years ago). Most of these feedthrus are loosely rated to 30kv. I think I was around 25-30kV when mine flashed over. The oil socket 100% fixed this problem.

Other than insufficient HV routing / insulation, the reason you may be flashing over is due to your vacuum system or deuterium flow control, of both. For example, if you are operating under load at 25kv and you loose plasma due to the aforementioned issues, the precip supply will immediately jump to it's unloaded voltage. That no-load voltage could be over 30kV and much higher with the 60kV precip supply! And then you will have instant flashover. I believe I previously explained the necessity to insulate precip based HV systems to the extreme maximum. They are great supplies for the price but absolutely mandate a beefed up HV routing arrangement. Just like the pricy GHVR, Spellman, etc HV supplies, these too do not respond well to arcing. It would not surprise me if it's already damaged. But let's hope not.

You'll have to experiment with gas flow. Capillary tubing would help as well as another needle valve but I've heard conflicting reports from very knowledgeable folks on which is better so I cant offer too much on this.

Your systems sweet spot should be around 28-30mTorr of deuterium, 2-3mA, 30kV. 40mTorr, which is too high for my system, would provide a lively sounding electronic detector at the parameters you stated earlier but probably not too many bubbles. And of course, all systems being somewhat different, your results may vary. Btw, that BTI detector being 9 months old is probably not as responsive as it was when new. I've heard varying reports but I'm not expecting much out of mine after 4 months.

Mark Rowley

[Mark Rowley]

Another thought...
How are you introducing deuterium to your system from a cold start?

Mark Rowley

[Bob Reite]

I'm able to run my system at 50KV without resorting to oil. Corona needs to be controlled. Get a 1" dia brass ball (Aluminum would be OK) and put that on the feedthrough terminal. Do dress the HV wire away from anything else. I would not trust the wire on those Chinese power supplies to be good for more than 20KV

[Mark Rowley]

Specific to the precip supply, I’d still recommend oil. Reason being it’s fool proof. A misjudgment with static field control (especially with someone new to the art) or environmental issues like a dusty insulator may still result in disaster.

Tbh, if I had a strong and forgiving 300lb unobtanium 1950’s xrt, i may opt for static field control. And that would probably be amplified by my taste for the aesthetics of such designs. But with a delicate yet potent (for a 2.75” system) precip supply, I highly recommend going for the bulletproof design. Overkill is a best friend in cases like these.

Mark Rowley

[Richard Hull]

If you have stuff on a PC board, arc tracking can kill it unless you can "dremel" out the track and refill the trench with epoxy. Oil is great, of course, as long as whatever you put in the oil is safe against leaking or spilling. Balls and toroids are always my choice for possible short radius arc points in air. They really distribute the field to a safe condition if installed correctly. Toroids are especially nice as they create a large field shadow over their area.

Richard Hull