Required Current Questions

This forum is for specialized infomation important to the construction and safe operation of the high voltage electrical supplies and related circuitry needed for fusor operation.
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Logan Holler
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Required Current Questions

Post by Logan Holler »

Hello!

My team is currently working through the power supply for our fusor device and I had a few questions about current. For our low voltage (about 35 kV at 30 mA) we are using a Variable Voltage Regulator (VVR), a Neon Transformer, and a diode ladder to rectify. This should be what we are using for preliminary testing and working and while working with our electrician he stated that it should work for that goal.

However, for our second set up we are connecting a power supply to the VVR and/or a 240 V wall outlet, we are still looking for this device so if you have any recommendations it would be appreciated. My questions comes about the current though. The goal is to achieve a voltage of 75 kV and we found a device that can output that voltage but only at 1.8 mA and our electrician said he thought we needed a higher current. Is there any textbook or paper that you know of about the current in other fusor devices because every paper we have found labels its voltage but never the currents. Any help or advice is apricated!

Thanks!
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Richard Hull
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Re: Required Current Questions

Post by Richard Hull »

Regardless, read all the FAQs related to the use of neon sign transformers and their limitations and the needs for specific currents required to do fusion in the FAQs.

20ma is not too much current to ask for as a minimum current at any fusion voltage. Good fusion is easy to do at 30kv and 12 ma applied. A supply capable of double the run current is always a good thing.

Try

viewtopic.php?t=10333

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Liam David
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Re: Required Current Questions

Post by Liam David »

You could probably get 1e5 at the full 75kV / 1.8mA, but for any realistic first few runs at say 30kV / 1.8mA, you'll have a hard time unless your detector is sensitive (e.g. big 3He tube). Getting 75kV into a chamber is no small feat either. The current requirements (and limits) are also dependent on your chamber--smaller fusors generally need less current.

I don't know how you set it up, but there is no way you will get 30kV @ 30mA out of a doubled NST. Look at the FAQ Richard linked and some other threads attempting the same that are archived here.

There are plenty of published fusor papers that give you the big three: voltage, current, pressure. Just search "inertial electrostatic confinement" or the like on AIP (scitation). I've found that the quality of these papers is kind of hit-or-miss, however. If necessary I could send you a repository I've assembled, on the condition that they are not redistributed, but it would be good to dig around some more.
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Dennis P Brown
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Re: Required Current Questions

Post by Dennis P Brown »

No where did you mention the polarity of your supply - it MUST be negative. Besides issues of a feed-thru for the fusor at those high voltages, the supply cable is a major issue for that voltage as well. The input current for the supply is trivial to figure and determine if your basic input equipment can handle that load - but your wattage for the fusor is rather low (well under 200 watts.)
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Dennis P Brown
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Re: Required Current Questions

Post by Dennis P Brown »

To more fully answer your question, the electrician is essentially correct. While 75 kV will do fusion and certainly at 1.8 ma, the issue is detection. That wattage is very low for detection (too few events.) As a rule of thumb (but this isn't absolute) a power supply system needs to be able to supply at least 200 watts total power. Obviously, something more like 400 watts (esp. for lower voltage range like 30 kV) is far better and much easier to detect neutrons using standard detection methods. Hope this helps to answer your question.

A important point - obviously a fusor power supply at 200 watts with 60 kV will produce more neutrons then a 30 kV system at the same power. The higher voltage (even though lower current) is likely to have more fusion events per ion. Yet power does matter but certainly voltage is important due to better fusion rates with higher voltage (up to a point, of course.)
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Dennis P Brown
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Re: Required Current Questions

Post by Dennis P Brown »

Also, while the interior of your chamber, cathode design, and window will vary I am including a pic of my fusor at 30 kV, 28 ma and about 15 microns with deuterium gas*. When you get your 'plasma' is struck, you should see a similar glow/color and plasma with a stable current. My supply is, apparently, very similar to yours in total power/voltage.



* Though my lecture bottle is nearing empty and I need to install my new bottle today.
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Logan Holler
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Re: Required Current Questions

Post by Logan Holler »

Thank you all for the replies! We have continued to look into other high voltage power supplies and have just been bouncing around to different companies looking for quotes. For our early workings we are planning to use a diode ladder to at least get our first tests going at a low voltage (about 30 kV at 30 mA) and then potentially a higher level diode ladder to get to 60-70ish kV at 25 microA. We are still working out a lot of things so it will likely be awhile until the first tests are done. Thanks!
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Dennis P Brown
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Re: Required Current Questions

Post by Dennis P Brown »

One can do very good levels of fusion at 30 kV and 30 ma. Kinda lost why you think higher voltage than your existing supply is needed. Sure, higher voltage gives more fusion and also, far more x-rays, and a greater electrical hazard. And higher voltage supplies often have rather low current unless very large units are used.

So your current supply provides 30 kV and 30 ma so you have 900 watts of power - that is excellent for fusion. At 60 kV and 25 microamps all you have is a tiny 0.03 watts of power! You can't do detectable fusion at that extremely low value - 200 watts is considered as low as one can go and still detect using typical equipment. Did you mean 25 milliamps, maybe?
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Bob Reite
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Re: Required Current Questions

Post by Bob Reite »

Very few girds can take 900 watt input power. 400 to 500 watts is the maximum even tungsten and graphite grids can take, unless liquid cooled, as a couple of experimenters have done.
The more reactive the materials, the more spectacular the failures.
The testing isn't over until the prototype is destroyed.
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Dennis P Brown
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Re: Required Current Questions

Post by Dennis P Brown »

Funny you mentioned that issue - for me, turned out to be the opposite problem that, for a while, concerned me. Not to derail the thread but I did do a thread on current/heating issue relative to my cathode - turned out even 900+ watts (even 32 kV, up to 38 MA continuous) had trouble getting my cathode hot enough to see anything at all after a few minutes of operation. Turned out it was just the heavy wire gauge of the cathode I used - apparently keeps it cool for some time - so, after five minutes plus, the cage finally does start to get hot enough to see a dull red glow; and then by ten minutes or so, parts of the cage finally glow red-orange. But 900 watts, apparently, can't cause it to heat up enough. But my cathode is a steel alloy welding rod.
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