#3 FAQ - Voltages needed in a fusor

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Richard Hull
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#3 FAQ - Voltages needed in a fusor

Post by Richard Hull » Thu Nov 17, 2011 4:04 pm

All fusors demand a fully variable, negative, DC high voltage. That is, the postive lead of the power supply is grounded and this makes the negative lead the "hot" lead.

Note: All fusor power supplies can kill! Proper safety precautions and insulation must be used to avoid fatal accidents.

Typically, the fusor shell is at ground potential and the inner grid is negative or "hot". (see diagrams for demo and full metal fusor below)

A "demo fusor", (one that will not do fusion but is a look-alike, act-alike), need only have a high voltage between 3,000 volts, (3kv), and 15,000 volts, (15kv), with 10kv being more the norm.

To do fusion with deuterium gas, a minimum of 10kv is needed but the average amateur just beginning will never detect this without somewhat expensive and sensitive neutron detection gear. To do easily detectable fusion which uses simpler detection systems, 20kv is a minimum with 25kv desirable. The object being to produce unambiguous proof that fusion is taking place.

Fusion becomes much more pronounced over 30kv and neutron activation can usually be done at a usable level over 35kv. Little is to be gained with voltages over 100kv that the lethality of the resultant x-radiation could justify, but a number of fusioneers have used as much as 60kv with good lead shields in place.

In summary....... All supplies must be negative hot with positive ground.

Demo fusor 3-10kv no x-rays of importance. Look-alike and act-alike a real fusor. No deuterium needed and thus, no fusion done. Neon transformer OK.
Real fusor with deuterium......20kv minimum but fusion nearly impossible to detect.......30kvfusion just starts to become easily detectable. Neon transformer not OK. You need a strong power supply.

It is important to remember that fusion, in our case, is pretty much voltage driven. You want to increase the probability of fusion and to do that you need to achieve a bigger cross section and that means more kinetic energy, which means more acceleratory voltage must be applied.

Note: All fusors will produce x-ray radiation especially at voltages over 15kv. On metal shelled fusors, these x-rays will penetrate the steel shell at about 35kv and shielding will be required. See the radiation forum for FAQs related to this issue.

Positive ground, negative hot output power supplies are relatively rare and at voltages over 30kv are very expensive and unbelievably rare. All real fusing, fusor supplies need to be able to supply a minimum of 15 milliamperes, ( 15ma), of current. All supplies must be fully variable from zero to their full KV rating.

The average amateur with a good understanding of electronic basics will usually have little trouble building their own power supply once they have a suitable transformer in hand. Ideally, this is an x-ray transformer. Some few advanced amateurs make or cobble up more modern high frequency "switch-mode" supplies with voltage multipliers to avoid the usual oil tanked, bulky x-ray transformers.

It is not the purpose of this post to give instruction on such assembly.

Richard Hull
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Re: FAQ - Voltages needed in a fusor

Post by Rob Pope » Sat Nov 19, 2011 5:18 pm

Thank you Richard, very helpful

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Re: FAQ - Voltages needed in a fusor

Post by clarkmcc » Tue Oct 23, 2012 3:14 pm

<""A "demo fusor", (one that will not do fusion but is a look-alike, act-alike), need only have a high voltage between 3,000 volts, (3kv), and 15,000 volts, (15kv), with 10kv being more the norm.

To do fusion with deuterium gas, a minimum of 10kv is needed"">

Does this mean that a demo fusor does not need deuterium to run? I am sorry for my uneducated questions.

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Re: FAQ - Voltages needed in a fusor

Post by Chris Bradley » Tue Oct 23, 2012 4:19 pm

Clark, the faqs are where to look, in this case the glossary might help you well at this stage of your understanding.

viewtopic.php?f=24&t=3223#p12733

Feel free to recommend any other terms for this list that you think are needed for the erudition of newbs.

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Re: FAQ - Voltages needed in a fusor

Post by clarkmcc » Tue Oct 23, 2012 4:32 pm

<"A simple bell jar or metal fusor that operates and looks like a real fusor except that there is no deuterium gas in the system and it is not doing fusion.">

What is the final product of a demo fusor? I assume that this is still in a vacuum? If deuterium is not being fused in a demo fusor, what is going on? Is there an FAQ about this somewhere?

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Re: FAQ - Voltages needed in a fusor

Post by Carl Willis » Tue Oct 23, 2012 5:37 pm

Here is a FAQ post--one of several--that answers your questions:

viewtopic.php?f=24&t=2674#p12184

My sense is that you are ignoring prior advice to use the search feature and read the introductory ("FAQ") material. You have probably noticed that most of your questions elicit the response that you need to simply read what is already here. Building understanding by poring through the forum archives takes time, motivation, and some thinking for yourself--resources you will need in much larger measure to actually build a fusion apparatus. Please get in the habit of respecting the wisdom that has been accumulating on this forum for as long as you've been alive, and reserve your posting for those occasions when your questions are specific. If you have the passion and the patience to build a fusor, you can certainly handle a little reading.

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Re: FAQ - Voltages needed in a fusor

Post by Richard Hull » Tue Oct 23, 2012 7:19 pm

Clark, re-read what you highlighted from my original FAQ above in your last posting.

<"A simple bell jar or metal fusor that operates and looks like a real fusor except that there is no deuterium gas in the system and it is not doing fusion.">

I meant precisely what I said and nothing more.

The demo LOOKS and OPERATES just like a real fusor. With no deuterium, it can't do any fusion. What it does is that it takes residual air molecules remaining in the demo fusor, which never has a secondary pump, and ionizes the various atmospheric gases. These ions and electrons look like and act like a real fusor to the eye and it also operationally mimes how a real fusor needs to be run.

A demo fusor is a "show and tell"... a.... "dog and pony show". the demo fusor is a safe fusor look-alike and act-alike device that uses lower voltages and produces no x-radiation when it is commonly operated. These are often science fair devices.

If a demo fusor is extremely well made from metal, all you need to do inorder to make it a real fusing fusor is add a secondary diff or turbo pump, 30,000 volts and deuterium gas to be doing real fusion.

In some cases, a real fusor will have to be "dumbed down" to a demo fusor if operated at a science fair or in a school by leaving the deuterium at home and running at reduced power so that it can be even brought into most public facilities.

Richard Hull
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Re: FAQ - Voltages needed in a fusor

Post by Scott Moroch » Sun Jun 16, 2013 3:56 am

I have read on many websites, pdf's and blogs about demo fusors and neutron producing fusion reactors. I understand the general rule on fusor.net to always read the FAQ's before asking a question. I have read all of the FAQ's and yet still do not understand the concept of grounding the outer grid. It may be just my lack of experience, because I am only a middle school student. I am building a demo fusor, however I don't understand how to ground the positive lead. Many diagrams I have seen say to go to the chamber and ground, whats the point of that? If I don't ground what will happen? If in a demo fusor I dont apply any voltage to the outer grid what will occur?

Scott Moroch
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Re: FAQ - Voltages needed in a fusor

Post by Rich Feldman » Mon Jun 17, 2013 2:07 am

fusionboy wrote:...am only a middle school student. I am building a demo fusor, however I don't understand how to ground the positive lead. Many diagrams I have seen say to go to the chamber and ground, whats the point of that? If I don't ground what will happen? If in a demo fusor I dont apply any voltage to the outer grid what will occur?
Scott,
Can you clarify your question by posting or linking to a drawing? Perhaps a fusor schematic (from one of those FAQs you have read), on which you can point out the detail that is giving you trouble.

Here's one thing to start learning right now. Nobody applies a voltage to some metal part. In fact there's no such thing as "voltage" at any single point in a circuit.
Voltage is another name for the electric potential difference between TWO places. All voltage sources, whether high or low, and all voltmeters, have two terminals. Generally they don't do much unless BOTH terminals are connected to something. Often, for convenience and/or safety, one terminal is connected to a node named Ground -- but that should not be considered implicit.

Draw yourself a chamber (and optional outer grid), an inner grid, a high voltage source with positive and negative leads, and a place (anywhere on the page) named Ground. How many ways can you connect them, with nothing left "floating" (EE talk for not connected to anything)?
Here's an even simpler exercise that may help to get the point across. Draw the circuit of a flashlight with two D cells in series. Draw a Ground and connect it to the D cell positive pole that goes directly to switch or light bulb. When switch is closed, what are the voltages (signed values, with respect to Ground) of the two light bulb terminals? How 'bout the voltage between Ground and the junction shared by both D cells?

Respectfully,
Mr. Feldman
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Re: FAQ - Voltages needed in a fusor

Post by JeffElzinga » Wed Jan 22, 2014 5:48 pm

Quick question
is the reason to have a hot ground (0 volts as your positive and -20kv as your negative) based on physics or on safety/practicality?
the core of my question is this:
voltage is simply potential difference. why cant i just ground the negative central terminal and let the base be high positive +20kv if this were normal electronics I would say the circuit would not know the difference but
I wondered if there was something in the physics that does indeed make a difference or is the downside simply that you would have the body of your fusor way way above ground and therefore a pretty dangerous device for everyone around it (not to mention complications with anything connected to it...)
I suppose the question is simply more about the electronics and less about practicality.
Cheers and thank you.

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