#6 FAQ: Quick fusion factoids

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Richard Hull
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#6 FAQ: Quick fusion factoids

Post by Richard Hull » Fri Mar 02, 2012 3:46 pm

We are besieged with questions specific to what is needed to do fusion. Here is a quick list.......

Fusion voltage needed:

Fusion, in the fusor, is achieved through supplying electrical energy in a reduced atmosphere of gas to generate a plasma. The voltage needed to achieve this depends on your detector type and sensitivity. In a fusor, fusion that can be detected begins at about 12 kilovolts (12kv) applied. No newbie without a very sensitive and expensive detector will be able to detect this. So, given the norm here, you will need about 25 kilovolts or more. At 35 kilovolts you will achieve a very easy fusion detect.

Your power supply must be a negative "hot" supply. This means that the positive high voltage lead must be connected to ground. You must have a minimum of 10-15 milliamps of available current at full potential with 20 or more milliamps being very desirable. Such supplies are very expensive if purchased new, ($2,000 - $5,000) but used supplies are often found on e-bay. Many fusioneers make up their own power supplies to avoid a major outlay of cash.

Fusion fuel:

There is only one fusion fuel that you will ever be able to obtain, and even then, with some variable degree of difficulty. That fuel is deuterium gas. Forget all other supposed fusion fuels that you may have read about in the fusion literature here or elsewhere.

Fusion reactor pressure, (environment within the fusor):

You will find that you can only do creditable fusion in a metallic, sealed vessel filled with a nearly 100% pure atmosphere of deuterium gas at a pressure of between 5 and 20 microns. (nearly 1 millionth of earth's normal atmospheric pressure). This means you will need to take your vessel down to nearly 1 billionth of an atmosphere with two tandem vacuum pump systems and back fill to one millionth of an atmosphere with deuterium gas.

Vacuum pumps consist of a foreline pump and a high vacuum pump. Both of these pumps can be found used and in good shape for a total of about $500.00. If you look about and get some good deals this cost figure can be reduced further.

Fusion Temperature:

This is a term involving total public confusion through both mis-information and lack of knowledge in what temperature really is. So, forget all about temperature until you are ready to really study and learn by digging into the literature or reading various FAQs here and the many postings related to it. Suffice it to say that the working fusor reaches outside temperatures, on the metallic shell, of over 200 degrees F which is very hot to the touch.

Fusor chamber or reactor vessel:

This must be metallic! Stainless steel is the normal vessel material used. The vessel can be almost any shape, but cylindrical and spherical fusors are the norm. The normal diameter is in the 6 to 8-inch range. You cannot do sustained fusion in a glass bell jar as it can't withstand the localized, internal heating found at detectable levels of fusion operations.

Fusion detection:

You can't claim fusion until you prove it here. The norm is to detect neutrons which are a common deuterium fusion by-product. Neutrons are the only fusion "ash" product that can be detected outside of the fusor reactor vessel. Sensitive, already made up, neutron detectors are extremely expensive with a very cheap new one being over $2,000.00. Bubble detectors that have a limited life span of about 6 months or more are avaialble for about $200.00 - $300.00.

If a fusor is operated at very high levels of easy detection, neutron induced silver activation detectable by an inexpensive geiger counter is possible. Also, special scintillation detection schemes can be fashioned by the electronically adroit fusioneer.

Radiation:

The radiation emitted from the normal stainless steel type fusor working under 25kv is very minimal both from a neutron and x-ray standpoint. However, at voltages much above 25kv, the stronger x-radiation will start to penetrate the metallic shell. (normally .060 thick). For voltages above 30kv, either remote operation, (10 feet or more operator-to-fusor distance), or some sort of thin lead shield around the fusor is advisable to reduce x-ray exposure. Above 40 kv, only a well constructed lead shield should be used. See the radiation forum for all the FAQs on this subject. Neutron radiation has never been a big issue, but at 70kv and above, a neutron absorber shield might also be in order. Thus far, no amateur operates in this upper high voltage region and no fusioneer has ever been exposed to any significant x-ray or neutron radiation.

Fusion energy out of the fusor....Power!

The average successful fusor will never demand more than about 500 watts of power from its high voltage supply as input. The absolute maximum fusion power generated from the best fusor ever made might be about 10 millionths of one watt.
Thus, the fusor demands about 50 million times more input power than it generates.
Bottom line? Forget about producing net fusion energy.....Ever!

Other stuff:

There are a myriad of fine details. Look up the requisite FAQs in the forums specific to your questions.

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Re: FAQ: Quick fusion factoids

Post by Jim Kovalchick » Fri Mar 02, 2012 4:19 pm

Thanks for putting this out. Most, if not all of it is already in the various other FAQ's and posts, but given the amount of questions that come from starters that would be answered by your post, I think it is very worthwhile. I especially appreciate the cost information you have added. I'm not sure that many understand what they are getting into.

A question: I agree with your voltage range for standard neutron detection. Regarding expense related to low neutron rate detection, it would seem to me that CR-39 plastic detection might be accomplished inexpensively for low neutron production rates. Thoughts?

Some other thoughts:
To add to remarks about bell jar fusion, if one is tempted to do it for visual purposes, you may as well not bother because glass will become coated over time by sputtering of grid components. It's hard enough keeping small view ports clean.

A common question worthy of a factoid is about radiation safety. Fusor's do not emit hazardous radiation operating below 15 kV. Above 15 kV, use of shielding should be considered.

Another common question worthy of a factoid is compliance with regulations. The Nuclear Regulatory Commission is on record as stating that they have no jurisdiction to regulate fusion reactors. The NRC does limit export of deuterium. Otherwise, many individual states have laws governing devices that emit radiation, but in general amateur fusors operate at energy levels far below state limits.

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Re: FAQ: Quick fusion factoids

Post by Richard Hull » Fri Mar 02, 2012 4:36 pm

Jim,

Thanks for the comments and I have added a radiation portion to this original at your suggestion. I also covered the bases related to fusion temperatures and output energy or power.

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Re: FAQ: Quick fusion factoids

Post by DaveC » Fri Mar 02, 2012 11:01 pm

Richard -

Nicely done. Most newcomers will be able to get a handle on the outlines of what it takes from this.


Thanks for collecting the wisdom....

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Re: FAQ: Quick fusion factoids

Post by David Geer » Sat Mar 03, 2012 3:52 am

Ah but Jim! There have been at least 1 or 2 bell jar type fusors that have produced neutrons. They were constructed by the veterans on here but it has been done. Bell jars are dangerous and hence, why stainless steel chambers have been used.

There are a few other tweaks that could be done that the others have missed so far but they are minor. Just this one point really caught my eye.

-David Geer
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Re: FAQ: Quick fusion factoids

Post by JakeJHecla » Sun Mar 04, 2012 1:25 am

Carl Greninger and Northwest Nuclear Consortium (nwnc.us.com) have a belljar fusor that is well documented to produce neutrons. It's far from ideal, but it does fuse reliably.

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Re: FAQ: Quick fusion factoids

Post by Richard Hull » Mon Mar 05, 2012 6:11 pm

I would like to know who on our fusor club listing, was inducted, while using, has proved beyond all doubt and by what means of measurement, a glass bell jar fusor. I may have forgotten.
There have been many stainless steel bell jar/cylinder type fusors that have been successful.

Still, I will militant against even attempting fusion in any non-metallic reactor vessel.

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
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Re: FAQ: Quick fusion factoids

Post by DaveC » Mon Mar 05, 2012 8:08 pm

I also share Richard's concern about the use of glass bell jars, where there is even a remote possibility of intense beam formation. The localized heating (and failure) may occur before one is even aware of the conditions within the jar.

And.... no one should ever use a glass bell jar without a full implosion shield in place. Mine goes on before any pumping begins.

I've only had one bell jar crack (from a mechanical stress issue, not heating) and it did not implode. But every time my system pumps down, I am on a full alert for strange sounds of distress.

There are obvious benefits to being able to observe processes under vacuum. For quick tests of a fusor concept, one can easily build a SS shield for the interior of a glass bell jar. For a spherical IEC device, a pair of stainless steel salad bowls will work nicely. Just mind that there is a definite overlap at the bowl edges.

But the all stainless steel system, generally gives superior outgassing performance (lower rate of outgassing, ultimately) and has the thermal robustness that gives a little peace of mind during experiments.

All this has been said a lot of times over the years. You can never be too careful.

Dave Cooper

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Re: FAQ: Quick fusion factoids

Post by Frank Sanns » Mon Mar 05, 2012 9:41 pm

While a bell jar exposes all sides to flying glass in an implosion, a sight glass (view port) in an all metal fusor is often an overlooked risk. Any glass surface in a metal or a bell jar setup is a potential weak link waiting for catastrophe. Yes, there are some fusors out there in bell jars doing fusion at low power and are pretty for demonstrations and learning. If a fusor will be pushed to maximize fusion, it should not have any viewports as Richard has stated.

Another point that you will not find in this fine document of Richard's, is a how to do all of this. Making a neutron producing fusor will not come from reading directions. It will come by reading and doing. Learning, and relearning. There will be failures as well as triumphs. It is the process that counts most.

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Re: FAQ: Quick fusion factoids

Post by David Housley » Tue Mar 06, 2012 12:14 am

As Jake mentioned, we readily do repeatable fusion in a bell jar. We also have over an inch thick polycarbonate implosion sheild in front of the bell jar, strict rules about where people are while the bell jar is under vacuum, temperature probes on the bell jar to monitor heating of the glass, regular acid washes to clear out the sputtering products, and what amounts to the most massive radiation shield for probably any fusor in the world, which also provides a great deal of implosion protection. Safety is the number ONE requirement, and a great deal of focus and expense (some say massive overkill, but we aren't going to have injuries or exposure, either). Having said all that, Richard is absolutely correct that the bell jar is far from optimum for fusion. You can't do sustained runs, you have to take a lot of extra precautions and go to a lot more work to make them reliably produce neutrons. For that reason, we are moving towards a stainless steel chamber for the next revision. The bell jar will be retained mainly for the demonstration---it shows up better for the wow factor. Our goal is primarily to get the kids and public excited about science again, and provide a venue and means to do things the schools can't or won't do. The fusor is a tool that demands a high level of work and commitment to get going, and a high level of self education, both acedemic and hands on. It provides a real introduction to the down and dirty aspects of making a science project work. For this reason, it is far from cookbook laboratory science, but the concepts involved and the work done already ensures a reasonable level of promised success if someone puts in the effort. It provides tangible rewards for the effort, and thus motivates rather than discourages continued exploration. Net energy production was never a goal, or possible, but it can be used as a tool into the study of nuclear phenomenon, and who knows what discoveries might be made? Ok, end of philosophizing. Thanks.

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