FAQ - How small and how big can I make a fusor??

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Richard Hull
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FAQ - How small and how big can I make a fusor??

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The answer to this question depends a great deal of you and your answering a number of key questions. Before elaborating further, I will note a few things we have noted over the years about those who arrive here and about their mind set and goals that are in question.

In the end, do you want to just say, "I've done fusion", or do your want to do experiments and learn using fusion of a significant experimental nature? A vast gulf exists between these two worlds and mindsets. The former goal is easy to accomplish and is typically the task of the youthful, DIY "dabbler" and not found in the scientific man who would experience, experiment and learn from doing fusion. The latter goal is a serious one, a committed one and one to which, extreme youth, by its very nature, is not attuned.

Saying you have merely done fusion and made the neutron club can be and has been done with a measured 30,000 n/s. As noted, this is relatively easy in a first build in a small 2.75 conflat cross. More on this relative term, "easy", as we progress in this FAQ.

Fusion, as an experimental quest, at the amateur level, is one in which size does, indeed, matter! However, even this is to be carried only to a point. Sufficient experimental fusion would more or less begin at 1 million fusions per second, (500,000 neutrons per second Isotropic). Fusion, in a fusor, at the amateur experimental level might have an upper limit of 10 million fusions per second or (5 million n/s iso). There are many reasons for these upper and lower limits.

This FAQ will not give precise size expectations related to fixed fusion numbers. It will give well recognized limits for the new builder. Old hands at amateur fusion can and have stretched these general limits given in the end of this FAQ.

Now to the questions

1. How old are you?
If under 21 with no job or significant source of revenue, you are at an extreme disadvantage for doing fusion, even in the "smallest" successful sized fusor. Making the neutron club, with acceptable proof of performance with rather pitiful reported fusion returns is typically a $1000-$2000 expenditure.

2. Are you here for the "win" just to say I did fusion?
This goal really limits you, as it is a prideful goal, and one usually espoused only by the very young. Most wind up making the plasma club and going no further due to funds or failure to have the commitment, verve and grit to move much further along the path. In the end it boils down to the will to persevere and a good bit of disposable cash. Usually the fusor is smallish, the power supply voltage limited, etc., if they make the neutron club. Such "wins" are usually in smaller chambers with barely acceptable power supplies. Such "wins" always signals the end for them, forever, with fusion.

3. How are your mechanical, electrical, electronic, welding and machining skills?
It is important to bring one or two of these skills to the table before starting the effort. This assumes you have the cash, the guts and verve to learn, and ultimately acquire the other skills that you lack along the way to the build ahead of you. You will need to read a lot and develop a "hands-on-imperative" to do significant fusion. Money by the boat load can always buy other people's skills. You can totally farm the build out to welding and machine shops. But you will only have a chamber, be it big or small. Electrical wiring and electronic construction of a minimal nature will be required. There is so much more.

4. Are you an experimenter and wish to experiment with you finished fusor?
If not, you are forced to go back and seriously consider questions #1 and #2. If you answered yes, it is only now that size really matters in your fusor. Let us, for the sake of argument, assume that you are at least handy and have a few skill sets. Let us further assume you have a good deal of cash to be spent either in the short haul in bits and pieces or a gang-o-bread to blast through to an experimental fusion win at any cost rather quickly.

Now as to what size - My fusor - big? or small?

Assuming you answered #4 in the hard-nosed affirmative, You cannot go too small for you have experimental plans and quests ahead for your finished fusor. In general, if you go small, you are now limited to a 4" sphere or cylinder as the absolute smallest system and perhaps an 8" cylinder or sphere at the very high end of the amateur experimental fusor scale. Let me say 4" is damned small! Likewise, 8" is really almost too big. A 6" fusor will be your best bet. Now to discuss issues with big vs small.

Small, at 4-inches, will limit your voltage due to arc over in the chamber, (perhaps 30,000 volts). This limits how much fusion you can do. You will, if successful, be limited in your experimental work. the small size will limit the ports for experiments that you can place on the fusor reactor vessel or chamber. The cost will be rather low here and with good instrumentation, you might come in under $4000. With tremendous skill sets and a scrounger mindset, maybe even under $2000.

Big at 8-inches or more, and you can consider yourself, officially, to be in very deep, expensive, and dangerous waters. While the experimental scope and fusion resultant numbers can be fabulous, the costs regardless of skills will be astronomical. The power supply will be a major expense and deadly dangerous. The radiation levels in both x-ray and neutron radiation will demand extensive and expensive shielding if built in the home or even a nearby out building! The volume of consumed deuterium in such a device will demand excellent control and be a continuous and on-going expense. Useful instrumentation will also go beyond the simple neutron counter of a 4" system. $20,000 might not get it done for the average person going this big. Neutron numbers at close to 100kv applied in such a system could go to 10,000,000 n/s or well beyond!

The ideal is a 6 or 8-inch reactor for those looking to do simple experimental work with some ease. Certainly, here at fusor.net, the 6-8 inch system in a sphere, cross or cylinder are the success stories for easy, successful, amateur experimental fusion and neutron activation work. Most successful people working in this size range are older, experienced and well skilled people who are older than 25 now. They have a good job with disposable incomes or are retired with savings and investments that provide them with the monies needed, as needed to follow an experimental path in fusion. Costs might be expected to range from $5,000 on a 6-inch system to $7,000 on an 8-inch system, if starting from scratch. However most of the type of people above arrived here with skills, money, and often, some of the gear needed, in hand! They typically arrive with a life long work ethic and "work-around" capability that such large expenditures are rarely needed to get the work done. A good rule of thumb on a good experimental fusor system is $1,000 per inch of useful interior dimension at or over 4" size.

These medium sized experimental fusors have all done over 2 million fusions per second, (1 million n/s or the "mega mark") and have even done up to 10 million fusions per second at the top end. Voltages have ranged from as low as 40,000 volts up to 70,000 volts. Significant shielding is demanded over 40,000 volts. This is mostly due to x-ray protection issues.

As we differentially pump deuterium through the chamber for continuous operation, the larger the chamber, the more deuterium is needed and the more it is wasted as it is ultimately being pumped wastefully to the outside world as a net loss. Remember, deuterium in and then deuterium out. More volume to fill means more wasted deuterium.

How small is too small?

If you are talking a demo fusor a 1" diameter chamber will do fine. If you are talking a "win" at fusion" the smallest yet is in a 2.75 inch cross. You just can't get much controlled fusion in anything much smaller without arcing and damaging your supply. This all goes back to how little fusion can you detect at the low end? A race for the smallest successful fusor is yet another prideful goal. Such feats will get you an atta-boy and little else. Try to keep the 4-6-inch size in mind.

Summary

Make of the above, what you will. You must decide, well in advance of spending the first dime, what are your goals. In this, you must answer all the questions above honestly and not become self-deceptive of your capabilities and resources in the answers you give yourself. Your goals, capabilities and resources will determine the size of your fusor and your fusion efforts.

For this writer making the smallest fusing fusor is a goal set by an egotistical fool. The person shooting for the largest fusor ever built is a dreamer who is often limited in almost every category needed to bring the work to fruition and who has no concept of what he or she is getting into. An epic fail or even a failure to start will await most anyone with these too small and super big goals in mind.

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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