Fusor energy output/neutron

The title says it all. This is for established factual (we hope) things.

Fusor energy output/neutron

Postby Doug Coulter » Fri Dec 14, 2012 1:02 pm

Yes, it's quite low, but not as low as some have reported. Just a post to put out the rather simple math, only intended to get the order of magnitude correct, since some of the bright lights in the field are off by 10e4 on the low side.

Most fusions are either the type that makes a neutron and 3He, or the type that makes a proton and tritium - the ratio is roughly 50% for each. Thus for every neutron output, there are most likely two fusions with very approximately 3.5 MeV output per fusion. So, for every neutron output, there is about 7 MeV output. Going to an online energy unit conversion site (since my Halliday is temporarily somewhere else), we find that this is:
7 000 000 electronvolt = 1.12152411e-12 joule.

Multiply that by 10e6 for a fusor making around 1 million neuts/second - a very achievable amount, and we have: 1.12152411e-6 joule/second.

This is about 1 microwatt per million neuts/second. Not one billionth or ten billionth, one millionth of a watt.
This will be off by a few percent, since both reactions aren't precisely 3.5 MeV, nor do they split exactly 50-50, but it's pretty close.

Sorry to dip so low as to put you know, real numbers on this via simple calculations, but it seemed needed since some of the bright lights in the "cult of personality" on another fusion board are getting it so wrong. Yeah, you're not going to boil that cup of tea with a microwatt, or ten microwatts (numbers we've reached here) but it's not quite as grim as some say.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Re: Fusor energy output/neutron

Postby Alex Biersack » Mon Dec 17, 2012 4:26 pm

At what Voltages and currents did you reach 10 microWatt? Normally the input is about a kW for example if you have 30kV at 30mA you have roughly 1kW of power to get 1 mcroWatt in fusion energy.
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Re: Fusor energy output/neutron

Postby Doug Coulter » Mon Dec 17, 2012 4:44 pm

Roughly speaking, about 50kv/20ma (1kw, more or less). This is NOT the highest Q I've reached, however - see the youtube stuff on Q I've put up elsewhere here where I 4d plot my data. I got my highest Q at much lower current - about 7 ma. Neutron/fusion output goes up with current, but not as fast as the current does. My current theory on that has to do with space charge limitations, and that would be proved out if I could go to 60,70,80kv and so on (I need a better feedthrough and power supply to get there) - the space charge limit current on the Q peak should move up in current at the higher voltages if that's the real reason. This is not the only possible explanation, which is why I mined my data several ways, and am looking hard into a new phenomenon I've got, which appears to be a large number of negatively charged ions coming out the end of my grid. When I coated my tank walls with Pd + Ti, and loaded that with D, my Q doubled till the walls got warm and drove out the D.

Charge exchange is pretty rare going from D+ to D- - has to pick up two electrons, very unlikely. But how else does one explain the doubling of output when there's D embedded in the walls? There is no (simple) reason I can think of that a D+ would hit the outer walls moving fast enough to do significant beam on target fusion.

The more likely (to me) explanation is that fusion as done in a fusor is so horribly unlikely that even a very unlikely event (double charge exchange) is of the same order of magnitude or even later (after all, it's quite unlikely that everything that hits the wall fuses - we'd be done with our power plant fusion if it was that easy). A single charge-exchange at just the right instant might make some fast moving neutrals hitting the wall. But you have to remember, that when I put on a 50kv field, that's not the field the ions see - they see each other, canceling a lot of that, so they're not in general going 50kv worth of fast.
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Re: Fusor energy output/neutron

Postby chrismb » Mon Dec 17, 2012 5:41 pm

Doug Coulter wrote:Charge exchange is pretty rare going from D+ to D- - has to pick up two electrons, very unlikely. But how else does one explain the doubling of output when there's D embedded in the walls? There is no (simple) reason I can think of that a D+ would hit the outer walls moving fast enough to do significant beam on target fusion.

Just D* + D -> D + D* is the only charge exchange reaction you need to worry about to explain your fast neutrals heading into the shell.

Below 100keV, charge exchange has a higher cross-section than ionisation! It's not until some 300keV that re-ionisation gets to be an oom above charge-exchange.

I'm generally convinced that charge exchange pretty much explains some 90% (+/- 10%) of a fusor's performance.

D* + D -> D + D* Charge-exchange actually peaks at around 15 to 20keV! Is there any small surprise this is where neutrons begin to get detected in a fusor?
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Re: Fusor energy output/neutron

Postby Doug Coulter » Mon Dec 17, 2012 5:45 pm

I'd tend to agree, depending on whether you mean the * to mean + or just "excited but neutral" as is the common usage.
The only problem I have is that at a mere few tens of KV, beam on target fusion (and with a better target than my tank walls) produces very few fusion reactions according to all my old books on the topic.
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Re: Fusor energy output/neutron

Postby chrismb » Mon Dec 17, 2012 6:39 pm

Doug Coulter wrote:I'd tend to agree, depending on whether you mean the * to mean + or just "excited but neutral" as is the common usage.
The only problem I have is that at a mere few tens of KV, beam on target fusion (and with a better target than my tank walls) produces very few fusion reactions according to all my old books on the topic.

That's true - about 1^E-9 fusions per collision, by unit energy!.. very few indeed ;)
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