Thought Experiment Regarding Breakeven

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simey_binker
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Thought Experiment Regarding Breakeven

Post by simey_binker » Sun Mar 08, 2020 12:20 am

ok. you see the evil "breakeven" word in the title, and your brain either shuts off, or dives into a rage. even better, this punk thinks of himself as an "armchair physicist" with some sort of "thought experiment".

Alright fair enough.

I've been lurking on the forum for 8 years now. I'm a 34 year old professional mechanical engineer who has worked at many start ups - currently at an electrical vehicle start up in California. So although I'm about to prove the fact that I'm an idiot, don't immediately jump to the fact I'm an idiot... yet.

Yes, I recognize that breakeven is a looong way off with a fusor. Orders of magnitude away from breakeven. Input 100W, and you're only getting back a fraction of a watt output.

How is that "fraction of a watt" being harnessed? I know the INPUT to a fusor is a massive potential difference between the grids, but how is that "fraction of a watt" output being measured? (lets put aside p-B>alpha fusion for now)


So if I put 100W into an incandescent light bulb, perhaps only 6W is actually converted into useful light. You may call it inefficient. But in reality it's operating precisely as expected. You put 100W of electrical power in, and you will get 100W of power out. The vast majority of the output is heat, and we call this a "loss", but not a single power plant on the earth considers heat as loss. Every power plant is just an expensive kettle; they produce heat to create steam.

An incandescent bulb may be a crap producer of light, but it's a great producer of heat. Can you run a turbine off it?... I'm not going to get into different heat cycles or infrared photosensitive diodes or what size of filament would be required etc - but lets just say, theoretically*, one should be able to get 100W of power out. (*ignoring the capture system inefficiencies)

Well, you know where I'm going with this; some people have likened a fusor to "an expensive night light". There's no chance of "getting close to break even" because of "heat losses". I always hear there is "tremendous loss into the inner grid". Has anyone used this "loss" to harness power?

What if the inner grid was comprised of hollow copper tubing? you apply the voltage potential on the copper, and the working fluid on the inside carries the heat out of the chamber. Depending on the size and time in the reactor, a suitable fluid, flow rate, and inner grid geometry is chosen. Yes, I know that the tube will have a certain thickness which is greater than a wire - but assume that we scale the fusor according to the "larger" inner grid conductor. Is the inner grid heating up the main point of loss?

Now, is this like an incandescent bulb where you'd be fighting to get your original 100W back? I... wouldn't think so. We're talking about fusion here!

In reality, if you put 100W into a fusor, you're getting much MUCH more than 100W out; but we don't have a way of capturing that power yet. We call the fusor inefficient, but it's operating precisely as expected - it creates heat.

For as much as we've dedicated time to achieve fusion, have we dedicated time to capturing power? Perhaps a fluid-filled inner grid isn't the solution. But what have we tried?

Now that you've read this far, you can now call me an idiot,
Sim

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Richard Hull
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Re: Thought Experiment Regarding Breakeven

Post by Richard Hull » Sun Mar 08, 2020 12:48 am

I have long ago, (2000) stated that the fusor as commonly made and producing 1 million n/s has and efficiency of 1.000001. More net energy is there than is put in if all energy is carefully traced. The COP, however, in an energy recovery scheme, is much lower as the thermal or Carnot cycle efficiency is lucky to be 20% even with today's recovery and distribution levels and methods.

Think like a power company ...... a 5 megawatt fusion plant would require a 4.999999 megawatt coal fired plant to power it. Losses in the coal plant would mime the losses in the fusion plant and there is still the Carnot losses in both. Thus, a net power and energy loss. One hundred watts into a fusor with the best recovery possible might be on the order of 10 watts. Heat energy is the lowest possible form of energy. The best possible Carnot efficiency is on the order of 0.7 in the ideal conditions. (never met).

The only extra energy created over and above the input energy is the fusion energy and that is a fraction of one microwatt per 100 watts poured into the system.

If anyone here wants to try this and suffer the huge extra costs and issues to get a few recovered watts from the 100 watts in, be my guest.

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.

simey_binker
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Re: Thought Experiment Regarding Breakeven

Post by simey_binker » Sun Mar 08, 2020 4:29 am

ok, this is fascinating...

lets just assume a 100% conversion from heat to electrical power; put that aside for now. But yes, I do see your point.

You're saying that fundamentally a fusor only produces one, one millionth of a net power gain? Perhaps a little tongue in cheek of a claim - but at the particle level, is not a fusion reaction producing many orders of magnitude more power than a chemical or fission reaction? Are we then, not producing enough fusion reactions to proportionally make a difference?

As anyone ramps up the potential on the grids, they increase the fusion rate, but very soon find that they are A: consuming a lot of power to make fusion occur, B: have no real way of preventing the grids or chamber from melting and C: have no way of collecting any power produced to close the feedback loop. So yes, we chuck tones of power in, we get only a handful of fusion reactions, and we nearly melt the place down. So the experiment is stopped. The majority of the power inputted is used to create heat in the grids, light, plasma and x-rays, with a very small portion of power goes towards actual fusions. Consider, even before neutrons are detected, the amount of power required to make the star pattern - and fusion hasn't even been achieved yet.

Hypothetically, if we had infinitely robust grids, and we could ramp the input power up, would we not find an increase in fusion reactions, and produce orders of magnitude more heat than the input power?

To pull it full circle; if the Carnot cycle is something like 50%, if you produced enough fusion reactions to double the heat output, as compared to the electrical input, you would be at breakeven. Theoretically.

I mean, we are talking about fusion here. Can we not create double the heat power, for a given input of electrical power?

(this is where a p-B reaction would be great, because you could harness the electricity directly instead of sending the heat through a kettle)

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Rich Feldman
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Re: Thought Experiment Regarding Breakeven

Post by Rich Feldman » Sun Mar 08, 2020 6:11 am

>> but at the particle level, is not a fusion reaction producing many orders of magnitude more power than a chemical or fission reaction?
Are we then, not producing enough fusion reactions to proportionally make a difference?

You got it!

With hundreds of watts of electricity going in, fusioneers get hundreds of watts of heat, less than a watt of light and x-rays,
and maybe a millionth of a watt of fusion power yield.
Order of 1 million fusions/second, when you would need 1 trillion fusions/second to make 1 watt of atomic energy.
Even at 1 trillion, the contribution of fusion energy output to induce more fusion reactions is negligible. It's substantial only in hydrogen bombs.

As you said, chemical reactions are much less energetic. To get 1 watt of combustion heat you might need to combine 1 million trillion fuel and oxygen molecules per second.

The numbers I just gave are scientific wild guesses. The real factors, at least for fusors, are in one of Richard's FAQ documents,
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Re: Thought Experiment Regarding Breakeven

Post by ian_krase » Sun Mar 08, 2020 7:49 am

To give my own version of an explanation:

Currently existing fusors are primarily useful as machines that convert electric power and deuterium gas into a small amount of neutron radiation (along with a bunch of light, heat, and X-rays). This is a very useful thing, since most other ways of getting neutron radiation are problematic! But it is a very long way from being useful as a power plant.

And yes, that is exactly the problem. Not enough fusion reactions happening. This by itself would not be too problematic, but you get them to happen fast enough to keep up with energy losses, of which there are many.


The basic issues for a fusor meant to provide useful energy are:

1. A lot of energy is wasted passing an electric current through the gas. (Accelerator-type fusion systems, or those using ion guns, have less of this problem. However, they are moderately to substantially more complicated to build.)

2. It takes a lot of power (on a small scale) to accelerate each deuterium ion.

3. Not all of the deuterium ions collide with other deuterium ions as opposed to the inner grid, wall, etc.

4. Only a very small fraction of the ones that collide with each other, actually fuse. (if they did, you would get a dangerous dose of neutron radiation and also make any aluminum object in your lab radioactive).

5. Typically, when a deuterium atom fails to undergo fusion, it releases all the energy used to accelerate it in a way that wastes it (for example, by giving off X-rays or by hitting the wall or inner grid and sticking).



Items 1, 3, and 5 are mostly subject to being improved, and there are a LOT of things that can potentially be done. Most of them are very difficult, though, to improve by the needed orders of magnitude to make fusion viable as an energy source. There are a number of processes by which the energy tends to leak out of high-energy particles no matter what you do.


The problem can be compared to trying to make a usable power plant fueled by fuel that only gradually oxidizes when you direct a blowtorch at it. There is no reason to think it is impossible (and, after all, thermonuclear bombs clearly exist) but it seems to be pretty difficult.

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Re: Thought Experiment Regarding Breakeven

Post by Richard Hull » Sun Mar 08, 2020 11:25 am

read the PDF file in the FAQ located at

viewtopic.php?f=42&t=13284

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.

simey_binker
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Re: Thought Experiment Regarding Breakeven

Post by simey_binker » Mon Mar 09, 2020 4:25 am

ah.

that PDF is helpful. Some of it I was familiar with. Other parts I wasn't.

I can understand how a fusor (or other method of confinement) will just create a soup of ions that are at a variety of energies - the best one can do is dial up the potential on the grids to achieve largest cross sectional area on average, and hopefully some ions are at the right conditions (velocity, trajectory, planets aligned etc) to fuse via tunnelling. in the meantime, you've scrubbed off tones of input power in the form of heat, which as previous stated, is difficult to recuperate.

Even a hydrogen bomb successfully fuses less than 1% of it's hydrogen. However, it does exceed "breakeven". Emphasis on the "break".

So one way of dialling in the energies, is to use a particle accelerator... wait... reading...

https://en.wikipedia.org/wiki/Colliding_beam_fusion

Does anyone have that paper handy wherein someone proposed two oval particle accelerators in opposing directions? I remember reading it a while back.


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Re: Thought Experiment Regarding Breakeven

Post by Pablo Llaguno » Mon Mar 09, 2020 6:30 pm

One possible upgrade to the fusor is a “virtual” cathode, as to fix the issue with thermionic emissions (which are a waste of input energy). EMC2 tried to achieve that with their pollywell. According to a paper by Robert Bussard with a 10kV well depth (out of a 12.5kV drive) they got 2E5 n/s out of DD fusion over a period of 0.4msec, so about 1E9 fusions/s. “100,000 times higher than Farnsworth/Hirsch results at similar low energies for DD”.

Ultimately, EMC2 got stuck by fundings I believe. Last year there was also a study at the university of Sydney that basically indicates the concept is dead on the water. To many issues with the concept of a virtual negative cathode.

http://www.enthea.org/docs/Bussard-Clea ... ulsion.pdf

https://en.wikipedia.org/wiki/Polywell

https://ses.library.usyd.edu.au/handle/2123/21070

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Re: Thought Experiment Regarding Breakeven

Post by simey_binker » Tue Mar 10, 2020 1:51 am

yeah, I'm familiar with the polywell. I liked the idea of making it a dodecahedron of maximum awesomeness. but yeah, it has it's own fair share of difficulties. I like this colliding beam business - anyone want to build one of these in their basement? coooome ooooon it can't be that difficult, can it? ;)

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