Deuterium-Tritium fusion

It may be difficult to separate "theory" from "application," but let''s see if this helps facilitate the discussion.
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Akshat Sharma
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Deuterium-Tritium fusion

Post by Akshat Sharma »

Hello guys,
I have surfed this Forum and realized that most people are conducting Deuterium-Deuterium fusion. Looking at my prior knowledge, deuterium-deuterium needs higher temperatures than deuterium-tritium Fusion. According to what I know, correct me if wrong, Nuclear fusion with Deuterium-Tritium requires 40 million Kelvins to break the coulomb barrier and allow the atoms to fuse whereas Deuterium-Deuterium Requires considerably more; therefore, wouldn't it (d-t) require, theoretically, less energy.

Linking onto that, a theory states that every volt an ionized atom accelerates, it gains 11,604 Kelvins. To reach 40 million Kelvins, it only requires 3,447 volts. Even if we use excess of 100 million Kelvins, it would only require 8,618 volts. What I don't understand is why people use transformers which step the voltage up to 15,000 volts (15Kv) as that would produce 174,060,000 Kelvins!!! Isn't that more than needed???

Thanks,
Akshat
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Richard Hull
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Re: Deuterium-Tritium fusion

Post by Richard Hull »

We have posted on this many times in the past. As the amateur cannot under, any circumstances, legally obtain or utilize tritium, the entire issue is one of worthless discussion. Everyone who knows about fusion fuels, knows D-T fusion is easy and at least 100 times as productive at most fusion energy levels over D-D fusion. The amateur is pretty much doomed to a single fuel solution of D-D fusion which does just fine in the right and talented hand.

Thus, we have banned such discussions related to any actual use of illegal fuels and processes in amateur hands.

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
Akshat Sharma
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Re: Deuterium-Tritium fusion

Post by Akshat Sharma »

Thanks for the quick reply Richard.
Dan Tibbets
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Re: Deuterium-Tritium fusion

Post by Dan Tibbets »

Deuterium- tritium fusion easier, but as stated it is essentially impossible for anyone other than a large government lab. Tritium is not only controlled, it is non existent, well almost. It has to be made (in tiny amounts) as it does not exist in nature in any meaningful amount. It is generally made at nuclear (fission) power plants by bombarding lithium with neutrons from the fission reactor.
As for temperature, it is not a certain temperature that is required, it is a range of temperatures that might be chosen as the best compromise. Generally, 5,000 eV is the minimum for D-T, perhaps 10,000 eV for D-D. This minimum is because of Bremsstruhlung radiation. This cools the plasma faster than any fusion reaction can heat it at lower temperatures. Higher temperatures are better up to limits imposed by the fusion cross section for the selected fuel.

Don't think that D-D fusion is only a hobby though. It can produce net positive energy output, though it is harder than D-T. The tritium is also a major hurdle as you have to produce it in your reactor at least as fast as you consume it. This is a tremendous challenge for D-T Tokamaks involving liquid lithium and possibly beryllium and /or lead inside the reactor chamber. Note that Tokamaks (and I assume other machines like Stellaraters, Spheromaks) have a hard time heating plasmas to the higher temperatures. That is partially why they only have the potential to work with the D-T fuel.
Also, a Japanese lab has used D-D fuel in their Tokamak and achieved fusion rates that while not at breakeven, would have been if they had substituted D-T fuel. At least that is their claim. By using D-D they presumably established much of the physics requirements without the cost and complexity of handling tritium. Note that physics breakeven is not the same as profitable net fusion. The magnet power may be ignored, and the fusion heat has to be converted to electricity which is useful. There is considerable distance to go to reach these goals. Even ~ 20 billion dollars spent on ITER may exceed breakeven but will be marginal in producing enough excess power to produce more electricity than is consumed. And it does not address many other issues like tritium production.

Meanwhile there are at least 4 or more multimillion dollar efforts to build D-D reactors that might (eventually) exceed breakeven. These include the Polywell, several versions of the Field Reversed Configuration, several magnetic pinch approaches (Z-pinch at Zandia Labs, Theta pinch at Lawrenceville Plasma Physics), and General Fusion's approach.
What is exciting about at least some of these approaches is that they might also work with other fusion fuels that do not produce many neutrons. This offers tremendous advantages if these most difficult fuels can be made to work. And, these machines are very much cheaper than any envisioned working D-T Tokamak- either as working reactors or as research efforts.

The approach that draws on Fusor concepts the most is the Polywell.

Dan Tibbets
Akshat Sharma
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Re: Deuterium-Tritium fusion

Post by Akshat Sharma »

Thanks for the thorough explanation Dan.
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Richard Hull
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Re: Deuterium-Tritium fusion

Post by Richard Hull »

The key point that Dan noted was that even a break even with fusion, you are not power-ready! Even at 5 times better than break even, you are not power ready, unless you are willing to have a 500 megawatt fusion plant with a 100 megawatt coal-fired or fission power plant built right beside it to power the fusion plant. Fuels are not the issue. There are many fusion ready fuels, some better than others, but none are self-starting or in reactors that are self-sustaining. Amateurs are out of this business completely and from all aspects of it, of course.

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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