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[deleted] t1_iyvj5ib wrote

Reply to comment by DoubleDot7 in Why not use hydrogen and deuterium in fusion reaction rather than tritium and deuterium? by Curious_user4445

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treefor_js t1_iyvuhla wrote

This is not correct. Temperature is a measurement of the average kinetic energy of the particles - you express plasma temperature in units of eV (energy unit). If one element is heavier then it'll have a slower average velocity. DT reactions require lower temperatures to achieve their highest cross section for fusion reactions. Meaning you need to put less energy into the system.

  • HEDP plasma physicist
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ChipotleMayoFusion t1_iyw8hte wrote

Isn't that exactly what Robus said? The DT reaction is favorable because it reaches high reactivity at lower temperatures. https://upload.wikimedia.org/wikipedia/commons/thumb/d/d0/Fusion_rxnrate.svg/330px-Fusion_rxnrate.svg.png

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treefor_js t1_iyw9ick wrote

That was the conclusion, yes. However, the reasoning was not correct.

Edit: the other thing to note here is not just that it takes a lower temperature to reach higher reaction cross sections but the loss mechanisms that scale with temperature as well. It's a balancing act to keep the plasma warm to use the fusion products to keep burning the fuel without it cooling off rapidly. Bremsstrahlung radiation - x-rays generated by accelerated charged particles, is the main culprit here.

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ChipotleMayoFusion t1_iywmfex wrote

Ok, thanks for the clarification. Maybe I misunderstood what his post was getting at. I have heard that proton-Boron is basically impossible because the brems losses at the temperature where reactivity is sufficient will always be higher, or almost always higher. I think this is what you are saying, you can't just focus on the temperature. Sam Wurzel had a great talk on this at APS 2021, clarifying Qeng vs Qsci and how that changes depending on your recirculating power fraction and other factors.

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treefor_js t1_iywn305 wrote

Oh nice. I didn't get a chance to go to that one. Came down with a stomach bug for a day or two in Pittsburgh. Also wish I had time to go to the commercial fusion breakout this year, but alas. There's always next year.

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ChipotleMayoFusion t1_iywnxfg wrote

I'm glad you were able to attend at all, a lot of the US national labs people were not there due to COVID travel rules.

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treefor_js t1_iywoopg wrote

I sat in on one of the MagLIF sessions and I think there was one live talk with like 10 recorded ones. It was a weird conference. Basically just networked with university folks. So much better turn out this year with national lab folks returning.

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[deleted] t1_iyvl308 wrote

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TinnyOctopus t1_iyvpco3 wrote

As you suppose, it's the sourcing of the tritium that's the problem, but I think you're underselling the difficulty. For the DT fusion, the plasma composition can be mostly D, which is difficult but not impossible to purify out of naturally occurring water (prevalence is generally about 1 in 10,000 to 100,000 hydrogen atoms). Tritium is about 1 to 10^18th hydrogen atoms, which is a million million times less common than even the uncommon deuterium. Which means tritium needs to be manufactured, and at a certain point, the amount of energy being put in to make the tritium fuel will become prohibitive, making the economics of a T-T rector nonviable.

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