Is Positron-Catalyzed Fusion Possible?

[Vardaan Bhat]

How can one "heat up plasma as a whole" in general?

 

[mfb]

With electromagnetic radiation, compression, or by shooting fast particles into it.

 

[Vardaan Bhat]

... gamma rays are electromagnetic radiation, no?

 

[mheslep]

Yes, and why are they better than any other EM?

 

[Vardaan Bhat]

If they're higher energy, I'd imagine you'd need less and the setup would be more compact.

 

[Vardaan Bhat]

What other kind of em is used for fusion? With icf, why can't we just shoot X-rays with soft X-ray light at the fuel?

 

[mfb]

If they're higher energy, I'd imagine you'd need less and the setup would be more compact.

That argument doesn't work. They have more energy per photon. So what? It is much harder to produce those photons, and their interactions with matter are less helpful.

What other kind of em is used for fusion? With icf, why can't we just shoot X-rays with soft X-ray light at the fuel?

Tokamaks and stellarators use microwaves. Simply because it is easy to produce MW of microwave power, and they couple efficiently to the electrons in the plasma, heating it. ICF also needs something interacting strongly with the material. Gamma rays don't work. There is also no suitable conventional x-ray source strong enough, hence the detour with lasers heating some material that emits x-rays.

 

[e.bar.goum]

If they're higher energy, I'd imagine you'd need less and the setup would be more compact.

This has been said a bunch of times in this thread, but I think a plot might make this clearer. To heat up the plasma, you need the gamma rays to deposit energy in the plasma. The problem with using higher energy photons is that their probability of depositing this energy goes down. Have a plot:

On the y-axis is the attenuation coefficient for photons in different materials, and on the x-axis is the photon energy. Note the log-log scale. If you want to deposit a lot of energy in a material, you're better off using low energy photons.

 

[Vardaan Bhat]

Have a plot:

On the y-axis is the attenuation coefficient for photons in different materials, and on the x-axis is the photon energy. Note the log-log scale. If you want to deposit a lot of energy in a material, you're better off using low energy photons.

Wow! Thank you for the graph. That helps me visualize the problems with my idea.

With electromagnetic radiation, compression, or by shooting fast particles into it.

What kinds of fast particles?

 

[mfb]

What kinds of fast particles?

Deuterium, sometimes deuterium with tritium. The neutral beams heat the plasma and become part of it, so you don't want other isotopes in the plasma.

 

[Vardaan Bhat]

How do you make controlled beams of a neutral particle or atom?

 

[mfb]

You make an ionized beam and then add electrons to make it neutral.

 

[Vardaan Bhat]

So, to be clear, you take some deuterium, ionize it, accelerate it, and add electrons at the end? What defines the end? When it's in the plasma?

Why does this work, and can it be applied to other fuels? Can it be used to ignite fusion alone (even just theoretically) or does it need to be coupled with something else (electric fields or magnetic fields or something like that)?

 

[mfb]

So, to be clear, you take some deuterium, ionize it, accelerate it, and add electrons at the end? What defines the end? When it's in the plasma?

No, before it enters the plasma. Before it enters the plasma chamber. As usual, Wikipedia has an article.

Why does this work, and can it be applied to other fuels?

The atoms are fast, they get slowed down in the plasma, heating it. It can be applied to other fuels.

The plasma still needs containment: strong magnetic fields.

Please start a new threads if you have follow-up questions because this is not about positrons any more.

 

[nikkkom]

A video of neutral beam injector in action

http://www.ccfe.ac.uk/news_detail.aspx?id=117

 

[rootone]

Why does it look bright pink, in the visible range.
Lots of blue and red there, almost no yellow/green.

 

[ChrisVer]

I don't want to sound evil but read the text and not only the video:

its visibility caused by the excitation of the background hydrogen gas

 

[rootone]

I don't want to sound evil but read the text and not only the video:

Ah, OK thanks.

 

[Pooua]

I've toyed with this subject for several years, but, as a non-specialist with very little University Physics behind him, I'm severely limited in what I've been able to do. Antimatter-catalyzed fusion has gotten a bit of interest, and even some government research grants over the years.

http://www.theverge.com/2013/8/28/4659834/unlocking-the-positron-fusion-annihilation-laser
http://large.stanford.edu/courses/2011/ph241/palke1/
http://ffden-2.phys.uaf.edu/213.web.stuff/Scott Kircher/fissionfusion.html

However, I think I concluded a few years ago that antimatter-catalyzed fission is more practical and potentially achievable in the near term than is AC fission.

https://en.wikipedia.org/wiki/Antimatter-catalyzed_nuclear_pulse_propulsion
http://www.universetoday.com/131494...rt-antimatter-propulsion-system-another-star/