What is wrong with particle acceleration based fusion?

In summary, Fusion is an energy process that occurs when two lighter particles, such as deuterium and electrons, come together and create a heavier particle, like a helium nucleus. However, because the particles are very small and the plasma follows a Boltzmann Maxwell distribution curve, only a few ions have enough energy to fuse. The energy is lost due to Bremsstrahlung radiation. If we somehow confined a low temp plasma comprised of deuterium ions and an equal amount of electrons (quasi-neutral and approx 60000K or lower) magnetically, and accelerate tritium ions (like a dense particle beam) and make them bombard the plasma. Could we gain net energy?Adding
  • #1
chandrahas
72
2
Recently, I was thinking about fusion and this thought struck my mind.

  • In tokamaks, the plasma is heated to extremely high temperatures in order to supply enough energy to the ions for them to fuse. But since, the plasma follows a Boltzmann maxwell distribution curve,only a few ions have have enough energy to fuse.
  • But, while this is happening, there also is a lot of energy loss due to Bremsstrahlung radiation.
Now, what I was thinking about is: If we somehow (rather mysteriously) confined a low temp plasma comprised of deuterium ions and an equal amount of electrons (quasi-neutral and approx 60000K or lower) magnetically, and accelerate tritium ions (like a dense particle beam) and make them bombard the plasma. Could we gain net energy?

The reasons I think this would produce a Net gain of energy:

  • Well apparently, since the accelerator beam isn't in thermal equilibrium (wasn't given enough time), almost all collisions would result in fusion.
  • Previously, many people told me that the reason this can't produce net energy is because the coulomb interaction cross-section is much higher than the nuclear cross section, But I suppose that given enough density of the confined plasma, even when the nuclear cross section is smaller than the coulomb cross section to produce more energy than is lost. This is also the case in tokamaks.
  • The low plasma temperature can be helpful in producing high number densities in favor of the above point.
  • Yes, the energy of the alpha particles resulting from fusion heats the gas, but we can find ways to cool the plasma to maintain confinement.
  • I don't think that the cross section of coulomb interactions or Bremsstrahlung radiation would be considerably different from tokamaks, since we are dealing with the same energy levels (This statement is probably wrong, so it would be great if some one can help me on this)
  • Now, compared to tokamks, in which electrons have substantial amounts of energy and extremely small mass and emit a lot more Bremsstrahlung radiation than the particle beam I was talking about or ions in the plasma, radiation losses in our model might actually be smaller.
And for the to compensate for the losses, thee particle beams energy per particle must be slightly higher, for example 30 Kev instead of 25 Kev

With all this in mind, I think that the model we were talking about can produce net energy. So, where am I going wrong in my thinking? Where am I making wrong assumptions?

Any help would be appreciated

EDIT: Forgot to mention that we would actually add an equal amount electrons to the plasma as the number of ions penetrating the plasma to maintain quasi neutrality.

EDIT: I just realized that we could use a helical magnetic field to make the particles spiral. So, the particles would spiral around the field lines and along the field lines. The lower the pitch of the helix, the more the particles interact with the plasma. So this would increase collision cross sections drastically wouldn't it? Are there any disadvantages in doing this?
 
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  • #2
chandrahas said:
Could we gain net energy?
No.
chandrahas said:
Well apparently, since the accelerator beam isn't in thermal equilibrium (wasn't given enough time), almost all collisions would result in fusion.
This is wrong, and I gave you the numbers for that comparison in a previous thread already. Only a tiny fraction of all tritium nuclei would fuse, most would just scatter from deuterium nuclei and electrons. This is independent of the densities of plasma and beam. High plasma density just means the whole process happens in a smaller volume.

Adding a magnetic field wouldn't change anything. You still have particles entering a plasma.
 
  • #3
But why is it so? What does cross section depend upon. I was thinking that the more density you have, the smaller the spaces in between the particles. And hence, the collision would increase compared to Colomb interactions. If the particle didn't go head on into the ion, it would get scattered, and the probability is extremely high compared to the probability of bombarding an ion. But a 30 Kev tritium nucleus has about 5 Kev to lose and still fuse. The only way a particle could lose energyis through Bremsstrahlung radiation. Otherwise, all collisions would result in fusion. So, how would a particle lose more than 5 Kev of energy just through Bremsstrahlung radiation? And if a particle really loses that much energy that fast in a Quasineutral plasma, Then wouldn't the same loss apply to tokamaks? How are they not losing their energy almost instantly? Thermalization occurs almost instantly though, I understand. But if the ions have enough energy to fuse when they get close, would an elastic collision even be possible without fusing? Then how do they even attain thermal equilibrium (the plasma) and how would the particle lose energy apart from Bremsstrahlung radiation? This is what I am extremely confused about. Would elastic collisions even be possible without the ions fusing, and hence, how will the plasma ever attain thermal equilibrium?
 
Last edited:
  • #4
First, your avatar. You're no Einstein. Sorry, but that's what it is.

Second, asking the same question over and over again is not going to work. Mfb answered you before.

Third, spreading things out over multiple threads makes it impossible to help you.
 
  • #5
They were actually supposed to have different themes but on the same topic which I kinda messed up somehow. But the 2 questions turned out to be kind of similar. Sorry. Anyway... you aren't vanadium, are you? Just kidding.

Yeah, I will be posting questions in different threads next time If they have a completely different topics. Got it.
 
  • #6
The Coulomb scattering increases in exactly the same way as fusion (if you consider it as probability per length).

A tritium nucleus scattering with a deuterium nucleus can easily lose more than 50% of its energy with the first scattering process. Scattering with electrons will lead to smaller losses per collision, but the cross section is much larger, so this process is important as well.
chandrahas said:
The only way a particle could lose energyis through Bremsstrahlung radiation. Otherwise, all collisions would result in fusion.
This is wrong, and it gets boring to repeat this over and over again. Elastic scattering will dominate the nucleus-nucleus interactions. Even at the LHC energy of 6.5 TeV per proton elastic scattering is still a common process.
chandrahas said:
Then wouldn't the same loss apply to tokamaks? How are they not losing their energy almost instantly?
If all particles are hot and thermal, elastic scattering is no energy loss, and emitted radiation can be re-absorbed by the plasma.
 

Related to What is wrong with particle acceleration based fusion?

1. What is particle acceleration based fusion?

Particle acceleration based fusion is a method of achieving nuclear fusion by accelerating particles to high energies and colliding them with a target material. This creates extreme temperatures and pressures, which can cause atoms to fuse together and release a large amount of energy.

2. What are the potential benefits of particle acceleration based fusion?

The main benefit of particle acceleration based fusion is the potential for a nearly limitless and clean source of energy. It also produces minimal radioactive waste compared to traditional nuclear power plants.

3. What are the challenges and limitations of particle acceleration based fusion?

One of the main challenges of particle acceleration based fusion is the immense amount of energy and complex technology needed to accelerate particles to high speeds and contain them in a controlled environment. The process also requires a constant and steady source of fuel, which can be difficult to obtain. Additionally, the high temperatures and pressures involved can cause damage to the equipment, making it difficult to sustain fusion reactions for extended periods of time.

4. How does particle acceleration based fusion differ from other forms of fusion?

Particle acceleration based fusion differs from other forms of fusion, such as magnetic confinement fusion, in that it uses particle accelerators to achieve fusion instead of magnetic fields. It also typically involves lighter elements, such as hydrogen, while magnetic confinement fusion often uses heavier elements like deuterium and tritium.

5. What is the current state of research and development in particle acceleration based fusion?

Particle acceleration based fusion is still in the research and development stage, with scientists and engineers working on improving the technology and overcoming the challenges mentioned earlier. Some experiments have shown promising results, but more research and advancements are needed before it can become a viable source of energy.

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