B Breit Wheeler Matter Production

[dansmith170]

TL;DR Summary

Mass producing electrons

Are there any limitations on producing a significant number of electron-positron pairs (say, 10E24 electrons) in one second using the Breit-Wheeler Process or Nonlinear Breit-Wheeler Process? What variables affect this outcome? I suspect it mostly comes down to the pulse repetition rate and intensity of the laser one is using. Is 10E24 electrons feasible? Is it possible in theory if not in current practice?

 

[hutchphd]

You should calculate the frequency (energy) of the photons required. Then you should calculate the flux of photons required. Then you should try to figure how to meet either requirement, then both requirements.
Probobly not easy to do by many many orders of magnitude..

 

[Astronuc]

Summary:: Mass producing electrons

say, 10E24 electrons

That is a substantial amount of electrons. Consider Avogadro's number.

 

[Astronuc]

Summary:: Mass producing electrons

10E24 electrons)

Charge on one electron is -1.602177 x 10^-19 C, so 5 E24 would provide -801.9 kC of charge, which is a lot of charge, and there is an equivalent magnitude of charge of positrons +801.9 kC. One might look into how one stores electrons in that quantity. Would could also calculate the force required to separate the charges as a function of distance. Positrons have to be stored in a magnetic field, since in contact with normal matter, they annihilate with electrons.

One should also look into the Breit-Wheeler process and the energy required to produce an electron positron pair with enough kinetic energy to separate far enough to avoid mutual attraction and annihilation. I suspect the process requires a lot more energy to produce two gammas of the required energy.
https://en.wikipedia.org/wiki/Breit–Wheeler_process#Experimental_observations
https://en.wikipedia.org/wiki/Two-photon_physics
https://physics.princeton.edu//~mcdonald/e144/e144trans_052897.pdf

Breit-Wheeler Process in Intense Short Laser Pulses
https://arxiv.org/abs/1209.2394

Normally, one would use gamma rays on a dense material (usually high Z) to induce pair production with an interaction of the gamma rays on nuclei, and then deflect positrons from electrons into a storage device.

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

What would be the purpose of generation such quantity of positrons?

 

[dansmith170]

Charge on one electron is -1.602177 x 10^-19 C, so 5 E24 would provide -801.9 kC of charge, which is a lot of charge, and there is an equivalent magnitude of charge of positrons +801.9 kC. One might look into how one stores electrons in that quantity. Would could also calculate the force required to separate the charges as a function of distance. Positrons have to be stored in a magnetic field, since in contact with normal matter, they annihilate with electrons.

One should also look into the Breit-Wheeler process and the energy required to produce an electron positron pair with enough kinetic energy to separate far enough to avoid mutual attraction and annihilation. I suspect the process requires a lot more energy to produce two gammas of the required energy.
https://en.wikipedia.org/wiki/Breit–Wheeler_process#Experimental_observations
https://en.wikipedia.org/wiki/Two-photon_physics
https://physics.princeton.edu//~mcdonald/e144/e144trans_052897.pdf

Breit-Wheeler Process in Intense Short Laser Pulses
https://arxiv.org/abs/1209.2394

Normally, one would use gamma rays on a dense material (usually high Z) to induce pair production with an interaction of the gamma rays on nuclei, and then deflect positrons from electrons into a storage device.

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

What would be the purpose of generation such quantity of positrons?

Astronuc, thanks for the links and info! I didn't want to use normal pair production because I'm trying to produce the matter without using-up some supply of "fuel." That is why I prefer the multiphoton production. The generation of positrons is not exactly what I'm interested in, it's the production of positrons and electrons that would then be used as propellant aboard a "propellantless" spaceship. See link below

https://www.physicsforums.com/threads/propellantless-rocket.1010721/

 

[Astronuc]

Astronuc, thanks for the links and info! I didn't want to use normal pair production because I'm trying to produce the matter without using-up some supply of "fuel." That is why I prefer the multiphoton production. The generation of positrons is not exactly what I'm interested in, it's the production of positrons and electrons that would then be used as propellant aboard a "propellantless" spaceship. See link below

One has to consider the energy necessary to produce the appropriate photons. One doesn't just generate electron-positron pairs out of thin air, or vacuum, as the case may be.

High energy photons (usually gammas) are generated by bremsstrahlung mechanism, which requires acceleration of electrons, which requires some electrical energy. If one requires production of energy to produce electron-positron pairs as propellant, then skip the pair production and simply accelerate whatever matter (propellant) one has.

There is no such thing as "propellantless" spacecraft , except for ballistic craft, which are accelerated then coast. To avoid decaying into a nearby mass, such a craft needs to achieve escape velocity. If one wishes the craft to speed up or slow down, then one needs propellant.

 

[dansmith170]

One has to consider the energy necessary to produce the appropriate photons. One doesn't just generate electron-positron pairs out of thin air, or vacuum, as the case may be.

High energy photons (usually gammas) are generated by bremsstrahlung mechanism, which requires acceleration of electrons, which requires some electrical energy. If one requires production of energy to produce electron-positron pairs as propellant, then skip the pair production and simply accelerate whatever matter (propellant) on has.

There is no such thing as "propellantless" spacecraft , except for ballistic craft, which are accelerated then coast. To avoid decaying into a nearby mass, such a craft needs to achieve escape velocity. If one wishes the craft to speed up or slow down, then one needs propellant.

I see, I guess I was thinking that the energy for accelerating the electrons and any other energy needed for pair production could be sourced externally as from an external laser aimed at the rocket (perhaps an array of lasers in the solar system). Although I suppose this would still be less efficient than just using light to propel the craft.