The discussion revolves around the concept of runaway electrons in magnetic fusion, exploring the potential benefits and costs of engineering devices that create beams of relativistic electrons. Participants consider energy extraction methods from such systems and the implications of electron speed on these processes.
Participants express a range of views on the feasibility and implications of using runaway electrons and relativistic electron beams for energy generation. No consensus is reached on the best methods or the practicality of these approaches.
Participants highlight various assumptions regarding energy conversion efficiency and the relationship between electron heating and plasma dynamics, which remain unresolved. The discussion also reflects differing perspectives on the relevance of runaway electrons to practical applications.
Was reading about runaway electrons in magnetic fusion. Had me thinking what would be the benefit/cost of engineering a device which creates a beam of relativistic electrons. What would be the best way to extract energy from this system and does it even matter the speed they are traveling?
For fusion, one wants to minimize the heat/energy of the plasma, in order to avoid unnecessary radiative losses. Plasma temperatures would be on the order of 10 to 50 keV, or perhaps up to 100 to 200 keV, depending on the species.
Fusion requires nuclei of a minimum energy in order to induce fusion, so heating of nuclei is critical. However, in a neutral plasma one cannot heat nuclei without heating electrons. Also, it is easier to impart energy to electrons, and heating electrons can heat the nuclei, but that is less desirable. Pushing electrons up to relativistic energies would unnecessary.
A fusion reactor requires an optimal balance of plasma heating to maximize reaction rate while minimizing radiative and leakage losses.
the_wolfman said:Currently there is a lot of research into plasma accelerators. Experiments using plasma accelerators have been able to create GeV electron beams over a distance of a few centimeters, where traditional rf accelerators do so over distances of tens of meters. Most of the research is into the plasma wakefield accelerator. To my knowledge, its operation is based on a principle unrelated to the runaway effect.
While true, I'm not sure what this has to do with runaway electrons? During disruptions conditions can occur where the plasma accelerates the high energy tail of the electron distribution to relativistic energies. These beams are a concern because they can cause serious damage the first wall. I think the OP's post was asking if we could design an accelerator that uses this effect for applications unrelated to fusion.
The most powerful pulse electron accelerators are the so-called induction linacs. Good example is "Advanced Test Accelerator" (ATA) http://accelconf.web.cern.ch/Accelconf/p83/PDF/PAC1983_2970.PDF producing 10 kA current of 50 MeV electrons (the rest mass of electron is about 511 keV and so 50 MeV is rather high relativistic).the_wolfman said:Experiments using plasma accelerators have been able to create GeV electron beams over a distance of a few centimeters, where traditional rf accelerators do so over distances of tens of meters.
Joseph Chikva said:The most powerful pulse electron accelerators are the so-called induction linacs. Good example is "Advanced Test Accelerator" (ATA) http://accelconf.web.cern.ch/Accelconf/p83/PDF/PAC1983_2970.PDF producing 10 kA current of 50 MeV electrons (the rest mass of electron is about 511 keV and so 50 MeV is rather high relativistic).
But usage of electron beam for heating plasma (background plasma) is less useful. As this is typical condition for development of Electron-electron two-stream instability.
But in frame of HIF (heavy ions fusion) program people are going to use induction linacs for acceleration of Cesium ions (current about 40-50 kA) which then have to be focused by propagation through plasma column and then to hit the target (hohlraum).
The inventor of induction linacs is Nick Christafilos http://www.hep.princeton.edu/~mcdonald/accel/christofilos.pdf
For acceleration of electrons you should spend energy: some form of energy converts into kinetic energy of electrons.Kidphysics said:Although this is very interesting, my question is as follows: How does one go from high energy, relativistic electrons and use them for power generation? Edit* also which of the Heavy ion fusion experiments look best to you?
Joseph Chikva said:Heavy Ions Fusion is a mature approach with rather strong theoretical team being sponsored by DOE but its development will be even more expensive than TOKAMAK program.
the_wolfman said:Currently there is a lot of research into plasma accelerators. Experiments using plasma accelerators have been able to create GeV electron beams over a distance of a few centimeters, where traditional rf accelerators do so over distances of tens of meters. Most of the research is into the plasma wakefield accelerator. To my knowledge, its operation is based on a principle unrelated to the runaway effect.
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Acceleration consumes energy, while deceleration by idea should produce energy.Kidphysics said:how would I at least try to extract electricity out of a beam of electrons is there any way?
Neutralized Drift Compression eXperiment (NDCX-II) is only the small part of very extensive Heavy Ions Fusion (HIF) program.Kidphysics said:The NDCX-II was built from the linac you showed me, they have acquired parts from all over. There is not much information coming out on the experiment but so far I think its complete.