Cosmic ray induced nuclear fusion

[CosmicKitten]

In theory I see no reason why an x ray 'solar' cell is not possible, don't materials with band gaps in the x ray region exist? Aluminum nitride, for example, has a band gap in the deep ultraviolet; I'm sure even greater band gaps exist. And quantum dots can be made any size, could they be small enough to efficiently absorb x-rays?

And wouldn't that be because of all the energy it takes just to keep it confined? ...even in a pot of relatively cool particles, there still exist some that are 'hot' enough to overcome the Coulomb barrier and fuse. Same principle that water evaporates, that is, expels its hotter molecules, emitted at steam velocities despite the water itself being in liquid form, leaving the rest of the water cooler than it was before, you know, skimming off the far end of the bell curve to shift the broad part backwards. Similarly, if one could cook a pot of deuterium to be -just- hot enough to ionize into a plasma state, but not too hot to overcome a reasonable magnetic field, except for the very hottest ones that will simmer off at fusion-ready speeds to fire at a target... um, is such a principle in development or research?

 

[Drakkith]

In theory I see no reason why an x ray 'solar' cell is not possible, don't materials with band gaps in the x ray region exist? Aluminum nitride, for example, has a band gap in the deep ultraviolet; I'm sure even greater band gaps exist. And quantum dots can be made any size, could they be small enough to efficiently absorb x-rays?

The minimum energy for x-rays is about 100 eV's. I don't know of any materials with a bandgap near that. Aluminum nitride has a bandgap of 6.2 eV.

And wouldn't that be because of all the energy it takes just to keep it confined? ...even in a pot of relatively cool particles, there still exist some that are 'hot' enough to overcome the Coulomb barrier and fuse. Same principle that water evaporates, that is, expels its hotter molecules, emitted at steam velocities despite the water itself being in liquid form, leaving the rest of the water cooler than it was before, you know, skimming off the far end of the bell curve to shift the broad part backwards. Similarly, if one could cook a pot of deuterium to be -just- hot enough to ionize into a plasma state, but not too hot to overcome a reasonable magnetic field, except for the very hottest ones that will simmer off at fusion-ready speeds to fire at a target... um, is such a principle in development or research?

No, as the reaction rate is practically zero at that temperature. Reaction rate is a function of temperature and density. To increase the reaction rate you must increase one or both of those parameters, and either way it takes energy to do so. And before you ask, even if we compress the plasma to a very dense state the temperature is still far too low to generate any appreciable reaction rate. You're talking about a few thousand kelvin, whereas we need the plasma at millions to hundreds of millions of kelvin. For comparison, the D-T reaction rate peaks around 800 million k. See below.

We are trying to hit the "sweet spot", where the temperature and density are high enough to generate more fusion power than we use to confine and heat it. We have yet to succeed for a large number of very complicated reasons.

 

[mfb]

And quantum dots can be made any size, could they be small enough to efficiently absorb x-rays?

They are made out of atoms, so the minimal size is the size of an atom - way too large for x-rays. For the same reason, the band gaps cannot reach the x-ray range.

...even in a pot of relatively cool particles, there still exist some that are 'hot' enough to overcome the Coulomb barrier and fuse.

Define "relatively". There are atoms with 10-20 times the average energy, no problem. A few atoms will even have up to 50 times the average energy. But fusion needs more than 1 million times the average energy of room temperature. That won't happen within the lifetime of the sun, not even for a single atom, even if your room temperature storage is the whole earth/moon system.
Even the fusion experiments, with ~100 million K, are below the Coulomb threshold and rely on particles with a high-than-average kinetic energy together with tunneling processes.

 

[fusion2022]

Cross section of any element is too little in the cosmic ray energy region
UV and X rays work better