X-Ray Reflection and Absorption

Discuss the technical details of an "open source" community-driven design of a polywell reactor.

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X-Ray Reflection and Absorption

Postby topher » Mon Feb 13, 2017 2:22 am

Hi everyone - this is my first post. Been excited about the polywell for years, finally decided I should start trying to contribute to the discussion instead of just waiting for it to happen. I was thinking about x-ray losses and looking for information about reflecting the x-rays back into the plasma, but haven't been able to find much (in general or regarding the polywell specifically). My idea is to coat the interior of the vacuum chamber with iridium, which is effective at reflecting x-rays as well as resistant to high temperatures and corrosion/oxidation. I know that there are conditions required for re-absorption of the x-rays (like the plasma being sufficiently dense) but overall this approach seems simple and straightforward. So, what I'm asking is if this won't work, why not? In general terms, what factors am I missing? And if anyone knows of some good sources/material covering absorption of x-rays by plasma that I can read, I'd love the direction. Thanks for reading!

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Re: X-Ray Reflection and Absorption

Postby paperburn1 » Wed Feb 15, 2017 2:49 am

Not my field of expertise but X-rays can only be reflected off smooth metallic surfaces at very shallow angles---grazing incidence. Such reflections are particularly efficient for metals with high density, such as gold, platinum or iridium. but mots x-rays would likely be at higher angles of incidence and therefore just be absorbed IMHO.
I am not a nuclear physicist, but play one on the internet.

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Re: X-Ray Reflection and Absorption

Postby topher » Wed Feb 15, 2017 6:35 am

Thank you, I knew I must have been missing something obvious. You're right, I found that the critical angle is less than generally less than 1 degree, even going from a vacuum to something dense like iridium. Yikes. I had assumed that a smooth, nearly spherical chamber would reflect the x-rays back toward the center, but I see that won't work, as the x-rays would be emanating from the center and perpendicular to the surface (and even those that were reflected would still not make it back to the core.)

Another possibility is to absorb the x-rays and convert it their energy into electricity... from what I can find this is less than 2% efficient, though:

http://www.tandfonline.com/doi/pdf/10.1 ... 11.9711683

But if that could be improved, then at least some of the energy lost to x-rays could be harnessed and cycled back to improve efficiency.

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Re: X-Ray Reflection and Absorption

Postby quixote » Fri Feb 17, 2017 8:48 pm

You might be interested in this old thread.

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Re: X-Ray Reflection and Absorption

Postby ohiovr » Mon Mar 06, 2017 3:30 pm

It is a toughie, I thought of the same thing just recently. Even if you could bend the Xrays back in on itself, you would probably lose too much energy from losses at the reflectors. To make matters worse, the X-rays would probably pass right through the ignited gas or plasma.

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