Reply To: General thought on old coal mines.

[zapkitty]

vansig wrote: Air has a strong absorption line near 1.3THz (230 µm). The idea is to superheat the air with a narrow-band, coherent beam that reflects off container surfaces.

I doubt heating air with x-ray can be done. x-rays are hard to focus,
though we’d want to carry away waste heat by convection, or radiation if possible.

X-rays can, however, efficiently heat some materials. My vague idea was that you’d place such a material around the FF core assembly to catch the x-rays and then while the air is entrained in your various manipulations you’d pass it around the heated FF containment.

… and weren’t relativistic electron beams the first option of Lerner-hakase for heating air and propellant since they are best driven by the extremely high voltages that FFs are expected to produce?

Starting with that premise my other idea was to just skip the conversion step and use the alphas directly.

As for ensuring the efficient transfer of beam energy to air… the people working on microwave electrothermal thrusters have already solved this by using focused energy to create a small spot of plasma in the propellant flow. The plasma is pretty much guaranteed to be opaque to infrared, electrons, alpha particles, microwaves and suchlike that you might want to throw at the propellant as long as you maintain the hotspot.
(you wouldn’t try to use this with the x-rays because as you noted the spherical x-ray flux couldn’t be easily focused)

So I’ve no objections per se to an FF-powered jet aircraft… it’s just that the energy density and conversion problems immediately bring up the question of how you would like to do this 🙂