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A previous question asked about the feasibility of reflective flakes of metal suspended in the plasma to absorb heat from the plasma and radiate it for cooling the craft: Plasma-shell and suspended flakes for cooling... As this initial question seems to be at least feasible, i.e. not violating any laws of physics, this follow up question asks about re-suing the configuration to drive a laser...

Is it possible to use the energy from a plasma-envelop to power a laser...

Background: SciFi book set 50-100 years into the future.

Spacecraft are able to control, with a high degree of precision, plasma envelopes surrounding them. This is used in-atmosphere for magnetohydrodynamic propulsion. In space, the plasma-envelope is used for stealth by absorbing/reflecting radiation from radar etc

radiator flakes suspended in plasma radiator flakes suspended in plasma

My Question: In a hot plasma, assuming the flakes could be oriented to form a 'laser cavity', would it be feasible for the ship to use the energy stored in the plasma to drive a Laser? The laser cavity would be external to the hull, similar to a the concept of a 'stellaser' see here and this answer on quora which uses the atmosphere of a star to drive a very powerful laser to push sail-craft between stars.

laser 'cavity' in the plasma envelope

laser 'cavity' in the plasma envelope

The laser would 'drain' the energy from the plasma for cooling, but also the beam could be used for offensive, defensive, and point defence purposes.

Edit: I am still hoping for more answers to the question if anybody has some thoughts.

Some additional detail:

  • What would be the main technological issues to be addressed with this configuration? e.g.
  • is super high 99.999% reflectivity of the flakes pre-requisite?
  • could non-linear magnetic/electric effects feasibly be harnessed to position the flakes assuming arrays of superconducting coils in the hull and pseudo crystal behaviour of the flakes?

Note: the 'intellects' of these ships are very smart so they could be constantly tweaking the plasma like a stellerator.

Many thanks in advance! I am happy to share more info!

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    $\begingroup$ This looks surprisingly similar to your previous question. Can you edit this post to clearly differentiate it so that it doesn't get closed as a duplicate. $\endgroup$
    – sphennings
    Dec 16, 2020 at 21:39
  • $\begingroup$ @sphennings, I have edited to make clear this is a separate follow on question. I had originally posted both questions in one but mods asked me to split them... $\endgroup$
    – Toby Weston
    Dec 16, 2020 at 22:31
  • $\begingroup$ @sphennings this would be the "part 2" of the OP's original question, that got split into two questions in response to Mod input. $\endgroup$
    – PcMan
    Dec 16, 2020 at 22:34

2 Answers 2

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Nope.

Assuming the flakes behave as planned, and you can align them with the ludicrous accuracy needed to form a laser resonant cavity...

It would still not work.

Your flakes are per design circulating around your ship in a plasma stream. They would have variable speed, depending on radial distance from the magnetic source of the plasma guide.

A laser cavity with walls moving at varying speeds, is a laser cavity with frequency drifting all over the place.

Besides, to use them to form a laser, you would need to get the reflectivity of the mirror side up to 99.(many)9% ... If your mirror side absorbs 1 part in 10000 of the light bouncing off it, that is enough to ruin your effect and cause your flakes to burn up.

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  • $\begingroup$ Thanks for the feedback. The issues you describe don't seem to violate any laws of physics, so I will put them down to technology. As I am 100 years in the future, I will assume some highly reflective surface. I will hold the flakes in place, relative to each other, with electric and magnetic fields. @PcMan I was thinking of layering the 'plasma shells' by creating complex shapes with magnetic fields and also internal interactions: e.g: journals.aps.org/prl/abstract/10.1103/PhysRevLett.106.215004 $\endgroup$
    – Toby Weston
    Dec 18, 2020 at 9:23
  • $\begingroup$ @TobyWeston You can handwave as needed for storytelling purposes, the world and content belong to you, not to the laws of physics. The idea of showing you the difficulties is so that you know what needs to be doubletalked away, vs. what can be accepted as 'normal and obvious'. $\endgroup$
    – PcMan
    Dec 18, 2020 at 10:46
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Nope, your bubble can't spin!

There's failure in physics lies in step one: the plasma bubble.

To create a bubble, you need to have an inside force and an outside force acting against each other. Think a soap bubble: The air inside wants to expand it, the air outside wants to compress it.

Now, for Plasma, we replace air with Electromagnetic fields, which are generated by charged items. Plasma is basically a shape of charged particles floating separately from another, so they are either positively charged or negatively charged.

When you get a positive charge close enough to it, the plasma starts to separate: the negative particles close in on the charge, the positive ones get repulsed. But how can we contain plasma if not with one static charge? Could we use two charges, a positive and a negative one? No, because if the fields of two sources overlay, we get an effective field of their sum. For a charge that is -1 and one that is +1 next to it, the effective field is 0. So we can't just use a "+ attractive" field and a "+ repulsive" field with the ship as origin, we need a field that effectively oscillates between positive and negative at a really fast rate to try and move the plasma particles in what would be an inner and an outer diameter. Let's call this huge thing the Field Generator. Well, at least we got a bubble with a field-generator inside now... but here comes the next problem:

Our particles now get a radial movement induced by the operation of the field generator, and at the same time, they all shall have circular movement. The result is, that each and every particle will end on complex movement paths around the ship. There will be spots where particle density will be much lower and spots where it will be much higher as particles collide. We can't allow our field to spin, we only can allow it to oscillate or we will get a patchy field.

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  • $\begingroup$ Thanks for the answer. What is the actual show-stopper here? A fast computer will be able to perform dynamic real-time adjustment of the magnetic fields to control the 'patchiness'. This is how I understand a stellarator(en.wikipedia.org/wiki/Stellarator) fusion reactor should work. A secondary magneto-hydro-dynamic 'pump' can circulate plasma through the engine. This should take care of 'moving heat around'. What am I missing? FYI: plasma-bubble used as a solar sail: colorado.edu/faculty/kantha/sites/default/files/attached-files/… $\endgroup$
    – Toby Weston
    Dec 21, 2020 at 13:28

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