u/the_syner

I've been thinking about lasers and the limits imposed by the focusing optics. I love the idea of a lens or mirror that doesn't need normal matter optics with their pesky chemical decomposition and melting/boiling points.

Metric lenses made of WIMP dark matter. Artificial gravitational lenses built from massive actively-supported matter storage structures AUs across. If we could use diffuse plasmas for this somehow that would also be pretty cool.

The goal is laser optics that can achieve the maximum theoretical beam intensities(before pair production or self-gravitation causes unavoidable divergence) without being destroyed and to a lesser extent to create lighter gargantuan optical apertures for intergalactic or even intercluster ranges. Granted it's not like i expect to ever need(or be able to practically build) lasers that can deliver 250,000 solar luminosities per square meter at a billion light years, but it would still be nice to know what the upper constraints were. I'm generally of the opinion that we can make light scalable monochromatic mirrors that can handle 1GW/m^2 but beyond that I don't know what the limits are, only that it's almost certainly not exceeding a few TW/m^2 with normal optical materials and only under the most extreme conditions even that. I want more.

Occurs to me that I haven't seen much anywhere about an insanely powerful, arguably the single most powerful, heat management technology out there. Based on the same technology as active-support(launch loops, orbital rings, space towers, etc) and capable of moving immense amounts of wasteheat through extremely small areas. Originally i just wanted to see how far I could push a matrioshka shellworld without having to worry about spacing shells out or limiting lighting levels too much, but this probably has a lot of other applications. Just useful for when you have a hell of a lot of matter and energy to plat with and a conpact machine that you want to run entirely too much power through. The mass and logistical overhead aint nothin to sneaze at even if you have crazy-efficient active-support tech available.

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Effectively it's just a way to move coolant over long distances as fast as possible, using as little energy as possible, and creating as little wasteheat as possible. If anyone is familiar with the game Satisfactory it's like packaging fluids to move them via conveyers(i hate fluids in satisfactory, but hey what do i know i haven't gotten to play in ages and maybe they've made them less annoying in the meantime). Anywho felt like going through an example to demonstrate the kind of nonsense this lets you get up to.

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Cylindrical Heat sinks 1m × 4m with 1m separation-

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Ethanol Specific Heat: 2.438 kJ/(kg K)

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Energy over range(-70°C-75°C): 353.51 kJ/kg.

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Density: 789 kg/m^3

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volume: 3.14159 m^3.

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Sink mass: 2478.71451 kg

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Total energy over range: 876.25 MJ/sink

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Rotor energy per meter: 175.25 MJ/m

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base area: 0.785398 m^2.

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If we assume that containment is half a meter thick(2m total diameter) heat pipe unit area is: 3.14159 m^2

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Energy flow: 55.7838546723 MW/m^2 for every meter/second of rotor speed. That's just about the areal luminosity of the sun per meter/second of rotor speed.

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Now the actual maximum numbers will end up less than this once we account for linear motor inefficiencies(hopefully incredibly small with the use of superconductors) & drymass of the heat sinks with their assciated radiators/RCS. There are also limits imposed by the amount of total heatsink mass spread across the huge eliptical orbit needed for these things to cool down to the target temperature. There's a compromise between drymass of radiators/tankage, time-to-target-temp, and total system mass for a given thernal throughput. Using water massively increases throughput tho accounting for the phase changes of water probably adds to heatsink complexity. But still it's an incredibly powerful way to move wasteheat around. Perfect for running incredibly powerful weapons, high-end compact computronium, or maximizing the numver of layers and per-layer energy expenditure. The more efficient your active-support tech the higher the throughput of the vactrain heatpipes.

To put all this in perspective if you had these vactrain heat pipes that were 99.5% efficient we are talking about 230.5 GW/m^2 assuming system wasteheat makes up half the wasteheat put out. If you had an earth-size megastructure with 25% of it's surface atea devoted to these vactrain heatpipes would allow running some 7.7% of the sun's luminosity through this artificial planet.