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I would describe this thread as being more about science fiction than actual science or engineering, because I am describing a technology that is probably theoretically possible but which is unlikely to exist any time soon.
Here's the idea: Plasma Optics.
Here's the theory:
Regular matter is opaque to regular light because of the energy difference between the electron energy levels in normal matter. These correspond generally to the energy levels of visible light, which can thus easily interact with the electron clouds that surround atoms and molecules. In principle, you could also create this kind of interaction in a plasma by creating electrical potentials, which will cause the plasma to interact with incident light. If we get really good at working with plasmas and electromagnetic fields (and the interaction I have described is actually possible) this creates a lot of potential technological applications.
I think of this as being a sort of "Tier 3" M2P2 (mini-magnetospheric plasma propulsion) system. Tier 1 is the system that was worked on and tested at NASA that uses plasma to inflate a magnetic field to use as a magnetic sail. Phase 2 is a hypothetical version with a translucent plasma that acts as a light sail, and this is Phase 3.
Anyway, here's some applications I can think of:
Reflecting sunlight into a solar thermal engine for thrust: Potentially high Isp (1000 s or more than that with advanced engines) and high thrust and T/W
Solar Sailing: Nothing has a lower mass than plasma so you can get high thrust compared to physical lightsails
Plasma Photovoltaics: At least in principle it should be possible to convert electrons moving up a potential well into electrical energy. Given the relative ease of building big structures from plasma as compared to matter you might be able to generate truly massive amounts of energy in this way
What I wonder is as follows: Is it possible? How would it be done? What else could plasma optics be useful for?
-Josh
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Josh,
You mean like this?:
Abstract:
We describe the first demonstration of plasma mirrors made using freely suspended, ultra-thin films formed dynamically and in-situ. We also present novel particle-in-cell simulations that for the first time incorporate multiphoton ionization and dielectric models that are necessary for describing plasma mirrors. Dielectric plasma mirrors are a crucial component for high intensity laser applications such as ion acceleration and solid target high harmonic generation because they greatly improve pulse contrast. We use the liquid crystal 8CB and introduce an innovative dynamic film formation device that can tune the film thickness so that it acts as its own antireflection coating. Films can be formed at a prolonged, high repetition rate without the need for subsequent realignment. High intensity reflectance above 75% and low-field reflectance below 0.2% are demonstrated, as well as initial ion acceleration experimental results that demonstrate increased ion energy and yield on shots cleaned with these plasma mirrors.
Brief Reflections from a Plasma Mirror
From the article:
It’s a reflective surface at the boundary of feasibility. A dense sheet of electrons is accelerated to almost the speed of light as a reflective surface. With the aid of this plasma mirror of fast electrons, physicists can modify the beam of light. An international team of physicists from the Max Planck Institute of Quantum Optics, LMU Munich and Umeå University in Sweden have used this phenomenon to generate isolated, high-intensity attosecond pulses. An attosecond lasts for a billionth of a billionth of a second.
A description of an experimental plasma mirror setup:
A plasma mirror optimization experiment:
Optimization of plasma mirror reflectivity and optical quality using double laser pulses
Abstract:
We measure a record 96 ±2.5% specularly reflected energy fraction from an interaction with a plasma mirror (PM) surface preionized by a controlled prepulse and find that the optical quality is dependent on the inter pulse time delay. Simulations show that the main pulse reflected energy is a strong function of plasma density scale length, which increases with the time delay and reaches a peak reflectivity for a scale length of 0.3 μm, which is achieved here for a pulse separation time of 3 ps. It is found that the incident laser quasi near field intensity distribution leads to nonuniformities in this plasma expansion and consequent critical surface position distribution. The PM optical quality is found to be governed by the resultant perturbations in the critical surface position, which become larger with inter pulse time delay.
Self-aligning concave relativistic plasma mirror with adjustable focus
Possible?: Clearly. Nobody thought it was possible to deflect gamma rays, either, but it turns out that mainstream science / accepted wisdom was wrong.
Practical in an open vacuum chamber?: Possibly, but it seems like every aspect of the experimental setup affects how useful it would be for generating massive amounts of focused power from solar radiation.
How would it be done?: As described above, most likely
What else could plasma optics be useful for?: It might be used for what originally interested our military enough to investigate it- stealth. Beyond that, I can see an application for deflection of relativistic ions, but that only starts happening at extreme laser pulse intensities.
It's definitely an interesting concept.
Oh, and by the way, Happy New Year.
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Josh,
I'm not sure if we could even come close to producing enough power to do this, but maybe we could fire pulses at the ions trapped in our radiation belts to reflect some of the incoming sunlight back out into space. If we're not about to mess with our shields, and I'm sure that there are plenty of good reasons not to do that, then maybe we could try the same experiment at L1 using plasma generated by a power station located there.
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Hey kbd512,
Happy New Year!
Glad to see I was on the track of something real and potentially useful.
Using one of these guys as a temporary fix for climate change seems like a definite possibility. From there I would say there are obvious applications also to Mars and Venus for their respective terraforming projects, and at that point possibly any outer-system body looking to heat itself up (in combination with other terraforming methods like greenhouse gases).
Looking even further into the future, plasma mirrors would definitely be useful for interstellar lightsail missions. By locating one close-in to the Sun you might direct concentrated light at a far-away lightsail hosting a similar plasma mirror array. You might achieve a multiplier of the intensity by bouncing the light back and forth between the craft and the concentrator array.
Plasma mirror telescopes? It's hard to imagine that this technology could achieve the necessary precision to get good imaging, but it's not impossible, and if planet-sized plasma mirrors are already in use I have to think astronomers will do anything to get that much signal. At that point (and this is unfounded speculation) I have to think you'd be able to look at extrasolar planets light-years away in substantial detail. As a point of comparison, James Webb Space Telescope is supposed to have a mirror 6.5m across; The one I'm talking about is literally a million times bigger, and thus would have a million million times more area/signal.
Where this ends, I suppose, is with a dyson sphere, which becomes at least conceivable when you do not need to build it from solid matter.
-Josh
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