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Post by Kerr on Jan 13, 2018 9:03:51 GMT
Increasing the length increases the top speed of your electron beam, which increases the energy of each electron, which means they'll emit a higher energy photon, which have a shorter wavelength. Increasing beam power is done simply by accelerating a larger number of electrons (meaning more photons) or accelerating electrons to a higher velocity (which increases the energy per photon). So there will be a specific length at which a FEL produces an x-ray laser, and to make the beam more powerful it needs to draw more power to push more electrons? Would that result in the accelerator/wiggler/whatever the long bit is being noticeably thicker if you're increasing the power significantly? There's so little information on free electron lasers that I've been able to find... The electrons just are faster, you have a certain acceleration per meter. Thickness wouldn't increase by any apparent amount. A 2.5m long 200nm 25 ton FEL that produces 250MW (Optimistic benchmark). A 500m long 1nm 500t FEL produces 5GW, it scales linearly with length.
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Post by lucubratory on Jan 13, 2018 11:43:23 GMT
I thought about doing free electron lasers, specifically trying for x-ray free electron lasers, but I'm limited by how little I know. I thought the length increased the energy which increases the wavelength, but assumed you wouldn't be able to increase the length if you were trying to stay within a specific wavelength (like x-rays so you can focus them with x-ray diffraction crystals). Can you increase the energy of the beam without pushing the wavelength past what can be focused, and would doing that increase the length? This ship and the setting was going to have free electron lasers anyway, so it'll be a realism concern if I've chosen to add a coilgun spitting Casaba howitzers when x-ray free electron lasers would have served better. The science of FEL's can be made rather easy if you just accept the ground concept, which is usually enough to understand it. Length equals to electron acceleration, so a longer FEL would be able to produce shorter wavelength. A 500m long FEL could produce 1.24 KeV electron with are more or less equal to 1nm hard x-rays. The limit of crystal diffraction is 30KeV, or 0.4 angström (0.04nm). So a few kilometers of FEL could be worthwhile, but the advantages diminish. As you get dozens light seconds of range from lenses a single meter in radius. Thank you, that does help. Part of it is that I will need to storyboard more and figure out what exactly will be happening to this ship that it needs to defend itself from, but the general idea at the moment is that it's going to be a very large ship, with a very high population housed in separate rotating cylinders, and fusion torch engines will not provide much acceleration and won't be available until later in the story. So to survive in a context where this ship is very large, full of people, and not able to dodge particularly fast, it has to have a very long and destructive standoff range. Does that sound like the sort of thing spinal mounted free electron lasers could enable? I had figured that a very long coilgun shooting Casaba howitzers would be the most destructive and longest range option, but light-second lasers sounds pretty good.
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Post by Kerr on Jan 13, 2018 17:00:46 GMT
The science of FEL's can be made rather easy if you just accept the ground concept, which is usually enough to understand it. Length equals to electron acceleration, so a longer FEL would be able to produce shorter wavelength. A 500m long FEL could produce 1.24 KeV electron with are more or less equal to 1nm hard x-rays. The limit of crystal diffraction is 30KeV, or 0.4 angström (0.04nm). So a few kilometers of FEL could be worthwhile, but the advantages diminish. As you get dozens light seconds of range from lenses a single meter in radius. Thank you, that does help. Part of it is that I will need to storyboard more and figure out what exactly will be happening to this ship that it needs to defend itself from, but the general idea at the moment is that it's going to be a very large ship, with a very high population housed in separate rotating cylinders, and fusion torch engines will not provide much acceleration and won't be available until later in the story. So to survive in a context where this ship is very large, full of people, and not able to dodge particularly fast, it has to have a very long and destructive standoff range. Does that sound like the sort of thing spinal mounted free electron lasers could enable? I had figured that a very long coilgun shooting Casaba howitzers would be the most destructive and longest range option, but light-second lasers sounds pretty good. Yes, they can. Even better than you think, let's assume a 10m diameter lens, it masses 25t and creates a spot size 2.196m in radius at 1.8e10 m, or a entire light minute! So your stand-off distance is only determined by how large you want to make your x-ray crystal diffraction lens and your supercomputers running algorithms to determine target position.
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Post by lucubratory on Jan 13, 2018 21:39:52 GMT
Thank you, that does help. Part of it is that I will need to storyboard more and figure out what exactly will be happening to this ship that it needs to defend itself from, but the general idea at the moment is that it's going to be a very large ship, with a very high population housed in separate rotating cylinders, and fusion torch engines will not provide much acceleration and won't be available until later in the story. So to survive in a context where this ship is very large, full of people, and not able to dodge particularly fast, it has to have a very long and destructive standoff range. Does that sound like the sort of thing spinal mounted free electron lasers could enable? I had figured that a very long coilgun shooting Casaba howitzers would be the most destructive and longest range option, but light-second lasers sounds pretty good. Yes, they can. Even better than you think, let's assume a 10m diameter lens, it masses 25t and creates a spot size 2.196m in radius at 1.8e10 m, or a entire light minute! So your stand-off distance is only determined by how large you want to make your x-ray crystal diffraction lens and your supercomputers running algorithms to determine target position. That sounds like the right option to pursue, then. I've got to get it all working in theory, then on paper, then fit them into the story appropriately. I really appreciate the help working things through.
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Post by Kerr on Jan 13, 2018 21:41:02 GMT
Yes, they can. Even better than you think, let's assume a 10m diameter lens, it masses 25t and creates a spot size 2.196m in radius at 1.8e10 m, or a entire light minute! So your stand-off distance is only determined by how large you want to make your x-ray crystal diffraction lens and your supercomputers running algorithms to determine target position. That sounds like the right option to pursue, then. I've got to get it all working in theory, then on paper, then fit them into the story appropriately. I really appreciate the help working things through. Sure, what has to be done?
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Post by lucubratory on Jan 15, 2018 6:03:15 GMT
That sounds like the right option to pursue, then. I've got to get it all working in theory, then on paper, then fit them into the story appropriately. I really appreciate the help working things through. Sure, what has to be done? Well so far I've got a storyboard on paper and some inspiration in existing writers (Ursula K Le Guin and Iain M Banks) and a good idea of the sort of story I want to read. I've also got no hope of ever being a commercially successful writer for several reasons and mostly just want to write for myself and my family to enjoy I'm committed to it being hard science fiction because that's the sort of science fiction I like to read, but the work I want to write is a lot more political/sociological than specifically military so it probably won't feature exposition on specific technologies, I just want them to work and be consistent for in my head, or maybe in an appendix. Also I find it's easier to write a story that's internally consistent if you just use a very well-established set of rules, specifically the ones we live in. I need to get a few chapters down before I get ahead of myself, but if all goes according to plan I'll probably be coming back to these and other forums over the next few months and years to learn new things and ask new questions. Anyway, that was kinda long winded but I want to get some writing done on the backstory and world before exploring the technology much farther, in answer to your question.
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WantsToPlayButIsBroke
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Post by WantsToPlayButIsBroke on Feb 13, 2018 2:50:25 GMT
A quick note on FELs is that there's currently something of a revolution in particle accelerator design in the form of Plasma Accelerators. en.wikipedia.org/wiki/Plasma_accelerationThis makes the idea of compact X-Ray FELs seem a lot more attainable in the near-ish future.
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Post by matterbeam on Feb 13, 2018 21:23:50 GMT
A quick note on FELs is that there's currently something of a revolution in particle accelerator design in the form of Plasma Accelerators. en.wikipedia.org/wiki/Plasma_accelerationThis makes the idea of compact X-Ray FELs seem a lot more attainable in the near-ish future. The downside is extremely poor efficiency - less than one percent.
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Post by lucubratory on Feb 15, 2018 0:15:24 GMT
A quick note on FELs is that there's currently something of a revolution in particle accelerator design in the form of Plasma Accelerators. en.wikipedia.org/wiki/Plasma_accelerationThis makes the idea of compact X-Ray FELs seem a lot more attainable in the near-ish future. The downside is extremely poor efficiency - less than one percent. That is a very important downside... Could have interesting sci-fi implications though
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Post by matterbeam on Jan 1, 2019 0:19:14 GMT
The downside is extremely poor efficiency - less than one percent. That is a very important downside... Could have interesting sci-fi implications though High particle energy but low beam power (due to low efficiency) fits the description of a 'radiation weapon' pretty well.
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Post by Mongoose on Dec 28, 2019 3:10:15 GMT
I realize this is a necro thread but I felt I should mention if you are in space what you accelerate stats accelerated ie Gatling guns would be useful because as long as they hit they do maximum damage but at long range there is actually return lag ie you are looking at something that has already happened if you get far enough away such as 1au then they could be anywhere in a few minutes sphere of where they were thus why missiles are probably the single best weapon for space
Lasers being a light speed weapon would be great as well but the tech isn’t here to get them to remain focused past a few kilometers and increasing their bore only gets you so far
Gatling guns can spray and pray across an entire area of space but they won’t be able to make targeted hits on specific components at range but could really deny an area of spay
Railguns coil guns and large bore cannons are great but like the navies of the wooden variety you would need a large number of guns pointing at your target to reliably get hits and then you would be constrained by how accurate your predictions of where the enemy have moved to and on top of that a standard firearm would generate a modest amount of rearward acceleration if they were not specifically designed to mitigate the recoil
The best question to ask yourself is how good is the tech , do I want to say nope to an entire area of space do I just want to fire a missile and have it go homing in on the target etc
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Post by bigbombr on Dec 28, 2019 7:29:36 GMT
I realize this is a necro thread but I felt I should mention if you are in space what you accelerate stats accelerated ie Gatling guns would be useful because as long as they hit they do maximum damage but at long range there is actually return lag ie you are looking at something that has already happened if you get far enough away such as 1au then they could be anywhere in a few minutes sphere of where they were thus why missiles are probably the single best weapon for space Lasers being a light speed weapon would be great as well but the tech isn’t here to get them to remain focused past a few kilometers and increasing their bore only gets you so far Gatling guns can spray and pray across an entire area of space but they won’t be able to make targeted hits on specific components at range but could really deny an area of spay Railguns coil guns and large bore cannons are great but like the navies of the wooden variety you would need a large number of guns pointing at your target to reliably get hits and then you would be constrained by how accurate your predictions of where the enemy have moved to and on top of that a standard firearm would generate a modest amount of rearward acceleration if they were not specifically designed to mitigate the recoil The best question to ask yourself is how good is the tech , do I want to say nope to an entire area of space do I just want to fire a missile and have it go homing in on the target etc The range at which lasers remain sufficient intensity to be damaging depends on beam quality, beam power, wavelength and the diameter of the focusing aperture. Current lasers are IR, in the dozen kW range, operate in atmosphere, and have focusing apertures with diameters of a few dozen cm at most. They don't really compare to our 20+ MW green, violet or UV lasers with focusing apertures measured in meters. Large bore guns offer the possibility of burst munition, but I got the impression that a large cannon that can deliver 60 bursting charges deploying a total of 6000 small rounds per minute is significantly heavier than a rapid fire small gun that fires 6000 small rounds a minute. I don't see much point in large cannons (of the chemical and electric variety). The only role I can see for large bore cannons is orbital bombardement, as large objects handle reentry better. I'd argue missiles are better suited for that role though.
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Post by AtomHeartDragon on Dec 29, 2019 13:25:16 GMT
Large bore guns offer the possibility of burst munition, but I got the impression that a large cannon that can deliver 60 bursting charges deploying a total of 6000 small rounds per minute is significantly heavier than a rapid fire small gun that fires 6000 small rounds a minute. I don't see much point in large cannons (of the chemical and electric variety). The only role I can see for large bore cannons is orbital bombardement, as large objects handle reentry better. I'd argue missiles are better suited for that role though. Bursting charges have an advantage of of allowing you to create denser pattern when and where you want it, though. Large electric cannons might be necessary to accelerate small projectiles to tremendous speeds. Large projectiles might indeed not have as much point at very high velocities as they seem to be more susceptible to whipple shields than an equivalent mass of small ones thrown in quick succession in tight pattern (but less than equivalent mass of small ones scattered in loose pattern).
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