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Post by matterbeam on Sept 8, 2017 1:54:55 GMT
TBH this is actually making me not want to write this novel. I feel bad for having de-railed this thread too. Is there any chance we can get this split out from the original thread? A good story doesn't really care about the setting, and that is what readers pick it up for. If you'd got a good story to tell, write that out first and then insert it into an appropriate setting. A great tool you have at your disposition, as a writer, is that you can keep numbers out of your book, keep descriptions vague and only name-drop a few key concepts to give a veneer of plausibility. Realism is great, but not even the most avid reader cares much about the percentage of fusion power your electromagnetic coils are absorbing. They just want to read that the radiators are glowing and the fusion reaction gives off nasty x-rays. Bonus points for including a second set of radiators that are not glowing and that the fusion engine needs a particle accelerator running the length of the ship. Does any of this need much of the maths going on between you and Kerr ? Another thing I have noticed is that you two started out with vague requirements on travel times, set no limits on the tech level and ran up and down the gamut of options like a xylophone. I am certain that you are fatigued right now from researching the myriad options available and might feel dissatisfied that all that work has not let to a clear solution so far. Problem is, there is no solution. It's your universe. Using NSWR or Orion, D-T or p-B11, laser-driven missiles or Casaba Howitzers... there is no 'right' answer. There's a set of options that might fit a vision better, or might have certain limitations you'd need to work around or secondary requirements which might hurt internal consistency... but would any of it be 'wrong', really? Again, I strongly suggest you return to your list of requirements and add more detail to what you want before you dive in again into all the maths and technology, ok?  |
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Post by Kerr on Sept 8, 2017 5:26:43 GMT
Awesome post and good math, but is the 0.01% the absorbed heat is for the blade shields or the magnets? For ironclad6's 5PW Fusion Drive the amount of waste heat the "system" has to deal with is 500GW. Which either means we have to operate 100t Hydrogen (or anything with a similar specific heat) at 300K to remove 500GW waste heat, this assumes that the heat just perfectly jumps from the coils to the coolant. If you meant the blade shields the waste heat drops drastically. using an 99% Reflective coating we will only have to deal with 2.5GW. requiring roughly a ton of coolant. Most decent Fusion torch drives would look kinda similar to the fusion drive of the firefly. Letting most radiation escape into space, use very thin coils and sharp blade shields and using an angled bottom to reflect X-rays As a side note, I've used this link to often back then when I made my firefly and when helping Astrogator with realistic fusion that I nearly memorized the entire chart.... But thanks for trying to share Project Rho links. I also found out that the bremsstrahlung power exceeds the fusion power by 1.75x in proton-boron fusion. Resulting in 36% Thermal power and 64% X-rays. The 0.01% is what reaches the cryogenic superconducting coils. Sorry for linking the fusion fuels page again. It's a reflex to source my claims How did you find out about proton-boron's bremsstrahlung power percent? Oh well, 500GW of room-temperature heat doesn't sound that good for your torchships. I found this number at the Aneutronic Fusion page, "For the p–11B reaction, some calculations indicate that the bremsstrahlung power will be at least 1.74 times larger than the fusion power." with the link bremsstrahlung losses in quasineutral, isotropic plasmas also lists a chart for Bremsstrahlung values . |
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Post by matterbeam on Sept 8, 2017 13:58:18 GMT
The 0.01% is what reaches the cryogenic superconducting coils. Sorry for linking the fusion fuels page again. It's a reflex to source my claims How did you find out about proton-boron's bremsstrahlung power percent? Oh well, 500GW of room-temperature heat doesn't sound that good for your torchships. I found this number at the Aneutronic Fusion page, "For the p–11B reaction, some calculations indicate that the bremsstrahlung power will be at least 1.74 times larger than the fusion power." with the link bremsstrahlung losses in quasineutral, isotropic plasmas also lists a chart for Bremsstrahlung values . Thanks, that was an interesting read. The confinement and power density issues strongly suggest that the only practical way of using p-B11 fusion is to encapsulate the fuel in an X-ray absorbent. They mention 1mm of stainless steel, but I am certain there is a better material. The wiki states most X-rays are in the 10 to 30MeV range. I used this calculation with this table for uranium and I got a 90% absorption of 20 MeV X-rays using 1.85cm thickness. 50% absorption requires 0.55cm. |
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Post by Kerr on Sept 8, 2017 14:07:04 GMT
Oh well, 500GW of room-temperature heat doesn't sound that good for your torchships. I found this number at the Aneutronic Fusion page, "For the p–11B reaction, some calculations indicate that the bremsstrahlung power will be at least 1.74 times larger than the fusion power." with the link bremsstrahlung losses in quasineutral, isotropic plasmas also lists a chart for Bremsstrahlung values . Thanks, that was an interesting read. The confinement and power density issues strongly suggest that the only practical way of using p-B11 fusion is to encapsulate the fuel in an X-ray absorbent. They mention 1mm of stainless steel, but I am certain there is a better material. The wiki states most X-rays are in the 10 to 30MeV range. I used this calculation with this table for uranium and I got a 90% absorption of 20 MeV X-rays using 1.85cm thickness. 50% absorption requires 0.55cm. X-ray photovoltalics might be an possible way. Which could be an effective absorptions material which also produces heat. But my best guess is that it is limited by operating temperature. So you have to go the old-school 65% Max efficient thermal turbine way if you want moderately compact fusion reactors. Do you have an similar document for Neutrons? |
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Post by matterbeam on Sept 8, 2017 14:45:38 GMT
Thanks, that was an interesting read. The confinement and power density issues strongly suggest that the only practical way of using p-B11 fusion is to encapsulate the fuel in an X-ray absorbent. They mention 1mm of stainless steel, but I am certain there is a better material. The wiki states most X-rays are in the 10 to 30MeV range. I used this calculation with this table for uranium and I got a 90% absorption of 20 MeV X-rays using 1.85cm thickness. 50% absorption requires 0.55cm. X-ray photovoltalics might be an possible way. Which could be an effective absorptions material which also produces heat. But my best guess is that it is limited by operating temperature. So you have to go the old-school 65% Max efficient thermal turbine way if you want moderately compact fusion reactors. Do you have an similar document for Neutrons? I was thinking in terms of inertially-confined fusion propulsion. You put the fusion fuel in a ball and surround it with X-ray absorbing materials. The blast produces over 90% thermal plasma and very little X-ray emissions. In an electrical reactor, you don't need to use 'naked' fusion reactions that reach millions of Kelvin. Tiny pellets ignited inside a cloud of hydrogen plasma will have their X-rays absorbed by meters of hydrogen before they reach the reactor walls. Neutron mass attenuation coefficients in neat tables are harder to come by  |
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Post by Kerr on Sept 8, 2017 15:07:08 GMT
en.wikipedia.org/wiki/Direct_energy_conversion X-ray photovoltalics might be an possible way. Which could be an effective absorptions material which also produces heat. But my best guess is that it is limited by operating temperature. So you have to go the old-school 65% Max efficient thermal turbine way if you want moderately compact fusion reactors. Do you have an similar document for Neutrons? I was thinking in terms of inertially-confined fusion propulsion. You put the fusion fuel in a ball and surround it with X-ray absorbing materials. The blast produces over 90% thermal plasma and very little X-ray emissions. In an electrical reactor, you don't need to use 'naked' fusion reactions that reach millions of Kelvin. Tiny pellets ignited inside a cloud of hydrogen plasma will have their X-rays absorbed by meters of hydrogen before they reach the reactor walls. Neutron mass attenuation coefficients in neat tables are harder to come by For ICF fusion? You can already forget it. The pellet mass would have to be in the hundred of kilos. Resulting in multi-megaton explosions in your nozzle. 100,000x 10t explosion are just more controllable than a single 1MT explosion. How does all of this new hydrogen plasma help me generate power? Pellet fusion doesn't have the best fusion rates. Also wouldn't the hydrogen act as an medium to transfer shockwaves and heat? I think the usual Stellarator/Tokamak type is alright. If we just made them work out properly. Oh well, tell me please when you happen to find one. |
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Post by matterbeam on Sept 8, 2017 17:13:23 GMT
I was thinking in terms of inertially-confined fusion propulsion. You put the fusion fuel in a ball and surround it with X-ray absorbing materials. The blast produces over 90% thermal plasma and very little X-ray emissions. In an electrical reactor, you don't need to use 'naked' fusion reactions that reach millions of Kelvin. Tiny pellets ignited inside a cloud of hydrogen plasma will have their X-rays absorbed by meters of hydrogen before they reach the reactor walls. Neutron mass attenuation coefficients in neat tables are harder to come by For ICF fusion? You can already forget it. The pellet mass would have to be in the hundred of kilos. Resulting in multi-megaton explosions in your nozzle. 100,000x 10t explosion are just more controllable than a single 1MT explosion. How does all of this new hydrogen plasma help me generate power? Pellet fusion doesn't have the best fusion rates. Also wouldn't the hydrogen act as an medium to transfer shockwaves and heat? I think the usual Stellarator/Tokamak type is alright. If we just made them work out properly. Oh well, tell me please when you happen to find one. Why would 'pellet fusion' require fusion fuel pellets of hundreds of kilograms?! A 10cm wide pellet of frozen deuterium and He3 would mass a bit more than 45 grams. With 10% fuel burnup, you get 1.5TJ of energy in your thermal plasma. You'd need to cover 314cm^2 with 1.85cm of uranium, which masses roughly 11.095kg. If used in an engine, you'll be heating 11.14kg of matter with 1.5TJ of energy. There'll be 18 moles of D/He3 and 47 moles of uranium for an average plasma molar mass of 170.6g/mol. Since the mass is dominated by uranium, let's use uranium's heat capacity of 116J/kg/K. 1.5TJ will heat up 11.14kg of uranium to 1160 million K. The root mean square gas velocity calculator tells me that this corresponds to an exhaust velocity of 412km/s or 42000 seconds. That is plenty enough for interplanetary travel! The pulse energy is equivalent to 0.358 kilotons yield. We can go smaller, but the fuel/uranium ratio would suffer and exhaust velocity will be lower. |
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Post by Kerr on Sept 8, 2017 18:41:08 GMT
For ICF fusion? You can already forget it. The pellet mass would have to be in the hundred of kilos. Resulting in multi-megaton explosions in your nozzle. 100,000x 10t explosion are just more controllable than a single 1MT explosion. How does all of this new hydrogen plasma help me generate power? Pellet fusion doesn't have the best fusion rates. Also wouldn't the hydrogen act as an medium to transfer shockwaves and heat? I think the usual Stellarator/Tokamak type is alright. If we just made them work out properly. Oh well, tell me please when you happen to find one. Why would 'pellet fusion' require fusion fuel pellets of hundreds of kilograms?! A 10cm wide pellet of frozen deuterium and He3 would mass a bit more than 45 grams. With 10% fuel burnup, you get 1.5TJ of energy in your thermal plasma. You'd need to cover 314cm^2 with 1.85cm of uranium, which masses roughly 11.095kg. If used in an engine, you'll be heating 11.14kg of matter with 1.5TJ of energy. There'll be 18 moles of D/He3 and 47 moles of uranium for an average plasma molar mass of 170.6g/mol. Since the mass is dominated by uranium, let's use uranium's heat capacity of 116J/kg/K. 1.5TJ will heat up 11.14kg of uranium to 1160 million K. The root mean square gas velocity calculator tells me that this corresponds to an exhaust velocity of 412km/s or 42000 seconds. That is plenty enough for interplanetary travel! The pulse energy is equivalent to 0.358 kilotons yield. We can go smaller, but the fuel/uranium ratio would suffer and exhaust velocity will be lower. You require pellets weighing hundreds of kilogram so that the fraction Uranium used doesn't lower the Isp but increases it or keep it constant. What you present here is basically an uranium afterburner. Also the heavy uranium ions have much more inertia and worse charge ratios compared to an 15 MeV proton. |
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Post by matterbeam on Sept 8, 2017 20:19:06 GMT
Why would 'pellet fusion' require fusion fuel pellets of hundreds of kilograms?! A 10cm wide pellet of frozen deuterium and He3 would mass a bit more than 45 grams. With 10% fuel burnup, you get 1.5TJ of energy in your thermal plasma. You'd need to cover 314cm^2 with 1.85cm of uranium, which masses roughly 11.095kg. If used in an engine, you'll be heating 11.14kg of matter with 1.5TJ of energy. There'll be 18 moles of D/He3 and 47 moles of uranium for an average plasma molar mass of 170.6g/mol. Since the mass is dominated by uranium, let's use uranium's heat capacity of 116J/kg/K. 1.5TJ will heat up 11.14kg of uranium to 1160 million K. The root mean square gas velocity calculator tells me that this corresponds to an exhaust velocity of 412km/s or 42000 seconds. That is plenty enough for interplanetary travel! The pulse energy is equivalent to 0.358 kilotons yield. We can go smaller, but the fuel/uranium ratio would suffer and exhaust velocity will be lower. You require pellets weighing hundreds of kilogram so that the fraction Uranium used doesn't lower the Isp but increases it or keep it constant. What you present here is basically an uranium afterburner. Also the heavy uranium ions have much more inertia and worse charge ratios compared to an 15 MeV proton. I don't see how the twelve kilogram pellet is so bad. There is a thing as too much exhaust velocity for interplanetary travel. 412km/s and a decent mass ratio of 3 allows you to rocket between Earth and Jupiter with an average transit velocity of 226km/s - you'd make the trip in 30 days at that rate! Earth to Mars is less than three days. Uranium is seriously the best option. If you want to go with conventional hydrogen and have engines big enough to handle meters-wide propellant spheres as if they were ping-pong balls, then you could replace the uranium with frozen hydrogen. 0.086g/cm^3, mass attenuation coefficient of 0.02539... 90% absorption requires 1054cm thickness. A sphere containing a 10cm wide fusion fuel pellet would have a 'mantle' of 4/3*3.14*(1059^3-5^3):4911930042cm^3, which would mass 422346kg. That's 422346000 moles of molecular hydrogen. It would be heated to 248K and have negligible exhaust velocity. We seriously need the densest possible 'mantle'. |
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Post by Enderminion on Sept 8, 2017 21:59:49 GMT
sooo, Osmium?
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Post by Kerr on Sept 9, 2017 7:15:38 GMT
You require pellets weighing hundreds of kilogram so that the fraction Uranium used doesn't lower the Isp but increases it or keep it constant. What you present here is basically an uranium afterburner. Also the heavy uranium ions have much more inertia and worse charge ratios compared to an 15 MeV proton. I don't see how the twelve kilogram pellet is so bad. There is a thing as too much exhaust velocity for interplanetary travel. 412km/s and a decent mass ratio of 3 allows you to rocket between Earth and Jupiter with an average transit velocity of 226km/s - you'd make the trip in 30 days at that rate! Earth to Mars is less than three days. Uranium is seriously the best option. If you want to go with conventional hydrogen and have engines big enough to handle meters-wide propellant spheres as if they were ping-pong balls, then you could replace the uranium with frozen hydrogen. 0.086g/cm^3, mass attenuation coefficient of 0.02539... 90% absorption requires 1054cm thickness. A sphere containing a 10cm wide fusion fuel pellet would have a 'mantle' of 4/3*3.14*(1059^3-5^3):4911930042cm^3, which would mass 422346kg. That's 422346000 moles of molecular hydrogen. It would be heated to 248K and have negligible exhaust velocity. We seriously need the densest possible 'mantle'. I didn't said that other materials would be better, just that it is a uranium afterburner. And that the heavy ions might present a problem. Pure Fusion for Interstellar travel, and Fusion Thermal (Using fusion energy to heat remass) is for high speed interplanetary travel. |
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Post by Kerr on Sept 9, 2017 11:37:28 GMT
matterbeamDo you think Metallic Hydrogen/Helium Isotopes would be useful for fusion? Their advantage lies within their increased density, which reduces tank size and maybe even decrease required energy to activate the fusion reaction because the fuel is pre-compressed. I am not talking about magitech UDD.
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Post by Enderminion on Sept 9, 2017 15:40:26 GMT
Metallic stuff might not be metastable, also the stuff explodes when heated
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Post by Kerr on Sept 9, 2017 15:51:09 GMT
Metallic stuff might not be metastable, also the stuff explodes when heated Let's assume it is. How does that really matter? |
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Post by Enderminion on Sept 9, 2017 16:05:08 GMT
Metallic stuff might not be metastable, also the stuff explodes when heated Let's assume it is. How does that really matter? if you don't compress it fast enough it explodes, also the injection parts must be kept cool |
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