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Do we even had a model for Fussion that is energy poasitive? The only Fusion reactors we know to work, work by converting gravitational potential energy into li

Do we even had a model for Fussion that is energy poasitive? The only Fusion reactors we know to work, work by converting gravitational potential energy into light/heat through fusion this is how stars operate. All fusion reactions so far require an external input of energy not only to start them but often to sustain them and even those which are self sustaining for a short period of time grind to a halt once you try to extract energy from the system. So in all honesty while I’m not by any stretch of the imagination an expert in fusion physics I can at least understand conservation laws, does any of the current experiments even relies on a model that is at least proven in principle to be energy positive?

dogma1138 8y ago
To the trolls downvoting all the questions here stellar fusion works because of hydrostatic equilibrium which is maintained between gravity and the outbound pressure of the fusion reaction of a star. ∆P · A = −GM(r)m http://www.ucolick.org/~woosley/lectures_fall2012/lecture12.12.pdf http://www.ucolick.org/~woosley/lectures_fall2012/lecture12.... So essentially they are giant springs in space that convert one form of energy into another by fusing matter. Now I hope someone would be able to answer my actual question regarding the energy positive fusion models.
- strainer 8y ago
  That was bad luck with the downvoting, I have heard the gravitational narrative of stellar evolution and element creation before, perhaps in a Feynman lecture? I recall the idea that a cloud of hydrogen atoms has more gravitational potential than the equivalent cloud of heavier elements, basically because the matter is more evenly dispersed. It seems to make a certain sense. Particles get very fast when they close distance, if they can then stick together their kinetic energy has to become something. Interesting to calculate the gravitational energy involved in a neutron and proton getting close enough to be held by each others nuclear forces, beginning from an average separation of say a few microns? I know they have to get through repulsive nuclear forces in order to stick, I don't know if the reaction always liberates kinetic energy. Maybe it depends on what element results. An interesting topic of stellar fusion should be supernova reaction/s. The creation of heavier elements there can clearly release enough kinetic energy to explode the condensed body. Does that energy owe to the distance that has been closed by particles forming heavier elements, or to loss of mass in the nuclear reactions? I wonder about the gravitational energy of a cloud of billard balls rather than atoms. If another cloud has the same volume but half the number of larger balls that are twice as heavy. I guess if the two clouds have the same size, weight and density, they have the same gravitational potential - if they start cold, they will both implode with the same force at the center. But this seems to contradict the narrative that conversion of hydrogen to helium should consume or liberate that potential energy.
theothermkn 8y ago
Stars simply do not "work by converting gravitational potential energy into light/heat through fusion." The "light/heat," or energy, that stars produce comes from the mass defect of the fused atoms. Basically, the binding energy of He is less than the binding energy of the (net) 4 H atoms that go into the reaction. It works so well in the sun because of the long confinement times and the long transit time for energy to get from the center of the the star to the exterior. "...while I’m not by any stretch of the imagination an expert in fusion physics...I can at least understand conservation laws..." I don't think that you have a firm a grasp on their application as you seem to suspect, though I agree you don't understand the physics of fusion. Your reasoning is analogous to neglecting the contribution of smokeless powder to the performance of a rifle, because a rifle is just "converting" the energy stored in the hammer spring into energy in the bullet. That's the best I can do for you. Good luck!
- dogma1138 8y ago
  Again gravity is what maintains the reaction going, without it the gas would expand and the reaction would stop. I understand how fusion works, what you neglect is that gravity is what allows you to counter the nuclear forces to cause protons to fuse in the first place, and what keeps the entire thing from blowing out. Hence stars are in constant balance between gravitational collapse and their outward pressure caused by fusion. “An interstellar cloud of gas will remain in hydrostatic equilibrium as long as the kinetic energy of the gas pressure is in balance with the potential energy of the internal gravitational force. Mathematically this is expressed using the virial theorem, which states that, to maintain equilibrium, the gravitational potential energy must equal twice the internal thermal energy.” On earth we exchange gravitational potential with electromagnetism but we still need to apply the same force to counter the nuclear forces and the pressure from the reaction once it starts. All I want to know is if we have a proven net positive model for this reaction because so far I haven’t been able to find one. Because as far as I know the vital theroem stands so it doesn’t matter if it’s gravitational potential or any other force it still needs to be twice the thermal energy of the reaction. But you can continue to downvote without actually addressing anything while ingoring everything we know about stellar fusion and the fact that is triggered and constantly maintained by gravitational collapse. So no I don’t ignore the role of gunpowder in a gun, you ignore the energy needed to create the gunpowder and cartridge in the first place. That's the best I can do for you. Good luck!

dogma1138 8y ago

To the trolls downvoting all the questions here stellar fusion works because of hydrostatic equilibrium which is maintained between gravity and the outbound pressure of the fusion reaction of a star. ∆P · A = −GM(r)m http://www.ucolick.org/~woosley/lectures_fall2012/lecture12.12.pdf http://www.ucolick.org/~woosley/lectures_fall2012/lecture12.... So essentially they are giant springs in space that convert one form of energy into another by fusing matter. Now I hope someone would be able to answer my actual question regarding the energy positive fusion models.

strainer 8y ago
That was bad luck with the downvoting, I have heard the gravitational narrative of stellar evolution and element creation before, perhaps in a Feynman lecture? I recall the idea that a cloud of hydrogen atoms has more gravitational potential than the equivalent cloud of heavier elements, basically because the matter is more evenly dispersed. It seems to make a certain sense. Particles get very fast when they close distance, if they can then stick together their kinetic energy has to become something. Interesting to calculate the gravitational energy involved in a neutron and proton getting close enough to be held by each others nuclear forces, beginning from an average separation of say a few microns? I know they have to get through repulsive nuclear forces in order to stick, I don't know if the reaction always liberates kinetic energy. Maybe it depends on what element results. An interesting topic of stellar fusion should be supernova reaction/s. The creation of heavier elements there can clearly release enough kinetic energy to explode the condensed body. Does that energy owe to the distance that has been closed by particles forming heavier elements, or to loss of mass in the nuclear reactions? I wonder about the gravitational energy of a cloud of billard balls rather than atoms. If another cloud has the same volume but half the number of larger balls that are twice as heavy. I guess if the two clouds have the same size, weight and density, they have the same gravitational potential - if they start cold, they will both implode with the same force at the center. But this seems to contradict the narrative that conversion of hydrogen to helium should consume or liberate that potential energy.

theothermkn 8y ago

Stars simply do not "work by converting gravitational potential energy into light/heat through fusion." The "light/heat," or energy, that stars produce comes from the mass defect of the fused atoms. Basically, the binding energy of He is less than the binding energy of the (net) 4 H atoms that go into the reaction. It works so well in the sun because of the long confinement times and the long transit time for energy to get from the center of the the star to the exterior. "...while I’m not by any stretch of the imagination an expert in fusion physics...I can at least understand conservation laws..." I don't think that you have a firm a grasp on their application as you seem to suspect, though I agree you don't understand the physics of fusion. Your reasoning is analogous to neglecting the contribution of smokeless powder to the performance of a rifle, because a rifle is just "converting" the energy stored in the hammer spring into energy in the bullet. That's the best I can do for you. Good luck!

dogma1138 8y ago
Again gravity is what maintains the reaction going, without it the gas would expand and the reaction would stop. I understand how fusion works, what you neglect is that gravity is what allows you to counter the nuclear forces to cause protons to fuse in the first place, and what keeps the entire thing from blowing out. Hence stars are in constant balance between gravitational collapse and their outward pressure caused by fusion. “An interstellar cloud of gas will remain in hydrostatic equilibrium as long as the kinetic energy of the gas pressure is in balance with the potential energy of the internal gravitational force. Mathematically this is expressed using the virial theorem, which states that, to maintain equilibrium, the gravitational potential energy must equal twice the internal thermal energy.” On earth we exchange gravitational potential with electromagnetism but we still need to apply the same force to counter the nuclear forces and the pressure from the reaction once it starts. All I want to know is if we have a proven net positive model for this reaction because so far I haven’t been able to find one. Because as far as I know the vital theroem stands so it doesn’t matter if it’s gravitational potential or any other force it still needs to be twice the thermal energy of the reaction. But you can continue to downvote without actually addressing anything while ingoring everything we know about stellar fusion and the fact that is triggered and constantly maintained by gravitational collapse. So no I don’t ignore the role of gunpowder in a gun, you ignore the energy needed to create the gunpowder and cartridge in the first place. That's the best I can do for you. Good luck!