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one thing i never understood about fusion is how you can capture all the released energy efficiently enough. isn't it released in many ways that cannot really b

one thing i never understood about fusion is how you can capture all the released energy efficiently enough. isn't it released in many ways that cannot really be harnessed directly eg: gamma radiation, x-rays, emf. that makes me think that the input:output ratio would need to be not just marginally better, but sufficiently better. does anyone know what the current best input:captured number is?

InclinedPlane 14y ago
Almost all of the energy comes out as kinetic energy of the fusion byproducts, which are mainly atomic nuclei and neutrons. Sadly, a great deal of the energy of the easiest to achieve fusion reactions (D-D and D-T) tends to exist in the neutrons released by the reactions. And those neutrons tend to fly right out of the charged plasma quite readily. This makes creating a self-sustaining magnetically confined fusion reaction more difficult but it also makes building a fusion reactor slightly challenging. But far from impossible. Neutrons can penetrate fairly deeply through many materials but fortunately ordinary water serves as a robust shield. So by surrounding a fusion reaction with water you can quite easily capture most of the energy of the fusion reactions and can use an ordinary steam turbine generator to produce electricity.
snarfy 14y ago
It depends on the type of fuel used. The holy grail is a boron + hydrogen reaction, which produces three helium nuclei. Since the nuclei are positively charged and moving quickly, the net voltage is around 2 million volts. When done correctly, fusion will create electricity directly. At that point it's just a matter of stepping it down to a usable voltage, but we have lots of ways to do that.
gryphonic 14y ago
Usually you are trying to catch neutrons in a lithium blanket, and using the fission products to extract energy. At least that is what they are doing at ITER. The electromagnetic energy goes back into the plasma and helps with keeping things hot. The energy extraction is one of the biggest challenges with sustained fusion.
uvdiv 14y ago
isn't it released in many ways that cannot really be harnessed directly eg: gamma radiation, x-rays, emf. Yes, just like nuclear fission! All this radiation gets absorbed by surrounding matter, and its energy becomes heat. Powers a steam or gas turbine -- just another heat engine (tm). With fusion reactors, the radiation absorber is a blanket of pipes filled with molten metal, several meters thick and several tens of meters in inner diameter. There's a critical second purpose to this: creating fusion fuel. The molten metal contains lithium, which on absorbing neutrons transmutes to tritium (hydrogen-3), which can be scrubbed out and recycled. Tritium is fusion fuel; fusion reactors must create it like this in self-sufficient quantities. About the fraction of energy captured; it's very close to 100% (only neutrinos escape), with the subsequent conversion from heat to electricity being some 30-50% efficient. http://www.iter-industry.ch/wp-content/uploads/2010/01/Pr__sentation_Poitevin.pdf http://www.iter-industry.ch/wp-content/uploads/2010/01/Pr__s... (particularly first few slides) http://aries.ucsd.edu/raffray/publications/JNM/ICFRM_10_Raffray.pdf http://aries.ucsd.edu/raffray/publications/JNM/ICFRM_10_Raff...

InclinedPlane 14y ago

Almost all of the energy comes out as kinetic energy of the fusion byproducts, which are mainly atomic nuclei and neutrons. Sadly, a great deal of the energy of the easiest to achieve fusion reactions (D-D and D-T) tends to exist in the neutrons released by the reactions. And those neutrons tend to fly right out of the charged plasma quite readily. This makes creating a self-sustaining magnetically confined fusion reaction more difficult but it also makes building a fusion reactor slightly challenging. But far from impossible. Neutrons can penetrate fairly deeply through many materials but fortunately ordinary water serves as a robust shield. So by surrounding a fusion reaction with water you can quite easily capture most of the energy of the fusion reactions and can use an ordinary steam turbine generator to produce electricity.

snarfy 14y ago

It depends on the type of fuel used. The holy grail is a boron + hydrogen reaction, which produces three helium nuclei. Since the nuclei are positively charged and moving quickly, the net voltage is around 2 million volts. When done correctly, fusion will create electricity directly. At that point it's just a matter of stepping it down to a usable voltage, but we have lots of ways to do that.

gryphonic 14y ago

Usually you are trying to catch neutrons in a lithium blanket, and using the fission products to extract energy. At least that is what they are doing at ITER. The electromagnetic energy goes back into the plasma and helps with keeping things hot. The energy extraction is one of the biggest challenges with sustained fusion.

uvdiv 14y ago

isn't it released in many ways that cannot really be harnessed directly eg: gamma radiation, x-rays, emf. Yes, just like nuclear fission! All this radiation gets absorbed by surrounding matter, and its energy becomes heat. Powers a steam or gas turbine -- just another heat engine (tm). With fusion reactors, the radiation absorber is a blanket of pipes filled with molten metal, several meters thick and several tens of meters in inner diameter. There's a critical second purpose to this: creating fusion fuel. The molten metal contains lithium, which on absorbing neutrons transmutes to tritium (hydrogen-3), which can be scrubbed out and recycled. Tritium is fusion fuel; fusion reactors must create it like this in self-sufficient quantities. About the fraction of energy captured; it's very close to 100% (only neutrinos escape), with the subsequent conversion from heat to electricity being some 30-50% efficient. http://www.iter-industry.ch/wp-content/uploads/2010/01/Pr__sentation_Poitevin.pdf http://www.iter-industry.ch/wp-content/uploads/2010/01/Pr__s... (particularly first few slides) http://aries.ucsd.edu/raffray/publications/JNM/ICFRM_10_Raffray.pdf http://aries.ucsd.edu/raffray/publications/JNM/ICFRM_10_Raff...