7 ms·

Fusion bombs soon with a laser primer instead of fission for heat generation? Not yet I guess. Clean power? Perhaps never.

by a3w 4y ago

the_third_wave 4y ago
I think you're overestimating the amount of energy released in a single fusion event and underestimating the machinery needed to generate and focus the laser pulses on the hohlraum. Remember there is no fusion chain reaction, the thing would need to keep on pumping pellets into the "primer" while firing laser pulses to keep the energy flowing. Compared to a 'simple' fission primer with a neutron reflector I don't really see the gain in a laser-primed fusion weapon, at least not one in the line of current fusion bombs.
fallingknife 4y ago
Actually, the tech that you are hinting at would guarantee clean fusion power. If you could generate clean fusion explosions, detonate underground and use the heat to generate power. Nuclear bombs are currently the only net energy positive fusion devices we have.
- arethuza 4y ago
  Most bomb designs are fission-fusion-fission - most of the energy comes from the fission of the casing of the secondary by neutrons from the fusion process in the secondary. Edit: Mind you - there were tests like the huge Tsar Bomba that de-rated at 100+ Mt design to 50Mt be leaving out the final fission stage - the output being mostly from fusion. https://en.wikipedia.org/wiki/Tsar_Bomba https://en.wikipedia.org/wiki/Tsar_Bomba
  - denton-scratch 4y ago
    My understanding is that what you're referring to as a "fusion" stage is really a fusion-enhanced fission stage. All the stages of normal "H-bombs" are fission stages, using a small fusion core to generate a flood of neutrons, which results in the fission fuel combusting more completely. Pure fission bombs tend to disintegrate long before enough neutrons have been generated to achieve complete combustion. The inclusion of a small core of lithium deuteride results in a much more efficient fission bomb. I suppose these NIF tests are tiny pure fusion explosions; but I'm not aware of any practical weapon that generated energy mainly from fusion.
    - arethuza 4y ago
      "fusion-enhanced fission stage" The primary is fusion boosted fission, the core ("spark-plug") of the secondary is also fusion boosted fission surrounded by dry fusion fuel (lithium deuteride) and then a fissionable tamper. My understanding is that X rays from the primary compress the entire secondary package - which ignites the spark-plug and then the fusion fuel is caught between the incoming tamper and the exploding spark-plug at its core and ignited. So there does appear to be a real "fusion" stage - with a lot of other steps involving fission and fusion. https://en.wikipedia.org/wiki/Thermonuclear_weapon https://en.wikipedia.org/wiki/Thermonuclear_weapon
      - denton-scratch 4y ago
        The cited article says: "Fast fission of the tamper and radiation case is the main contribution to the total yield and is the dominant process that produces radioactive fission product fallout." The way I read that, even in a large H-bomb, little of the yield is the direct result of fusion reactions. Rather, the neutrons produced by the fusion reaction dramatically increase the efficiency of the fission reactions, which on their own would not produce enough neutrons to fission more than a small part of the fissile material before the device disintegrates.
        arethuza 4y ago
        There is still a considerable about directly from fusion e.g. in the Tsar Bomba the fusion stage produced about 47Mt of the 50Mt total (it had two smaller H-bombs as primaries for the fusion stage). The full design was 100+ Mt so about 50% from the final fission stage seems a rule of thumb, which is also mentioned in this article about "neutron bombs": https://en.wikipedia.org/wiki/Neutron_bomb https://en.wikipedia.org/wiki/Neutron_bomb Neutron bombs don't have fissile tampers on the secondary exposing the neutrons from fusion directly rather than using them to fission the tamper.
- rgmerk 4y ago
  It might guarantee clean fusion power, but there's no guarantee it would be in any way economic. Edward Teller proposed something along these lines with conventional two-stage nuclear explosives back in the 1970s, but it was rapidly abandoned as horribly inefficient and costly: https://en.wikipedia.org/wiki/Project_PACER https://en.wikipedia.org/wiki/Project_PACER I know this stuff is fun to speculate about but the boring and unsexy option of more solar panels, wind turbines, and transmission lines is likely to be both cheaper and more politically saleable.
  - denton-scratch 4y ago
    > clean fusion power From what I understand, practical routes to fusion all produce a lot of fast neutrons, and tritium. The neutrons make the surrounding equipment radioactive, and create toxic elements. The tritium is itself toxic, and is hard to contain. And the high neutron flux means that such a machine could easily be used to create weapons-grade plutonium, by irradiating uranium. And come decommissioning time, the reactor itself is a pile of toxic waste that will need long-term storage. I don't believe that fusion is inherently dirty; just that none of the technologies currently being investigated can be described as "clean". And they all run the risk of nuclear proliferation. IANAP.
    - DennisP 4y ago
      These issues apply to D-T fuel, whose output energy is 80% high-energy neutrons. Helion is using D-D/D-He3, whose output would be only 6% neutrons, at lower energy. If you do the D-D reactions in specialized fuel production facilities, you could sell the He3 to anyone with an He3 power plant and they'll have zero neutron radiation to deal with or misuse. Even with D-T, the reactor waste would stop being dangerously radioactive in a few decades.
    - LarryMullins 4y ago
      All of what you say is true. But on the plus side, you don't have the transuranic waste. Transuranic waste is the worst waste, the most dangerous and the most expensive and vital to store properly.
    - 4y ago

Fusion bombs soon with a laser primer instead of fission for heat generation? Not yet I guess. Clean power? Perhaps never.

by a3w 4y ago

Fusion bombs soon with a laser primer instead of fission for heat generation? Not yet I guess. Clean power? Perhaps never.

the_third_wave 4y ago

I think you're overestimating the amount of energy released in a single fusion event and underestimating the machinery needed to generate and focus the laser pulses on the hohlraum. Remember there is no fusion chain reaction, the thing would need to keep on pumping pellets into the "primer" while firing laser pulses to keep the energy flowing. Compared to a 'simple' fission primer with a neutron reflector I don't really see the gain in a laser-primed fusion weapon, at least not one in the line of current fusion bombs.

fallingknife 4y ago

Actually, the tech that you are hinting at would guarantee clean fusion power. If you could generate clean fusion explosions, detonate underground and use the heat to generate power. Nuclear bombs are currently the only net energy positive fusion devices we have.

arethuza 4y ago
Most bomb designs are fission-fusion-fission - most of the energy comes from the fission of the casing of the secondary by neutrons from the fusion process in the secondary. Edit: Mind you - there were tests like the huge Tsar Bomba that de-rated at 100+ Mt design to 50Mt be leaving out the final fission stage - the output being mostly from fusion. https://en.wikipedia.org/wiki/Tsar_Bomba https://en.wikipedia.org/wiki/Tsar_Bomba
- denton-scratch 4y ago
  My understanding is that what you're referring to as a "fusion" stage is really a fusion-enhanced fission stage. All the stages of normal "H-bombs" are fission stages, using a small fusion core to generate a flood of neutrons, which results in the fission fuel combusting more completely. Pure fission bombs tend to disintegrate long before enough neutrons have been generated to achieve complete combustion. The inclusion of a small core of lithium deuteride results in a much more efficient fission bomb. I suppose these NIF tests are tiny pure fusion explosions; but I'm not aware of any practical weapon that generated energy mainly from fusion.
  - arethuza 4y ago
    "fusion-enhanced fission stage" The primary is fusion boosted fission, the core ("spark-plug") of the secondary is also fusion boosted fission surrounded by dry fusion fuel (lithium deuteride) and then a fissionable tamper. My understanding is that X rays from the primary compress the entire secondary package - which ignites the spark-plug and then the fusion fuel is caught between the incoming tamper and the exploding spark-plug at its core and ignited. So there does appear to be a real "fusion" stage - with a lot of other steps involving fission and fusion. https://en.wikipedia.org/wiki/Thermonuclear_weapon https://en.wikipedia.org/wiki/Thermonuclear_weapon
    - denton-scratch 4y ago
      The cited article says: "Fast fission of the tamper and radiation case is the main contribution to the total yield and is the dominant process that produces radioactive fission product fallout." The way I read that, even in a large H-bomb, little of the yield is the direct result of fusion reactions. Rather, the neutrons produced by the fusion reaction dramatically increase the efficiency of the fission reactions, which on their own would not produce enough neutrons to fission more than a small part of the fissile material before the device disintegrates.
      - arethuza 4y ago
        There is still a considerable about directly from fusion e.g. in the Tsar Bomba the fusion stage produced about 47Mt of the 50Mt total (it had two smaller H-bombs as primaries for the fusion stage). The full design was 100+ Mt so about 50% from the final fission stage seems a rule of thumb, which is also mentioned in this article about "neutron bombs": https://en.wikipedia.org/wiki/Neutron_bomb https://en.wikipedia.org/wiki/Neutron_bomb Neutron bombs don't have fissile tampers on the secondary exposing the neutrons from fusion directly rather than using them to fission the tamper.
rgmerk 4y ago
It might guarantee clean fusion power, but there's no guarantee it would be in any way economic. Edward Teller proposed something along these lines with conventional two-stage nuclear explosives back in the 1970s, but it was rapidly abandoned as horribly inefficient and costly: https://en.wikipedia.org/wiki/Project_PACER https://en.wikipedia.org/wiki/Project_PACER I know this stuff is fun to speculate about but the boring and unsexy option of more solar panels, wind turbines, and transmission lines is likely to be both cheaper and more politically saleable.
- denton-scratch 4y ago
  > clean fusion power From what I understand, practical routes to fusion all produce a lot of fast neutrons, and tritium. The neutrons make the surrounding equipment radioactive, and create toxic elements. The tritium is itself toxic, and is hard to contain. And the high neutron flux means that such a machine could easily be used to create weapons-grade plutonium, by irradiating uranium. And come decommissioning time, the reactor itself is a pile of toxic waste that will need long-term storage. I don't believe that fusion is inherently dirty; just that none of the technologies currently being investigated can be described as "clean". And they all run the risk of nuclear proliferation. IANAP.
  - DennisP 4y ago
    These issues apply to D-T fuel, whose output energy is 80% high-energy neutrons. Helion is using D-D/D-He3, whose output would be only 6% neutrons, at lower energy. If you do the D-D reactions in specialized fuel production facilities, you could sell the He3 to anyone with an He3 power plant and they'll have zero neutron radiation to deal with or misuse. Even with D-T, the reactor waste would stop being dangerously radioactive in a few decades.
  - LarryMullins 4y ago
    All of what you say is true. But on the plus side, you don't have the transuranic waste. Transuranic waste is the worst waste, the most dangerous and the most expensive and vital to store properly.
  - 4y ago