- #1
artis
- 1,479
- 976
More or less all ICF schemes seem to be similar to the first artificial fusion method (also inertial) of the secondary of the hydrogen bomb.
Before I present the question let me show just another ICF approach recently done. The company is called "first light fusion", Their method is essentially a different form of inertial compression similar to the Sandia Z imploding liner method but different in the aspect that it is not symmetrical as is the liner. Instead they use a plastic cube with a spherical fuel cavity inside and hit it from one side with a high velocity EM accelerated projectile.
It is hard to find any good schematics and papers from them but this youtube video in the middle and towards the end should do it for a simple explanation
Their webpage
https://firstlightfusion.com/Aside from the practical capability of either of mentioned approaches I have two questions.
1) In order for the implosion/compression fusion approach to be realistic/practical I get the impression that one would need to rely on the outwards propagating wave of alpha heating that starts from the center at the moment ignition conditions are reached in the collapsing/imploding fuel mass, so in order to "use" this heating wave as it travels outwards one would need to do subsequent fresh fuel implosions quickly enough so that the new fuel being compressed passes onto and through the outwards moving heat wave of the previous fuel while it's still "burning"
If the repetition rate is too slow (as it is for all current ICF approaches) then the heating done by the alpha particles is lost to the surrounding volume after each shot, just like the neutrons are lost from each shot.
Without the ability to conserve at least some of the heat from any previous shot for next shot fuel mass , more energy needs to be put in for each shot. In theory is such low repetition rate ICF viable in terms of energy gain over energy input?
2) Due to the brief high density of the fuel mass close to/at the and soon after implosion, do neutrons also contribute to fuel heating? I would think the man free path gets smaller for neutrons when fuel reaches high density.
And lastly there is one effect that is present in some of the ICF schemes but not others.
In the original ICF which was thermonuke secondary, the fusion fuel is surrounded by a tamper/pusher whereby the Xray radiation within the radiation channel hits the spherical secondary and the ablation of the surface of the high Z material creates a plasma of said material that propels outwards and pushes the tamper material inwards respectively, thereby compression is achieved. I think what happens when the fusion fuel achieves ignition is the pressure inside now pushes back outwards but this push is retarded by the still present high mass spherical tamper.
This I think limits the expansion velocity and gives more time for the fusion to be in the ignition state.
I do not see the same mechanism present in NIF for example, as the laser pulse implodes the fuel pellet the compressed and hot fuel is free to expand into vacuum and there is nothing in place to retard it's expansion prolonging the "burn".
On the other hand in other ICF approaches like the copper liner Sandia approach and aforementioned first light approach the fuel is either surrounded by a liner or within a plastic cube which I think somewhat performs the retardation role of the expanding plasma once the fuel mass achieves fusion conditions.
How important is this retardation aka slowing down of outwards expansion for ICF designs in order to increase efficiency of the burn?Would the ideal ICF approach be high repetition rate symmetrical implosion of fresh fuel doses onto the center , where the rate of repetition is high enough so that each next dose is imploded while the previous one is still in it's "outward expansion burn" state?
Before I present the question let me show just another ICF approach recently done. The company is called "first light fusion", Their method is essentially a different form of inertial compression similar to the Sandia Z imploding liner method but different in the aspect that it is not symmetrical as is the liner. Instead they use a plastic cube with a spherical fuel cavity inside and hit it from one side with a high velocity EM accelerated projectile.
It is hard to find any good schematics and papers from them but this youtube video in the middle and towards the end should do it for a simple explanation
Their webpage
https://firstlightfusion.com/Aside from the practical capability of either of mentioned approaches I have two questions.
1) In order for the implosion/compression fusion approach to be realistic/practical I get the impression that one would need to rely on the outwards propagating wave of alpha heating that starts from the center at the moment ignition conditions are reached in the collapsing/imploding fuel mass, so in order to "use" this heating wave as it travels outwards one would need to do subsequent fresh fuel implosions quickly enough so that the new fuel being compressed passes onto and through the outwards moving heat wave of the previous fuel while it's still "burning"
If the repetition rate is too slow (as it is for all current ICF approaches) then the heating done by the alpha particles is lost to the surrounding volume after each shot, just like the neutrons are lost from each shot.
Without the ability to conserve at least some of the heat from any previous shot for next shot fuel mass , more energy needs to be put in for each shot. In theory is such low repetition rate ICF viable in terms of energy gain over energy input?
2) Due to the brief high density of the fuel mass close to/at the and soon after implosion, do neutrons also contribute to fuel heating? I would think the man free path gets smaller for neutrons when fuel reaches high density.
And lastly there is one effect that is present in some of the ICF schemes but not others.
In the original ICF which was thermonuke secondary, the fusion fuel is surrounded by a tamper/pusher whereby the Xray radiation within the radiation channel hits the spherical secondary and the ablation of the surface of the high Z material creates a plasma of said material that propels outwards and pushes the tamper material inwards respectively, thereby compression is achieved. I think what happens when the fusion fuel achieves ignition is the pressure inside now pushes back outwards but this push is retarded by the still present high mass spherical tamper.
This I think limits the expansion velocity and gives more time for the fusion to be in the ignition state.
I do not see the same mechanism present in NIF for example, as the laser pulse implodes the fuel pellet the compressed and hot fuel is free to expand into vacuum and there is nothing in place to retard it's expansion prolonging the "burn".
On the other hand in other ICF approaches like the copper liner Sandia approach and aforementioned first light approach the fuel is either surrounded by a liner or within a plastic cube which I think somewhat performs the retardation role of the expanding plasma once the fuel mass achieves fusion conditions.
How important is this retardation aka slowing down of outwards expansion for ICF designs in order to increase efficiency of the burn?Would the ideal ICF approach be high repetition rate symmetrical implosion of fresh fuel doses onto the center , where the rate of repetition is high enough so that each next dose is imploded while the previous one is still in it's "outward expansion burn" state?
