Fusion Instabilities Lessened by Unexpected Effect

[Francisl]

Helmholz coil offers clues about how to achieve controlled nuclear fusion at Sandia National Laboratories’ powerful Z machine.

[ikanreed]

Francisl wrote: Helmholz coil offers clues about how to achieve controlled nuclear fusion at Sandia National Laboratories’ powerful Z machine.

I’m nowhere near the physicist it would take to even know if Rayleigh-Taylor instabilities even affect FocusFusion. All I know is that both experiments are Z-pinch based. Is there any applicability of this info on FoFu-1?

[Francisl]

ikanreed wrote:

I’m nowhere near the physicist it would take to even know if Rayleigh-Taylor instabilities even affect FocusFusion. All I know is that both experiments are Z-pinch based. Is there any applicability of this info on FoFu-1?

Please consider two points:
1. This demonstrates that progress and innovation are occurring in the fusion field.
2. LPPx showed the effectiveness of a small axial magnetic field to improve the intensity of a pinch. This is similar.

[zapkitty]

Francisl wrote:

I’m nowhere near the physicist it would take to even know if Rayleigh-Taylor instabilities even affect FocusFusion. All I know is that both experiments are Z-pinch based. Is there any applicability of this info on FoFu-1?

Please consider two points:
1. This demonstrates that progress and innovation is occurring in the fusion field.
2. LPPx showed the effectiveness of a small axial magnetic field to improve the intensity of a pinch. This is similar.

Well, similar in the concept of small magnetic fields being capable of having a beneficial effect in the midst of far more powerful fields.

But just as a Focus Fusion DPF and a MagLIF device are very different devices, the small fields that each uses and their respective purposes are also very different.

[asymmetric_implosion]

The ideas are nearly identical during the radial compression. Both system are trying to compress magnetic flux and stabilize the implosion. Both will add some measure of angular momentum to the implosion. In both cases, the applied fields are small compared to the induced fields from the current. In both cases, the compressed field reduces electron transport and keeps the plasma hot.

[zapkitty]

asymmetric_implosion wrote: The ideas are nearly identical during the radial compression…

But I’m thinking that if the axial spin is applied during the DPF’s rundown phase by, say, a helical configuration of the electrodes instead of, and not as efficiently controlled as, FF’s axial coil (an option that has been considered elsewhere) then all that follows after the rundown, the events during the radial compression that you mention, would all happen in the DPF [em]without[/em] benefit of the initial axial field.

[asymmetric_implosion]

The purpose of the axial field per Slutz’s original paper is to limit Rayleigh-Taylor instabilities during implosion and to confine pre-heated electrons. The instability arises due to a light fluid, the magnetic field, pressing on a heavy fluid, the plasma or a metal can. The axial field is compressed which changes the radial implosion velocity profile. The other consideration for the MagLif is to preheat the fuel to 100 eV with a laser.

The helical electrodes are an old idea but they have problems. The biggest challenge is forcing the plasma to stay connected to the electrodes. If you build a helical electrode the plasma current is still radial with an azimuthal field. The bulk of the force is still in the axial direction. The force will push the plasma along the helix and it may skip the valley and jump to the next hill in the helix. The initial axial field is the best way to add some angular momentum to the plasma.

[Henning]

As far I understood Eric, the effect of the axial coil in FF1 is to get the plasma sheath into filaments as early as possible.

[zapkitty]

Henning wrote: As far I understood Eric, the effect of the axial coil in FF1 is to get the plasma sheath into filaments as early as possible.

That’s what the tungsten “crown” at the base of the anode is meant to do… encourage the start of filamentation in the sheath.

The axial field is meant to impart a small rotational component to the sheath/filaments as they travel down the electrodes so that when the pinch comes the filaments more readily swirl into a vortex rather than clashing together and thus losing energy.

[Author]

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