Inductance?

[Francisl]

Is self-inductance in the cables and distribution system the main problem preventing faster discharges? I suggest making inductance a useful thing. That would require using a second circuit to pre-charge the conduction system with a large current to create a strong stable magnetic field around the conductors just before the high voltage system discharges.

[Aeronaut]

Francisl wrote: Is self-inductance in the cables and distribution system the main problem preventing faster discharges? I suggest making inductance a useful thing. That would require using a second circuit to pre-charge the conduction system with a large current to create a strong stable magnetic field around the conductors just before the high voltage system discharges.

Another way to use the inductance could be to synchronize 2 or more FFs and switch the destination when a core’s inductance generates reverse EMF. Last time I sketched it out, it favored utility scale installations better suited for the PolyWell architecture.

We might be able to take that ground, but I’m thinking its faster and cheaper to build a full-scale PW with private funds for a change and see if the theory holds at full scale.

[vansig]

Francisl wrote: Is self-inductance in the cables and distribution system the main problem preventing faster discharges? I suggest making inductance a useful thing. That would require using a second circuit to pre-charge the conduction system with a large current to create a strong stable magnetic field around the conductors just before the high voltage system discharges.

I don’t see how that can work.

But i dont see induction as the problem. It’s a matter of synchronization. You have up to 2.4 MA current, fed by 12 switches, so each one rises from nothing to 200 kA, in as few nanoseconds as possible.

[Aeronaut]

I have sketched out some alternate basic system geometries placing 9 to 16 caps in a rectangular base and the DPF built above the HV plates to minimize inductance.

[Francisl]

vansig wrote:

Is self-inductance in the cables and distribution system the main problem preventing faster discharges? I suggest making inductance a useful thing. That would require using a second circuit to pre-charge the conduction system with a large current to create a strong stable magnetic field around the conductors just before the high voltage system discharges.

I don’t see how that can work.

But i dont see induction as the problem. It’s a matter of synchronization. You have up to 2.4 MA current, fed by 12 switches, so each one rises from nothing to 200 kA, in as few nanoseconds as possible.

I have attached my concept of how this would work. I hope you can open the file.
The idea is that an auxiliary low voltage, high current power source would be connected to the conductors for a few nanoseconds or however long it takes to establish a stable magnetic field. Then the high voltage capacitor discharges before the magnetic field collapses in the conductors. That way the high voltage current isn’t slowed down by having to establish the magnetic field that is the cause of self-inductance.

The capacitor could represent a single unit or all of the units tied together. If this concept works and self-inductance is no longer a problem, then all of the capacitors can be tied in parallel to one switch and eliminate the synchronization problem.

Taking it one step further, an inductance coil can be in series in the high voltage circuit. When the charging current is shut off there could be an inductive voltage boost that could cause the high voltage current to jump the spark gap and remove the need for a spark plug.

Attached files

Inductance circuit.pdf (18 B) 

[vansig]

Francisl wrote:
The idea is that an auxiliary low voltage, high current power source would be connected to the conductors for a few nanoseconds or however long it takes to establish a stable magnetic field. Then the high voltage capacitor discharges before the magnetic field collapses in the conductors. That way the high voltage current isn’t slowed down by having to establish the magnetic field that is the cause of self-inductance.

i understand what you’re saying, but i don’t believe the physics works that way. the magnetic field isn’t the cause of self-inductance, but a consequence of the current flow. there will be no effect on the high-voltage current.

[mchargue]

vansig wrote:

The idea is that an auxiliary low voltage, high current power source would be connected to the conductors for a few nanoseconds or however long it takes to establish a stable magnetic field. Then the high voltage capacitor discharges before the magnetic field collapses in the conductors. That way the high voltage current isn’t slowed down by having to establish the magnetic field that is the cause of self-inductance.

i understand what you’re saying, but i don’t believe the physics works that way. the magnetic field isn’t the cause of self-inductance, but a consequence of the current flow. there will be no effect on the high-voltage current.

From my understanding, I don’t think that there’s any way to ‘prime the pump’, so to speak, as a way of reducing the inductance (reluctance) of the FF reactor. The use of non-ferrous materials, and short, well shielded/terminated, cable lengths, is probably the best that can be done. A magnetic field is created when charges are moved, and inductance (reluctance) is related to how easily the magnetic field can propagate through space – which is related to the permeability of the material the magnetic field propagates through. Low permeability means low inductance, (copper) while high permeability means high inductance. (iron)

Pat

[Francisl]

vansig wrote:

The idea is that an auxiliary low voltage, high current power source would be connected to the conductors for a few nanoseconds or however long it takes to establish a stable magnetic field. Then the high voltage capacitor discharges before the magnetic field collapses in the conductors. That way the high voltage current isn’t slowed down by having to establish the magnetic field that is the cause of self-inductance.

i understand what you’re saying, but i don’t believe the physics works that way. the magnetic field isn’t the cause of self-inductance, but a consequence of the current flow. there will be no effect on the high-voltage current.

I agree with you that the current flow is the cause of the magnetic field. As current in a conductor increases the corresponding magnetic field increases and energy is stored in that magnetic field. It takes time to establish a magnetic field in a coil and less time in a straight conductor. Once the current flow and consequent magnetic field have reached a stable peak, then the only restriction is ohmic resistance.
My crude diagram and short explanation probably weren’t clear. I suggest using an auxiliary power source to supply a relatively low voltage, high amperage current to establish the stable magnetic field in the conductors. The high voltage capacitors are discharged after the magnetic field is established. The high voltage discharges occurs before the auxiliary power shuts off. There would be no break in the current flow and no loss in the magnetic field until the capacitors are finished firing and their current declines. The magnetic field in the conductors collapses and returns the stored energy to the current flow.

[Francisl]

mchargue wrote:

The idea is that an auxiliary low voltage, high current power source would be connected to the conductors for a few nanoseconds or however long it takes to establish a stable magnetic field. Then the high voltage capacitor discharges before the magnetic field collapses in the conductors. That way the high voltage current isn’t slowed down by having to establish the magnetic field that is the cause of self-inductance.

i understand what you’re saying, but i don’t believe the physics works that way. the magnetic field isn’t the cause of self-inductance, but a consequence of the current flow. there will be no effect on the high-voltage current.

From my understanding, I don’t think that there’s any way to ‘prime the pump’, so to speak, as a way of reducing the inductance (reluctance) of the FF reactor. The use of non-ferrous materials, and short, well shielded/terminated, cable lengths, is probably the best that can be done. A magnetic field is created when charges are moved, and inductance (reluctance) is related to how easily the magnetic field can propagate through space – which is related to the permeability of the material the magnetic field propagates through. Low permeability means low inductance, (copper) while high permeability means high inductance. (iron)

Pat

Please look at my explanation to vansig and see if it makes any sense. In a way I am trying to prime the pump. Inductance is a form of resistance that occurs when the current flow changes. It occurs in AC but not DC circuits. A pulsed circuit is like an AC circuit because the current flow is changing and the corresponding magnetic field is changing. This inductance is a form of resistance that is added to ohmic resistance to slow down the speed of discharging the capacitors. I am trying to create a DC type of circuit for a very brief time by removing the inductive resistance. The auxiliary power source would provide a 2.4 megamp current to prime the circuit and create the stable current flow and magnetic field. The high voltage capacitors would immediately discharge their 2.4 megamps before the auxiliary power is exhausted. There would be no break or change in the current flow resulting in DC type of circuit with no inductive resistance only ohmic resistance.
I guess that impedance is what I am really describing. This is not my area of expertise and my terminology may not be precise enough. I hope that my speculation and enthusiasm are not getting in the way of serious research.

[vansig]

the feed conductors in the FoFu are flat sheets, placed some distance apart. the capacitor discharge propagates along these sheets, from outside to inside.
for total current of 2.5MA, there are four sections of 3 each, (total of 12 switches).

the problems with your notion, are two:
1) there is no practical way to wrap a coil around, to test this; but,
2) i am unconvinced that there is any physical effect, regardless.

i don’t believe your description is unclear. it’s just wrong.

[Francisl]

I didn’t know it at the time but I was trying to describe a circuit using a Plasma Opening Switch POS. It basically works like a DPF. A fast unit is hard to find. Perhaps the LPPX technology could be used to create a very fast switch that could be patented.

[Aeronaut]

Francisl wrote: I didn’t know it at the time but I was trying to describe a circuit using a Plasma Opening Switch POS. It basically works like a DPF. A fast unit is hard to find. Perhaps the LPPX technology could be used to create a very fast switch that could be patented.

Looks like it’ll handle enough voltage and current (when the switch ‘opens’) to make a single switch practical for the FF’s input power pulse. A similar 2nd switch could perhaps send the trapped inductive energy and the surplus electrical energy into the output cap bank. Might really increase design flexibility while reducing system costs and parts cost. But I doubt the DPF would be practical for what you propose.

[Author]

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