Q and the Dpf

[Rezwan]

Folks, I want to put together something to explain the objective/deliverable of fusion research.

Looking up Q, we see:

The fusion energy gain factor, usually expressed with the symbol Q, is the ratio of fusion power produced in a nuclear fusion reactor to the power required to maintain the plasma in steady state.

How does this relate to LPPX’s DPF?

Similar discussion at this thread. Mergeable?

[JimmyT]

Rezwan wrote: Folks, I want to put together something to explain the objective/deliverable of fusion research.

Looking up Q, we see:

The fusion energy gain factor, usually expressed with the symbol Q, is the ratio of fusion power produced in a nuclear fusion reactor to the power required to maintain the plasma in steady state.

How does this relate to LPPX’s DPF?

Similar discussion at this thread. Mergeable?

This definition doesn’t work very well with the DPF process. Since DPF’s are never really in a steady state. I wonder if some alternative definition would work better ?

[Tulse]

Isn’t Q more generally the ratio of power out vs. power required to run the reaction? That presumably would apply to transient fusion as well as steady state.

[JimmyT]

Tulse, I was thinking something similar. But this is getting pretty close to the defination of theoretical break even. I wonder if we should just be happy with an adequate defination of that term.

[Brian H]

My understanding is that since FF powers itself once initiated, the Q would be infinite. You can’t just count the first “pinch”, since that powers the second and so on. A steady-state reactor (which I personally doubt will ever be achieved on the human scale) requires continuous input to power the super-conducting magnets, etc., that restrain the nasty plasma. Then there’s the overhead of the inefficient extraction of power from the steam cycle, etc.

[Tulse]

Brian H wrote: My understanding is that since FF powers itself once initiated, the Q would be infinite.

Presumably all above-breakeven fusion devices would be able to power themselves, and thus under that criterion have infinite Q. Perhaps I’m misunderstanding something here.

[Brian H]

Tulse wrote:

My understanding is that since FF powers itself once initiated, the Q would be infinite.

Presumably all above-breakeven fusion devices would be able to power themselves, and thus under that criterion have infinite Q. Perhaps I’m misunderstanding something here.
Well, a steady-state reactor requires continuous power input for magnets, etc., which pulsed does not. I don’t think Q applies well to pulsed generation, actually.

[Tulse]

Brian H wrote:
Well, a steady-state reactor requires continuous power input for magnets, etc., which pulsed does not.

But a pulsed device does require power input for each pulse — surely it is reasonable to define Q as simply the ratio of the amount of power produced by a fusion reaction to the amount of power required to produce the reaction. That definition is agnostic as to whether the reaction is steady state or pulsed. At the very least, we can integrate over a period of time for pulsed devices to make such issues irrelevant.

And I think it is a red herring to factor in the energy fed back into the FF device, since a steady-state device over unity could also feed its own energy back into maintaining the plasma, just not as directly. (And there is no reason in principle why the FF capacitors have to be charged directly from the device itself — that is just the potentially most efficient way to do so.)

[Brian H]

I think the relevance is to thermal fusion, since the steam cycle is so lossy. The heat surplus has to be enough to push through enough to generate the input to the reactor from a steam turbine. Then to get any useful power requires more. So I’ve seen suggestions that Q needs to be around 5 for a steady-state thermal fusion system to be viable.

For FF, all the excess from the direct electric output is usable/salable. So Q loses its relevance, IMO.

[vansig]

JimmyT wrote: this is getting pretty close to the defination of theoretical break even.

Although not continuous, the principle of dynamic equilibrium easily translates to plasma focus, when you consider it to be a sequence of repeating cycles. Q shouldn’t really be that hard to understand.

but you also have: gain

let’s not redefine/muddle the terms. they’re supposed to be mathematically concise.

i understand gain more in terms of each individual fusion reaction, where it should be the simple ratio of
(energy out) / (energy in).

if you think about it, if ANY fusion occurs, at all, this should be >1. which is why, i think its more useful to have
Q = (energy out – energy in) / (energy in), per cycle.

[Brian H]

vansig wrote:

this is getting pretty close to the defination of theoretical break even.

Although not continuous, the principle of dynamic equilibrium easily translates to plasma focus, when you consider it to be a sequence of repeating cycles. Q shouldn’t really be that hard to understand.

but you also have: gain

let’s not redefine/muddle the terms. they’re supposed to be mathematically concise.

i understand gain more in terms of each individual fusion reaction, where it should be the simple ratio of
(energy out) / (energy in).

if you think about it, if ANY fusion occurs, at all, this should be >1. which is why, i think its more useful to have
Q = (energy out – energy in) / (energy in), per cycle.
You can get fusion in a basement fusor, but the total fusion energy is far less than the electrical power used to force it to happen.

[Aeronaut]

Tulse wrote:
But a pulsed device does require power input for each pulse — surely it is reasonable to define Q as simply the ratio of the amount of power produced by a fusion reaction to the amount of power required to produce the reaction. That definition is agnostic as to whether the reaction is steady state or pulsed. At the very least, we can integrate over a period of time for pulsed devices to make such issues irrelevant.

And I think it is a red herring to factor in the energy fed back into the FF device, since a steady-state device over unity could also feed its own energy back into maintaining the plasma, just not as directly. (And there is no reason in principle why the FF capacitors have to be charged directly from the device itself — that is just the potentially most efficient way to do so.)

I think Eric refers to this as ‘wall plug efficiency’, which I like for how simple and direct it is. Its also the way most people will perceive Q without a long conversation, imo. You also have a great point about integrating the pulses into a sort of average over time.

And why not extend the concept of a ‘net zero’ house (the solar and wind features sell as much power as it consumes) into a net positive business location? The higher the thermal to electrical profit ratio, the more critical it will be to charge the caps from the grid. Would it take an ultra brawny cap bank regulator to charge around 200 to 300hz?

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