Heat produced by Focus Fusion and cooling

[Brian H]

vansig wrote: part of me wants to go ultra-low tech, here, and only use parts for this that were available to Benjamin Franklin in 1752.

a high Tc superconductor could have interesting effects on the plasmoid’s magnetic field, pushing it away from the anode; will a proper plasmoid even form?

Within the hollow anode, would that not increase and assist compression/collapse? The actual fusion occurs as the plasmoid self-annihilates, no?

[vansig]

such effects are probably worth testing

[Henning]

We will not be able to use even high-Tc superconductors (highest claim to date around 250K), because that’s still pretty chilly in an environment where you want to pump out heat generated. There is a discussion on Talk-Polywell with Johan Prins who claims to have obtained a much much higher Tc with his own diamond based process and theory. But still that might be doubtable.

So there is something called ultraconductors based on polymers which should have several magnitudes more conductivity than copper. Yes, polymers are insulator, but they claim with films that’s different.

Maybe overall it’s similar to graphene.

[Henning]

Oh, and anything with high Z gets heated by x-rays anyway. So superconduction with heavy metals (Yb, or whatever) is a bad idea.

[Aeronaut]

The fastest way to double current is to halve the electrode length. Eric mentioned what seemed to be a very short anode in the Google Talks presentation.

[Allan Brewer]

Henning wrote: We will not be able to use even high-Tc superconductors (highest claim to date around 250K), because that’s still pretty chilly in an environment where you want to pump out heat generated. .

1) But if we superconduct the current in and out, then we eliminate the vast majority (maybe 4MW) of the resistive heat by-product i.e. we have much less cooling to achieve.
2) Some copper oxide superconductors can still operate at 50 degrees above liquid nitrogen boiling temperature giving a lot of margin.

There is a discussion on Talk-Polywell with Johan Prins who claims to have obtained a much much higher Tc with his own diamond based process and theory. But still that might be doubtable.

…mmmm??

So there is something called ultraconductors based on polymers which should have several magnitudes more conductivity than copper. Yes, polymers are insulator, but they claim with films that’s different. Maybe overall it’s similar to graphene.

That sounds very promising – let’s hope.

Oh, and anything with high Z gets heated by x-rays anyway. So superconduction with heavy metals (Yb, or whatever) is a bad idea. .

But the superconductor can be extremely thin so it matters less.
Indeed the whole problem arises because the fast-rising current is only conducted in the outer film of the metal anode. Another possible approach to this might be laminating the metal so there are effectively a very large number of separate parallel metal conductors all of which have an outer film and can carry current?

Aeronaut wrote: The fastest way to double current is to halve the electrode length. Eric mentioned what seemed to be a very short anode in the Google Talks presentation.

Absolutely, we are not only talking about heat produced and cooling requirement, but inversely about the capability of the capacitors to deliver current to the plasmoid, which might also be a limiting factor.

[Allan Brewer]

Oh, and not forgetting that the resistance of the metal electrode willl triple if we let it heat from room temperature to 600 degrees C, tripling the heat produced and the problem. Cool running would definitely help all round.

[Henning]

You have a point there.

[vansig]

Allan Brewer wrote:
Indeed the whole problem arises because the fast-rising current is only conducted in the outer film of the metal anode. Another possible approach to this might be laminating the metal so there are effectively a very large number of separate parallel metal conductors all of which have an outer film and can carry current?

you have to consider *why* the fast-rising current is only conducted in the outer film: it’s because like-charges repel. they will seek to be as far from each other as possible.

if we had, say, a bunch of separate, concentric, conducting tubes, insulated layer-to-layer, then yes it might be possible to spill high current into each, if we adjust the timing slightly, since the rising edge will travel at different rates in different diameter tubes.

note, also, that this is affected by eddy currents. a moving charge in one tube induces a counter-current in another layer. this is potentially helpful: electrons travelling towards the tips of the cathodes will help induce desired anode counter-currents.

but eddy currents in adjacent layers would be detrimental, so it’s tough to say there would be overall improvement.

the sum of all these effects is a worthy modeling exercise, anyway.

[Allan Brewer]

That’s really interesting vansig – I’ve been trying to find out why. Can you name the effect or give a link to a description, and I’ll see if its within my modelling capability.

[vansig]

let’s see.. search terms could be,
coaxial signal propagation speed; coaxial eddy currents; coaxial velocity factor
much of the discussion is around radio frequency propagation, but the same reasoning should apply to the rising edge of the pulse, here.

the inter-layer coupling capacitance and inductance yields velocity factor,
http://en.wikipedia.org/wiki/Wave_propagation_speed#Calculating_velocity_factor
which depends on respective conductor diameters and dielectric constant of the insulator.

eddy currents are responsible for the skin effect
http://en.wikipedia.org/wiki/Eddy_current#Strength_of_eddy_currents

skin depth depends on the frequency. we’re rather wide-band, here, with the rising edge in ~25 ns, and the pulse lasting microseconds. if 25 ns is 1/2 wave, then f=20 MHz; whereas the bulk of the current is delivered as though it is, say, a ~500 kHz pulse, and skin depth increases through the pulse, as δ = sqrt( (2 ρ) / (ω μ) ).
http://en.wikipedia.org/wiki/Skin_effect

em-field calculations for single and multi-layer coax
http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=119816

and there is a book on signal propagation black magic
http://tinyurl.com/33nrh8p

[psupine]

and there is a book on signal propagation black magic
http://tinyurl.com/33nrh8p

I have this fantastic book. It is mostly about measurement and keeping the loop areas as small as possible so the high frequencies are still visable.

The emphasis with DPF is I think slightly different in that we are trying to get as much energy into the plasma as we can before it detaches from the electrodes and forms the plasmoid.

Maybe we should be thinking about what can be done to delay the plasmoid formation so that the energy transfer can be maximised?

(edit) Actually, a lot of the book is about good termination too

[vansig]

increasing the angular momentum on the external magnetic field might delay the pinch.
i thought the pinch occurred at the end of the pulse, anyway?

but i seem to recall Eric writing something about the possibility of a double pinch if rise times are not closely synchronized.
so it makes sense that rise time is the critical parameter

[benf]

jamesr 04 July 2010 03:30 PM

The anode would have helium gas pumped through, in order to keep its surface below 800K or so. The outside of the vacuum chamber and other parts (eg. the capacitors) can be conventionally water cooled.

What temperatures would you anticipate stemming from the fusion produced electron particle beam meeting the solenoid? Will the beam be collimated like a laser beam or more diffused as we see with jets in space. Does the solenoid need special materials and cooling treatment as well?

[Brian H]

benf wrote: jamesr 04 July 2010 03:30 PM

The anode would have helium gas pumped through, in order to keep its surface below 800K or so. The outside of the vacuum chamber and other parts (eg. the capacitors) can be conventionally water cooled.

What temperatures would you anticipate stemming from the fusion produced electron particle beam meeting the solenoid? Will the beam be collimated like a laser beam or more diffused as we see with jets in space. Does the solenoid need special materials and cooling treatment as well?

When I asked that question (more or less) Eric communicated that the plasmoid, in the final incarnation, will intercept and absorb most of the electron beam directly, so that it doesn’t significantly erode the base of the anode. So I take it that there will be no exiting electron beam at all.

[Author]

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