how small can a focus fusion device get?

[meemoe_uk]

Has any theoretical limit been established for how small a focus fusion device could be?

Say if focus fusion is a success, how small could future devices could get?

I’m guessing the biggest part of a FF device is the capacitor bank. Hopefully the rapid advance of super capacitors will help reduce the size of future FF devices.

Size of a car battery? That would be awesome.

[asymmetric_implosion]

You are correct that the largest piece is the capacitors. Super capacitor technology is advancing quickly but they are the wrong kind of capacitors. The capacitors for FoFu require low inductance, fast discharge current and high voltage. Super capacitors tend to be low voltage, slow discharge capacitors. It is challenging to reduce the size of high voltage capacitors that can discharge as needed in FoFu. Other technologies may replace capacitors but a FoFu reactor will still need shielding. I can imagine a 5 MW reactor with everything fitting in a 1 car garage but much small than that is unlikely.

[vansig]

meemoe_uk2 wrote: Hopefully the rapid advance of super capacitors will help reduce the size of future FF devices.

while researching capacitors i found some practical advice that must be kept in mind: focus fusion requires caps that are pulse rated.
here is a discussion http://www.youtube.com/watch?v=g1SN3rMTFok

this will impact whether we can use super capacitors for it.

[Tulse]

asymmetric_implosion wrote: You are correct that the largest piece is the capacitors. Super capacitor technology is advancing quickly but they are the wrong kind of capacitors. The capacitors for FoFu require low inductance, fast discharge current and high voltage. Super capacitors tend to be low voltage, slow discharge capacitors. It is challenging to reduce the size of high voltage capacitors that can discharge as needed in FoFu. Other technologies may replace capacitors but a FoFu reactor will still need shielding. I can imagine a 5 MW reactor with everything fitting in a 1 car garage but much small than that is unlikely.

So sized appropriately for use in ships, and maybe even trains, but not planes or cars. Perhaps shipping-container-sized?

Speaking of ships, it seems there is a nice confluence of the types of caps that FF needs and that the Navy will need for directed energy weapons and railguns. It looks like FF would be ideal for an electric Navy.

[zapkitty]

Tulse wrote:
So sized appropriately for use in ships, and maybe even trains, but not planes or cars. Perhaps shipping-container-sized?

Large subsonic transports, which comprise the bulk of current-day commercial aircraft operations, could be designed to work with FF units… if the carbon-11 issue could be dealt with in case of a crash.

And yep… a turnkey FF installation should fit into a 40′ TEU shipping container.

Tulse wrote: It looks like FF would be ideal for an electric Navy.

As would any aneutronic fusion system… that’s why they funded polywell research.

[Reactor1967]

The fusion part itself can be made small as far as I know but the shielding and power requirements would be hard to miniaturize with current technology.

But, with out of the box thinking and developments in technology it might be possible in the future to make this small.

Off the top of my head I can think of a few things that might help but those things are a little unconventional and not publicly tested at this time. But, yeah I would say it is possible to make this small.

[mchargue]

asymmetric_implosion wrote: You are correct that the largest piece is the capacitors. Super capacitor technology is advancing quickly but they are the wrong kind of capacitors. The capacitors for FoFu require low inductance, fast discharge current and high voltage. Super capacitors tend to be low voltage, slow discharge capacitors. It is challenging to reduce the size of high voltage capacitors that can discharge as needed in FoFu. Other technologies may replace capacitors but a FoFu reactor will still need shielding. I can imagine a 5 MW reactor with everything fitting in a 1 car garage but much small than that is unlikely.

What other technology might replace capacitors in this application?

TIA;
Pat

[Tulse]

mchargue wrote: What other technology might replace capacitors in this application?

How about a focus fusion device? When a FF fires, would the pulse it produces be short enough to get another FF to fire? If so you could daisy chain the suckers, and just need a set of caps to get things rolling. It’s not perpetual motion exactly, but…

🙂

[pschmidt]

Tulse wrote:

What other technology might replace capacitors in this application?

How about a focus fusion device? When a FF fires, would the pulse it produces be short enough to get another FF to fire? If so you could daisy chain the suckers, and just need a set of caps to get things rolling. It’s not perpetual motion exactly, but…

🙂

From what I understand, the caps can charge/discharge at 500KHz. The FoFu device is expected to operate at 200Hz or less (for heat dissipation reasons.) It is therefore possible to multiplex multiple FoFu devices with fast switching (in theory >1000). However, the amount of heat that would produce is daunting. You might also find new physical limitations in the caps – I highly doubt anyone has actually driven these caps that hard.

From what I understand of the early estimates, 5MW of solid-state output electricity will also result in somewhere around 7MW of waste heat. If you had 10, you would generate 50MW of electricity, but have 70MW of heat to get rid of. With jet engines, this is naturally expelled out of the back of the engine. With the FoFu in a plane (for example), you’d have to vent this heat. (I have no idea how much heat jet engines generate compared to this, but I recall a modern 747 as having engines that can generate something like 150MW of force. I don’t know how much heat they generate.) An interesting idea would be to design a turbofan with its FoFu unit(s) built into the front or rear of it so the force of the thrust is also used to vent the heat.

It is amusing to contemplate that it may be possible to build a multiplexed system to generate a 5GW power plant using a single capacitor bank as a primary buffer. I suspect the switching requirements for this are impractical. Also, there are very few applications where extremely high power output from a single source would be a better idea than localizing the power generation in smaller units. (Fault tolerance, etc.)

[mchargue]

mchargue wrote:

You are correct that the largest piece is the capacitors. Super capacitor technology is advancing quickly but they are the wrong kind of capacitors. The capacitors for FoFu require low inductance, fast discharge current and high voltage. Super capacitors tend to be low voltage, slow discharge capacitors. It is challenging to reduce the size of high voltage capacitors that can discharge as needed in FoFu. Other technologies may replace capacitors but a FoFu reactor will still need shielding. I can imagine a 5 MW reactor with everything fitting in a 1 car garage but much small than that is unlikely.

What other technology might replace capacitors in this application?

TIA;
Pat

Well, here’s something interesting in pulse-power systems: a ‘Compensated pulsed alternator’, or compulsator
https://en.wikipedia.org/wiki/Compensated_pulsed_alternator

This takes the energy of motion, and uses that to drive a high-current systems, like railguns. Not sure what the output voltage is, though I expect that can be tuned. Given that something like this can be used, would this eliminate the high-current, high-voltage switch? (spark-gap now) If you’re switching on a (relatively) low-power excitation field used to stop the flywheel – which will then give up it’s energy as a high-current, high-voltage spike – can your use that to shape the FoFu power pulse?

Maybe this in combination with something that can compress the compulsator’s output pulse into something more usable by FoFu…?

Maybe this?
http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=6191525&url=http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=6191525

Or some of these?
http://ieeexplore.ieee.org/xpl/mostRecentIssue.jsp?punumber=6188417

You folks need to fins a grad student trying to make his bones in the pulsed-power field, and convince him there’s a thesis topic in this.

Patrick

[Henning]

Please be aware, that the discharge time is crucial. The switch has to operate 45 kV / 2.8 MA within 100 µs or better (something of this order). And the capacitors / electric sources have to supply them within that time.

I don’t have the graphs currently, but this is a steep increase in power over time.

[zapkitty]

Henning wrote: Please be aware, that the discharge time is crucial. The switch has to operate 45 kV / 2.8 MA within 100 µs or better (something of this order). And the capacitors / electric sources have to supply them within that time.

I don’t have the graphs currently, but this is a steep increase in power over time.

Gonna need some hefty wall plugs 🙂

[mchargue]

Henning wrote: Please be aware, that the discharge time is crucial. The switch has to operate 45 kV / 2.8 MA within 100 µs or better (something of this order). And the capacitors / electric sources have to supply them within that time.

I don’t have the graphs currently, but this is a steep increase in power over time.

True that. but if you look at what many compulsator’s are used for – railguns – the need is the same. Right now, a railgun’s payload spends very little time in the barrel. Projections for future needs – higher velocities & shorter barrels – means that the time is only going to decrease. From what I can determine, the technology’s not quite there yet – but mine was not an exhaustive search.

Mostly, I’m considering the advantages that would come from having to switch a much smaller current (on the order of 10kA) through the rotor field winding to control a much larger output current from the stator. The ‘compensated alternator’ (compulsator) is designed in such a way to produce large current/voltage spikes, and may be applicable to FoFu’s needs.

From what I can find, it’s not a hot topic of research outside of DARPA, but there are some PDFs that describe this well. In addition to this, I have seen other descriptions of experiments that have devices that come much closer (factor of 40) to what FoFu needs.

Some FYI:
http://digitalcommons.calpoly.edu/cgi/viewcontent.cgi?article=1108&context=aerosp

Pat

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