First light (bootstrapping FoFus)

[Brian H]

It occurs to me that starting up an FF generator in a remote location or carried on/powering a vehicle (distant from either other (operating) generators or the grid) will take some arranging. The capacitors have to be charged up to initiate the self-sustaining sequence, and that would have to be from either the grid, a small auxilliary generator, or batteries, I suppose. The capacitors couldn’t be counted on to hold charge for any useful period of time after a shutdown, either.

Is this likely to be much of a concern or problem?

[zapkitty]

Brian H wrote: It occurs to me that starting up an FF generator in a remote location or carried on/powering a vehicle (distant from either other (operating) generators or the grid) will take some arranging. The capacitors have to be charged up to initiate the self-sustaining sequence, and that would have to be from either the grid, a small auxilliary generator, or batteries, I suppose. The capacitors couldn’t be counted on to hold charge for any useful period of time after a shutdown, either.

Is this likely to be much of a concern or problem?

For my idea of a DPF in a shipping container I’d decided on a small gas turbine generator, designed for neither quiet operation nor optimized for fuel efficiency… and it doesn’t have to charge the caps all at once.

500 kW at 800 amps are common ratings for a gear set sufficiently small (>1.6m3) to be folded into the container’s cooling system area, and the exhaust would be ducted up through the tower… but I wasn’t going to actually go there until I had sanity-checked some ideas I have for the basic cooling mechanisms in the tower.

But wherever the generator winds up just run it until the caps are charged and let the DPF rip…

An auxiliary idea I’d had, but not required, is to have the DPF container with the ability to draw power from its transport the same as a reefer container would. Enough to keep the caps partially charged up, but short of the point on their discharge curve where the caps start leaking excessively… even if the caps are nowhere near a full charge this would save charge-up time when the order to start the DPF is given.

Offworld operations would seem to require either solar panels or fuel cells.

[Brian H]

zapkitty wrote:
…
Offworld operations would seem to require either solar panels or fuel cells.

Yeah; I wasn’t thinking of quite THAT remote, of course, above. For isolated communities just about any source that could be cranked up at will would do, I suppose. But since the FoFuz are so cheap, maybe it would be better to install in pairs, so one could carry the load (or enough of it) whenever the other was being serviced. Or link 2+ community sites for the purpose. Or …

[zapkitty]

Brian H wrote: … But since the FoFuz are so cheap, maybe it would be better to install in pairs, so one could carry the load (or enough of it) whenever the other was being serviced. Or link 2+ community sites for the purpose. Or …

Let’s think inside the box for a moment… how about configuring the container so that the DPF can run at just over breakeven without having to deploy the tower?

(Assuming that the tower block is even required in the end… might not be…)

You’d only start it up just before the DPF is deployed to the worksite but being either towed on a semi or hanging under a fusion-powered cargo copter it should be okay if only venting maybe a 100 kW of heat or less…

[Breakable]

I shared this idea before before, that reducing the frequency of operation should reduce the requirements for thermal management as well as radiation shielding. And this is what should be done for first prototypes as well as commercial units to avoid engineering complexity.

[Brian H]

Well, initially the idea was to get 25MW out of a FoFu by running it at much higher Hertz. I think 330Hz –> 5MW was decided pro tem to be the best balance of useful power and feasible cooling given current tech. But there will always be the same ratio of heat waste to electricity generated, more or less, so running slower would just mean using more generators to get the desired output, with the same total heat waste. What would be gained?

[zapkitty]

Brian H wrote: Well, initially the idea was to get 25MW out of a FoFu by running it at much higher Hertz. I think 330Hz –> 5MW was decided pro tem to be the best balance of useful power and feasible cooling given current tech. But there will always be the same ratio of heat waste to electricity generated, more or less, so running slower would just mean using more generators to get the desired output, with the same total heat waste. What would be gained?

Well, remember, that for the container DPF the target was already 2MWe to simplify cooling and to fit a known market for portable 2MWe generators.

My current idea of having the option to be able to skip the “bootstrapping in the wilderness” step entirely by having the unit capable of just barely idlng while in transport from wherever power is last available before the worksite… is a different implementation of the same concept…

Sp while you two discuss different rollout strategems for the tech as a whole… 🙂

… would it seem safe to assume at this point that the bootstrap will probably not be an big issue?

[Tulse]

I have to imagine that regulators are not going to be at all happy with an untended nuclear device running as it is driving across the country. Just sayin’.

[Brian H]

Tulse wrote: I have to imagine that regulators are not going to be at all happy with an untended nuclear device running as it is driving across the country. Just sayin’.

Have it hooked up to a booster electric motor, etc. Then it’s part of the drive train.

Anyhoo, I think “the regulators” are going to be under economic survival mandate to be accommodating and reasonable. Or “the universe [state, country, etc.] next door” is going to start advertising their sudden new energy cost advantage (not that much would need to be budgeted to the campaign!)

[jamesr]

Brian H wrote: It occurs to me that starting up an FF generator in a remote location or carried on/powering a vehicle (distant from either other (operating) generators or the grid) will take some arranging. The capacitors have to be charged up to initiate the self-sustaining sequence, and that would have to be from either the grid, a small auxilliary generator, or batteries, I suppose. The capacitors couldn’t be counted on to hold charge for any useful period of time after a shutdown, either.

Is this likely to be much of a concern or problem?

I don’t see a problem with charging the capacitors?? The capacitors only need to hold enough energy for one pulse to start. With a bit of margin say 100kJ, ie to charge them you could supply for example 200W for 500s. A small solar panel on the roof could do that, or for that matter a person with an crank handle winding a dynamo for a few minutes.

The main startup power would be the vacuum system, since it needs to have pumped down the chamber, preheated it etc. The cooling system (helium & water pumps) could be ramped up as you increase the pulse rate. So you could have for example all the excess power output for the first few minutes of operation is used purely to get all the pumping systems & flow rates up to speed as you increase the pulse rate to its normal output rate, then you can sync up to the grid and start supplying power when everything is ready.

[Henning]

Suppose we don’t get enough energy out of coil and onion for break-even, the thermal system needs to get to its operating temperature. That means, we’ll need the energy of maybe a few thousand shots of the DPF. So a petrol engine in combination with a conventional generator (or similar) needs to provide enough electricity continuously to recharge the capacitors enough before the system runs at its desired frequency. The first shots may take place every ten seconds or so, getting gradually faster.

Pretty much what James writes, but with respect the thermal system is needed to come into gear before the FF device can support itself.

[zapkitty]

… so… going by jamesr’s figures then, onion or no onion, a 50
kW generator capable of running for a half-hour should be able to bring even one of the newly-popular (if somewhat bowdlerized) thermal DPF systems up to speed?…

… that’s not a bootstrap problem.

[Aeronaut]

Great thread. The vacuum system is probably going to be 3 phase power, with single phase for the cap bank charger. But from the first shot on, we’re going to need to deal with 8MWt regardless of operating frequency at that point.

Eric mentions in the patent that the preferred pulse freq is ~1 khz to keep the fuel ionized. Also, if we can offer 5MWe in the package of 2, and do it for only slightly higher cost, I’d expect the existing market to be very interested in The Clean Machine.

[vansig]

Aeronaut wrote:
Eric mentions in the patent that the preferred pulse freq is ~1 khz to keep the fuel ionized.

This changes some assumptions, and the numbers around them. If we assume therefore that a 5 MW generator is pulsing at 1kHz instead of like 330 Hz, then this triples the heat rejection requirements.

However, I read this spring that the plasmoid size is turning out to be smaller than expected — at least in deuterium. if that turns out to be true for boron also, then it would tend to reduce the yield per shot. That isn’t a disaster, but it places tighter constraints on power conversion efficiency, throughout the system.

I think it’s time to get intimate with the properties of the exit beam, and work out how to capture it. I’m assuming it will look like this…

Attached files

[Breakable]

Brian H wrote: Well, initially the idea was to get 25MW out of a FoFu by running it at much higher Hertz. I think 330Hz –> 5MW was decided pro tem to be the best balance of useful power and feasible cooling given current tech. But there will always be the same ratio of heat waste to electricity generated, more or less, so running slower would just mean using more generators to get the desired output, with the same total heat waste. What would be gained?

Lower overall power means lower heating requirements and simpler thermal management per reactor.
If it it outputs only 5KW instead of 5MW, you don’t need a cooling tower or liquid helium moving at supersonic speeds anymore and can put it in the backyard as the bulk of the system should be cooling.
I even think it would output less radiation, so maybe you wont need as much shielding.

[Author]

Posts