[Henning]

Brian H wrote: Certainly the speed is there; < 0.1 ns. But the voltage is quite low so far, 4.5kV.

An increase of ten times the voltage could be possible, ie. with a gap of about 10mm, or with different fill gases. It doesn’t say anything about the maximum current, though. Currents would be constrained by the diameter of the electrodes, so this is maybe not a problem (anyone with more background please weight in).

They create a plasma that spans the complete gap, that’s what makes it so fast.

I haven’t read the paper as it’s behind a paywall. Anyone around who has read it?

[Henning]

I think it will have synchronisation problems, ie. not all switches working in an equally narrow time frame than we have today, as for mechanical designs taking longer to switch than the ionisation of gases. If it’s possible to build bigger switches than with ionising gas switches, and then just using one of them, it might be worth a second thought.

[Henning]

Brian H wrote:

Hi everybody, I’m new on this forum.
I can colaborate with this task. I have Solidworks 10 & Comsol 4.0 and some experience with simulation of spark gaps. What’s the next step?

Felix

Email Eric at the above address?

Definitely. Glad to have you on board.

[Henning]

zapkitty wrote: Last I heard the regular maintenance cycle for the notional 5MWe FF unit is 24 hours downtime out of every 90 days for electrode changeout and a general checkup, and that includes a 12 hour cooling period while the short-term radiation dies down.

Well, yeah, but those numbers are all very speculative.

[Henning]

mchargue wrote: Continuing with what I talked about yesterday, here are few ideas that may help…

Assuming that we’re using a plate to screw the rods into, (the electrodes) in order to make the whole thing easier to make, lets make that plate metallic. (conductive) This metallic plate would be used to host all of the rods (the electrodes) in bores that are threaded to accept the threaded rods. This plate is now the ‘common’ side of the switch, and connects the the FF device. (maybe directly, as in ‘bolted on’)

Across from the metallic plate that holds the threaded rods is a non-conductive plate that holds the opposite electrodes that complement each of the rods. These electrodes would be fixed into their plate, protrude through it into the switch body, and would not be movable. Each of these fixed electrodes would be connected to each of the capacitors that comprise the bank. One side of the high-voltage initiator would also connect to this fixed electrode, with the second pole of the high-voltage initiator connected to the ‘common’ plate.

The volume between the two plates, one a metallic ‘common’ plate hosting the threaded rods, and the other a non-conductive plate bearing the fixed electrodes, would be walled in to isolate the switch gas from outside air. This means that all switches use the same switch gas, so differences based on differences in switch gas should be minimized. Additional supports between the two plates may be needed to minimize flexure-induced changes in the gap distance.

With this, you should be able to make the fixed electrodes a bit more robust, and make the threaded rods a bit easier to work with, as they have no electrical connections made to them. (all the current is borne by the metallic plate) The metallic plate could be bolted directly to whatever needs to use the current. Mechanically, this might be easier to wire as the large gauge wire from the capacitors connects to fixed terminals on the non-conductive plate, and the metallic ‘common’ plate needs only a single connection from it to the FF reactor.

Service should be easier with the simplified connections. The non-conductive plate could be removed to open the switch, or the threaded rods could be individually removed for service without having to remove any wires.

Materials selection remains open, but note that all the machined parts comprise a plate, and the rods that thread into the plate. The non-conductive plate may need holes in it, but machining should be a lot simpler. I’m thinking a hole with a carriage-bolt in it. The threaded side of the bolt would hold the connections to the capacitor bank & initiator, while the smooth side would be in the switch body.

Switch gas selection is still up for grabs, but the switch should allow you to try a bevy of different gases. I’d certainly try something in place of SF6. Another enhancement would be the use of a transparent window on the switch body wall to visualize the switch process. Perhaps a port that can be opened to permit a ‘feeler gauge’ to be fished through to each gap for calibration.

Well, I think that’s it. Given the design, I’m not sure how much simpler this could be made. I’d love to hear more about what’s actually happening, thouh, and ideas other folks have.

Pat

Pat, I think you’re describing something like this:
https://focusfusion.org/index.php/gallery/image_med/28/
https://focusfusion.org/index.php/gallery/image_med/84/

[Henning]

Breakable wrote: Before someone starts playing with lasers, could someone please explain to me what is the problem with Ignitrons?
http://en.wikipedia.org/wiki/Ignitron

I think the difference here is, that you need to vaporize the mercury first before the current can flow. So it’s much slower, or you cannot orchestrate all ignitrons to switch simultanously enough.

[Henning]

Behind that video there is a community. Check out the projects they support: http://www.coalitionblog.org/category/campaigns-we-support/

For one, there is a wiki where solutions asked for and can be collected. They got an Energy section: http://www.appropedia.org/Category:Energy
Warning: Don’t just add links and marketing-speech to a focus fusion entry. Same thing as on Wikipedia might happen. It got deleted.

Please check out these communities yourself. At the moment it’s just too much input…

[Henning]

Brian H wrote:

The manufacturer of LPP’s switches R.E. Beverley (see here) also offers laser spark gap switches (see specs).

I think Eric and team have a good reason not to use them, be it costs or complicated laser beam setup. Another reason could be, that with every shot the optical system gets misaligned, because of the whole construct moving with the applied force.

On a quick skim thru the specs, I note that they have a max firing rate around 100 Hz, and an expected life from 5-20,000 shots. This would be a minute at most of FF operation.

Given life time is for maximum voltage/amperage. If you stay well beneath it, a million shots are possible. Not very much either as it’s maybe a day of full operation.

[Henning]

The manufacturer of LPP’s switches R.E. Beverley (see here) also offers laser spark gap switches (see specs).

I think Eric and team have a good reason not to use them, be it costs or complicated laser beam setup. Another reason could be, that with every shot the optical system gets misaligned, because of the whole construct moving with the applied force.

[Henning]

Here’a bit about it on PESWiki.

And a working link to his research company: johnsonrd.com

And his battery company: Excellatron

[Henning]

It’s a long and exhausting story but its general function is cited here:

Johnson’s latest JTEC prototype, which looks like a desktop model for a next-generation moonshine still, features two fuel-cell-like stacks, or chambers, filled with hydrogen gas and connected by steel tubes with round pressure gauges. Where a steam engine uses the heat generated by burning coal to create steam pressure and move mechanical elements, the JTEC uses heat (from the sun, for instance) to expand hydrogen atoms in one stack. The expanding atoms, each made up of a proton and an electron, split apart, and the freed electrons travel through an external circuit as electric current, charging a battery or performing some other useful work. Meanwhile the positively charged protons, also known as ions, squeeze through a specially designed proton-exchange membrane (one of the JTEC elements borrowed from fuel cells) and combine with the electrons on the other side, reconstituting the hydrogen, which is compressed and pumped back into the hot stack. As long as heat is supplied, the cycle continues indefinitely.

As he is just using hydrogen gas, this makes a great drop-in for the cooling circuits of the electrodes and onion. Where we’ve intended elsewhere in the forum to use helium. So the gas is not used in a steam/liquid cycle.

Maybe it’s worth contacting him with the intention of introducing him to the idea of focus fusion. An invitation to LPP’s lab? Maybe he’s curious?

[Henning]

Found something interesting on Wikipedia: Nitrogen Laser (Sub-Section: Spark Gap)

Connection between spark gap and laser channel based on traveling wave theory:
* The low inductance spark gap may be inserted into a strip transmission line
* biconical spark gap
* biconical spark gap
* biconical spark gap

The breakdown voltage is low for helium, medium for nitrogen and high for SF6 (Patent 4237404), though nothing is said about the spark thickness variations.

8E10A/s are possible with a spark gap (see here), this nicely matches the typical rise times of 1E-8s and typical currents of 1E3A occurring in nitrogen lasers.

I’ve modified some links, so they reference better.

So after all it is patentable.

[Henning]

So it would be something like this:

Attached files

[Henning]

JimmyT wrote:

Patrick: I think your proposal was ignored, because it was similar to Eric’s initial idea of using a diamond/laser switch. Diamonds are insulators, but conduct pretty well when ultra violet light is shined upon. This was considered to be too expensive, and no-one ever built a switch that big. So Eric and Murali fell back to ionizing spark plug switches (don’t know if it’s the right name). But what you’re now proposing is something different.

patentable?

Don’t think so. But it’s no easy part either. You need to ionize the gas enough to create plasma. That might require a fairly strong laser (I don’t know, just suspecting it). Then the glass to chamber holding the reaction gas where the laser passes through needs to stay clear, so the laser doesn’t break the glass because auf resudials blocking the sight.

BTW: I’m no expert in this.

[Henning]

Patrick: I think your proposal was ignored, because it was similar to Eric’s initial idea of using a diamond/laser switch. Diamonds are insulators, but conduct pretty well when ultra violet light is shined upon. This was considered to be too expensive, and no-one ever built a switch that big. So Eric and Murali fell back to ionizing spark plug switches (don’t know if it’s the right name). But what you’re now proposing is something different.

[Author]

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