spark plugs?

[Brian H]

Those all sound like superb ideas to me, especially for the longer term (mass reproduction.)

[Breakable]

I just want to point out that any work that LPP does on the spark plug distracts them of the actual work on fusion. So the best ideas would be as simple as possible, easy to implement and not require any extensive engineering, prototyping, testing. The best ones would be already existing products – are there really none?

[zapkitty]

Breakable wrote: I just want to point out that any work that LPP does on the spark plug distracts them of the actual work on fusion. So the best ideas would be as simple as possible, easy to implement and not require any extensive engineering, prototyping, testing. The best ones would be already existing products – are there really none?

What other applications require switching that much current with that level of precision timing? Power stations need the current but don’t need the timing. Many applications need the same or better timing but don’t need the current.

[Aeronaut]

Breakable wrote: I just want to point out that any work that LPP does on the spark plug distracts them of the actual work on fusion. So the best ideas would be as simple as possible, easy to implement and not require any extensive engineering, prototyping, testing. The best ones would be already existing products – are there really none?

Repeatability of the current pulse IS the foundation of the FF/DPF theory. Without it, anything else veers rapidly toward speculation. Additionally, this could lead to a self-financing product technology.

[MTd2]

A simple proposal here: Fire once, check if the spark plugs are ok, prepare the experimental set up again, and fire again. Repeat.

I’ve been following LPPX twitter and it seems that shots are done just once every week, on average, because the spark plugs are too fragile. Since this stage of research is about exploring the feasibility of the technique, I guess fast repeatability should not be of concern right now. Taking the september 30th video, it seems that there was a shot every few seconds or so, maybe this is too much stress on the system. I guess there shouldn’t be this kind of thing and instead be cautious like in the suggestion. Maybe the number of shots per week would be much higher.

[mchargue]

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

[mchargue]

Folks;

Just asking, but has anyone contacted Sandia Labs, and asked after the switching system they use for their Z-machine? The Z-machine also shunts huge currents – sending them through a fine mesh of wires to produce a ‘z-pinch’ – to produce X-rays. I think they’re using oil-bathed switches, but I may be wrong.

Pat

[mchargue]

Now this sounds quite close tho what you’re trying to do… It’s behind a pay-wall, but maybe you’re already a part of this?

Pat

—–
Design and testing of a multi-triggered spark gap switch for 2-15 kJ plasma focus device
http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=1228882

yun-Jong Woo; Hyun-Jong You; Yong-Sup Choi; Kyu-Sun Chung;
Dept. of Nucl. Eng., Hanyang Univ., Seoul, South Korea

This paper appears in: Plasma Science, 2003. ICOPS 2003. IEEE Conference Record – Abstracts. The 30th International Conference on
Issue Date: 2-5 June 2003
On page(s): 308
ISSN: 0730-9244
Print ISBN: 0-7803-7911-X
INSPEC Accession Number: 7797019
Digital Object Identifier: 10.1109/PLASMA.2003.1228882
Date of Current Version: 29 September 2003
ABSTRACT

A multi-channel spark gap switch has been widely used in high current and low inductance pulse forming network to obtain switching of fast rise time and high current pulses. Inductance and resistance of a spark gap switch rapidly decrease with increase of channels and electrode erosion is reduced by lower current density. In this work, an electrically multi-triggered spark gap switch was developed to be used as a multi-channel spark gap switch in a 2-15 kJ plasma focus device with a capacitor of Maxwell No 32169 (capacitance, 32 uF, inductance 65 nH). The geometry of the multi-triggered spark gap switch is similar to an annular-type rail gap switch. The large bodies of dielectric that surround the electrodes were designed to prevent arcing along the exterior of the gap. The dielectric material is translucent polycarbonate which has high Izod impact strength. By using translucent polycarbonate, the breakdown in the gap switch could be visually observed. The main electrodes and trigger are made of stainless steel. The minimum gap spacing in this switch is 7 mm and the trigger is located between two main electrodes. The trigger is similar to the main electrode of the trigatron switch. In parenthesis, five different trigger-pins are located in the main trigger-plate and these are isolated with dielectric material. Therefore, six different trigger signals can be generated with a time difference of a few micro-seconds.
—–

[mchargue]

Help

I can’t seem to post my last submission to the thread, “Volunteer for LPPX Sparkplug Simulation Team”
https://focusfusion.org/index.php/forums/viewthread/722/

Can someone else do this, please, or grant me access?

TIA;
Pat

[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/

[mchargue]

Henning wrote:
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/

Yep.

This thread, and earlier ones, got me to thinking about this switch system. It was a fun thought experiment, and a good opportunity to contribute. It turns out that there is A LOT of prior art on this issue of high-voltage, high-current, spark-gap switches. Everything from materials to use, to triggering strategies.

I’ve become convinced that there’s likely a drop-in design available somewhere at, or – especially given the low repetition firing rate of the experimental FF system.

I hope that the team can use what ideas were presented here, and from other resources, to improve their design for the experiments they’re running, and for more robust demonstration systems.

Pat

[Francisl]

Is there a diagram or wiring schematic somewhere for the spark plugs and switches so we have solid information to work with?

[Author]

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