triggered spark gap peak power design for energy transfer/switching - Page 1
Forum section: electronics / projects

author: CopperCone
author_rank: Super Contributor
timestamp: March 27, 2018, 08:52:39 pm
content: So typically when I look at information about sparkgaps (and triggered spark gaps), there is alot of engineering that goes into them including-radioactive doping-using lasers to trigger em faster-gas mixture choice-parallelism-electrode shapeBut, most of the research I see is interested in making theirdelayshort, but it does not mention much aboutcommutation speedSo having low, repeatable delay and jitter performance is useful for things like nuclear weapons and ESD protection.... but, I am not interested in this parameter. I am only interested in the commutation speed, which I am defining here (there seems to be contention) as being proportional to peak current.If I have a spark gap/GDT connected to a capacitor bank, what are engineering design considerations for making maximum peak current?I wanted to make my own triggered spark gap. I can fill it with argon, hydrogen, helium, nitrogen at pressure if necessary.I have a hydrogen thyratron circuit ( I believe made for radar use) that I wanted to use to trigger the spark gap. It is capable of operation up to 10kV with a current slew rate of 1500A/microsecond... Currently outfitted with a 2kV PSU and a 0.02uF / 5kV capacitor.however, I read that trigger spark gaps /krytrons can do something like 5kA in nanoseconds.. which is why I am interested in them. I am worried that significant capacitance on the thyratron I have will end up destroying it (the peak current is not defined for a veryyyy short pulse like from a 0.02uF capacitor, but I am wary to hook up like 2kV@1uF to it.With a triggered spark gap I can do alot more , like 20kV with multiple uF.Again, only interested in jitter/delay time if it impacts commutation time (time for a low impedance plasma/arc to form), I don't care about focusing explosive lens or sequencing beam laser arrays at this time lol

author: dmills
author_rank: Super Contributor
timestamp: March 27, 2018, 09:12:34 pm
content: Not my area, but I would note that the classic use of the krytron at those levels is only required to work once, get the shockwave from the slapper on its way, job done!73 Dan.

author: CopperCone
author_rank: Super Contributor
timestamp: March 27, 2018, 10:52:07 pm
content: No, I don't want something disposableI wanted to make durable heavy long life lab equipmentgranted, the spark gap can be a replaceable element.And also, I think if you look at it, TSG had better specs then krytrons (despite being almost the same but wihtout the pilot arc) in terms of voltage and current handling, but had more jitter or something like this?Actually, it would be interesting to know if the commutation time of a krytron is better then a TSG, or is it just the delay time that's better.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 28, 2018, 04:45:57 am
content: Quote from: dmills on March 27, 2018, 09:12:34 pmCuriously, those krytrons were typically rated for 100 to 10^5 operations; likely they saw use in limited industrial and scientific applications, as well as their most notorious use. There'd be some advantage to having the device operate at least a few cycles, too (initial testing, plus the assurance that the device be very likely to function when eventually called upon).Tim

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 28, 2018, 04:48:45 am
content: Quote from: CopperCone on March 27, 2018, 08:52:39 pmAFAIK, air spark gaps commutate* in single digit nanoseconds, and can be pushed to fractional nanoseconds with care. Nothing you're doing cares about this, it's all more than fast enough (discharge circuit time constant ~us).*Not determined by current, BTW. Current is determined by the geometry of your surrounding circuit. Commutation is the voltage fall time, i.e., how long it takes the arc to become fully conductive. After that initial breakdown, current is determined by the impedances around the electrodes.Tim

author: jbb
author_rank: Super Contributor
timestamp: March 28, 2018, 05:30:07 am
content: Quote from: CopperCone on March 27, 2018, 08:52:39 pmDanger Will Robinson! May cause all your insurance policies to shrivel up and die. If you're in a commercial enterprise you could probably negotiate with your insurer. If you're in your garage with a standard domestic policy, your insurer may just say 'no.'Quote from: CopperCone on March 27, 2018, 08:52:39 pmErr,ITAR is a thing, and it is possible to really go to jail. I expect there are some limits listed somewhere that you should look up and respect. Maybe there are size limits so you could just go big & chunky?

author: CopperCone
author_rank: Super Contributor
timestamp: March 28, 2018, 01:48:12 pm
content: What goes into shortening the rise time to the picosecond regieme?I dont really care about export treaties etc. Its for private use and only very few if more then one will be made.Btw there was a case in the 80s of some guy selling krytrons to russians lol

author: Marco
author_rank: Super Contributor
timestamp: March 28, 2018, 03:28:38 pm
content: Quote from: CopperCone on March 27, 2018, 08:52:39 pmI don't think I have ever seen it used in this context, commutation is generally used in the context of opening a switch ie. commutating a thyristor.Lets use normal words for a moment, what do you want to minimize. Rise time, resistance, both?

author: CopperCone
author_rank: Super Contributor
timestamp: March 28, 2018, 04:08:07 pm
content: I am after whatever allows for highest peak power.I dont know where the balance is of rise time and energy loss in the spark formation (as heat and light). If i get a really fast arc formation but all the energy of the peak is lost to the voltage drop on the arc thats not great.Btw i dont know much about this stuff so explaining the relationships/differential equations would be useful.

author: CopperCone
author_rank: Super Contributor
timestamp: March 28, 2018, 04:11:06 pm
content: Renamed the thread to peak power to clarify.I forgot to think about the arc formation and hold losses that may be assosiated with different design decisions lik gas mix, pressure, electrode shape,spacing, etcHaving monsterous energy loss in the formation of the arc for a protection device is acceptable, if the thermals are ok, but i am interested in energy transfer. There exist triggered spark gaps for protection but this is not my application. High losses to arc formation means the peak power is attenuated.

author: CopperCone
author_rank: Super Contributor
timestamp: March 28, 2018, 04:20:52 pm
content: Would a high pressure high force mechanical relay be better? Like a contactor that slams through some kinda strong dielectric liquid. I thought that if the right liquid existed, the spark can be made really short, so there are lower losses?I dont think it woll be very repeatable (bad) but will it outperform a spark gap trigger for small numbers of uses?Or would it require special geometry like spikes on the electrodes?How much shorter would the arc lenght need to be to outperform a spark gap? Or would fluid dynamic effects at high pressures can slow things down?andthe mechanical travel that occurs during the coarse of the peak energy transfer is neglegible, so the difference in spark lenght due to electrode motion is probobly close to 0

author: KD4PBS
author_rank: Contributor
timestamp: March 28, 2018, 04:33:50 pm
content: Thyratrons are available that can sink several microfarads at 40KV effectively and quickly. We're talking millions of joules of dissipation here!They aren't cheap though.In the TV transmitting business, we used them as crowbar circuits protecting high-value IOTs in the HPAs of our transmitters.Eventually we phased them out though, as we discovered that with digital transmission, we could get by with a much smaller sized HV capacitor, and as such, the speed of simply killing the supply to the HV transmitters was adequate enough to prevent damage to the IOT.Long story longer... look at the surplus market. You might be able to find some of these decommissioned crowbar assemblies to play with. They'd be quite suitable in HV experimentation use as they already have all of the driver circuitry for the tube.I seem to remember CX1154 being the thyratron these assemblies used, if that gives you any kind of idea of what it's capable of.

author: Cyberdragon
author_rank: Super Contributor
timestamp: March 28, 2018, 04:44:22 pm
content: Oh hell no. Spark gaps will be way faster than any mechanical device could ever dream. A spark gap would be over before the coil would even be fully magnetized in a relay (roughly).Good spark gaps can go way bigger than thyratrons.Here's this...

author: Marco
author_rank: Super Contributor
timestamp: March 28, 2018, 06:30:27 pm
content: AFAICS the fastest sparkgaps are sharpeners, not triggered. The requirements for stand-of in a slowly charged triggered sparkgap work against fast rise times.

author: KD4PBS
author_rank: Contributor
timestamp: March 28, 2018, 08:11:12 pm
content: Sorry - my mistake. It's the CX2708 that is commonly used in this application.Complete assembly with (I believe) a rogawski coil current sensor (recently discussed in another forum).

author: CopperCone
author_rank: Super Contributor
timestamp: March 29, 2018, 12:10:59 am
content: Quote from: Cyberdragon on March 28, 2018, 04:44:22 pmI will read this, but what I meant is that, some kind of very insulating material can be used, for instance:Lets say you are switching 5kV capacitor bank:Case 1:spark gap required trigger voltage for 5mm in gas might be like, 5kV.So, the spark has to jump 5mm. This means the arc will be 5mm long.Case 2:Spark gap required trigger voltage in oil/dielectric might be like, 50kV for 5mm.The relay fires, and the contacts are nearing each other. The dielectric breakdown distance at 5kV might be, 0.1mm.So, when the relay fires, eventually the contacts will be 0.1mm away from each other, so the arc will spark here\In case 2, there is a long mechanical delay time due to energizing the coil and the travel of the contactor, but when the spark finally does form in a high dielectric resistance material, it will be much shorter. Possibly shorter then any practical triggered spark gap dimensions.It seems the me that the voltage drop and the formation duration of the plasma channel will be much lower/faster then in case 1. Am I wrong here? Does the dielectric material slow down the spark/cause more losses some how despite of the reduced distance?

author: CopperCone
author_rank: Super Contributor
timestamp: March 29, 2018, 12:23:41 am
content: Quote from: KD4PBS on March 28, 2018, 08:11:12 pmI am looking at the specifications of your recommended tube:Peak forward anode current......1.5 kA maxRate of rise of anode current .......50kA/usSo, to reach the peak forward anode current, which is 3% of the rate of rise, we need 30nS.My thyratron that I have now will reach the same peak anode current in 60nS, but it is only rated to 10kV (vs your tubes 40kV)Unfortunately, I expect that the peak forward anode current will be higher then 1.5kA, and, it appears that the triggered spark gap will have peak anode current in less then 10nS if done right.Does the peak current get derated for lower voltages? Or is it a pure current specification due to heating (I think so)?Unless this is the case, I think a TSG will be more versatile as I can do higher currents without worrying to damage a tube that costs 300$ on ebay, however in the future I might get one for its own purposes.I am probably going to stick to the 5kV region, because power transfer at these voltage over distance is relatively easy, but things like coaxial cable may be easily destroyed by higher voltage experiments, not to mention the cost of capacitors and all other components goes up astronomically.I can't really justify 300$ on something that will reduce the speed from 60ns to 30ns when it looks like two ball bearings brazed to some threaded rod possibly in a pvc enclosure filled with argon or hydrogen will do the same job at higher currents in 10ns or less, not to mention I need alot more support electronics (my thyratron driver board is already completed and neat).

author: CopperCone
author_rank: Super Contributor
timestamp: March 29, 2018, 12:26:29 am
content: Quote from: Marco on March 28, 2018, 06:30:27 pmCan you elaborate? Will this still be a problem if I trigger the SG with a thyratron?Could I use a triggered spark gap followed up by a sharpener?It seems their peak currents are kinda low...same as the thyratron but alot faster.I want something say, 5kA capable.I have my doubts about paralleling such fast devices. I think one will melt.Great information though, a compendium of rise time/vs peak current solutions is good to have on hand.

author: CopperCone
author_rank: Super Contributor
timestamp: March 29, 2018, 01:07:50 am
content: I also think that a triggered spark gap can be improved by triggering it with a really high voltage, alot more then what its passing, but from a smaller capacitance.

author: Marco
author_rank: Super Contributor
timestamp: March 29, 2018, 09:07:58 am
content: Quote from: CopperCone on March 29, 2018, 12:26:29 amMaybe, but it might not be fast enough. It still has to hold off for long enough for the initial rise time. Looking around, the way to get subns istriggered->Marx->sharpener.Of course you'll have to make your own 10+ GHz 10000:1 capacitive divider probe to diagnose this stuff if you try to build it, with a 10+ GHz scope, shielding so you don't fry everything near and interlocks and other safety measures so you don't fry yourself ... and what load do you have that it can absorb that kind of pulse?

author: CopperCone
author_rank: Super Contributor
timestamp: March 29, 2018, 01:50:53 pm
content: Maybe with 10ghz you can try to measure the highest harmonic with a spectrum analyzer and antenna.But i see your point its way outside my capabilities to do this at the moment. Especially with 1ns.

author: KD4PBS
author_rank: Contributor
timestamp: March 29, 2018, 02:44:35 pm
content: Quote from: CopperCone on March 29, 2018, 12:23:41 amI'm pretty certain the current is total, regardless of the voltage. Still, we're talking about a tube that is used to shunt a very large (over 10 microfarad) bank of capacitors riding along at 36KV directly to groundbeforean arc can form inside the cavity of a 60KW vacuum tube, so I imagine it's fast enough to be able to generate a spark pretty quickly. Would a triggered spark gap be faster? Well, consider that this thyratron is basically a deuterium hydrogen filled triggerable spark gap and go from there. I imagine the smaller the tube, the faster it is, but the less current and voltage it can handle.QuoteUnderstood. I have zero experience with a true TSG, nor if they're even available for an experimenter, but hopefully this recommendation gives you something you can use.QuoteHT wire isn't too expensive. The stuff we use to feed the HV to these transmitters is not much larger than a typical #2 pencil in diameter.https://catalog.belden.com/techdata/EN/8866_techdata.pdfI see it on the auction site for 1-2$ per foot.Capacitors? yeah - they can get pricey. Even used ones. But, you got to pay to play, as the saying goesQuoteAgreed! I hope you can make it work. That would be cool!

author: CopperCone
author_rank: Super Contributor
timestamp: March 29, 2018, 03:00:11 pm
content: Actually i renembered my datasheet wrong , the tube you mentioned has 15 times more current handling capability and it is twice as fast.It is on my wishlist, i guess you need to collect a few of these, no different then having a bunch of lab power supplies.The thyratron i have is hooked up to some kind of stepup transformer, i need to measure its step up parameter. According to some research i did, triggering a spark gap with a massive overvoltage up to 4 times greater then its breakdown voltage causes it to break down faster because the plasma formation process belongs to some other regieme, i think its called a streamer.I got the book gaseous conductors, i need to read it to see if i get any ideasAlso the vaporization of the electrode materials effects the plasma formation time

author: KD4PBS
author_rank: Contributor
timestamp: March 29, 2018, 03:37:16 pm
content: Yeah - that whole "money" thing... it can be a real bear for an experimenter. Especially one who toys with high voltage!Best wishes, and be sure to let us see your results whenever you get there!

author: CopperCone
author_rank: Super Contributor
timestamp: April 03, 2018, 02:00:18 pm
content: Ok i made a crude spark gap ehich is triggerable.I had some old mouseballs laying around, so i stripped the rubber off of them,, put em in a vise, ground the top flat with a stone and drilled 3/8 inch holes in em, not all the way through.In one of the balls i drilled a .15 inch hole, which fits some coaxial hardline, and i also drilled this hole through a 3/8 inch piece of threaded rod. I used a 3/8 inch 16tpi tap to thread both of the larger holes.I inserted a lenght of hardline through the threaded rod and mated it with the steel ball very tightly.Resistance measurements on the ball rod junctions were less then 20miliohms on a 34401a.The center conductor of the hardline will act as the trigger spark. The threaded rods wil be used for adjustment of the gap through some nuts in a wooden fixture.I need to make some kind of bushing to contact the threaded rod with heave gauge electrical wire.I also have some steel ball bearings which will ofer a much better surface finish but i will need acetylene to silver braze them to a copper rod.I think for initial tests the above setup will do, i think the center conductor of the hardline is the weakest link right now, i would need a tungsten needle here. Since it is not carrying significant energy i may pull it in a bit and try to press fit a bit of tungsten from a light bulb or something

author: daqq
author_rank: Super Contributor
timestamp: April 03, 2018, 03:45:32 pm
content: QuoteTake a look at the offerings of Behlke... nasty pricing, but you can get insane parameters.http://www.behlke.com/separations/separation_c2.htm(or search their catalogue some more...)

author: CopperCone
author_rank: Super Contributor
timestamp: April 03, 2018, 04:02:55 pm
content: Damn those specs are tight and they make me feel like a cave manAnyway word on the street is that you can fire spark gaps using a bbq starter pretty good.Hopefully it will have a kickass rise tieme but i feel that some kind of extension rod should be used to fire the bbq starter, just incaseI wonder if thrre is any benefit to the third electrode since the bbq starter voltage is like 6 times greater then the gap firing voltage

author: Cyberdragon
author_rank: Super Contributor
timestamp: April 04, 2018, 06:05:20 pm
content: A piezoelectric igniter? I thought you wanted something automatic.I'm not sure if the electrodes are always connected to the crystal inside, or if the piston/hammer is one of the electrodes. If they are connected, or since the gap will probably fire before the hammer retracts, remember that piezo's work both ways. If the crystal experiences repeated voltage shifts before recovering from the initial deformations, the stress may eventually shatter it. Would definitely depend on several things, but might be a long term issue.Another thing, although it might shorten the igniter life even faster, would be to hit it with a rubber mallet.

author: CopperCone
author_rank: Super Contributor
timestamp: April 04, 2018, 06:53:28 pm
content: Well I think its a good choice for testingThe fastest arcs are produced by trigger sparks several times greater then the gap spark voltageThe BBQ starter makes a arc that I read is between 15 to 30kV. Right now my capacitor bank is only 2kV, but at 5kV, the spark is still 3-6 times greater voltage then the main discharge energy. This should form the 'streamer discharge' discussed in some literature I read.If I like what happens I will consider a making a very high voltage trigger circuit, but I don't have any ultra high voltage capacitors and shit lying around. I would consider making a oil/foil one for the trigger, if it works well.http://www.gocs1.com/gocs1/Psionics/CHEAP-5Kv-CAPACITOR.htmI think this can easily be modified to work with like 15-20kV.I was hoping that since the BBQ piezeoelectric sparker generates a voltage much greater then the voltage of the spark gap, it will be OK.I wonder if it is possible to isolate it by using a second spark gap, just for the piezo, that has a gap greater then the one required for the transmission of the load voltage, possibly with a delay.