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optically triggered spark gap

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LAN_403

Signification

Wed Dec 23 2015, 09:44PM

Registered Member #54278 Joined: Sat Jan 17 2015, 04:42AM
Location: Amite, La.
Posts: 367

I was wondering about the chance of triggering a high voltage spark gap by tightly focusing (or otherwise using) a >=1000mW laser beam, such as that from a 405nm module, between the main HV electrodes. If not, what is -optically- required to ionize air?

Patrick

Thu Dec 24 2015, 12:02AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

I think the field intensity and geometry will play a large role in the power and laser technique needed. Maybe you could use that as an advantage though. are you trying to trigger 5kV or 30kV for example. the air behaves different.

Signification

Thu Dec 24 2015, 01:31AM

Registered Member #54278 Joined: Sat Jan 17 2015, 04:42AM
Location: Amite, La.
Posts: 367

Patrick wrote ...

I think the field intensity and geometry will play a large role in the power and laser technique needed. Maybe you could use that as an advantage though. are you trying to trigger 5kV or 30kV for example. the air behaves different.

Yes, 20kV to 30kV (max 35-40kV). I saw something somewhere--I am almost certain it was on this board--about ionizing an air gap and having current 'follow' the path of ionization. **does anyone remember**?
I guess I should be able to -mess- with the geometry with no major problems.

Patrick

Thu Dec 24 2015, 03:51AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Signification wrote ...

. . . . should be able to -mess- with the geometry with no major problems.

use FEMM 4.2 its free, draw a .DXF cad file. load it in itll give you a pretty colored picture. mine are some where in my HV measurement probe thread.

Signification

Thu Dec 24 2015, 05:22AM

Registered Member #54278 Joined: Sat Jan 17 2015, 04:42AM
Location: Amite, La.
Posts: 367

Patrick wrote ...

Signification wrote ...

. . . . should be able to -mess- with the geometry with no major problems.

use FEMM 4.2 its free, draw a .DXF cad file. load it in itll give you a pretty colored picture. mine are some where in my HV measurement probe thread.

Yeah...about that--I really, really have got to get some of these simulators...I never even saw SPICE which I hear so much about here. I used QuickBasic+GXgraphics in the 90's and before DOS went out and windows took over (I always said that "once DOS/DEBUG was gone, I would be done with it"). the last simulation I did was with a program I wrote in a language called "Processing" It calculated the -entire- B-Field inside a whole slice of a solenoid at any distance from an end. I used the continuous spectrum 2^24 colors, 8 bits each in RGB (I did bias a bit). I was looking for a maxima at some wild currents (specifically cylindrical WRT the axis) but this never showed up. Max. B was always at the outer internal area nearest the inner wire surface. Minimum B was always along the central axis, with the max of the center axis at the center of the solenoid section/length. The program was based on the BIOT-SAVART LAW, which let me plot -ANY- point in space. HR runs took days to hours to run--max run was almost a week--but worth it--I gained a lot of useful info (esp. for coilgun fields).

Where/how would you suggest I start with simulators??

Electroholic

Thu Dec 24 2015, 06:37AM

Registered Member #191 Joined: Fri Feb 17 2006, 02:01AM
Location: Esbjerg Denmark
Posts: 720

What about a pulse laser that vaporize a target to produce plasma?

GrantX

Thu Dec 24 2015, 06:44AM

Registered Member #4074 Joined: Mon Aug 29 2011, 06:58AM
Location: Australia
Posts: 335

I just downloaded FEMM 4.2, the website is here:

I haven't attempted anything serious yet, just slowly picking through tutorials and guides. Its got a very steep learning curve, but thats to be expected with software like this I guess.

Patrick, do you have any suggestions for a starting point to learn the basics of FEMM? I'm interested in using it for high voltage structures, similar to your probe simulations. My limited experience with 3D Maya and TinyCAD just ain't cutting it!

RateReducer

Thu Dec 24 2015, 03:00PM

Registered Member #4603 Joined: Wed Apr 25 2012, 07:33PM
Location: Austria
Posts: 159

I donÂ´t know if this is helpful but here is an inerresting video:

Patrick

Thu Dec 24 2015, 08:22PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

RateReducer wrote ...

I donÂ´t know if this is helpful but here is an inerresting video:

yeah I would suggest UV but that's a harder laser to get right?

look here first. But do you know how to generate a .DXF file ?

hboy007

Thu Dec 24 2015, 09:43PM

Registered Member #1667 Joined: Sat Aug 30 2008, 09:57PM
Location:
Posts: 373

There are actually multiple ways to get a breakdown to happen but I find it hard to come up with something that doesn't involve pulsed high power lasers:
- dielectric breakdown: pick the favourite wavelength of your q-switched nanosecond or picosecond laser and just get the field strength in the focus high enough to start ionizing
- two-photon processes: actually you can break molecules with a homebrew TEA N2 laser but you'd have to flood the spark gap with something like a methane+argon mixture
- picosecond and femtosecond lasers: instead of getting the focus right, self-focusing and breakdown can produce filamentation - I guess that would be suitable for igniting larger sparkgaps that are not so close to spontaneous breakdown that opening a door or a change in humidity initiates breakdowns

a workaround for air breakdown is, as mentioned above, to produce a plasma on the surface of a target.

ps. let's just check the first ionization energies of the main air constituents to figure out: atomic nitrogen, oxygen and argon are notoriously in the 12-16 eV ballpark, D0 (

) energies are lower but we're going to end up with neutral constituents.
Before I say something stupid, let me finish with a link on heterolytic dissociation:

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