vacuum spark gap
Coronafix, Mon Jun 19 2006, 03:40AMHas anyone done any testing using a static spark gap ander vacuum?
I'm just wondering what the pros and cons of this would be.
Seems that it would be fairly simple to build one.
Re: vacuum spark gap
Madgyver, Mon Jun 19 2006, 06:08AM
Is it? Unless you have good vacuum 'source' at hand that will prove difficult. Just pumping out lots of air an leaving behind a lot pressure gas, won't make a good spark gap.
Even if you could, x-rays could be a major issue here.
Madgyver, Mon Jun 19 2006, 06:08AM
Is it? Unless you have good vacuum 'source' at hand that will prove difficult. Just pumping out lots of air an leaving behind a lot pressure gas, won't make a good spark gap.
Even if you could, x-rays could be a major issue here.
Re: vacuum spark gap
ragnar, Mon Jun 19 2006, 07:32AM
X-rays? Pshhh... what's new? ^^
You'd need a real 'high' vacuum... how about a sulfur-hexaflouride filled relay / sealed contactor box instead? :)
ragnar, Mon Jun 19 2006, 07:32AM
X-rays? Pshhh... what's new? ^^
You'd need a real 'high' vacuum... how about a sulfur-hexaflouride filled relay / sealed contactor box instead? :)
Re: vacuum spark gap
Coronafix, Mon Jun 19 2006, 10:13AM
What about using an old fridge compressor, or two? That would get a decent vacuum.
A lead box over the vacuum would stop the x-rays.
Coronafix, Mon Jun 19 2006, 10:13AM
What about using an old fridge compressor, or two? That would get a decent vacuum.
A lead box over the vacuum would stop the x-rays.
Re: vacuum spark gap
SpyrosF, Mon Jun 19 2006, 10:28AM
Vacuum is not conductive, except of course thermionic emissions.
look here ->
SpyrosF, Mon Jun 19 2006, 10:28AM
Vacuum is not conductive, except of course thermionic emissions.
look here ->
Re: vacuum spark gap
Dr. Shark, Mon Jun 19 2006, 12:01PM
Nope, an old fridge compressor would be _very_ far from sufficient. Even a $2000 two-stage rotary vane pump hardly gets you down to "real" vacuum where you begin to get x-rays, for a serious hard vacuum you need a two stage vacuum system with a turbomolecular (figure $5000) or similar pump. You will run into lots of issues with contamination, and you will have to bake the system (oven, another couple of k$) while pumping it down. Expect to spend several $1000 even if you buy used or make your own equipment.
That being said, vacuum gaps make excellent HV switches, and I have come aross them several times in a railgun context. Similar to big thyratrons they can switch 100s of kA and are very fast. I don't quite know how they work, but I expect some of the metal from the electrodes evaporates to produce a conductive plasma.
Dr. Shark, Mon Jun 19 2006, 12:01PM
Nope, an old fridge compressor would be _very_ far from sufficient. Even a $2000 two-stage rotary vane pump hardly gets you down to "real" vacuum where you begin to get x-rays, for a serious hard vacuum you need a two stage vacuum system with a turbomolecular (figure $5000) or similar pump. You will run into lots of issues with contamination, and you will have to bake the system (oven, another couple of k$) while pumping it down. Expect to spend several $1000 even if you buy used or make your own equipment.
That being said, vacuum gaps make excellent HV switches, and I have come aross them several times in a railgun context. Similar to big thyratrons they can switch 100s of kA and are very fast. I don't quite know how they work, but I expect some of the metal from the electrodes evaporates to produce a conductive plasma.
Re: vacuum spark gap
Coronafix, Tue Jun 20 2006, 02:28AM
We are talking electron transfer, and I'm not wanting to produce x-rays anyway, just improve the efficiency of the static spark gap.
Maybe I should have asked the question..."Has anyone used a static gap under a partial vacuum and if so, are there any noticable benefits?"
Coronafix, Tue Jun 20 2006, 02:28AM
SpyrosF wrote ...
Vacuum is not conductive, except of course thermionic emissions.
Vacuum is not conductive, except of course thermionic emissions.
We are talking electron transfer, and I'm not wanting to produce x-rays anyway, just improve the efficiency of the static spark gap.
Maybe I should have asked the question..."Has anyone used a static gap under a partial vacuum and if so, are there any noticable benefits?"
Re: vacuum spark gap
Michael W., Tue Jun 20 2006, 04:03AM
Heres a small one for sale on ebay
Its sort of expensive...
Michael W., Tue Jun 20 2006, 04:03AM
Heres a small one for sale on ebay
Its sort of expensive...
Re: vacuum spark gap
Coronafix, Tue Jun 20 2006, 05:30AM
now thats what i'm talking about!!
that one looks adjustable, but I don't know how that would work and keep a good seal.
I read somewhere of someone getting 50% effeciency, but no details were mentioned.
Coronafix, Tue Jun 20 2006, 05:30AM
now thats what i'm talking about!!
that one looks adjustable, but I don't know how that would work and keep a good seal.
I read somewhere of someone getting 50% effeciency, but no details were mentioned.
Re: vacuum spark gap
SpyrosF, Tue Jun 20 2006, 05:45AM
Try a pressurized spark gap, it's able to handling higher currents and has faster switching,
better timings, lower losses and lower jitter.
Take a look at this links:
SpyrosF, Tue Jun 20 2006, 05:45AM
We are talking electron transfer, and I'm not wanting to produce x-rays anyway, just improve the efficiency of the static spark gap.
Try a pressurized spark gap, it's able to handling higher currents and has faster switching,
better timings, lower losses and lower jitter.
Take a look at this links:
Re: vacuum spark gap
johnf, Tue Jun 20 2006, 08:58AM
Good vacuum is related to mean free path ie the distance between gas molecules. The longer the path between molecules the better the vacuum. Current flow in a vacuum can result from either ion flow or electron flow. Ion flow happens when gas atoms are ionised and are repelled / attracted and tend to happen at poor vacuums ie low mean free path. Electron flow needs either field emmision or thermionc emmision and requires a good vacuum ie long mean free path as electrons will hit gas molecules ionising them but reducing current flow.
Now down to your question of a switch.
Yes a good vacuum without field or thermionic emitters will withstand many tens of kV per inch but will be hard to switch as there is nothing to breakdown and carry charge.
A cheap pressurised gas mix of 25% co2 and N2 75% at 20 atmospheres will withstand 20Mv per meter and if it does break down the gap readily ionises to provide an almost lossless channel for the current ie big dI/DT and resets quickly.
We use the gas mix at work on our two linear accelerators 6Mv and 3Mv and tank sparks from terminal to earth are rare but are over very quickly so as to not influence our measurements. SF5 would also work but we stay clear of it as if you do spark in it it breaks down to sulphur and flourine gas the later is not good for most metals/ insulators
johnf, Tue Jun 20 2006, 08:58AM
Good vacuum is related to mean free path ie the distance between gas molecules. The longer the path between molecules the better the vacuum. Current flow in a vacuum can result from either ion flow or electron flow. Ion flow happens when gas atoms are ionised and are repelled / attracted and tend to happen at poor vacuums ie low mean free path. Electron flow needs either field emmision or thermionc emmision and requires a good vacuum ie long mean free path as electrons will hit gas molecules ionising them but reducing current flow.
Now down to your question of a switch.
Yes a good vacuum without field or thermionic emitters will withstand many tens of kV per inch but will be hard to switch as there is nothing to breakdown and carry charge.
A cheap pressurised gas mix of 25% co2 and N2 75% at 20 atmospheres will withstand 20Mv per meter and if it does break down the gap readily ionises to provide an almost lossless channel for the current ie big dI/DT and resets quickly.
We use the gas mix at work on our two linear accelerators 6Mv and 3Mv and tank sparks from terminal to earth are rare but are over very quickly so as to not influence our measurements. SF5 would also work but we stay clear of it as if you do spark in it it breaks down to sulphur and flourine gas the later is not good for most metals/ insulators
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