Can a spark form through vacuum?

[error404]

Hey guys,

I was looking online at sparks and how they form, and the amount of energy needed to form them when this question came up to my mind.
can a spark form through vacuum? or it actually needs particles to go through them?
and if it can form...what is the value of the breakthrough for vacuum??

Thanks
Error404

 

[berkeman]

Hey guys,

I was looking online at sparks and how they form, and the amount of energy needed to form them when this question came up to my mind.
can a spark form through vacuum? or it actually needs particles to go through them?
and if it can form...what is the value of the breakthrough for vacuum??

Thanks
Error404

The traditional tool for estimating the breakdown at very low pressures is the Paschen Curve:

http://en.wikipedia.org/wiki/Paschen_curve

I'm not sure what happens at very hard vacuum levels, though...

 

[haxor489]

It actually needs a medium. The breakdown voltage is relative to medium. No medium (vacuum) hence no spark

 

[error404]

Berkeman, thanks for your reply. I can understand from this figure that either at very low pressure or at very high pressure, we need a HUGE voltage to make a spark, is that correct?

Haxo489, thanks for your clear answer. however, i am wondering how much vacuum we could actually achieve in real life, is 100% vacuum possible?

Error404

 

[ZVdP]

An arc through a vacuum gap is possible, but it will be invisible, since there is no medium to light up.
Since there is no medium, there is nothing to break down. But there is another mechanism: the electric field just has te be large enough to pull the electrons out of the metal. You could probably calculate this using the work function of the metal crystal.

 

[DrZoidberg]

An arc through a vacuum is called an electron beam. It was used in CRTs (cathod ray tubes).

 

[NascentOxygen]

Do I correctly recall reading that there is lightning between one of the large planets and one of its moons?

 

[Enthalpy]

Vacuum is a good insulator but hardly reproducible. Brutal discharges do happen, but their mechanis isn't very clear yet; it may involve X-rays in the anode-to-cathode feedback, and is not purely a tunnelling emission.

At usual distances, the breakdown field is similar to the best solid insulators, like 50 to 100MV/m. It depends a lot on the smoothness and external layer of the electrodes; values of 200MV/m have been reported.

Even more so than in solids and liquids, the breakdown "field" depends much on the distance between the electrodes and on the insulating volume; the breakdown "field" varies still more slowly with the distance than the breakdown voltage.

Vacuum insulation is heavily used industrially at medium and high voltage to make switches, protections and so on, because vacuum insulates better than a gas does. Hence it is the subject of much ongoing research.

 

[nsaspook]

Vacuum insulation is heavily used industrially at medium and high voltage to make switches, protections and so on, because vacuum insulates better than a gas does. Hence it is the subject of much ongoing research.

HV breakers, switches and electrical equipment are increasingly using SF6 (an ELECTRONEGATIVE GAS) as it has a higher dielectric strength under pressure than high vacuum (it suppresses the effects of field emission in a vacuum)and makes a better switching medium for some types of loads.

http://www.gigavac.com/apps/relays/physics/index.htm

 

[Pkruse]

We have had some very expensive failures in spacecraft caused by arcing and sparking in a vacuum or near vacuum. That is why NASA tests all equipment in a vacuum chamber before sending it up into space.

Every once in a while some bean counter will save money by not doing these tests, and we get to see another spectacular failure.

I once toured a lab at JSC where they do the design of tools used on EVAs by the astronauts. I now understand why a power drill you buy at Home Depot is used inside the ISS, but the one they use outside exceeds a million dollars. Much of that related directly to arcing in a vacuum or near vacuum.

 

[yungman]

I don't know about perfect vacuum, but there is no perfect vacuum. Any molecule or anything in vacuum will eventually arc if you put high enough voltage. We do 10EE-9 in our spectrometer, we still have to pump it down, let it arc to smooth out the rough machined edges!

 

[phinds]

If you could not spark through a vacuum, you could make an infinite-voltage capacitor just by putting the two plates in a vacuum since you would never get dielectric breakdown. See how silly that sounds?

 

[davenn]

Do I correctly recall reading that there is lightning between one of the large planets and one of its moons?

yeah Jupiter and its moon Io

I don't know if its in the form of actual lightning type zaps tho
but there are huge discharges between the two. Io looses a lot of surface material to space, this trails behind the moon in its orbit and forms a huge torus ring around Jupiter

Dave

 

[davenn]

If you could not spark through a vacuum, you could make an infinite-voltage capacitor just by putting the two plates in a vacuum since you would never get dielectric breakdown. See how silly that sounds?

Well in RF electronics we do use vacuum capacitors that won't break down under EHT voltages


Dave

 

[yungman]

This is really empty talk. In real instrument or circuit, creepage is a much bigger problem than jumping through space. You might have a perfect vacuum, but in order to have two electrodes facing each other, you have to have support, feed through, so there is a continuous surface connecting between the two. The surface it what it's going to break down. You look at CE or even UL spec, insulation distance is less than 1/10 the creepage distance, it's the surface creepage that is the limiting factor.

You really worry about two planet arcing across? seriously. I am not expert in vacuum, but even if you can somehow conquer the creepage and have a perfect vacuum, if you put enough potential to create some serious E field, don't the surface of the metal start ionized and form some sort of conductive plasma or something. Again, I don't know the physics behind it, just a guess. But like vacuum tubes, if you put enough E field across, something is going to happen!

 

[davenn]

This is really empty talk. In real instrument or circuit, creepage is a much bigger problem than jumping through space. You might have a perfect vacuum, but in order to have two electrodes facing each other, you have to have support, feed through, so there is a continuous surface connecting between the two. The surface it what it's going to break down. You look at CE or even UL spec, insulation distance is less than 1/10 the creepage distance, it's the surface creepage that is the limiting factor.

You really worry about two planet arcing across? seriously. I am not expert in vacuum, but even if you can somehow conquer the creepage and have a perfect vacuum, if you put enough potential to create some serious E field, don't the surface of the metal start ionized and form some sort of conductive plasma or something. Again, I don't know the physics behind it, just a guess. But like vacuum tubes, if you put enough E field across, something is going to happen!

maybe you are missing the point ?

yes there will be a voltage that the vacuum cap will eventually fail at, but its many many 1000's of volts higher than a standard capacitor with a ceramic or other dielectric

Dave

 

[yungman]

maybe you are missing the point ?

yes there will be a voltage that the vacuum cap will eventually fail at, but its many many 1000's of volts higher than a standard capacitor with a ceramic or other dielectric

Dave

I am responding to the original post and in general. The post go into arcing between planets and vacuum cap. As I said, the creepage break down is more likely to be the limiting factor in real life case. The important thing is there is no perfect vacuum, as long as there is ions floating around, it will break down. From my experience, people count on about 400V/mil either in good vacuum or dielectric as the limiting factor in practical situation. And our problems are mainly on creepage, not on insulation that you are talking about.

 

[error404]

maybe you are missing the point ?

yes there will be a voltage that the vacuum cap will eventually fail at, but its many many 1000's of volts higher than a standard capacitor with a ceramic or other dielectric

Dave

Thanks for replies everyone.
As i can understand from the replies above... A 100% vacuum has a dielectric constant almost the same as air, but prevents the formation of a spark like...a 100 times more?
Note: my question might sound very silly but i am not an expert in the field of electrical engineering...and i had some questions for you...experts!

Error404

 

[Enthalpy]

HV breakers, switches and electrical equipment are increasingly using SF6 (an ELECTRONEGATIVE GAS) as it has a higher dielectric strength under pressure than high vacuum (it suppresses the effects of field emission in a vacuum)and makes a better switching medium for some types of loads.

http://www.gigavac.com/apps/relays/physics/index.htm

This is what Gigavac would like customers to believe.

Vacuum has nearly replaced SF6 in high-voltage circuit breaker. As a gas, even at pressure, SF6 is nowhere near the dielectric strength of vacuum, which exceeds solids and liquids.

SF6 is being phased out, alas, because it's both an ozone killer and a greenhouse gas. Same for CF4.

 

[Enthalpy]

This is really empty talk. In real instrument or circuit, creepage is a much bigger problem than jumping through space. You might have a perfect vacuum, but in order to have two electrodes facing each other, you have to have support, feed through, so there is a continuous surface connecting between the two. The surface it what it's going to break down. You look at CE or even UL spec, insulation distance is less than 1/10 the creepage distance, it's the surface creepage that is the limiting factor.

This is true and so much known that designers have even found solutions.

 

[Enthalpy]

A 100% vacuum has a dielectric constant almost the same as air, but prevents the formation of a spark like...a 100 times more?

Rounding the figures, yes.

Gasses are no good insulators, though pure N2 is good and SF6 better. Dense materials are good, vacuum is similar to them.

 

[Ratch]

error404,

Have you seen the article? http://fieldp.com/myblog/2011/electric-field-limits-vacuum-breakdown/

Ratch

 

[Ratch]

DrZoidberg,

An arc through a vacuum is called an electron beam. It was used in CRTs (cathod ray tubes).

Not quite the same. Sending free electrons boiled off by thermionic emission through a vacuum is not the same as arcing across two cold conductors.

Ratch