Electrical conductivity of absolute vacuum

oz93666

Joined Sep 7, 2010
739
A very reasonable and clear question .... A vacuum tube of course does not have a vacuum in it ....

In an Absolute vacuum the only way for current to move is by the electrons emitted by the -ve terminal ...

the hotter the temperature of the -ve terminal , the more easily electrons "boil off" and they will travel to the +ve terminal and cause a current .. but I would imagine this flow would be extremely low ... if there were molecules in the space they would ionise at some point and cause a large current flow , but there are none .
 

triksarr

Joined Jan 25, 2019
2
Current in the vacuum cannot exist independently since the vacuum is a dielectric. In this case, the current can be created using thermionic emission. Thermoelectronic emission is a phenomenon in which electrons escape from metals when heated. Such electrons are called thermoelectrons, and the whole body is an emitter (taken from). Electrons will be able to fly out of the metal if they have sufficient kinetic energy. It must be greater than the electron work function for the metal. Electrons emitted from the cathode form an electronic cloud. Half of them return to the starting position. In the equilibrium state, the number of emitted electrons is equal to the number of returned. The density of the electron cloud is directly proportional to the temperature (i.e. as the temperature rises, the density of the cloud becomes greater).
 

nsaspook

Joined Aug 27, 2009
10,715
Current in the vacuum cannot exist independently since the vacuum is a dielectric. In this case, the current can be created using thermionic emission. Thermoelectronic emission is a phenomenon in which electrons escape from metals when heated. Such electrons are called thermoelectrons, and the whole body is an emitter (taken from). Electrons will be able to fly out of the metal if they have sufficient kinetic energy. It must be greater than the electron work function for the metal. Electrons emitted from the cathode form an electronic cloud. Half of them return to the starting position. In the equilibrium state, the number of emitted electrons is equal to the number of returned. The density of the electron cloud is directly proportional to the temperature (i.e. as the temperature rises, the density of the cloud becomes greater).
Electron currents can also be created by field emission. Field emission is usually the primary underlying causes of vacuum breakdown and electrical discharge phenomena.
 

bertus

Joined Apr 5, 2008
22,121
Hello,

Also arcing in the vacuum will influence the vaccuum.
Once we had a detector in a mass spectrometer that was arcing and the vacuum detector noticed the ions coming from the arcing and closed down the system.

Bertus
 

triksarr

Joined Jan 25, 2019
2
OK. In all cases, ion emission can occur as the emission of particles of the emitter itself and impurity particles, which are unavoidable in real materials. Field ion emission is used to prepare the sample in an ion projector and in an electronic projector (taken from <SNIP>). To obtain a sharp image using an ion projector, it is necessary to create an atomic-smooth sample surface. Field ion emission smoothes the surface of the tip, since at the edges and sharp protrusions the electric field is stronger, which leads to the preferred evaporation of ions from these places.

Moderators note : removed commercial link
 
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Wendy

Joined Mar 24, 2008
23,082
In practical use, We referred to a high vacuum and lo vacuum, In our sputtering machine at my old job we used a cryo pump to create a high vacuum. A plate was cooled to 3° Absolute, and gas molecules that touched it stuck. A roughing pump (AKA oil pump or vacuum pump) started the initial vacuum. Vacuum tubes use something called getters to create their final vacuum A reactive metal the reacts with the residual gas molecules the glass tube in a induction furnace
 

Danko

Joined Nov 22, 2017
1,493
Current in the vacuum cannot exist independently since the vacuum is a dielectric.
Electrons can exist and run in vacuum only.
Vacuum is superconductor. No resistance.
Electrons can moving in vacuum infinitely, without kinetic energy losses.
Metal is isolator, prison for electrons. They are arrested inside proton matrix.
(It is like water inside pipe is isolated from ambient).
Inside metals, free electrons are moving in vacuum, residing between partially ionized atoms.
Surface of metal is dielectric, electrons can not easily exceed from surface
to superconductive medium (vacuum) because of protons electric field.
Di-electric is for potential barrier, formed by two types of electrical charges (protons, electrons).
Field emission is usually the primary underlying causes of vacuum breakdown and electrical discharge phenomena.
Vacuum breakdown sure enough is breakdown of metal surface potential barrier.
Even without any breakdowns, vacuum always prepared to conduct any particles,
each of charged and neutral.
 
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Glenn Holland

Joined Dec 26, 2014
703
Electrons can exist and run in vacuum only.
Vacuum is superconductor. No resistance.
Electrons can moving in vacuum infinitely, without kinetic energy losses.
Metal is isolator, prison for electrons. They are arrested inside proton matrix.
(It is like water inside pipe is isolated from ambient).
Inside metals, free electrons are moving in vacuum, residing between partially ionized atoms.
Surface of metal is dielectric, electrons can not easily exceed from surface
to superconductive medium (vacuum) because of protons electric field.
Di-electric is for potential barrier, formed by two types of electrical charges (protons, electrons).

Vacuum breakdown sure enough is breakdown of metal surface potential barrier.
Even without any breakdowns, vacuum always prepared to conduct any particles,
each of charged and neutral.
Did you get your electrical/electronics training from a mail order place?
 

BR-549

Joined Sep 22, 2013
4,928
I think charge particles have sides. A front and back side. Top side and bottom side. A left side and right side. And an inside and outside.

I also think that under most circumstances, a charge has to be turned around to change direction.

Accelerating a charge backwards.....gives you anti matter.
 

Comrade Pingu

Joined Aug 30, 2018
25
If by "vacuum" you mean an area without air then yeah, there is conductivity. Electrons can move through free space. All particles can. Even a current can. If you're talking about a place where there aren't any particles at all, then there wouldn't be any conductivity in the first place since there aren't any particles. By introducing particles you're taking away it's what makes the vacuum a vacuum.

We can actually get the admittance of free space by taking the impedance of free space and just using Y = 1/Z to find it. Using the value from the 2018 Review of Particle Physics, we get that the admittance of free space is about 0.0027 S.
 

MrAl

Joined Jun 17, 2014
9,638
Hi,

The vacuum seems to be purely coincidental to anything that can be called 'conduction'.

Yeah there are electrical properties of free space that could be used here. But the definition of a vacuum seems to have changed over time. Now i think a vacuum is described by a bunch of particles that are created and destroyed. However, i dont think these particles have any influence over anything that happens in the space so externally they may be considered to be "not there".

Normally a vacuum does not conduct in the same way that a wire does, in fact can a vacuum really be said to conduct? It's more like things are shot through it in order to get anything to move through it. Waves can travel through because they have that ability but not sure if you want to call that conduction because that's not DC current either.

These kinds of questions come up now and then and the result usually defaults to trying to define what a current really is. For example, in a CRT oscilloscope is the electron beam a current? That might be a current but that's not what i think of when i think of "conduction". When i think of conduction to me that means a process that takes place little by little, like a bucket brigade, where the charge is continually handed off one step at a time NOT forced to fly in some direction like a missile. So going back to the characteristic of free space where the particles do not affect the process, the vacuum is merely coincidental not supportive of the process like a copper wire would be.
The electric field is different however and that has the ability to extend outward and i think that says a lot about the 'conductivity' of a vacuum, if it was conductive then the field would be reduced significantly in every case, but it is not.
 

Darkstar

Joined Sep 3, 2010
177
There's no need to introduce fancy field effect emission or other means of getting electrons to move through even a 'perfect' vacuum. Two things come to mind that work fine by themselves. One is the Sun. It has no trouble spitting out many planets mass of electrons and protons into the interstellar vacuum every second. Second, a more controlled way to neutralize a surface charge (which I think someone mentioned somewhere) in a vacuum would be to simply expose the surface to a radioactive alpha or beta emitter until the charge is neutralized.

Smoke detectors, and other similar devices, can monitor the increase or decrease in charge delivered to a detector to tell if any particles are present. I'm sure they'd work fine in a vacuum as long as they weren't some type that relied on a particle or gas molecule becoming ionized first in order to be detected.

As for a vacuum being a 'forbidden' place where free electrons are not allowed, maybe that's on a quantum scale because it doesn't seem to be a problem in the cases I've just mentioned.
 

MrAl

Joined Jun 17, 2014
9,638
There's no need to introduce fancy field effect emission or other means of getting electrons to move through even a 'perfect' vacuum. Two things come to mind that work fine by themselves. One is the Sun. It has no trouble spitting out many planets mass of electrons and protons into the interstellar vacuum every second. Second, a more controlled way to neutralize a surface charge (which I think someone mentioned somewhere) in a vacuum would be to simply expose the surface to a radioactive alpha or beta emitter until the charge is neutralized.

Smoke detectors, and other similar devices, can monitor the increase or decrease in charge delivered to a detector to tell if any particles are present. I'm sure they'd work fine in a vacuum as long as they weren't some type that relied on a particle or gas molecule becoming ionized first in order to be detected.


As for a vacuum being a 'forbidden' place where free electrons are not allowed, maybe that's on a quantum scale because it doesn't seem to be a problem in the cases I've just mentioned.

Hi,

Not sure what point you are trying to make here. It sounds like you are saying a bucket can not be empty because it is possible to put something into the bucket :)
The real question is does the bucket already have something in it i think.
 

Darkstar

Joined Sep 3, 2010
177
Hi,

Not sure what point you are trying to make here. It sounds like you are saying a bucket can not be empty because it is possible to put something into the bucket :)
The real question is does the bucket already have something in it i think.

Hello,
HotFurnace asked "...could the absolute vacuum conduct electricity?"

I meant exactly what I said. I don't think it's a question of whether the bucket already has something in it or not. It sounded to me like the discussion got off on a bit of a tangent. As for current flowing in an absolute vacuum, I gave several examples where it would. It's not a problem so there's no need to make the question more complicated by looking at unnecessarily complex scenarios & solutions. The discussion has been interesting and informative but it seemed to me that a simple "yes" could suffice (although I personally prefer some explanation of what I'm basing my answer on which is why I gave examples.)

Maybe what he meant to ask is "can a current be detected in a vacuum apart from any external current source?" That may be why he brought up virtual particles. In this case the answer would still be "yes". Virtual particles, as I recall, can and do form spontaneously anywhere as matter/antimatter pairs. As long as there was a charge to pull them apart so they couldn't recombine then one would detect a current. BTW, the strong gravitational field at the event horizon of a black hole can separate the particles. In this case, when formed, one goes into the black hole and the other gets away. This is called Hawking Radiation and is how black holes "evaporate", I'm sure you've heard. The accretion disk around the black hole is anything but a vacuum, but I've never heard anyone say it would hinder the virtual particles, though I suspect that at some point it would be dense enough to get in their way. The important point is that one particle goes in and the other doesn't.

This just occurred to me. If the particle that gets away gets caught up in the inward rushing accretion disk and gets carried into the black hole anyway, then both particles are inside so there would be no Hawking Radiation. But that's another discussion.
Excuse the italics, I did something wrong trying to insert the second quote.
 

nsaspook

Joined Aug 27, 2009
10,715
Excuse the italics, I did something wrong trying to insert the second quote.
First, virtual particles are always non-physical in isolation. They never exist as particles. They are used as a mathematical short cut to explain the actions of real particles/fields like the use of 'holes' (quasiparticles) in semiconductors.
https://profmattstrassler.com/artic...ysics-basics/virtual-particles-what-are-they/
Virtual Particles: What are they?
The term “virtual particle” is an endlessly confusing and confused subject for the layperson, and even for the non-expert scientist. I have read many books for laypeople (yes, I was a layperson once myself, and I remember, at the age of 16, reading about this stuff) and all of them talk about virtual particles and not one of them has ever made any sense to me. So I am going to try a different approach in explaining it to you.

The best way to approach this concept, I believe, is to forget you ever saw the word “particle” in the term. A virtual particle is not a particle at all. It refers precisely to a disturbance in a field that is not a particle. A particle is a nice, regular ripple in a field, one that can travel smoothly and effortlessly through space, like a clear tone of a bell moving through the air. A “virtual particle”, generally, is a disturbance in a field that will never be found on its own, but instead is something that is caused by the presence of other particles, often of other fields.
 
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Darkstar

Joined Sep 3, 2010
177
First, virtual particles are always non-physical. They never exist. They are used as a mathematical short cut to explain the actions of real particles/fields like the use of 'holes' in semiconductors.
https://profmattstrassler.com/artic...ysics-basics/virtual-particles-what-are-they/
You'll have to excuse my terminology, but I was taught to think of these things as particles. The newer "everything is field perturbations" had not come along yet and I'm still trying to merge it with what I learned. In any case, particles are an easy way to visualize what's happening. In videos I've seen by real physicists they have no problem talking about particles and antiparticles. I have books with diagrams of Hawking radiation & more and they all use the terms particles and field interactions between them (i.e. Such as between Quarks.) My field is chemistry and it's all about electrons moving between or being shared by molecules & atoms. HotFurnace brought up the subject first, I was replying with the same terminology. Anyway, my comment was just a spur of the moment thought, it's not part of the answer to this question.
 

djsfantasi

Joined Apr 11, 2010
8,682
My limited interpretation tells me that an absolute vacuum is NOT the absence of EVERYTHING in the volume of the absolute vacuum.

There’s always SOMETHING there.

Consider a thought experiment. Place a large magnet in a glass (or any non-magnetic material) containment vessel. Before evacuating the vessel, measure the strength of the magnetic field at the periphery of the vessel. Do you get a reading? Write it down. Then start evacuating the vessel. At a pre-determined vacuum delta values, document the degree of the vacuum and the measured magnetic field.

Vote. How many say the magnetic strength will change? How many believe it will be constant.

My point is that while particles maybe absent, a field will still exist in a vacuum.
 

nsaspook

Joined Aug 27, 2009
10,715
You'll have to excuse my terminology, but I was taught to think of these things as particles. The newer "everything is field perturbations" had not come along yet and I'm still trying to merge it with what I learned. In any case, particles are an easy way to visualize what's happening. In videos I've seen by real physicists they have no problem talking about particles and antiparticles. I have books with diagrams of Hawking radiation & more and they all use the terms particles and field interactions between them (i.e. Such as between Quarks.) My field is chemistry and it's all about electrons moving between or being shared by molecules & atoms. HotFurnace brought up the subject first, I was replying with the same terminology. Anyway, my comment was just a spur of the moment thought, it's not part of the answer to this question.
Sure, particles and antiparticles are 'real' and must obey the rules of mass, momentum and charge. This idea that somehow virtual particles (that don't need to obey all the rules of mass, momentum and charge) can become 'real' particles is misleading even without "everything is field perturbations". They are very real in the context of describing particles and field interactions between them.
 
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