What is this picture trying to say
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ggunn
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I guess anything's possible but that doesn't seem reasonable to me.
Well you don't want incandescent lamps emitting neutron radiation, so it's under special conditions. If you get into something like the Farnsworth Phasor or some of the cold fusion experiments, they look for isotope changes. Unless you specifically want a neutron source, it would be something to be avoided.
Otherwise, I believe the picture is showing plasma in the gap.
Otherwise, I believe the picture is showing plasma in the gap.
mbrooke
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Is plasma arcing?
I was probably using the word interchangeably, plasma is ionized high temp gas, arc creates plasma. Arc and plasma are coincident. I believe that's what is shown in the gap, zones 'a b c', an arc that creates plasma.
It is showing more than just an electron stream. The cathode material is vaporizing and redepositing back onto the cathode.
https://en.wikipedia.org/wiki/Halogen_lamp
winnie
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I don't understand what is being shown here particularly well.
K is the Cathode, the negatively charged electrode. A is the anode, and positively charged.
The arc is composed of electrons and metal ions. Both carry charge; the metal ions are positively charged because they have lost electrons. (Atoms can be neutral, with the same number of positive and negative charges, or they can be 'ionized' meaning that they've gained or lost electrons.)
During arcing conditions, the charged species in the arc distort the electric field, so while you might have 20V between the two electrodes, that voltage drop could be concentrated near one of the electrodes.
As drawn, there is a 20V drop over regions a and b, and very little voltage drop in region c. Ukf is the 'cathode voltage'. This voltage drop accelerates metal ions toward the cathode, and the hot cathode emits electrons. The electrons are accelerated away from the cathode by the voltage; the metal ions are accelerated _toward_ the cathode. Some electrons crash into neutral metal atoms, knocking electrons off and ionizing the atoms.
In regions a and b the metal ions always get accelerated toward the cathode. However some metal ions in region b have enough kinetic energy that they can still make it to region c.
In region c you have a neutral plasma of electrons and ions; both moving toward the anode. In this region there isn't much voltage drop, so the ions can ride their kinetic energy 'up stream'.
But that is really just me guessing.
-Jon
K is the Cathode, the negatively charged electrode. A is the anode, and positively charged.
The arc is composed of electrons and metal ions. Both carry charge; the metal ions are positively charged because they have lost electrons. (Atoms can be neutral, with the same number of positive and negative charges, or they can be 'ionized' meaning that they've gained or lost electrons.)
During arcing conditions, the charged species in the arc distort the electric field, so while you might have 20V between the two electrodes, that voltage drop could be concentrated near one of the electrodes.
As drawn, there is a 20V drop over regions a and b, and very little voltage drop in region c. Ukf is the 'cathode voltage'. This voltage drop accelerates metal ions toward the cathode, and the hot cathode emits electrons. The electrons are accelerated away from the cathode by the voltage; the metal ions are accelerated _toward_ the cathode. Some electrons crash into neutral metal atoms, knocking electrons off and ionizing the atoms.
In regions a and b the metal ions always get accelerated toward the cathode. However some metal ions in region b have enough kinetic energy that they can still make it to region c.
In region c you have a neutral plasma of electrons and ions; both moving toward the anode. In this region there isn't much voltage drop, so the ions can ride their kinetic energy 'up stream'.
But that is really just me guessing.
-Jon
gar
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What is being described in post #1 is an arc with unidirectional current flow. Most likely in air. The negative electrode emits electrons (see work function at https://en.wikipedia.org/wiki/Work_function ). I believe the described plasma, to a substantial extent, is formed from ionized gas. However, with heat developed there is some vaporization of material from the anode (positive electrode), ionization of the material, and transfer of the material to the cathode.
A lot of work was done in the past to select or create materials for switch contacts to minimize metal transfer. Silver cadmium oxide has better high current capability than pure silver, but has poor low voltage characteristics because of contact resistance that is not broken down at low voltages. Most electricians don't know this and make some bad substitution mistakes. The same relay with silver cadmium oxide contacts will have double the contact rating at 120 V as will pure silver contacts, 10 A vs 5 A.
If you look at a relay contact that has switched an inductive load of only 1 A at 107 V DC for possibly 100,000 or less cycles you will find a conical mound on the cathode contact and a conical hole in the anode contact.
This was always a problem for automotive ignition contacts. In the early 1940s Henry Ford and Emil Zorelein invented a distributor that alternated the direction of current flow thru the breaker points every mechanical cycle. I would expect they had worked on ideas for this much earlier. This never went into production. Later in the early 1950s a Ford engineer invented breaker points with a hole in the center of the cathode contact. This greatly reduced the build up of the cathode cone and thus increased breaker life. This went into production.
See "Fundamentals of Engineering Electronics", William G. Dow, John Wiley, 1937 and 1952, Chapters XII, XV, XVI, and XVII for discussions on spark, arc, and plasma.
.
What is being described in post #1 is an arc with unidirectional current flow. Most likely in air. The negative electrode emits electrons (see work function at https://en.wikipedia.org/wiki/Work_function ). I believe the described plasma, to a substantial extent, is formed from ionized gas. However, with heat developed there is some vaporization of material from the anode (positive electrode), ionization of the material, and transfer of the material to the cathode.
A lot of work was done in the past to select or create materials for switch contacts to minimize metal transfer. Silver cadmium oxide has better high current capability than pure silver, but has poor low voltage characteristics because of contact resistance that is not broken down at low voltages. Most electricians don't know this and make some bad substitution mistakes. The same relay with silver cadmium oxide contacts will have double the contact rating at 120 V as will pure silver contacts, 10 A vs 5 A.
If you look at a relay contact that has switched an inductive load of only 1 A at 107 V DC for possibly 100,000 or less cycles you will find a conical mound on the cathode contact and a conical hole in the anode contact.
This was always a problem for automotive ignition contacts. In the early 1940s Henry Ford and Emil Zorelein invented a distributor that alternated the direction of current flow thru the breaker points every mechanical cycle. I would expect they had worked on ideas for this much earlier. This never went into production. Later in the early 1950s a Ford engineer invented breaker points with a hole in the center of the cathode contact. This greatly reduced the build up of the cathode cone and thus increased breaker life. This went into production.
See "Fundamentals of Engineering Electronics", William G. Dow, John Wiley, 1937 and 1952, Chapters XII, XV, XVI, and XVII for discussions on spark, arc, and plasma.
.
gar
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The Wiki discussion at https://en.wikipedia.org/wiki/Electric_arc may be of some value to you.
Another useful reference is https://www.tankonyvtar.hu/en/tartalom/tamop425/0048_VIVEM174EN/ch02s02.html .
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The Wiki discussion at https://en.wikipedia.org/wiki/Electric_arc may be of some value to you.
Another useful reference is https://www.tankonyvtar.hu/en/tartalom/tamop425/0048_VIVEM174EN/ch02s02.html .
.
mbrooke
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gar
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mbrooke:
At very high electric field intensities and very low currents you have corona discharges. At higher currents and lower electric field intensities you have spark discharges, an automotive spark plug. Hundreds or thousands of volts drop across the spark gap during conduction. A spark plug might breakdown around 10,000 V and conduct at possibly 1000 V (from memory).
Raise the current enough by lowering the current source impedance enough (amperes) and the spark discharge changes to an arc (plasma in the major conductive path). Now the voltage for short gaps drops to 10 to 100 V (arc welding and arc lamps).
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mbrooke:
At very high electric field intensities and very low currents you have corona discharges. At higher currents and lower electric field intensities you have spark discharges, an automotive spark plug. Hundreds or thousands of volts drop across the spark gap during conduction. A spark plug might breakdown around 10,000 V and conduct at possibly 1000 V (from memory).
Raise the current enough by lowering the current source impedance enough (amperes) and the spark discharge changes to an arc (plasma in the major conductive path). Now the voltage for short gaps drops to 10 to 100 V (arc welding and arc lamps).
.
ggunn
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hmy:gar
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mbrooke:
The article http://www.physics.csbsju.edu/370/jcalvert/dischg.htm.html is very good, but possibly much too detailed for your needs.
This reference might be somewhat more useful https://physics.stackexchange.com/q...e-relationship-between-glow-and-arc-discharge .
You can search for other discussions.
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The article http://www.physics.csbsju.edu/370/jcalvert/dischg.htm.html is very good, but possibly much too detailed for your needs.
This reference might be somewhat more useful https://physics.stackexchange.com/q...e-relationship-between-glow-and-arc-discharge .
You can search for other discussions.
.
gar
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- Ann Arbor, Michigan
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180906-1030 EDT
At room temperature virtually all materials emit very few electrons into the space around the material. An emitted electron is one that escapes the material from where it came. Emitted electrons from a material form a negative space charge around that material. Electron emission increases as the material temperature increases. Some materials at a particular temperature are more efficient at emitting electrons than others. The work function of the material is a measure of this efficiency. Thermionic emission requires no external electric field to cause emission. With no external electric field these emitted electrons will fall back to the emitting surface. High current density at a cathode can produce self induced thermionic emission. This happens in an arc. Results in a low cathode fall of potential.
Without substantial thermionic emission electrons can be pulled from the material by a high electric field gradient at the cathode surface. This occurs in a spark (glow) discharge. Result is a much higher cathode fall of potential than in an arc.
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At room temperature virtually all materials emit very few electrons into the space around the material. An emitted electron is one that escapes the material from where it came. Emitted electrons from a material form a negative space charge around that material. Electron emission increases as the material temperature increases. Some materials at a particular temperature are more efficient at emitting electrons than others. The work function of the material is a measure of this efficiency. Thermionic emission requires no external electric field to cause emission. With no external electric field these emitted electrons will fall back to the emitting surface. High current density at a cathode can produce self induced thermionic emission. This happens in an arc. Results in a low cathode fall of potential.
Without substantial thermionic emission electrons can be pulled from the material by a high electric field gradient at the cathode surface. This occurs in a spark (glow) discharge. Result is a much higher cathode fall of potential than in an arc.
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ggunn
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