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#1 Handy andy

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Posted 17 April 2017 - 10:57 AM

First some background to my reasoning.

 

I am interested in different methods of ionisation of gases. Typically gamma rays and X-rays including extra high frequency radio waves can be used as well as very high voltage DC. I recently read a very old physics  book written by JJ Thompson, he pointed out at the instant switch contacts are opened a bunching effect of charges occurs due to inertia. This can create an extremely large momentary EM impulse, and explode wires or electronics if the current does not find an alternative path.

 

A parallel pair of wires is the easiest way to envisage, my question, various other configurations could be used.

Thinking of 2 long parallel wires connected at one end with a switched high frequency DC electrical impulse applied to the wire at sufficiently high frequency so that the outgoing impulses would pass an incoming impulses, what exactly happens at the instant the outgoing impulses pass the incoming impulses.

 

When the current impulses pass each other the magnetic fields will cancel depending on coupling, do the charges bunch momentarily become stationary, slow down or what.? Can any one direct me to any information on this effect. Also what happens at the point the charge starts its return journey. 

 

Has the method described above been used to ionize gas before, I could easily switch 1000Volts DC for 1us or less depending on power switching device used. Could this induce a momentary EM pulse that would ionize the air around it, using both high voltage and high frequency.

 

I am a retired electrical engineer, whose maths is a little rusty, but maths is like riding a bike I can quickly get up to speed(hopefully).

 

Apologies if I have posted on the wrong thread.

 

 

 


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#2 Sensei

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Posted 17 April 2017 - 05:23 PM

Thinking of 2 long parallel wires connected at one end with a switched high frequency DC electrical impulse applied to the wire at sufficiently high frequency


Typical DC does not have frequency, does not have pulses..
It's constant voltage with constant amperage (+- some tolerance).

If on one end of wire will be appearing positive charge, and then in the next stage of phase, there will appear negative charge, it's AC.

What you're interested is delta between the most extreme levels.
 

I could easily switch 1000Volts DC for 1us or less depending on power switching device used.


1000 Volts is way too small for air at STP.

You should use Cockcroft-Walton generator to generate many thousands of volts (cost less than $10),
if you don't have vacuum pump (cost >= $300)..

 

This is what you can have with 50 kV:

Discharge 50 kV.png


Edited by Sensei, 17 April 2017 - 05:40 PM.

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#3 Handy andy

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Posted 18 April 2017 - 09:29 AM

Typical DC does not have frequency, does not have pulses..
It's constant voltage with constant amperage (+- some tolerance).

If on one end of wire will be appearing positive charge, and then in the next stage of phase, there will appear negative charge, it's AC.

What you're interested is delta between the most extreme levels.
 


1000 Volts is way too small for air at STP.

You should use Cockcroft-Walton generator to generate many thousands of volts (cost less than $10),
if you don't have vacuum pump (cost >= $300)..

 

This is what you can have with 50 kV:

attachicon.gifDischarge 50 kV.png

 

Thank you very much for your answer, it is much appreciated.

 

By DC I was meaning unidirectional current flow, ie current only flowing one way in the circuit, not AC. Being able to create a high voltage DELTA function would be ideal for my purposes, I will look into the Cockcroft generator, it is not one I have heard of. I considered a Tesla coil, but it only generates a single high voltage point at the end of its secondary coil, and ionizes the air by generating extreme voltages via resonance. I am specifically thinking high voltage caused by current bunching.

 

I am aware using DC that circa 3000000 V/m the air will break down and ionize, when scaled down is around 3V/um. I am thinking of generating multiple impulses, with very short wavelengths, < 1mm if possible, preferable with wavelengths approaching X-Ray or gamma ray lengths. Under transient conditions with impulses the air can momentarily easily withstand 10000000V/m. I am considering trying to create multiple impulses within an area, to ionize a large amount of air. (on electron recombination it would look like st elmos fire, or the aurora borealis)

 

What I am trying to get my head around is being able to create multiple, high voltage impulses with very short wavelengths all capable of ionizing the air.

 

Perhaps the parallel wire concept was an over simplification. If we slightly complicate the concept, and twist it around into a flat bifilar wound pancake coil, with multiple pulses travelling around it. When the outgoing pulses pass the incoming pulses they may generate multiple high voltage IMPULSES with very short wavelengths due to the current bunching effect outlined by JJ Thompson around 100 years ago.

 

JJ Thompsons old physics book points out the bunching effect at switch off causing high voltage impulses, in inductive circuits. What I am trying to understand will current pulses bunch when passing each other in parallel wires creating a very short duration impulse, that could be used to ionize the air.

 

Using MOSFETS I can easily switch currents into a circuit with nano second rise times. Looking at other technologies I may be able to exceed this. With low inductance circuits I can switch currents off with little overshoot or BEMF, using parallel wires the inductance would be minimized, circa 10nH/m

 

I am aware that around the 2-4mm wavelength band, this creates a burning sensation in the skin. I am thinking of trying to generate impulses, not AC, over a wide surface area. If impulses are generated in a partial vacuum the production of stable ions may be improved, (I am thinking ionosphere, or even thunderclouds).

 

Thank you very much for your input. The Cockcroft generator is very interesting, and very HV.

 

I was hoping for a pointer in the right direction mathematically to analyse the charges travelling in different directions or the electric field strength at the point the charges pass each other, taking into account inertia magnetic fields etc. My Laplace and Fourier are a little rusty and I am about 4 months away from being reunited with my library, also I wondered if quantum effects might come into play.

 

The concept of inducing a short lowish voltage impulse to ionize gas will keep me amused for a little while yet.


Edited by Handy andy, 18 April 2017 - 07:02 PM.

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#4 Handy andy

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Posted 20 April 2017 - 11:59 AM

Could someone please give me a pointer on how to analize what is happening as the two current pulses pass each other in opposite directions on their conductors, incoorporating charge, mass and inertia.  


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#5 studiot

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Posted 24 April 2017 - 02:09 PM

I really don't follow what the aim of your experiment is. That is what are you intending to do with the ionised gas once you have it?

 

Why do you need two wires?

 

And why wires?

These have significant inductance at high rise times.

 

Flat strips are better.

 

Rise times are adversely affected by the use of traditional diode-capacitor voltage multipliers, especially for repetitive waveforms.

 

I note you mentioned HV mosfets. If you can get high enough ratings you might like to investigate this article. An amateur might try valves as an alternative.

 

The MOSMAX voltage multiplier Wireless World August 1988 page 748 ff.

 

Everyday Electronics did a constructional article about air ionizers

 

EE Feb 1984 page 82ff

 

I wonder if another approach might be to strip and remodel the EHT supply from an old cathode ray scope.

These are more likely to be modular and suitable than a TV EHT.

 

Remember the usual HT/ EHT precautions and keep your other hand in your pocket.

 

:)


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#6 Handy andy

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Posted 24 April 2017 - 03:40 PM

I really don't follow what the aim of your experiment is. That is what are you intending to do with the ionised gas once you have it?

 

Why do you need two wires?

 

And why wires?

These have significant inductance at high rise times.

 

Flat strips are better.

 

Rise times are adversely affected by the use of traditional diode-capacitor voltage multipliers, especially for repetitive waveforms.

 

I note you mentioned HV mosfets. If you can get high enough ratings you might like to investigate this article. An amateur might try valves as an alternative.

 

The MOSMAX voltage multiplier Wireless World August 1988 page 748 ff.

 

Everyday Electronics did a constructional article about air ionizers

 

EE Feb 1984 page 82ff

 

I wonder if another approach might be to strip and remodel the EHT supply from an old cathode ray scope.

These are more likely to be modular and suitable than a TV EHT.

 

Remember the usual HT/ EHT precautions and keep your other hand in your pocket.

 

:-)

 

Hi Thanks for coming back.

 

What I am considering trying to achieve is an impulse emf in space radiating away from the source. Gamma rays and Xrays have very short wavelength and high energy, E=hf. They are also not good for the health.

 

I want to investigate a possible current bunching effect mentioned by JJ Thompson, and "possibly" utilised by Tesla. When a current is switched off the current bunches causing a rise in electric field strength due to inertia of electrons. E= Q/(4.pi.E​o.r​) The local charge Q bunches resulting in a very large impulse voltage which radiates outwards. This effect is momentary and very fast causing ionization in the air, possibly only due to very high voltage, but maybe due also to a very short pulse duration, ie an impulse. The air glows when electrons recombine with the ionized atoms. This momentary voltage is difficult to handle and can blow up switching devices etc.

 

Using 2 wires in parallel it may be possible to create a similar bunching effect.

 

To create a pulse with sufficient energy to ionise a gas is not easily possible with todays technology.

 

When two pulses of current pass each other in opposite directions, the magnetic fields will cancel, the local electric field will as a minimum double. What I want to try and investigate is will the charges slow in any way and bunch giving an intensified electric field, and ionize the air more efficiently, due to shortened wavelength and intensified voltage.

 

Two straight parallel wires are the easiest thing to envisage, however Tesla utilised a bifilar flat pancake coil which he claimed was 100 000 times more effective at generating radiant electricity(ionised air) than his standard system. Many different coil configurations could be used to cause a similar effect, from simple loops to all kinds of knotted type coils. What I wanted to investigate first was a simple system. 2 parallel wires is I think about as simple as the idea gets. Except perhaps using a standard tesla coil and resonating a current up and down the length of the tube to create a standing wave or multiple standing waves.

 

To ionize the air with any noticeable effect from pulses the frequency needs to go up, and the pulse lengths to come down. By forcing a bunching effect this might be possible. Tesla stated that he felt a physical pain when he was running his system, this sounds a little like the microwave none lethal weapon systems being developed today.

 

Once I have the basic idea on paper, I wish to start and investigate separating the ions by modulating magnetic fields in the ionized gas, or using static charged or electron rich materials to attract the ions. Some one posted on the engineering thread area ref ionizing gases in a vacuum, I alluded to my interest there, however I wish to use very high frequency and very short wavelengths if I can create them. Bifilar coils with opposing currents on them have very low inductance and will allow me to pulse them at very high frequency with little BEMF.  

 

I take on board what you are saying about the valve technologies they were incredibly fast, I was surprised also to find just how fast the old crystal diodes were when I looked into them. I also fully understand the concept of using flat conductors in parallel to minimise inductive effects.

 

I want to force the current to bunch momentarily to create an impulse wave, that may ionize gas locally. Two 100A current pulses with a leading edge rise time of 1ns moving in opposite directions at 0.5c is a little difficult for me to analise, my maths is rusty. But given a pointer in the right direction I can work it out for myself, it doesn't take me long to come up to speed on a subject I once new well. I am not sure if relativistic effects would come into the calculation, JJ Thompsons stuff was before Einsteins ideas. I want to push the edge of what is achievable with electric field strength and impulse duration, to improve the rate of ionisation in air. running the circuit in a reduced atmosphere is a good way of prolonging the ion separation, perhaps using different gases will ionize more easily. Putting the circuit inside a metal enclosure is also a good idea, to prevent microwaving myself by mistake. :) Yes If I use HV I wont have an issue with microwaving myself, but other people have done that already. The U tube link under the engineering section I mentioned above shows some good examples of ionization ethods and is incredibly interesting to me, albeit at this stage a little more basic than what I have in mind, I will monitor it and see where he is headed.

 

Any tips on the maths would be appreciated, two charges travelling in opposite directions on two parallel wires how do the currents interact, possibly bunch(shorten wavelength) and peak(how how will the emf peak at.). I am looking specifically at the pulse interactions as they pass each other. A reflected AC wave along a transmission line will create a standing wave as it meets other waves going out. I am specifically interested in DC pulses travelling along a line.

 

Andy


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#7 studiot

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Posted 24 April 2017 - 04:40 PM

No disrespect intended, but yours posts seem to me to be a combination of half remembered facts and fancy.

 

So I find it difficult to determine your actual intent.

 

You mention 'current bunching' and in particular electron bunching in a conductor.

 

Do you have a reference?

 

And you seem to want to build an ion generator.

 

What is the connection between the two?

 

 

 

I know of space charge limited and retarded current in free space and gases. That is well known and commonly analysed by what is known as the Child's equation.

It was very important in electronics the days of valves.

 

You seem to have some understanding of pulse technology but it is all mixed up.

You mention rise time, but also frequency.

 

Pulses do not have a frequency.

They have a duration and a repetition rate, in addition to rise and fall times.

 

From your posts it is unclear whether you want a single pulse or a pulse train?

 

You believe that by brute force you can pass enough current to create sufficient electric field to cause ionisation.

That is certainly the steamroller and nut method.

 

Other methods to achieve this generally focus on lowering the ionisation threshold.

For example by heating the gas

By seeding the gas with conductive particles eg potassium as in magnetohydrodynamic generators.

 

As to the conductors I stand by what I said about wires.

They are inductive.

Bifilar winding does not reduce the inductance, it (merely) reduces the external field.

This was used in the days of high quality valve (them again) amplifiers to reduce the external field of coupling transformers.

 

So please put up a modest summary of not more than 10 lines in logical order of what you are trying to achieve.


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#8 Handy andy

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Posted Yesterday, 10:21 AM

No disrespect intended, but yours posts seem to me to be a combination of half remembered facts and fancy.

 

So I find it difficult to determine your actual intent.

 

You mention 'current bunching' and in particular electron bunching in a conductor.

 

Do you have a reference?

 

And you seem to want to build an ion generator.

 

What is the connection between the two?

 

 

 

I know of space charge limited and retarded current in free space and gases. That is well known and commonly analysed by what is known as the Child's equation.

It was very important in electronics the days of valves.

 

You seem to have some understanding of pulse technology but it is all mixed up.

You mention rise time, but also frequency.

 

Pulses do not have a frequency.

They have a duration and a repetition rate, in addition to rise and fall times.

 

From your posts it is unclear whether you want a single pulse or a pulse train?

 

You believe that by brute force you can pass enough current to create sufficient electric field to cause ionisation.

That is certainly the steamroller and nut method.

 

Other methods to achieve this generally focus on lowering the ionisation threshold.

For example by heating the gas

By seeding the gas with conductive particles eg potassium as in magnetohydrodynamic generators.

 

As to the conductors I stand by what I said about wires.

They are inductive.

Bifilar winding does not reduce the inductance, it (merely) reduces the external field.

This was used in the days of high quality valve (them again) amplifiers to reduce the external field of coupling transformers.

 

So please put up a modest summary of not more than 10 lines in logical order of what you are trying to achieve.

 

Thank you for stating the above. I was trying to keep the question simple, so as not to lose focus. I am not familiar with the magnetohydrodynamic generator, so will look it up. Apologies for using the word frequency instead of pulse train. How much does seeding a gas reduce its ionisation thresh hold by.? This is something I considered but could not get a handle on how well this would work.

 

I know all wires are inductive I measured typically 10nH/metre would you agree with this figure.

 

I am considering building a circuit to ionize air, not using brute force, but by trying to use a current impulse. Before attempting this I would like to analise mathematically the circuit I am considering. I am considering using a high speed DC pulse train, and trying to shorten the pulse duration of the pulse by forcing it to bunch. I am considering two parallel wires, what will happen if an out going pulse passes an incoming pulse? Will it cause the current to bunch momentarily. If not then I need to look at different methods.

 

Tesla developed the bifilar flat pancake coil, which if straightened out, it is two parallel conductors, it is this coil I wish to investigate further under pulsed conditions with a very fast pulse train.

 

This Bifalar pancake is used only in circuit boards today as a low inductance resistors, as far as I am aware. This was not its original purpose, as indicated on Teslas patents.

 

I know I could use a variety of methods to generate a high voltage. I was involved in building a Tesla coil lots of years ago on which we achieved 1.5MV.

 

I will look into all your suggestions above further.

 

Thank you very much for your reply.


The purposes of what I am thinking about are two fold.

 

The first is can I come up with a more efficient way of ionizing gases.

 

The second is a little more interesting: Can I seperate the ions using magnetic fields and extract useful current. If I can, then this idea could be expanded into some more interesting areas such as coal fired power stations blast furnaces etc. Anywhere flames are produced the air is ionized. When the atoms cool down the electrons recombine and give of photons. Blast furnaces must be full off ionized charges, and it may be a neat way of improving the overall efficiency of a system by returning some power.


Edited by Handy andy, Yesterday, 10:22 AM.

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