I hope that you are not suggesting that as some point in the fusor that there are a significant percentage of 30kev neutrals which is absurd. One such neutral in a quintillion would be a huge number. Secondly, such neutrals, by definition, can have no source and no focus in the collisional sense. As there is no way possible to characterize the gas temperature in the fusor the equation can't be quantitatively solved but only qualitatively arrived at. I figure 4X over STP gas for MFP is about right for a full 30kev deuteron which is, in itself, rare in a 30kv applied, fusor. At least it has a mission as it has an origin, a focus and is fully, electrostatically directed, unlike the missionless, brownian limited, bumbling, be-dazed, neutrals.
Speedy, tiny, lightweigh 1/3th C electrons only have there paths extended by a factor of 30 or so. A huge Ion like a deuteron at a mere 30kev would be a real slow mover.
I guess someone needs to figure out or find someway to measure the gas temp in the inter-grid volume for the question to be answered to any degree of satisfaction.
Richard Hull
IOn Guns, Pressure and Mean Free Paths..etc.
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Richard Hull
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Re: IOn Guns, Pressure and Mean Free Paths..etc.
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Richard Hull
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Re: IOn Guns, Pressure and Mean Free Paths..etc.
I just posted a cool URL as part of a mean free path FAQ on the vacuum forum. All MUST check it out.
Dave Cooper put me on the quest.
It turns out that he is right on the temp idea but without any knowledge on our behalf of what the hell actually is in a running fusor, we are as muddled as we ever were inspite of a new insight.
It turns out that the less than ideal gas law has a special equation for mean free path and this URL has a solver built into it.
I punched in some numbers. here is the result.
The mean free path of a D neutral in a gas of itself at 300 kelvin at 10 micron's pressure is about 70mm, as I guessed.
Amazingly the deuteron is so microscopic that in a gas of its fellow deuterons, only, all with only an average energy of 1000ev, (~10,000,000 kelvin) the mean free path is 10e 13 meters!!!! (That's 60 billion miles!!!)
This is, of course, meaningless in the fusor as every gas atom would have to be a deuteron. Impossible. And, the temperature inside would be a real 10,000,000 degrees.
I likewise assumed, as Dave might desire, a 70,000 kelvin heated neutral gas temperature in a 10 micron fusor. This is still less than only 6ev per molecule of neutrals. The mean free path jumps to nearly 16 meters. If this were the case, virtually every moving neutral would forever result in a wall collision (they would be doomed to this fate) and never impact with microscopic, nearly five order of magnitude smaller, deuterons.
It turns out that any neutral that ever acquires a kinetic energy of over 0.1ev will virtually always impact the fusor chamber's wall and virtually never hit another brother neutral and certainly never impact with a micro deuteron, on a statistcally notable level!
Again, we know nothing about the fusor's interior! It s internal gas temperature?.....The ratio of the species contained in it..........The energy ranges of significance with in it. Calculations are just not viable without good data. The data we might hope to obtain via experiment would be an averaged intergrated data which might hide some significant and novel processes.
It's a crap shoot guys!
Richard Hull
Dave Cooper put me on the quest.
It turns out that he is right on the temp idea but without any knowledge on our behalf of what the hell actually is in a running fusor, we are as muddled as we ever were inspite of a new insight.
It turns out that the less than ideal gas law has a special equation for mean free path and this URL has a solver built into it.
I punched in some numbers. here is the result.
The mean free path of a D neutral in a gas of itself at 300 kelvin at 10 micron's pressure is about 70mm, as I guessed.
Amazingly the deuteron is so microscopic that in a gas of its fellow deuterons, only, all with only an average energy of 1000ev, (~10,000,000 kelvin) the mean free path is 10e 13 meters!!!! (That's 60 billion miles!!!)
This is, of course, meaningless in the fusor as every gas atom would have to be a deuteron. Impossible. And, the temperature inside would be a real 10,000,000 degrees.
I likewise assumed, as Dave might desire, a 70,000 kelvin heated neutral gas temperature in a 10 micron fusor. This is still less than only 6ev per molecule of neutrals. The mean free path jumps to nearly 16 meters. If this were the case, virtually every moving neutral would forever result in a wall collision (they would be doomed to this fate) and never impact with microscopic, nearly five order of magnitude smaller, deuterons.
It turns out that any neutral that ever acquires a kinetic energy of over 0.1ev will virtually always impact the fusor chamber's wall and virtually never hit another brother neutral and certainly never impact with a micro deuteron, on a statistcally notable level!
Again, we know nothing about the fusor's interior! It s internal gas temperature?.....The ratio of the species contained in it..........The energy ranges of significance with in it. Calculations are just not viable without good data. The data we might hope to obtain via experiment would be an averaged intergrated data which might hide some significant and novel processes.
It's a crap shoot guys!
Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Re: IOn Guns, Pressure and Mean Free Paths..etc.
Have to check out the URL,,,, but I did get the 16.8 m path length for 6eV neutrals.
With the fully ionized Deuteron, D+one is dealing with a very tiny cross sectional area... and very high speed.... So the 10^13 m mean free path, while surprising initially, is right in line.
I am just beginning to think along these lines in more detail...It is probably ok to consider that any ion thus formed, will have a long mean free path...but.... couldn't really be much longer than Fusor diameter. Unless a mechanism is asserted that reflection and riccochet could occur without neutralizing the ion. And THAT I just don't find credible. Sooo.. the ions mean free path at high energy might well be only limited by the fusor size.
There much here to consider.
Dave Cooper
With the fully ionized Deuteron, D+one is dealing with a very tiny cross sectional area... and very high speed.... So the 10^13 m mean free path, while surprising initially, is right in line.
I am just beginning to think along these lines in more detail...It is probably ok to consider that any ion thus formed, will have a long mean free path...but.... couldn't really be much longer than Fusor diameter. Unless a mechanism is asserted that reflection and riccochet could occur without neutralizing the ion. And THAT I just don't find credible. Sooo.. the ions mean free path at high energy might well be only limited by the fusor size.
There much here to consider.
Dave Cooper
Re: IOn Guns, Pressure and Mean Free Paths..etc.
Just a bt more on the long mean free path idea of ions.
My last post.. suggested the Fusor diameter as the practical limit to mean free path. Obviously, that would ONLY be true if the path were rifle straight. A curved path could easily circle the fusor for a number of orbits... maybe a big number!.
But this is not a new idea either... didn't Farnsworth have the "recirculation" idea as an integral part of his design.??
So Methods to create ion trajectories that curve significantly should be on our design, and theory dicsussion agendae.
Dave Cooper
My last post.. suggested the Fusor diameter as the practical limit to mean free path. Obviously, that would ONLY be true if the path were rifle straight. A curved path could easily circle the fusor for a number of orbits... maybe a big number!.
But this is not a new idea either... didn't Farnsworth have the "recirculation" idea as an integral part of his design.??
So Methods to create ion trajectories that curve significantly should be on our design, and theory dicsussion agendae.
Dave Cooper
Re: IOn Guns, Pressure and Mean Free Paths..etc.
A curved path for charged particles at high speed is self defeating. They emit energy is you try and that doesn't help the cause.
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Frank Sanns
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Re: IOn Guns, Pressure and Mean Free Paths..etc.
Dave,
Yes! Yes! Yes! Curved paths conserve energy. There will be synchrotron radiation but at our low energies it should be no where near the factor of everything crashing into solid objects and dissipating ALL of thier energy with every pass.
I like the resonant RF idea from a circulating ion and resonance stand point but it uses just as much energy to slow down the charged particles as it does to just let them strike the wall except that they have the chance of phase bunching and increasing the odds of collision as they bunch up at the center.
A figure 8 cylotron is also an interesting approach. Let there be two counter rotating and independent paths of electrons and deuterons. Each wil have thier own orbit and will circulate. This removes the chance for recombination of electrons with the deuterons giving longer ion life. Plus, when the 2 deuteron nodes from each loop of the figure 8 collide, those that miss or just graze by, will still keep thier energy and go into the next loop pass.
Yes much to explore, so little time.
Frank S.
Yes! Yes! Yes! Curved paths conserve energy. There will be synchrotron radiation but at our low energies it should be no where near the factor of everything crashing into solid objects and dissipating ALL of thier energy with every pass.
I like the resonant RF idea from a circulating ion and resonance stand point but it uses just as much energy to slow down the charged particles as it does to just let them strike the wall except that they have the chance of phase bunching and increasing the odds of collision as they bunch up at the center.
A figure 8 cylotron is also an interesting approach. Let there be two counter rotating and independent paths of electrons and deuterons. Each wil have thier own orbit and will circulate. This removes the chance for recombination of electrons with the deuterons giving longer ion life. Plus, when the 2 deuteron nodes from each loop of the figure 8 collide, those that miss or just graze by, will still keep thier energy and go into the next loop pass.
Yes much to explore, so little time.
Frank S.
Achiever's madness; when enough is still not enough. ---FS
We have to stop looking at the world through our physical eyes. The universe is NOT what we see. It is the quantum world that is real. The rest is just an electron illusion. ---FS
We have to stop looking at the world through our physical eyes. The universe is NOT what we see. It is the quantum world that is real. The rest is just an electron illusion. ---FS
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Jon Rosenstiel
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Re: IOn Guns, Pressure and Mean Free Paths..etc.
Frank,
You've probably seen this, but just in case you haven't, here's the link:
http://fti.neep.wisc.edu/iecworkshop/agenda.html
Go down to Session 4 and click on the second item's pdf. (Effects of cathode structure on neutron production in IEC devices). See page 13, Ion Trajectories.
Jon Rosenstiel
You've probably seen this, but just in case you haven't, here's the link:
http://fti.neep.wisc.edu/iecworkshop/agenda.html
Go down to Session 4 and click on the second item's pdf. (Effects of cathode structure on neutron production in IEC devices). See page 13, Ion Trajectories.
Jon Rosenstiel
Re: IOn Guns, Pressure and Mean Free Paths..etc.
If I may use Jack's response and Frank's and Jon's as comparisons to illustrate the need for careful calculations....
The energy, radiated by a charged particle, is significant witness the radiation from a Magnetron from a uWave oven. The power produced there is a large fraction of the input power. We should be able to quantify this in terms of trajectory radius, and keV. IT would be a very useful result to have at hand in these discussions.
Actually, some of the ions, (those launched with the proper initial directions) will not collide with the inner grid wires but will be curved by the field into a spiralling open curved path. The conference the Jon referred to, is very interesting... I think we should all have that Conference paper for reference... Many thanks Jon, excellent citation.
In typical Japanese thoroughness, they determined that the grid structure details have little or no effect on neutron production and only a minimal effect on V-I characteristics for a fixed pressure, and similarly minimal differences in kV vs pressure effects for fixed input current. All good examples of carefully taken data. The more open the gird, the more easily modeled ions can circulate... no surprise here either. But conjecture is now replaced with experimental result.(aka... fact).
The modeling setup is tedius, and can only take us so far... models are always better than the quality of our experimens... the surfaces of the model is perfectly smooth, the curvature impossibly uniform, the metal's work function a true constant, etc and etc.... None of this is true in the actual experiment, so our results WILL differ. But the theory provides some expectations, targets and predictions with which we can flog our experimental technique into obedience, or illustrate that a showdown is demanded...meaning the theory is inadequate to describe the results.
Some good information and ideas here.
Dave Cooper.
The energy, radiated by a charged particle, is significant witness the radiation from a Magnetron from a uWave oven. The power produced there is a large fraction of the input power. We should be able to quantify this in terms of trajectory radius, and keV. IT would be a very useful result to have at hand in these discussions.
Actually, some of the ions, (those launched with the proper initial directions) will not collide with the inner grid wires but will be curved by the field into a spiralling open curved path. The conference the Jon referred to, is very interesting... I think we should all have that Conference paper for reference... Many thanks Jon, excellent citation.
In typical Japanese thoroughness, they determined that the grid structure details have little or no effect on neutron production and only a minimal effect on V-I characteristics for a fixed pressure, and similarly minimal differences in kV vs pressure effects for fixed input current. All good examples of carefully taken data. The more open the gird, the more easily modeled ions can circulate... no surprise here either. But conjecture is now replaced with experimental result.(aka... fact).
The modeling setup is tedius, and can only take us so far... models are always better than the quality of our experimens... the surfaces of the model is perfectly smooth, the curvature impossibly uniform, the metal's work function a true constant, etc and etc.... None of this is true in the actual experiment, so our results WILL differ. But the theory provides some expectations, targets and predictions with which we can flog our experimental technique into obedience, or illustrate that a showdown is demanded...meaning the theory is inadequate to describe the results.
Some good information and ideas here.
Dave Cooper.
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Frank Sanns
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Re: IOn Guns, Pressure and Mean Free Paths..etc.
Jon,
Thanks for the reference. I do remember reading it a couple of years ago. Nice work but I wish they would have had larger grid size differences to at least see some differences. I hate when everything equals out. Then you have no idea of the sensitiviy of detection of a variable. I think I will reread the paper again. The mind is getting foggy and I forgot about that one. Thanks.
Dave,
A magnetron produces the energy from electrons. Becasue they are 2000 times less massive than a deuteron, they are accelerated to a higer velocity at the same eV. Sychrotron radiation is proportional to the velocity^4/radius^2 so a little bit in velocity really jumps up the loss.
For a 15 KeV deuteron, the velocity is around 1.3E6 meters/sec. The equation for sychrotron radiation is:
Power=(2*K*e^2*)/(3*c^3)*(v^2/r)^2 so for a deuteron whirling around in a 6 inch (0.17 meter) radius cyclotron, that is around 10^-28 watts/deuteron. At one amp at 15 kv that is 6.3e18 deuterons/second. The loss then would be <1 millionth of the 15Kw or <1mW.
Frank S.
Thanks for the reference. I do remember reading it a couple of years ago. Nice work but I wish they would have had larger grid size differences to at least see some differences. I hate when everything equals out. Then you have no idea of the sensitiviy of detection of a variable. I think I will reread the paper again. The mind is getting foggy and I forgot about that one. Thanks.
Dave,
A magnetron produces the energy from electrons. Becasue they are 2000 times less massive than a deuteron, they are accelerated to a higer velocity at the same eV. Sychrotron radiation is proportional to the velocity^4/radius^2 so a little bit in velocity really jumps up the loss.
For a 15 KeV deuteron, the velocity is around 1.3E6 meters/sec. The equation for sychrotron radiation is:
Power=(2*K*e^2*)/(3*c^3)*(v^2/r)^2 so for a deuteron whirling around in a 6 inch (0.17 meter) radius cyclotron, that is around 10^-28 watts/deuteron. At one amp at 15 kv that is 6.3e18 deuterons/second. The loss then would be <1 millionth of the 15Kw or <1mW.
Frank S.
Achiever's madness; when enough is still not enough. ---FS
We have to stop looking at the world through our physical eyes. The universe is NOT what we see. It is the quantum world that is real. The rest is just an electron illusion. ---FS
We have to stop looking at the world through our physical eyes. The universe is NOT what we see. It is the quantum world that is real. The rest is just an electron illusion. ---FS
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Richard Hull
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Re: IOn Guns, Pressure and Mean Free Paths..etc.
I figured that our stuff is so slow that any turning radiation via synchrotron would be insignificant. The fusor avoids a lot of hassles common to big accelerators.
Frank's deuteron current figures would be in the tenth of an amp range which is something we have never witnessed in a fusor.
Our fusing deuteron current in a 10e5n/s fusor is normally about 100 fempto amps while I would imagine the fusible but missed deuteron current is on the order of a few tens of picoamps and the total deuteron current is about a few milliamps. This is all for the simple fusion, of course.
Richard Hull
Frank's deuteron current figures would be in the tenth of an amp range which is something we have never witnessed in a fusor.
Our fusing deuteron current in a 10e5n/s fusor is normally about 100 fempto amps while I would imagine the fusible but missed deuteron current is on the order of a few tens of picoamps and the total deuteron current is about a few milliamps. This is all for the simple fusion, of course.
Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment