Hi Noah
Corona rings have an important function: They prevent breakdown of the air by distributing charge on a surface with sufficiently-low electric field on it. The field strength is proportional to potential and inversely proportional to the local curvature radius of the charged surface, and in dry air at standard conditions, fields much above about 20 kV / cm are to be avoided. This principle, and the 20 kV / cm value, are a good starting point when figuring out the radii and separation of corona rings and terminals, but exact geometry, polarity, air pressure, humidity, and even the metals and construction techniques of the terminals all figure in.
Electrical breakdown in vacuum is also of concern. Values exceeding about 100 kV / cm are problematic. Sometimes one finds sharp edges around apertures in beamlines, or in the Houskeeper seals encountered in glass-metal construction, or the metallized seals in ceramic-metal construction. A terminal like an external corona ring can often shield these sensitive features, in addition to doing the job of preventing corona per se on the air side.
It's hard to qualify what a "proper" reaction is, since that is a subjective idea critically depending on your own criteria and detection capabilities. The Li-7(p,a) reaction is well-known for its high Q-value (it is strongly exothermic and has no energy threshold) and high cross-section even at low energies. It's a good choice among a variety of possible low-energy reactions. But you will have to plan for how to detect it.
-Carl
Questions about the practical construction of a Linac
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Carl Willis
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Noah C Hoppis
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Re: Questions about the practical construction of a Linac
So, from what I've read, the breakdown of lithium would produce alpha particles, which could be measured with the humble geiger counter, correct me if you se any inherent problems, but the geiger tube could be submerged in the vacuum with the target angled to project the beam at it. My only question is whether the tube could stand the vacuum, and if there are any ways to get the alpha particles through the wall of the chamber without compromising it?
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Carl Willis
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Re: Questions about the practical construction of a Linac
Hi Noah,
You have identified some of the most important challenges in detecting the alpha particles.
Thin-window Geiger tubes are pressurized and will burst if subject to vacuum. With careful engineering (perhaps a support lattice on the vacuum side of the window), you may be able to solve that problem. But Geiger counters have other issues too: they are sensitive to ALL radiation that reaches them. That includes x-rays from the accelerator, prompt gamma rays from various (p,g) reactions, and the normal range of background cosmic rays and emissions from naturally-occurring radioactive material. It may be impossible to distinguish alpha particles from the target using a Geiger tube in the presence of all this competition. Some other kinds of detectors permit better discrimination of the alpha particles, such as surface-barrier detectors, scintillators, and proportional tubes. Some thin-window Geiger tubes can be carefully operated at reduced voltage to behave somewhat like proportional tubes. Having the ability to determine the energy spectrum of detected particles would be a real advantage here, since with that information, there would be little doubt about the origin of the particles in the (p,a) reaction.
-Carl
You have identified some of the most important challenges in detecting the alpha particles.
Thin-window Geiger tubes are pressurized and will burst if subject to vacuum. With careful engineering (perhaps a support lattice on the vacuum side of the window), you may be able to solve that problem. But Geiger counters have other issues too: they are sensitive to ALL radiation that reaches them. That includes x-rays from the accelerator, prompt gamma rays from various (p,g) reactions, and the normal range of background cosmic rays and emissions from naturally-occurring radioactive material. It may be impossible to distinguish alpha particles from the target using a Geiger tube in the presence of all this competition. Some other kinds of detectors permit better discrimination of the alpha particles, such as surface-barrier detectors, scintillators, and proportional tubes. Some thin-window Geiger tubes can be carefully operated at reduced voltage to behave somewhat like proportional tubes. Having the ability to determine the energy spectrum of detected particles would be a real advantage here, since with that information, there would be little doubt about the origin of the particles in the (p,a) reaction.
-Carl
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Noah C Hoppis
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Re: Questions about the practical construction of a Linac
In my quest for avoiding total bankruptcy, I stumbled upon the original idea of using a phosphor to detect the alpha emissions, I could coat the inside of a window of the chamber with said phosphor and remotely record for any light, however, I'm not sure where to go for an alpha florescent material.
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Rich Feldman
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Re: Questions about the practical construction of a Linac
Noah C Hoppis wrote:
> In my quest for avoiding total bankruptcy, I stumbled upon the original idea of using a phosphor to detect the alpha emissions, I could coat the inside of a window of the chamber with said phosphor and remotely record for any light, however, I'm not sure where to go for an alpha florescent material.
Cockroft and Walton eventually put scintillation screens on opposite sides of their lithium target. Simultaneous flashes of light on both screens further cemented their previous conclusion (see below) that the bombardment produced pairs of alpha particles.
http://www.nature.com/physics/looking-b ... index.html
"We have employed the same method to examine the effect of the bombardment of a layer of lithium by a stream of these ions, the lithium being placed inside the tube at 45° to the beam. A mica window of stopping power of 2 cm. of air was sealed on to the side of the tube, and the existence of radiation from the lithium was investigated by the scintillation method outside the tube. The thickness of the mica window was much more than sufficient to prevent any scattered protons from escaping into the air even at the highest voltages used.
...
"The brightness of the scintillations and the density of the tracks observed in the expansion chamber suggest that the particles are normal a-particles. If this point of view turns out to be correct, it seems not unlikely that the lithium isotope of mass 7 occasionally captures a proton and the resulting nucleus of mass 8 breaks into two a-particles, each of mass four and each with an energy of about eight million electron volts.The evolution of energy on this view is about sixteen million electron volts per disintegration, agreeing approximately with that to be expected from the decrease of atomic mass involved in such a disintegration."
> In my quest for avoiding total bankruptcy, I stumbled upon the original idea of using a phosphor to detect the alpha emissions, I could coat the inside of a window of the chamber with said phosphor and remotely record for any light, however, I'm not sure where to go for an alpha florescent material.
Cockroft and Walton eventually put scintillation screens on opposite sides of their lithium target. Simultaneous flashes of light on both screens further cemented their previous conclusion (see below) that the bombardment produced pairs of alpha particles.
http://www.nature.com/physics/looking-b ... index.html
"We have employed the same method to examine the effect of the bombardment of a layer of lithium by a stream of these ions, the lithium being placed inside the tube at 45° to the beam. A mica window of stopping power of 2 cm. of air was sealed on to the side of the tube, and the existence of radiation from the lithium was investigated by the scintillation method outside the tube. The thickness of the mica window was much more than sufficient to prevent any scattered protons from escaping into the air even at the highest voltages used.
...
"The brightness of the scintillations and the density of the tracks observed in the expansion chamber suggest that the particles are normal a-particles. If this point of view turns out to be correct, it seems not unlikely that the lithium isotope of mass 7 occasionally captures a proton and the resulting nucleus of mass 8 breaks into two a-particles, each of mass four and each with an energy of about eight million electron volts.The evolution of energy on this view is about sixteen million electron volts per disintegration, agreeing approximately with that to be expected from the decrease of atomic mass involved in such a disintegration."
All models are wrong; some models are useful. -- George Box
Re: Questions about the practical construction of a Linac
All of the copied in text translates to (In lay persons terms):-
Coat a bit of view port with ZnS (Ag) and watch for it sparkling.
Bottom line though, is that if you haven’t got dark adapted eyes (Not trivial) and enough flux use a PMT.
Trying to do the work of Rutherford, Cockroft & walton without the fortitude to avoid loosing it via sensory deprivation. Is certainly not trivial. Doing the same and still turning in a valid result. is even less trivial.
There have been some stunningly poor results turned in by folk who thought that watching scintillation screens after being sat in complete darkness for stupidly long periods of time, were a good scientific method.
Don't do it.
Use technology or leave it alone.
Coat a bit of view port with ZnS (Ag) and watch for it sparkling.
Bottom line though, is that if you haven’t got dark adapted eyes (Not trivial) and enough flux use a PMT.
Trying to do the work of Rutherford, Cockroft & walton without the fortitude to avoid loosing it via sensory deprivation. Is certainly not trivial. Doing the same and still turning in a valid result. is even less trivial.
There have been some stunningly poor results turned in by folk who thought that watching scintillation screens after being sat in complete darkness for stupidly long periods of time, were a good scientific method.
Don't do it.
Use technology or leave it alone.
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Noah C Hoppis
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Re: Questions about the practical construction of a Linac
You took the word out of my mouth, I was just about to ask about zinc sulfide, so I take it that a camera focused at the scintillator with the brightness up would circumvent the beta and gamma particles as well as X rays and only give me the alpha particles in the form of computer enhanced flashes?
"No missile ever flew before 10 pm"
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Richard Hull
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Re: Questions about the practical construction of a Linac
It all sounds trivial, but a good alpha only detector does use a ZnS:Ag screen of usually opaque mylar, aluminum or beryllium that is hyper thin attached to a PMT. The intensity of the flashes in this arrangement will not generally yield any useful alpha energy data due to a number of physical considerations.
For alpha energy data that is reliable for spectro work you need a PIPS detector as Carl has noted.
Richard Hull
For alpha energy data that is reliable for spectro work you need a PIPS detector as Carl has noted.
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
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Noah C Hoppis
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Re: Questions about the practical construction of a Linac
Now I'm wondering how you would supply hydrogen to this, Up till this point I thought I was going to run the gas through a store bought brass ball valve (purged with acetone and the grease replaced with diff pump oil) running the gas through a medicinal metal needle in the chamber attached to the 400kV which would break down the Hydrogen into protons which it would accelerate. I'm questioning if this would kill my vacuum or not and whether I need to separate the Hydrogen by any other means.
"No missile ever flew before 10 pm"
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Rich Feldman
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Re: Questions about the practical construction of a Linac
Noah C Hoppis wrote:
> Now I'm wondering how you would supply hydrogen to ... the 400kV which would break down the Hydrogen into protons which it would accelerate. I'm questioning if this would kill my vacuum or not and whether I need to separate the Hydrogen by any other means.
Been answered many times, starting with Cockroft and Walton. I see we are already in the Ion Gun forum. How many threads, aside from this one, have you read here? Here's one that just caught my eye: viewtopic.php?f=12&t=5043#p32351
> Now I'm wondering how you would supply hydrogen to ... the 400kV which would break down the Hydrogen into protons which it would accelerate. I'm questioning if this would kill my vacuum or not and whether I need to separate the Hydrogen by any other means.
Been answered many times, starting with Cockroft and Walton. I see we are already in the Ion Gun forum. How many threads, aside from this one, have you read here? Here's one that just caught my eye: viewtopic.php?f=12&t=5043#p32351
All models are wrong; some models are useful. -- George Box
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Dennis P Brown
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Re: Questions about the practical construction of a Linac
Been dealing with a host of issues the last year and only now getting back to my electro-static accelerator (ESA) project relative to fusion. The unit itself is 100% completed, fully shielded for 0.5 MeV x-rays, and just lacking tune up issues to be addressed (as pointed out here and that person was correct - the accelerator tube needs mid- to low 10^-6 Pa to work; that was a bear to get even with a turbo and all KF fittings.) Do have to finish my detector system but that is mostly done - just needs wiring work.
Mr. Hoppis, any accelerator except a simple electron one is not a build it and it works exactly like you think project; especially as seen in articles and that video - by the way, that video has a serious issues with their electro-static lens design due to their lack of conduction between the focus tubes and collectors ring *(I now guess that part is to be designed later.) This design might work for all I know but looks like trouble. The classic SA design has a host of issues and that is rather simple compared to the video design.
Your idea for diffusion pump based vacuum will be hard to use in any ESA unless you use a cold trap (very cold) and that could be an issue on pumping speed. By the way, an ESA is not a Linac, which, as Carl Willis pointed out, requires very special RF supplies. The primary driving supply for a Linac is rather expensive unless you build it yourself and it is not an off-the-self item you will find on ebay. Building one is not a trivial issue and the mechanical issues in the project require very complex (precise) construction. I assume (limited budget) that an ESA is what you are considering.
Even metering the gas into the gun (I have had great success on my design holding vacuum) is difficult without very careful design. You can reference my system here if you want pictures - just search for Linear Accel. Shorting your Van de Graaf (VdG) can be an issue through the higher pressure gas leading up and into the gun via plasma feedback and was a simple issue I overlooked (amoung many - very good people here who catch mistakes very well!) until someone pointed that design flaw out in my pictures - missing stuff is all too easy and can kill a fully complete project. Then you will be lost on what is wrong and get side tracked. I did but that is what spending free time is about with complex projects ... .
Avoiding a VdG is a good idea in some ways but does require a big build for the high voltage source. Some have made Tesla coils - that is a special project in-of-itself, though. Yet a simple, complete and off the self VdG has a lot of merit and makes the project more simple.
Another issue is using hydrogen gas. That is great for creating protons but of no real use for neutron production; you will need deuterium gas for that. Also, for the target design/material, that is a complex problem and I and others here have written long discussions on that subject (such as a target needing a material containing deuterium and that target does not out gas and kill the vacuum when it is hit by the deuterons; the electrons that are freed from the target can back stream up the accelerator tube and that, in turn, can create serious issues of charge buildup on the tube. That then disrupts the proton beam ... and so on.) Depending on the current, water-cooling may be needed. I decided to add that just to be on the safe side rather than dealing with any possible issues later when my design was already built.
Radiation is a serious and possibly deadly issue if ignored; the beam could be up to 0.5 MeV (unlikely that high as a real flux but worse case is always what you design for.) Lead near the ESA should not be used - that would destroy the electro-static lens system unless extremely well design; the very least, it will bleed away charge in a manner that could compromise your ability to create a large electro-static field required to guide and accelerate the beam. Trying to then shield yourself from a distance using Pb would require massive amounts. Proper shielding is not a trivial issue. Solid concrete blocks were used in the SA article but that too can cause construction issues. Do buy dosimeters (ebay) and a good radiation detector – they can save your life.
Detectors for the beam or neutrons is last on the list of issues that you need to address for such a project to be successful. As I see you are doing, creating the high vacuum system is the best way to get a start.
I'm still at it three years later ... so, do allow yourself time. A lot of fun in the building and learning.
Mr. Hoppis, any accelerator except a simple electron one is not a build it and it works exactly like you think project; especially as seen in articles and that video - by the way, that video has a serious issues with their electro-static lens design due to their lack of conduction between the focus tubes and collectors ring *(I now guess that part is to be designed later.) This design might work for all I know but looks like trouble. The classic SA design has a host of issues and that is rather simple compared to the video design.
Your idea for diffusion pump based vacuum will be hard to use in any ESA unless you use a cold trap (very cold) and that could be an issue on pumping speed. By the way, an ESA is not a Linac, which, as Carl Willis pointed out, requires very special RF supplies. The primary driving supply for a Linac is rather expensive unless you build it yourself and it is not an off-the-self item you will find on ebay. Building one is not a trivial issue and the mechanical issues in the project require very complex (precise) construction. I assume (limited budget) that an ESA is what you are considering.
Even metering the gas into the gun (I have had great success on my design holding vacuum) is difficult without very careful design. You can reference my system here if you want pictures - just search for Linear Accel. Shorting your Van de Graaf (VdG) can be an issue through the higher pressure gas leading up and into the gun via plasma feedback and was a simple issue I overlooked (amoung many - very good people here who catch mistakes very well!) until someone pointed that design flaw out in my pictures - missing stuff is all too easy and can kill a fully complete project. Then you will be lost on what is wrong and get side tracked. I did but that is what spending free time is about with complex projects ... .
Avoiding a VdG is a good idea in some ways but does require a big build for the high voltage source. Some have made Tesla coils - that is a special project in-of-itself, though. Yet a simple, complete and off the self VdG has a lot of merit and makes the project more simple.
Another issue is using hydrogen gas. That is great for creating protons but of no real use for neutron production; you will need deuterium gas for that. Also, for the target design/material, that is a complex problem and I and others here have written long discussions on that subject (such as a target needing a material containing deuterium and that target does not out gas and kill the vacuum when it is hit by the deuterons; the electrons that are freed from the target can back stream up the accelerator tube and that, in turn, can create serious issues of charge buildup on the tube. That then disrupts the proton beam ... and so on.) Depending on the current, water-cooling may be needed. I decided to add that just to be on the safe side rather than dealing with any possible issues later when my design was already built.
Radiation is a serious and possibly deadly issue if ignored; the beam could be up to 0.5 MeV (unlikely that high as a real flux but worse case is always what you design for.) Lead near the ESA should not be used - that would destroy the electro-static lens system unless extremely well design; the very least, it will bleed away charge in a manner that could compromise your ability to create a large electro-static field required to guide and accelerate the beam. Trying to then shield yourself from a distance using Pb would require massive amounts. Proper shielding is not a trivial issue. Solid concrete blocks were used in the SA article but that too can cause construction issues. Do buy dosimeters (ebay) and a good radiation detector – they can save your life.
Detectors for the beam or neutrons is last on the list of issues that you need to address for such a project to be successful. As I see you are doing, creating the high vacuum system is the best way to get a start.
I'm still at it three years later ... so, do allow yourself time. A lot of fun in the building and learning.
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Noah C Hoppis
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Re: Questions about the practical construction of a Linac
Dennis, It is true that it isn't a propper linac (more of a potencial drop accelorator).
I decided on a FW cockroft walton Multiplier do to stability of supply and the ability to supply each drift tube from a stage. The flanges would also be drilled on the rim to alow better gas purging.
I decided on a FW cockroft walton Multiplier do to stability of supply and the ability to supply each drift tube from a stage. The flanges would also be drilled on the rim to alow better gas purging.
"No missile ever flew before 10 pm"
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Dennis P Brown
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Re: Questions about the practical construction of a Linac
Keep us informed on your progress and as time permits, add photos; as someone who has gotten a lot of critically important and very useful information from all the people here this is a win-win for everyone.
While my project is finished, clean up work and adding diagnostics is a pain but the instrument would be almost useless without these (diagnostics: a beam current display needs wiring, proton illumination screen (for focusing) needs alignment, a neutron detector built; clean up projects: anti-electron back stream grid also needs wiring, the removable target alienment system needs testing (works while under high vac), installation of accelerator potential needles, and VdG upgrades – HV spray, column potential rings.) Even with the accelerator completed, these secondary issues are still there. This assuming it really works, that is. If it does, confirming my radiation shielding covers all risk areas and is sufficient then becomes priority one before I do even my first experiment … . So, building the accelerator is only part of the job.
By the way, if you use a diffusion pump for your system, consider getting a cold trap that fits it (does not need liquid nitrogen.) An accelerator must get into the low 10^-6 torr as I’ve learned from people here. An untrapped DP will not do that and worse, will contaminate your accelerator tube with back streaming oil.
Good luck.
While my project is finished, clean up work and adding diagnostics is a pain but the instrument would be almost useless without these (diagnostics: a beam current display needs wiring, proton illumination screen (for focusing) needs alignment, a neutron detector built; clean up projects: anti-electron back stream grid also needs wiring, the removable target alienment system needs testing (works while under high vac), installation of accelerator potential needles, and VdG upgrades – HV spray, column potential rings.) Even with the accelerator completed, these secondary issues are still there. This assuming it really works, that is. If it does, confirming my radiation shielding covers all risk areas and is sufficient then becomes priority one before I do even my first experiment … . So, building the accelerator is only part of the job.
By the way, if you use a diffusion pump for your system, consider getting a cold trap that fits it (does not need liquid nitrogen.) An accelerator must get into the low 10^-6 torr as I’ve learned from people here. An untrapped DP will not do that and worse, will contaminate your accelerator tube with back streaming oil.
Good luck.
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Noah C Hoppis
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Re: Questions about the practical construction of a Linac
I know I'm going to get a lot of guff about this but here I go...
I was wondering if (since I am still in the accumulation phase and yet to acquire parts for the actual acceleration cavity) a 8" cyclotron would be a viable replacement (A, I am aware of the difficulty of constructing a cyclotron, and B, Yes I have spent too much time on Cyclotrons.net). I have seen little to no info on this topic on the web, but being oriented towards being the top of the pyramid (in the least egotistic way possible) I saw a cyclotron as the most difficult and rewarding thing possible. Cyclotrons being based around a large set of yolk shaped electromagnets, give me a distinct advantage over a glass PT accelerator because I can get steel, and a lot of steel. To me the idea of an atom traveling circularly is much more exiting than linearly. The system I picture would have a 2' by 2' by 4" wide yolk with 8" diameter faces and 12" diameter H20 cooled coils. from this point forth this should be about the practical construction of a 8" cyclotron vs. a potential drop accelerator.
(please don't say this is off topic, it is and I fervently apologize, but rather than make a whole new thread I would rather beg forgiveness)
-thanks!
I was wondering if (since I am still in the accumulation phase and yet to acquire parts for the actual acceleration cavity) a 8" cyclotron would be a viable replacement (A, I am aware of the difficulty of constructing a cyclotron, and B, Yes I have spent too much time on Cyclotrons.net). I have seen little to no info on this topic on the web, but being oriented towards being the top of the pyramid (in the least egotistic way possible) I saw a cyclotron as the most difficult and rewarding thing possible. Cyclotrons being based around a large set of yolk shaped electromagnets, give me a distinct advantage over a glass PT accelerator because I can get steel, and a lot of steel. To me the idea of an atom traveling circularly is much more exiting than linearly. The system I picture would have a 2' by 2' by 4" wide yolk with 8" diameter faces and 12" diameter H20 cooled coils. from this point forth this should be about the practical construction of a 8" cyclotron vs. a potential drop accelerator.
(please don't say this is off topic, it is and I fervently apologize, but rather than make a whole new thread I would rather beg forgiveness)
-thanks!
"No missile ever flew before 10 pm"
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Dennis P Brown
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Re: Questions about the practical construction of a Linac
If you have a magnet that can cover a 8" diameter cyclotron, you should do this - if you think you can buy such a massive magnet off ebay, best of luck - the shipping would be a nightmare and handling that monster wouldn't be fun. Even a six inch magnetic face area would be rather large and heavy. The magnetic "Dee's" can be a little smaller but must be fairly close to the diameter of the cycltron. If the magnet is electro-magnetic, the power is not trival.
If you are suggesting winding your own ... that would be a project. The cost isn't steel but wire and copper cooling tubes just to name the most massive parts ... . Maybe you need to determine the required field and what it takes to generate that high a field that is uniform over that area. You should do that before going any further with a build it idea.
This has been covered before so I am puzzled that you haven't already read these posts on this topic.
In any case, I feel a linear electro-static accelerator (ESLA) is easier (in my opinon) because all parts are available on ebay. (But then, I have built one so I'm not neutral on the subject - my ES accelerator is currently in a test vacuum phase with all bell's and whistless's installed; it has just reached 2 * 10^ -6 torr in about 30 minutes. I might be able to test the deuteron gun in a few weeks. After that, finish the upgraded VdG and I could finally test the beast. Been over two years but that happens with projects and I started with the high vac system components.)
One thing I'd like to add - a linear accelerator is mostly about a high vacuum system and you are just about there - the machine work and minor electronics work is what any skilled HS student could do; also, nearly everything is available on ebay at reasonible costs.
A cyclotron is all about a massive and costly magnet, then issues like a high vac system and complex driver oscil. for the cyclotron's internal Dee's are then add on to the project. Consider carefully and look at what others have managed to construct.
Again, if you have access or own a large electro-magnetic, then I'd think that might be the way to go but even then, the remaining work is still more difficult than an ESLA. For a project to succeed you need the components or at least a way to get them; otherwise, a pile of expensive stuff will end up collecting dust in a storage room.
Finally, why do you want to build an atomic accelerator - either a electro-static, or true linear accelerator or even a cyclotron? If for nuclear reactions, then the type of energy you need determines the machine you should build; if for a neutron source (what I want it for) most the machines will do that if you have deuterium (gas and/or target). If I wasn't after building a neutron detector, I'd never have built the ESLA but rather a fusor. Hope this helps to clarify what you plan to do.
Here is a site where students built the the lowest cost LA machine I have yet seen and it works.
http://www.ifpan.edu.pl/firststep/aw-wo ... neller.pdf
Best of luck.
If you are suggesting winding your own ... that would be a project. The cost isn't steel but wire and copper cooling tubes just to name the most massive parts ... . Maybe you need to determine the required field and what it takes to generate that high a field that is uniform over that area. You should do that before going any further with a build it idea.
This has been covered before so I am puzzled that you haven't already read these posts on this topic.
In any case, I feel a linear electro-static accelerator (ESLA) is easier (in my opinon) because all parts are available on ebay. (But then, I have built one so I'm not neutral on the subject - my ES accelerator is currently in a test vacuum phase with all bell's and whistless's installed; it has just reached 2 * 10^ -6 torr in about 30 minutes. I might be able to test the deuteron gun in a few weeks. After that, finish the upgraded VdG and I could finally test the beast. Been over two years but that happens with projects and I started with the high vac system components.)
One thing I'd like to add - a linear accelerator is mostly about a high vacuum system and you are just about there - the machine work and minor electronics work is what any skilled HS student could do; also, nearly everything is available on ebay at reasonible costs.
A cyclotron is all about a massive and costly magnet, then issues like a high vac system and complex driver oscil. for the cyclotron's internal Dee's are then add on to the project. Consider carefully and look at what others have managed to construct.
Again, if you have access or own a large electro-magnetic, then I'd think that might be the way to go but even then, the remaining work is still more difficult than an ESLA. For a project to succeed you need the components or at least a way to get them; otherwise, a pile of expensive stuff will end up collecting dust in a storage room.
Finally, why do you want to build an atomic accelerator - either a electro-static, or true linear accelerator or even a cyclotron? If for nuclear reactions, then the type of energy you need determines the machine you should build; if for a neutron source (what I want it for) most the machines will do that if you have deuterium (gas and/or target). If I wasn't after building a neutron detector, I'd never have built the ESLA but rather a fusor. Hope this helps to clarify what you plan to do.
Here is a site where students built the the lowest cost LA machine I have yet seen and it works.
http://www.ifpan.edu.pl/firststep/aw-wo ... neller.pdf
Best of luck.
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Noah C Hoppis
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- Real name: Noah C Hoppis
Re: Questions about the practical construction of a Linac
Well I do have the advantage o knowing a place where i can purchase copper wire for only the price of copper. On the topic of other posts, I have in fact read them, and decided to post anyway because every situation is different and presents new problems. I haven't calculated much of anything and was and am still only toying with the idea. I'm basically looking for pictures and documentation of attempts at cyclotrons (I've already read the ones at coultersmithing, neill.org, and rutgers). Thanks for responding (and without comments on my butterfly attitude!)
"No missile ever flew before 10 pm"
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Noah C Hoppis
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- Real name: Noah C Hoppis
Re: Questions about the practical construction of a Cyclotron
Hello again! I have Cad drawings of the Accelerator now! does anyone know how you would go about calculating the turns of the beam in the cyclotron? (Sorry about the change of subject line but the previous was far too misleading)
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Carl Willis
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Re: Questions about the practical construction of a Cyclotron
Hi Noah,
Very nice, detailed solid models.
I think your question was about how many revolutions a particle will undergo in the cyclotron. If so, the answer depends on the injection energy, dee voltage, magnetic field, and the amount of space available for orbits (the dee radius, or wherever your extraction system is placed).
The particle has to have some injection energy Emin in order to clear the ion source structure on its first orbit. If the approximation that q*INT(E*dl) = qV is good for the accelerating gaps, where q is the particle charge and V is the dee voltage, then the particle gets a steady and easily-calculable boost of 2qV every orbit. The dee or extraction hardware supports a maximum radius R and thus a maximum classical particle energy of Emax = (qBR)^2/(2m). B is the magnetic field, m the particle mass. So the number of orbits can be approximated by (Emax - Emin)/2qV. The assumption that the particle gets 2qV every orbit is optimistic because of transit-time considerations--the particle takes time to accelerate, during which the field is changing sinusoidally. And relativistic effects may be significant but probably aren't.
I hope you are a member of the Cyclotrons.net forum. The experts on small amateur cyclotrons are all over there!
-Carl
Very nice, detailed solid models.
I think your question was about how many revolutions a particle will undergo in the cyclotron. If so, the answer depends on the injection energy, dee voltage, magnetic field, and the amount of space available for orbits (the dee radius, or wherever your extraction system is placed).
The particle has to have some injection energy Emin in order to clear the ion source structure on its first orbit. If the approximation that q*INT(E*dl) = qV is good for the accelerating gaps, where q is the particle charge and V is the dee voltage, then the particle gets a steady and easily-calculable boost of 2qV every orbit. The dee or extraction hardware supports a maximum radius R and thus a maximum classical particle energy of Emax = (qBR)^2/(2m). B is the magnetic field, m the particle mass. So the number of orbits can be approximated by (Emax - Emin)/2qV. The assumption that the particle gets 2qV every orbit is optimistic because of transit-time considerations--the particle takes time to accelerate, during which the field is changing sinusoidally. And relativistic effects may be significant but probably aren't.
I hope you are a member of the Cyclotrons.net forum. The experts on small amateur cyclotrons are all over there!
-Carl
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Noah C Hoppis
- Posts: 56
- Joined: Sat Dec 22, 2012 4:05 pm
- Real name: Noah C Hoppis
Re: Questions about the practical construction of a Cyclotron
Oh yes I am indeed a member of Cyclotrons.net (the site is a bit slow for Items that will get discussed back and forth, so I prefer fusor for things of this nature)! I also am glad to hear half a year of practice at Solidworks is paying off! (though it may be naive) I tried to calculate the equations and ended up with a grotesque number around ~1.25*10^25; which is a bit odd for a number of turns of a beam! Are the units involved all SI units? (most importantly the mass (G?) charge (elementary charge?) and field(T?)). Again I am new to physics and have come to expect each value to be painstakingly drawn out in some thesis! I really appreciate the concern and help;
Thanks!
Thanks!
"No missile ever flew before 10 pm"
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Dennis P Brown
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Re: Questions about the practical construction of a Cyclotron
If you really want the cyclotron, I will suggest that you read the very old Scientific American amateur science article on how some high school students built one (and the magnet) in the fifties – a google search should pull that up. A lot of good information and no physics equations. That said, you will really need to sit down and learn some of the physics – not knowing what energies will result from what field, and oscillator driver frequencies and so forth will create real design problems. Regardless, you also really need a plan of action or else this will just remain a though experiment that leads to a pile of equipment sitting in a room.
The first issue (if you are serious) and the one you still have not answered is what you want a cyclotron for? Without that, the design parameters cannot be set and you are just heading for problems – unless you just for a working cyclotron for its own sake.
The kids that made the one in the SA article did it for that very purpose but they had access to experts in the field for help, free access to big shops, and lots of people for free labor in a host of technical fields.
A one person attempt could be an issue (which, of course, money can go a long way to solving if one has deep pockets.) Simply offering computer drawings pulled from thin air is useless without the real numbers provided by the calculations on the particles (what you intend to accelerate), magnetic field strength/size, and oscillator energy/power all mixed in to determine a real world design so you can get started – not just have something to become wall art.
I would rather you approached this thinking realistic than waste your money – a small electro-static linear accelerator is vastly simpler because, frankly, I have built one (yet still not working!!!!) and know how what appears so simple can rapidly get complex and fail in ways that one could never think of until they bulid it - mine has cost very little money but lots of time. The whole reason I have spent so little is because I planed it out and have followed this plan closely - I've wasted little on anything that did not get me to the desired goal. That is the process that turns ideas into real world devices and not piles of useless (but expensive) equipment sitting in a room.
The first issue (if you are serious) and the one you still have not answered is what you want a cyclotron for? Without that, the design parameters cannot be set and you are just heading for problems – unless you just for a working cyclotron for its own sake.
The kids that made the one in the SA article did it for that very purpose but they had access to experts in the field for help, free access to big shops, and lots of people for free labor in a host of technical fields.
A one person attempt could be an issue (which, of course, money can go a long way to solving if one has deep pockets.) Simply offering computer drawings pulled from thin air is useless without the real numbers provided by the calculations on the particles (what you intend to accelerate), magnetic field strength/size, and oscillator energy/power all mixed in to determine a real world design so you can get started – not just have something to become wall art.
I would rather you approached this thinking realistic than waste your money – a small electro-static linear accelerator is vastly simpler because, frankly, I have built one (yet still not working!!!!) and know how what appears so simple can rapidly get complex and fail in ways that one could never think of until they bulid it - mine has cost very little money but lots of time. The whole reason I have spent so little is because I planed it out and have followed this plan closely - I've wasted little on anything that did not get me to the desired goal. That is the process that turns ideas into real world devices and not piles of useless (but expensive) equipment sitting in a room.
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Noah C Hoppis
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- Real name: Noah C Hoppis
Re: Questions about the practical construction of a Cyclotron
Oh Yes the specs! the Diameter is 8", the RF supply is 4kV @ 1-20 MHz, the magnet has 8" pole faces @ .8 T. The first experiment will be measuring for a beam current of accelerated Protons, and the second is for the break down of Li by Protons into Alpha particles. The plan is to net get the magnet / magnet core (and in the latter case, then wind the coils), then purchase the parts for the acceleration cavity, mill the necessary parts in the summer / fall, get access to a TIG and weld the vacuum assembly together. Then final assembly and testing.
"No missile ever flew before 10 pm"
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Richard Hull
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Re: Questions about the practical construction of a Cyclotron
Equations are cool things. They are SI, MKS and CGS independent in most cases where a system specific fudge factor has not been used. What is important is that every value you plug in must be in the same units system.
If you get a whacko result, go back and examine the unit system you used. Were all the variables you supplied in the same system?
Richard Hull
If you get a whacko result, go back and examine the unit system you used. Were all the variables you supplied in the same system?
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
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Noah C Hoppis
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- Real name: Noah C Hoppis
Re: Questions about the practical construction of a Cyclotron
That's what I thought, the problem is the radius of the Dee is either 4" or ~10cm and it isn't ever balanced, but I assume it is cm and after using coulombs instead of elementary charge I got -0.5 turns of the beam (well at least its not in SI notation anymore!) the Lack of units is really screwy though, I still am betting it is some kind of mix of units!
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Carl Willis
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Re: Questions about the practical construction of a Cyclotron
Elementary charge is a constant that has dimensions of charge in whatever unit system you choose. I recommend the MKS (SI) unit system. It's pretty much the standard.
So you have some specifications:
B = 0.8T (probably reasonable for a small cyclotron; this is already in MKS units)
m = 1.67E-27 kg (you mentioned your particles would be protons)
q = +1e = 1.602E-19 C (elementary charge)
V = 4kV assumed to be rms, so Vpeak = 1.414*4kV = 5700 V
R = (8"/2) = 4" = 0.102m
Emin isn't very influential in this situation, but I will assume it is 5 keV = 8E-16 joules (SI unit of energy) just for the hell of it.
Run the numbers. The first thing you find (if you didn't already have a handle on it) is that Emax is 5E-14 joules. Often this is reported in electronvolts instead; it's about 320 keV. Next you wanted to know approximate number of orbits:
(5E-14 - 8E-16)/(2*1.602E-19*5700) = 28 orbits
Emax is a good solid number you can take to the bank, as long as max radius and mag field strength are well-defined. The calculated number of orbits is just approximate and likely to be too small chiefly because of the transit time effect.
If you did this math using units of inches, slugs, foot-pounds, statcoulombs, etc., you would still get a right answer, strictly speaking. It would still be dimensionally correct. But you would have trouble contextualizing it. Best to stick with the same SI units that everyone else uses, and maybe convert to electronvolts for beam energy since that is in widespread use too.
-Carl
So you have some specifications:
B = 0.8T (probably reasonable for a small cyclotron; this is already in MKS units)
m = 1.67E-27 kg (you mentioned your particles would be protons)
q = +1e = 1.602E-19 C (elementary charge)
V = 4kV assumed to be rms, so Vpeak = 1.414*4kV = 5700 V
R = (8"/2) = 4" = 0.102m
Emin isn't very influential in this situation, but I will assume it is 5 keV = 8E-16 joules (SI unit of energy) just for the hell of it.
Run the numbers. The first thing you find (if you didn't already have a handle on it) is that Emax is 5E-14 joules. Often this is reported in electronvolts instead; it's about 320 keV. Next you wanted to know approximate number of orbits:
(5E-14 - 8E-16)/(2*1.602E-19*5700) = 28 orbits
Emax is a good solid number you can take to the bank, as long as max radius and mag field strength are well-defined. The calculated number of orbits is just approximate and likely to be too small chiefly because of the transit time effect.
If you did this math using units of inches, slugs, foot-pounds, statcoulombs, etc., you would still get a right answer, strictly speaking. It would still be dimensionally correct. But you would have trouble contextualizing it. Best to stick with the same SI units that everyone else uses, and maybe convert to electronvolts for beam energy since that is in widespread use too.
-Carl
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Rich Feldman
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Re: Questions about the practical construction of a Cyclotron
Noah,
Not just because of units issues, I urge you to run your numbers using a spreadsheet calculator program. If you don't have one, get one and learn how to use it. It's a great way to document your units and formulas, and facilitates debugging and changing variables.
Here's a freshly whipped example. Blue cells are the only numerical inputs, and three of them are physical constants you can look up.
I have included some unit conversions, as always NEVER in the same cell (calculation step) as a physics formula. Cutting corners invites mistakes. Remember, cells don't cost much at all. In fact, I make a habit of using separate formula cells to convert between SI values (hertz, farad) and practical I/O units (megahertz, microfarad).
The example has some sloppiness and minor mistakes. I should have given a B value of 8894 gauss, to match the 13.56 MHz ISM band. As if your flux uniformity could justify four significant figures.
-Rich
Not just because of units issues, I urge you to run your numbers using a spreadsheet calculator program. If you don't have one, get one and learn how to use it. It's a great way to document your units and formulas, and facilitates debugging and changing variables.
Here's a freshly whipped example. Blue cells are the only numerical inputs, and three of them are physical constants you can look up.
I have included some unit conversions, as always NEVER in the same cell (calculation step) as a physics formula. Cutting corners invites mistakes. Remember, cells don't cost much at all. In fact, I make a habit of using separate formula cells to convert between SI values (hertz, farad) and practical I/O units (megahertz, microfarad).
The example has some sloppiness and minor mistakes. I should have given a B value of 8894 gauss, to match the 13.56 MHz ISM band. As if your flux uniformity could justify four significant figures.
-Rich
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