accelerator physics
attune, Fri Aug 18 2006, 11:42PMI have recently aquired a vacuum system that can pump down a decent volume to 10-5 torr. I am also building a 100kV C-W multiplier. The idea of combining the two is exciting. I have seen various websites with vacuum tubes made of insulating material accelerating electrons with high voltage supplies. 100keV electrons are obviously cool and useful for many things. What would be the minimum tube length that allows for the electrons to be accelerated to the full velocity? The kinematic equations are basic, but what is the force on the electron as it travels through the tube? Is seems that it would change with distance. Any help appreciated!
Re: accelerator physics
Dr. Slack, Sat Aug 19 2006, 07:38AM
Rather than worry about integrating force and suchlike, go for the easy route and consider energy. Once the electron has fallen through 100kV, it will have an energy of 100keV. I think this is still non-relativistic speed, so if you want the velocity from this just invert E=1/2mv2 (in consistent units of course), where m is the electron rest mass.
The minimum tube length is that which will withstand the voltage difference without breaking down. A hard vacuum is very strong, but you might find that 5torr will support long discharge columns, do some research into gas discharges.
One thing 100keV electrons are very useful for is making Xrays when they hit heavy atoms in the anode. You might want to consider shielding, distance or only short run times to protect yourself from exposure
<edit> duh, idiot me, I wondered why I thought 5torr wasn't the good vacuum you asserted, but 10^-5 is rather better </edit>
Dr. Slack, Sat Aug 19 2006, 07:38AM
Rather than worry about integrating force and suchlike, go for the easy route and consider energy. Once the electron has fallen through 100kV, it will have an energy of 100keV. I think this is still non-relativistic speed, so if you want the velocity from this just invert E=1/2mv2 (in consistent units of course), where m is the electron rest mass.
The minimum tube length is that which will withstand the voltage difference without breaking down. A hard vacuum is very strong, but you might find that 5torr will support long discharge columns, do some research into gas discharges.
One thing 100keV electrons are very useful for is making Xrays when they hit heavy atoms in the anode. You might want to consider shielding, distance or only short run times to protect yourself from exposure
<edit> duh, idiot me, I wondered why I thought 5torr wasn't the good vacuum you asserted, but 10^-5 is rather better </edit>
Re: accelerator physics
Sulaiman, Sat Aug 19 2006, 09:25AM
As above, the minimum distance is that required to prevent flashover.
The maximum distance is determined by 'mean free path'
which for air at room temperature is approximately 5m @ 10-5 torr
(500mm @ 10-4 torr etc.)
so unlikely to be a problem at your working pressure.
100 keV electrons will not penetrate very far, about 0.1mm water/skin
so not very useful as an electron beam/death ray.
(you'd better check my figures, 25 year old memories here)
Also, as above, consider accidental x-ray generation hazard.
Sulaiman, Sat Aug 19 2006, 09:25AM
As above, the minimum distance is that required to prevent flashover.
The maximum distance is determined by 'mean free path'
which for air at room temperature is approximately 5m @ 10-5 torr
(500mm @ 10-4 torr etc.)
so unlikely to be a problem at your working pressure.
100 keV electrons will not penetrate very far, about 0.1mm water/skin
so not very useful as an electron beam/death ray.
(you'd better check my figures, 25 year old memories here)
Also, as above, consider accidental x-ray generation hazard.
Re: accelerator physics
Tesladownunder, Sat Aug 19 2006, 11:12AM
When making glassware more important is surface tracking which at 3 times a room air spark distance will be 15 inches minimum that needs to be allowed for on the outside.
The beam distance in an x-ray tube with a pretty good vacuum is only an inch on the outside and all oil enclosed.
Peter
Tesladownunder, Sat Aug 19 2006, 11:12AM
Sulaiman wrote ...
.... 100 keV electrons will not penetrate very far, about 0.1mm water/skin
so not very useful as an electron beam/death ray.
(you'd better check my figures, 25 year old memories here)..
As I understand, modern x-ray machines use perhaps 125 keV for "big" people so it certainly gets through more than 0.1mm. Also consider the x-ray aperture as a lot of simple glass blowing is lead glass and opaque to x-rays. Use soda glass instead perhaps..... 100 keV electrons will not penetrate very far, about 0.1mm water/skin
so not very useful as an electron beam/death ray.
(you'd better check my figures, 25 year old memories here)..
When making glassware more important is surface tracking which at 3 times a room air spark distance will be 15 inches minimum that needs to be allowed for on the outside.
The beam distance in an x-ray tube with a pretty good vacuum is only an inch on the outside and all oil enclosed.
Peter
Re: accelerator physics
Sulaiman, Sat Aug 19 2006, 01:20PM
I meant the actual electron beam, not x-rays generated by the beam.
Sulaiman, Sat Aug 19 2006, 01:20PM
I meant the actual electron beam, not x-rays generated by the beam.
Re: accelerator physics
Bored Chemist, Sat Aug 19 2006, 03:07PM
Any decent current at 100KV will produce a nasty set of Xrays. You should probably think about shielding before you do anything else.
Bored Chemist, Sat Aug 19 2006, 03:07PM
Any decent current at 100KV will produce a nasty set of Xrays. You should probably think about shielding before you do anything else.
Re: accelerator physics
attune, Sat Aug 19 2006, 03:45PM
15 inches to prevent the skin effect? I will to some testing of materials to find out just how small I can make it. As for shielding and exposure time, no kidding! I will be careful. Immersing a smaller tube in an oil was mentioned. Pyrex in Mineral Oil?
attune, Sat Aug 19 2006, 03:45PM
15 inches to prevent the skin effect? I will to some testing of materials to find out just how small I can make it. As for shielding and exposure time, no kidding! I will be careful. Immersing a smaller tube in an oil was mentioned. Pyrex in Mineral Oil?
Re: accelerator physics
IamSmooth, Sat Aug 19 2006, 08:07PM
Just to give a point of reference, in the radiology suite they use about 70-85KV routinely for flouroscopy on the average-sized individual. 100KV will certainly be a problem and I would avoid the exposure. If you really want to do this I suggest you get a radiation badge and monitor your exposure. You don't want to delude yourself that you are protected only to find out in 10 years as you look at a picture of your cool electron tube that you are dying from lymphoma.
IamSmooth, Sat Aug 19 2006, 08:07PM
Just to give a point of reference, in the radiology suite they use about 70-85KV routinely for flouroscopy on the average-sized individual. 100KV will certainly be a problem and I would avoid the exposure. If you really want to do this I suggest you get a radiation badge and monitor your exposure. You don't want to delude yourself that you are protected only to find out in 10 years as you look at a picture of your cool electron tube that you are dying from lymphoma.
Re: accelerator physics
Carbon_Rod, Sat Aug 19 2006, 09:25PM
NeilThomas and BC pointed out this can be a very unhealthy apparatus to be around -- and I fully agree.
Even multi-stage accelerators will have numerous shielding precautions and in fact can prove just as dangerous if one happened to wander into the targeting chamber during operation.
If you have to ask how it’s done then you are unlikely knowledgeable enough yet to safely handle the physics involved. Be patient in your studies as the nature of the universe is unlikely going to abruptly change anytime soon.
You get an A for effort though.
Cheers,
Carbon_Rod, Sat Aug 19 2006, 09:25PM
NeilThomas and BC pointed out this can be a very unhealthy apparatus to be around -- and I fully agree.
Even multi-stage accelerators will have numerous shielding precautions and in fact can prove just as dangerous if one happened to wander into the targeting chamber during operation.
If you have to ask how it’s done then you are unlikely knowledgeable enough yet to safely handle the physics involved. Be patient in your studies as the nature of the universe is unlikely going to abruptly change anytime soon.
You get an A for effort though.
Cheers,
Re: accelerator physics
attune, Sat Aug 19 2006, 09:59PM
Peter Bradly at Houghton college has a very good paper on the constuction of a similar accelerator, though of twice the voltage. He did a careful measurement of the x-ray and gamma radiation, and found that even right next to the fully energized device it would take 10 hours to reach the recommended yearly exposure. As for my own device, I will be purchasing a reliable geiger counter and will be working with an ex-nuclear engineer. Radmax Lead sheilding is cheap, and will cover the device with the greatest practical thickness. Distance will be kept to a maximum, with remote control unites, and exposure time a minimum, with only short pulses of power supply. Sound good?
attune, Sat Aug 19 2006, 09:59PM
Peter Bradly at Houghton college has a very good paper on the constuction of a similar accelerator, though of twice the voltage. He did a careful measurement of the x-ray and gamma radiation, and found that even right next to the fully energized device it would take 10 hours to reach the recommended yearly exposure. As for my own device, I will be purchasing a reliable geiger counter and will be working with an ex-nuclear engineer. Radmax Lead sheilding is cheap, and will cover the device with the greatest practical thickness. Distance will be kept to a maximum, with remote control unites, and exposure time a minimum, with only short pulses of power supply. Sound good?
Re: accelerator physics
Carbon_Rod, Sun Aug 20 2006, 03:20AM
Awards, citations, and rank get dropped in here very rarely. Many members would surprise you with their backgrounds and level of experience.
Actually there were studies done with shielded spacecraft that found some secondary radiation sources caused more DNA damage than normal exposure levels. A little off topic I know – but still notable if you plan on testing shielding.
A pulse system may work under certain constraints if it is a single stage accelerator – however from the vague description the generated beam will likely be inconsistent in its behaviour. Some meter based Geiger counters may integrate ambient exposure levels if the spike in levels is too intermittent. So the meter may falsely show lower than normal exposure. The name-badge unit advice is rather brilliant and inexpensive.
It seems rather curious for reproducible experimental use. However it does sound like an interesting project.
Good luck,
Carbon_Rod, Sun Aug 20 2006, 03:20AM
Awards, citations, and rank get dropped in here very rarely. Many members would surprise you with their backgrounds and level of experience.
Actually there were studies done with shielded spacecraft that found some secondary radiation sources caused more DNA damage than normal exposure levels. A little off topic I know – but still notable if you plan on testing shielding.
A pulse system may work under certain constraints if it is a single stage accelerator – however from the vague description the generated beam will likely be inconsistent in its behaviour. Some meter based Geiger counters may integrate ambient exposure levels if the spike in levels is too intermittent. So the meter may falsely show lower than normal exposure. The name-badge unit advice is rather brilliant and inexpensive.
It seems rather curious for reproducible experimental use. However it does sound like an interesting project.
Good luck,
Re: accelerator physics
Simon, Mon Aug 21 2006, 12:56AM
The rest mass energy of an electron is 511keV. Since the 100keV electron kinetic energy is a fifth of the rest mass energy I really would consider relativity applies. That's not too hard. Gamma = (511keV + 100keV) / 511keV = 1.20. So time and space will affected by a factor of about 20%.
If you want to work out the velocity, solve for Gamma = 1 / sqrt(1 - B^2), where B is the proportion of the speed of light (.5 = half speed of light = 1.5 x 10^8 m/s).
I don't think any of that will help you design the system but it's worth understanding.
As to x-rays, yes you'll definitely get them at this energy. You should do a little research if you weren't aware of this before.
Simon, Mon Aug 21 2006, 12:56AM
NeilThomas wrote ...
Rather than worry about integrating force and suchlike, go for the easy route and consider energy. Once the electron has fallen through 100kV, it will have an energy of 100keV. I think this is still non-relativistic speed, so if you want the velocity from this just invert E=1/2mv2 (in consistent units of course), where m is the electron rest mass.
Rather than worry about integrating force and suchlike, go for the easy route and consider energy. Once the electron has fallen through 100kV, it will have an energy of 100keV. I think this is still non-relativistic speed, so if you want the velocity from this just invert E=1/2mv2 (in consistent units of course), where m is the electron rest mass.
The rest mass energy of an electron is 511keV. Since the 100keV electron kinetic energy is a fifth of the rest mass energy I really would consider relativity applies. That's not too hard. Gamma = (511keV + 100keV) / 511keV = 1.20. So time and space will affected by a factor of about 20%.
If you want to work out the velocity, solve for Gamma = 1 / sqrt(1 - B^2), where B is the proportion of the speed of light (.5 = half speed of light = 1.5 x 10^8 m/s).
I don't think any of that will help you design the system but it's worth understanding.
As to x-rays, yes you'll definitely get them at this energy. You should do a little research if you weren't aware of this before.
Re: accelerator physics
Sulaiman, Mon Aug 21 2006, 07:39AM
Simon,
I don't understand your maths/formula
e.g. for a 50 MeV accelarator, Gamma = 100
what does this mean physically?
Sulaiman, Mon Aug 21 2006, 07:39AM
Simon,
I don't understand your maths/formula
e.g. for a 50 MeV accelarator, Gamma = 100
what does this mean physically?
Re: accelerator physics
attune, Mon Aug 21 2006, 04:40PM
Sweet! I was not aware that the effect of relativity was significant at this velocity. 511kV is within Marx capability...if such a voltage were applied to an accelerator, no matter what particle was being accelerated, would new electrons be created?
attune, Mon Aug 21 2006, 04:40PM
Sweet! I was not aware that the effect of relativity was significant at this velocity. 511kV is within Marx capability...if such a voltage were applied to an accelerator, no matter what particle was being accelerated, would new electrons be created?
Re: accelerator physics
Bored Chemist, Tue Aug 22 2006, 06:00AM
You need at least twice that.
Bored Chemist, Tue Aug 22 2006, 06:00AM
You need at least twice that.
Re: accelerator physics
Dr. Slack, Tue Aug 22 2006, 07:27AM
What does anything mean physically, especially when it goes relatavistic or quantum? For me, physically only works for good ol' Newton, relativistic mechanics gives that queasy feeling of having to imagine riding on electrons and seeing the world foreshortened in your direction of travel, and other easy-to-do things (not). In your frame of reference (stationary standing next to the accelerator), it means the electron has got heavier by the Lorentz factor (related to gamma by a sqrt)
Gamma as used/defined above is just (total energy) / (rest energy). For a good Newtonian approximation, gamma is close to 1, the higher it goes the less adequate Newton is.
There's a good reason for just considering energy, rather than speed, force or aceleration in acceletrators. Once gamma is into double figures, the particles barely get any faster, just get heavier as they absorb more energy.
I'd like to think that muons generated in the upper atmosphere by cosmic particles reach the surface of the earth in spite of their short lifetime not because their clocks run slow, or the atmosphere appears shorter in their direction of travel, but because they are actually travelling faster than light and somehow we contrive to measure it wrong, but, particles in a circular accelerator keep going round at the same speed as the energy goes up, and that configuration is much more difficult to mis-understand.
Dr. Slack, Tue Aug 22 2006, 07:27AM
e.g. for a 50 MeV accelarator, Gamma = 100
what does this mean physically?
What does anything mean physically, especially when it goes relatavistic or quantum? For me, physically only works for good ol' Newton, relativistic mechanics gives that queasy feeling of having to imagine riding on electrons and seeing the world foreshortened in your direction of travel, and other easy-to-do things (not). In your frame of reference (stationary standing next to the accelerator), it means the electron has got heavier by the Lorentz factor (related to gamma by a sqrt)
Gamma as used/defined above is just (total energy) / (rest energy). For a good Newtonian approximation, gamma is close to 1, the higher it goes the less adequate Newton is.
There's a good reason for just considering energy, rather than speed, force or aceleration in acceletrators. Once gamma is into double figures, the particles barely get any faster, just get heavier as they absorb more energy.
I'd like to think that muons generated in the upper atmosphere by cosmic particles reach the surface of the earth in spite of their short lifetime not because their clocks run slow, or the atmosphere appears shorter in their direction of travel, but because they are actually travelling faster than light and somehow we contrive to measure it wrong, but, particles in a circular accelerator keep going round at the same speed as the energy goes up, and that configuration is much more difficult to mis-understand.
Re: accelerator physics
Simon, Wed Aug 23 2006, 03:56AM
It's very simple, contrary to what most people expect of special relativity (it's general relativity that's hard). Simply put, gamma is the factor by which relativity does weird things.
For a 50MeV electron (gamma ~= 100) shooting down a 100m pipe (as measured by someone standing next to it), the distance would only seem like 1m. If it took 100 years to travel to a distant star (as measured by someone at the star), to the electron it would only seem like 1 year.
As to the idea of sticking 511kV somewhere and generating an electron, remember that my chocolate bar doesn't spontaneously burst into a gazillion electrons just because there's enough energy for it.
Simon, Wed Aug 23 2006, 03:56AM
Sulaiman wrote ...
Simon,
I don't understand your maths/formula
e.g. for a 50 MeV accelarator, Gamma = 100
what does this mean physically?
Simon,
I don't understand your maths/formula
e.g. for a 50 MeV accelarator, Gamma = 100
what does this mean physically?
It's very simple, contrary to what most people expect of special relativity (it's general relativity that's hard). Simply put, gamma is the factor by which relativity does weird things.
For a 50MeV electron (gamma ~= 100) shooting down a 100m pipe (as measured by someone standing next to it), the distance would only seem like 1m. If it took 100 years to travel to a distant star (as measured by someone at the star), to the electron it would only seem like 1 year.
As to the idea of sticking 511kV somewhere and generating an electron, remember that my chocolate bar doesn't spontaneously burst into a gazillion electrons just because there's enough energy for it.
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