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What creates the magnetic field on a cyclotron?

  1. Dec 10, 2009 #1


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    what creates the magnetic field on a cyclotron?
    in all of the schematics I am looking at it just says "magnetic field points up"
    like it is extremely apparent as to what creates the magnetic field.
    I was thinking that a bunch of small diameter solenoids packed side by side would be the best way to create a magnetic field like this.
    is this how it is done? do the wires get hot? do they need cooling?
    also the magnetic field would be resisted if the chamber for the particles was completely enclosed by metal and the solenoids were external?

    what keeps the particles from falling toward the earth?
    Cyclotron_with_glowing_beam.jpg it is just hard to see what is going on. Even the physics textbooks on particle accelerators just have crappy little black and white drawings.
    I just want to see where everything is. there must be a 3D model of these accelerators out there somewhere!
    Last edited: Dec 10, 2009
  2. jcsd
  3. Dec 10, 2009 #2


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    Re: Cyclotron

    Electromagnets, probably. You'd have to look at the construction schematics for a particular cyclotron to figure out what produces its magnetic field, since that can vary from one machine to another. It doesn't really matter how the field is produced when you're just analyzing the physics.

    For a cyclotron made with a powerful electromagnet, the wires do get hot and they would need cooling, but in some cases just leaving them open to the air is enough. For the really large synchrocyclotrons, like the LHC, Fermilab, etc., the magnetic material itself is cooled using liquid helium (I think), because the magnets work better when they're cold; that same coolant can also be used to support superconducting wires, which don't dissipate heat (they have zero resistance).

    Those large synchrocyclotrons also have various sorts of focusing magnets which keep the particles on track and prevent them from falling toward the Earth. In a small cyclotron... maybe nothing; the particles just do whatever they're supposed to do so quickly that they don't have time to fall very far at all. Remember that these are very very fast particles ;-)

    P.S. I'm not really an accelerator expert so any of the above could be wrong... I'm sure there are people here who know much more than I do about this stuff.
  4. Dec 10, 2009 #3


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    Re: Cyclotron

    wouldn't you have the particles spinning for quite a while?
    how are the particles accelerated?
    it seems to me that this does not explain what object accelerates these particles as they make laps.

    Also, on the accelerators like the LHC. Are quadrupoles the primary method for focusing the beam? I do not understand quadrupoles because it seems that they would only focus in one direction, and unfocus in the other.

    If quadropoles are put in a series, and each one is osscilated by 90 degrees will this focus the beam? or just do nothing?
    http://www.mediafire.com/file/gvzymozy2zk/magnet1.gif [Broken]
    Last edited by a moderator: May 4, 2017
  5. Dec 10, 2009 #4


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    Re: Cyclotron

    The original cyclotrons had whopping big electromagnets with pole faces large enough to accommodate the vacuum chamber that the particles actually traveled in. A Google search for "cyclotron pictures" led me quickly to this page:


    Notice in particular this picture: Lab staff standing on 184-inch cyclotron magnet


    As the particles travel through the gap between the two halves (traditionally called "dees"), the voltage between the halves produces an electric field which accelerates the particles.
    Last edited: Dec 10, 2009
  6. Dec 10, 2009 #5
    Re: Cyclotron

    Berkeley (University of California) used to have a cyclotron with pole tips about 184 inches (4.67 meters) in diameter. This was built just after World War II, and used until about 1980, when it was disassembled. It needed about 2 megawatts of power to run the coils. There is a slight vertical focusing that keeps the beam from hitting the vacuum chamber and the "dees" ("D" shaped electrodes) and falling down (gravity). Proton revolution frequencies range from perhaps 10 MHz to over 30 MHz, depending on the magnetic field strength.
    Bob S
  7. Dec 10, 2009 #6


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    Re: Cyclotron

    Thanks bob. Once I piece together all of this information I hope I can find the time to assemble some 3d Models in Maya for Educational purposes. I will probably start with modeling a linear accelerator though. I was just curious about cyclotrons because my grandfather worked on a Cyclotron at Berkeley, I think it was probably before WWII though. Unless he went back to school and did graduate work after the end of WWII.

    I am not sure.
  8. Dec 10, 2009 #7
    Re: Cyclotron

    The first cyclotron at Berkeley (about 6" dia) was built in ~1932. The 60" in 1939. the 184" in about 1946. There was also a betatron. And a Hilac. When I was there ~50 years ago there were still some people from before the War there. (Lawrence, McMillan, Thornton, Cooksley? etc. etc.).
    Bob S
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