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HUP and Particle Accelerators

  1. Jun 17, 2007 #1
    I hope this question relates closely enough:

    [Mentor note: Don't be afraid to start a new topic if your question isn't directly related to an existing one. :smile: Also, this is really a QM question so I'm moving this to the Quantum Physics forum while I'm at it.]

    If the 'controls' of an accelerator sends out impulses to the accelerator sometimes up to a billion times a second, does the process even care where along the path the 'particle' is that is being accelerated (except for re-routing)?

    With HUP, speed of the electrical signal involved to each plate/electromagnet, and the speed that the plate must 'charge', the interval between charges, AND knowing the location/'position' of the particle--it seems the process may tend toward a 'gross' process than a 'fine' process.


    (PS--I'm not rfwebster)

    thank you kind sir(Mentor, whomever you may be), for the:

    1) the advice
    2) the move
    3) the understanding
     
    Last edited: Jun 17, 2007
  2. jcsd
  3. Jun 17, 2007 #2

    jtbell

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    As far as I know, the design of particle accelerators does not involve QM (including the HUP) at all, that is, it's based on classical electrodynamics applied to beams of charged particles.

    On the other hand, the experiments done with those accelerators do usually need to be analyzed using QM (more properly, quantum field theory), of course.
     
  4. Jun 18, 2007 #3
    I threw in HUP thinking that if something is moving at .8 or .9, can you know very much else about the particle until it 'does'/(someone measures) something else about it (like even where it is on a five mile course)?
     
  5. Jun 18, 2007 #4

    ZapperZ

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    Charge particles in a particle accelerators are classical particles. All the software codes that do particle tracking such as PARMELA, etc. treat them as classical particles, and they work pretty well in accelerator design and beam physics.

    Zz.
     
  6. Jun 18, 2007 #5
    OK--thanks--but, is it 'known' where the particle is at any given moment (except at the point of collision, and maybe at the point of re-direction) in the accelerator?

    --------------------------
    http://pbpl.physics.ucla.edu/Computing/Code_Overview/


    simplified explanations
     
    Last edited: Jun 18, 2007
  7. Jun 18, 2007 #6

    ZapperZ

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    The macroscopic position, yes.

    We don't deal with position of a single particle in a particle accelerator. We deal with a glob of them. Since they are in bunches (the one I deal with is barely 0.5 cm in length), we know and can track where they are very well, since our LINAC has to be in just the right phase for the electron bunches to enter be accelerated. If we don't get that right, they'll come in at the wrong phase and it won't work.

    Besides, as soon as electrons reach MeV energies, they all can be easily estimated to move at c anyway, and that's how many of the particle tracking codes treat them, and treat them successfully that way.

    Zz.
     
  8. Jun 18, 2007 #7
    Ok--and 'the wrong phase' means..?? spin-position orientation? from the plate/electro-magnetic? not correct for the 'expected outcome' or...?
     
  9. Jun 18, 2007 #8

    ZapperZ

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    Er.. no. In an accelerating structure, an oscillating EM wave is "piped" into the structure, so you have an E-field along the axis that is oscillating. If a charge particle enters the structure at the wrong phase, i.e. the E-field is pointing in the wrong direction, or it is in the right direction but it is decaying, then the particle would not have the right force or the right timing to get accelerated.

    So it is the phase of the RF field in the accelerating structure.

    Zz.
     
  10. Jun 18, 2007 #9
    So, if the accelerator (if I read your answer correctly) is about .5 cm, how many times can it/does it occilate in one 'run'?--and it still gets close to LS?

    ---In my initial question about if an 'exact' position 'could' be known along the course, I was thinking more of a Fermi accelerator (miles).
     
  11. Jun 18, 2007 #10

    ZapperZ

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    No, the electron BUNCH length is about 0.5 cm.

    Actually, I made a typo, it should be 0.5 millimeter, not centimeter.

    Zz.
     
  12. Jun 18, 2007 #11
    Wow! Nano accelerators! Where can I buy one of them to play with in my freetime? :wink:
     
  13. Jun 22, 2007 #12
    Sorry for my ignorance. How BUNCH length is related to the (longitudinal/transversal) coherence length?

    The reference on the coherent review of the topic will be highly appreciated.

    Regards, Dany.
     
  14. Jun 26, 2007 #13
    I'm not an 'accelerated' person, but my guess it has something to do with the '+' and '-' of the wavelength, and the frequency and/or amplitude of the wavelength as the 'bunch' 'rides' the pulse between sin crests either directly or on a harmonic level.---and the 'bunch' fits in between the 'wave crests'. (?)


    ---------------------

    surf's up, dude
     
    Last edited: Jun 26, 2007
  15. Jun 26, 2007 #14

    ZapperZ

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    Er.. I don't think it is. There's no "coherence length" in the classical particles within a particle accelerator, at least not in the QM sense. There certainly is no analogue of the coherence length in superconductivity to the particles in an accelerator.

    Again, beam physics mainly deal with classical particles. Even the coulombic particle-particle interactions are dealt with classically, rather than what is dealt with in condensed matter.

    Zz.
     
  16. Jun 26, 2007 #15
    So, in the '50 words or less' category--how's my description?
     
  17. Jun 26, 2007 #16

    ZapperZ

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    Your description sucks! :rofl:

    Hey, you wanted 50 words or less! :)

    If you want MORE than 50 words, here it is:

    The bunch length in most particle accelerators that use a photoinjector source depends very much on the pulsed laser duration and the RF phase of the photoinjector. The photocathode sits in a cavity that has an oscillating E-field from the RF source. A pulsed laser hits the cathode. If it hits it at the right phase, then the generated photoelectrons can be accelerated and leave the photoinjector cavity to enter the rest of the accelerator line.

    Obviously, there's a range of phase in which the E-field has the right "sign" to do this. However, even if the sign is correct, if the laser hits the photocathodes at different phase within this correct sign, will will change the longitudinal bunch length of the charges that exit the photoinjector. The bunch length is different at 30 degrees when compared to 60 degrees, etc.

    So it isn't as simple as the "+" and "-" phase of the RF wave.

    Zz.
     
  18. Jun 26, 2007 #17
    Thanks--that helps QUITE a bit---



    but (in the 50 words or less category) --your MS WORD count is 141----

    so, one point subtracted for each 'extra' word (out of a possible 100 points) --you get a score of '9'
     
    Last edited: Jun 26, 2007
  19. Jun 26, 2007 #18
    My question is related to A. Tonomura et al. (1989) set-up which in the source section looks similar. The number you presented is pretty close.

    How do you know the difference between the classical electrons bunches and the coherent wave packet? How you define number of the electrons in the bunch?

    Regards, Dany.
     
  20. Jun 26, 2007 #19

    ZapperZ

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    Again, I can easily double the bunch length that I'm using by (i) increasing the laser pulse length and (ii) changing the phase that I shoot the laser at with respect to the RF in the photo injector. There's nothing "intrinsic" about this.

    1. The classical particle tracking code works.

    2. I measure the charge of the bunch using an ICT (integrated charge transformer), then divide by e. In fact, that is how I determine the quantum efficiency of the photocathode.

    Zz.
     
  21. Jun 26, 2007 #20
    What you get usually (average)?

    That is always good reason, but perhaps not sufficiently good (depend on your answer to the first question).

    Regards, Dany.
     
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