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Particle bunching +Lorentz contraction

  1. Sep 14, 2009 #1
    Hi Does anyone have any information or web links for layman followable explanations of how Lorentz contraction is connected with the accelerator bunching problem. I have found many references to the phenomena but no explication of the actual connection.
    A related question is: I have heard that particle tests have also revealed something comparable to clock desynchronization. ANy input on this????
    Thanks
     
  2. jcsd
  3. Sep 14, 2009 #2

    ZapperZ

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    Accelerator bunching problem? What is that?

    A "debunching" problem, I can understand, since there's space-charge issues. But a bunching problem? Can you give references to where you heard such a thing?

    Zz.
     
  4. Sep 14, 2009 #3
    Hello Zz It sounds like you know much more about it than I do. It also sounds like we are talking about the same thing. I actually first heard about it on this forum.
    I addressed a query to the person ,who sounded like a particle physicist but got no reply. It was a while ago so I have no idea where the thread is or what the actual topic was.
    I have googled for both bunching and debunching and there are many references for both but much too technical for me and never any direct correspondence to Lorentz contraction.
    If you have any simple description of the relationship it would be great.
    Thanks
     
  5. Sep 14, 2009 #4

    ZapperZ

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    The study of "accelerator and beam physics" is in fact, OUTSIDE the realm of what a particle physicist study. It is a totally different field. While accelerators are usually associated with particle physics, it has way more applications outside of that.

    So I still don't have any references from you of this so-called "bunching", so it is difficult to comment on exactly what you want without proper context. Not only that, I also don't have any idea why this would have any problem with Lorentz contraction. It is not as if I originally had to go from the beam reference frame back to the lab frame.

    Zz.
     
  6. Sep 14, 2009 #5
    Review the work of Tom Wangler on beam bunching (and debunching) in proton linear accelerators here:
    http://www94.web.cern.ch/Linac96/Proceedings/Monday/MOP39/Paper.html [Broken]
    [Edit] I apologize for accidentally posting Wadlinger's paper (above). See Wangler's paper here:
    http://prst-ab.aps.org/pdf/PRSTAB/v1/i8/e084201
    and references therein.
    Bob S.
     
    Last edited by a moderator: May 4, 2017
  7. Sep 15, 2009 #6
    Thanks Bob S from what I could get from these links the only relevance to the Lorentz factor seemed to be with axial velocity , but I did not see any explicit connection to contraction. But the math for the most part is beyond me . SO it appears I may have been misled about the contraction aspect. Thanks
     
    Last edited by a moderator: May 4, 2017
  8. Sep 15, 2009 #7
    What do you mean problem with Lorentz contraction??
    If you mean connection with Lorentz contraction then I dont know what that is.
    I simply heard on this forum that there was some relevant connection which was not explicitly stated or explained. If there was a connection , I was simply interested in finding what exactly this meant.
    SO as to references to this so-called bunching or debunching there are plenty on google for both , where it appears that it is a recognized phenomenon.
    If you mean a reference to the specific thread in this forum I dont have it.
    From what I got from the links from Bob S there is the possibility that there is no significant connection . Beyond this I dont know what you are asking. Thanks
     
  9. Sep 15, 2009 #8

    ZapperZ

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    Er... look at the title of this thread that you created, and the original post. You were the one who asked and made the connection. I was asking for clarification on that connection, because I see none.

    It is, but I have no way of knowing if THIS is what you were asking for. In beam physics, there are PLENTY of such effect due to different things (the phase of the RF, space-charge, etc... ). That's why I asked for the context in your question, i.e. where did you read/heard this so that the question can be answered within that context.

    Besides, this is such a "detailed" effect. Why would you be interested in it? The longitudinal bunch length of particle beams isn't a common question, nor is it THAT interesting for many people. Most of us in accelerator physics have to deal with it, and design ways to actually measure it (it isn't trivial). But what puzzles me is the connection with "lorentz contraction".

    Zz.
     
  10. Sep 15, 2009 #9
    Well this has turned out very interestingly.
    I figured out how to chase down my old posts and it turns out that the particle physicist
    that I refered to is you. The thread was Re:Lorentz contraction of a box filled with gas.
    My post to you that was unanswered was post #207 of that thread. Dec.1-08
    I got to that thread from another thread regarding Lorentz contraction through a link from Doc AL SO if you are puzzled by the connection with length contraction or how I got the idea there was one then I am even more puzzled. If you can't understand why I would be interested I dont know what to tell you.
    I am interested in abslutely everything that relates to SR or that can possibly increase my understanding. If you think there is nothing here then simply pull this thread it has already put me in contact with the relevant party I.e. you. Thanks
     
  11. Sep 15, 2009 #10

    ZapperZ

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    Bunch length is measured in lab frame. It is what it is. Unless there is a calculation that requires one to transform into the beam frame, the issue of Lorentz contraction is moot.

    For future reference, I am not a particle physicist.

    Zz.
     
  12. Sep 15, 2009 #11
    Hi Austin0-
    Most particle beam bunch lengths in the lab are actutally measured in the time domain, because the bunch separation is best known and most easily measured in the time domain. For example, the Fermilab Tevatron uses ~53 MHz for the accelerating (bunching) RF frequency for protons and anti-protons. (there are 1113 buckets in 6283 meters circumference). There are large Coulomb forces trying to blow up the bunch size, so a critical pert of accelerator design is to preserve the transverse and longitudinal beam "emittance" (product of bunch sizes and momentum distributions in bunch rest frame).
    SLAC uses 2856 MHz bunching frequency for accelerating electrons.
    Bob S
    [Edit] One desynchronization or bunch spreading (and compressing) that you might be interested in is the klystron amplifier. The Klystron has a 50 to 100 KeV pulsed electron beam (~ 1 amp +/-?) that passes several small RF cavities before the beam reaches the output cavity. The first cavity (Klystrons at SLAC) is modulated at 2856 MHz. This cavity accelelerates or decelerates the electrons based on their time of arrival at the input cavity. By the time they arrive at the output cavity, the electrons are tightly bunched at 2856 MHz. This is because the electrons that were accelerated at the input cavity had a higher velocity than the ones that were decelerated, and reached the output cavity faster. This modulated current of electrons produces a very large microwave signal in an S-band rectangular waveguide.
    Bob S
    [Edit 2] In circular accelerators, if the beam bunch is too short, the RF fields induced in the high-Q RF cavities by this current are too high, and it creates beam instabilities. The best way to cure this instabillity is to make the beam bunch longer (debunch) basically the longitudinal momentum spread is made longer, and the individual particles oscillate in position about the bunch center (synchrotron oscillation). This spreads out the instantaneous frequency spread of the beam and overcomes the instability.
    Bob S
     
    Last edited: Sep 15, 2009
  13. Sep 16, 2009 #12
    Your depiction was very clear. Even with only hazy ideas about the priciples, gained mainly through a slight study of railgun concepts , I at least feel like I got a basic idea.
    It seems like any Lorentzian effects regarding particle field contraction are handled through control of timing and energy on an overall statistical basis. Without the need to make specific calculations , but I could be completely off base in this idea. Thanks for your input, it has actually sparked a greater curiosity as to how the things actually work and pretty much settled the original question
     
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