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Accelerator Beam lifetime

  1. Jul 25, 2011 #1

    gbz

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    The main cause of decay of particle accelerator beams is the scattering due to residual gas particles in the vacuum rings. I read some research suggesting (in my understanding) that most of these free gas particles (CO2, CO etc) are the result of desorption from the surface of the vacuum tube (which carries the beam) due to synchrotron radiation from the beam. ie -- beam produces synchrotron radiation, which interacts with surface of the tube carrying the beam, resulting in desorption and release of residual gas particles which then collide with beam particles to cause scattering and beam decay. Is this correct? If we reduce beam velocity by a factor of 10, which would dramatically reduce synchrotron radiation (which in my understanding is proportional to 8th power of v), would that also proportionally increase beam lifetime? Any research on lower velocity beams out there?
     
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  3. Jul 25, 2011 #2

    Vanadium 50

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    First, you can't get high energy without high velocity, and second, it's not always gas interactions that limit the lifetime: at Fermilab's Tevatron its beam-beam tune shift.
     
  4. Jul 26, 2011 #3

    ZapperZ

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    You must always provide a reference. "I read some research" is very vague and tells us nothing on whether you read a valid source, or if you understood it correctly.

    Zz.
     
  5. Jul 26, 2011 #4

    gbz

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    Source: http://ieeexplore.ieee.org/Xplore/login.jsp?url=http%3A%2F%2Fieeexplore.ieee.org%2Fiel5%2F4915548%2F4931945%2F04932295.pdf%3Farnumber%3D4932295&authDecision=-203>

    @V50: How exactly does tune shift impact beam lifetime?
     
  6. Jul 26, 2011 #5

    gbz

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    Link doesn't seem to work, source again:

    Electron storage ring beam lifetime dependence on pressure and pumping speed
    Halama, Henry J.
    Brookhaven National Laboratory, Upton, New York 11973

    This paper appears in: Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films
    Issue Date: May 1985
    Volume: 3 Issue: 3
    On page(s): 1699 - 1702
    ISSN: 0734-2101
    Digital Object Identifier: 10.1116/1.573003
    Date of Current Version: 18 June 2009
     
  7. Jul 26, 2011 #6

    ZapperZ

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    If you read just the abstract, there are two issues that you should pay attention to:

    First, he's talking about conditioning and initial operation. During this period, certainly there will be a lot of 'stuff' coming out. However, after a while, this is no longer a factor, so the beam lifetime does not have any relevance to such outgassing.

    However, the 2nd point is a bit more puzzling. He is arguing that the beam lifetime depends on "... to a large extent on the interaction of the beam with heavier residual gas molecules...". Yet, in the very last sentence, he said that even when the concentration of CO, CO2, and CH4 dropped considerably after 3 months, no change to the beam lifetime could be observed! So how would one draw the conclusion that the interaction of the electron beam with these gas molecules is the dominant mechanism that affects the beam lifetime?

    Zz.
     
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