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Synchrotron radiation

  1. Sep 13, 2011 #1
    Hello everyone, first time poster.

    A fairly basic question: What is the mechanism by which synchrotrons produce x-rays? (in more detail than e-beam + varying magnetic flux = x-rays)

    I'm also still confused as to whether the mechanism is unique to magnetic fields or the same as Bremmstrahlung radiation, although even regarding that I'm coming across conflicting information on whether it is the retardation of the electrons or the interaction between electrons and the electric fields around atoms that produces radiation.

    When reading about the Maxwell equations I can find more derivations than I can shake a stick at, however a nice, layman's terms explanation seems to be lacking.

    Replies very much appreciated, condescending replies not so much, but expected since this is pretty fundamental.

    Thanks in advance,
    Billy
     
  2. jcsd
  3. Sep 13, 2011 #2
    I don't know if I can give you more understanding then you already have without going into Maxwell's equations, but I will try. The varying magnetic fields used to confine the particles to a circular (or near-circular) track do not directly create x-rays. They are varying too slowly for this. What they do accomplish is to exert a force on the charged particles to keep them bending around the circular track. Charged particles that are accelerating radiate electromagnetic waves.

    You can think of there being a radial electric field line pattern attached to every charged particle. When a particle jumps forward (accelerates), due to cause-and-effect and the finite speed of everything, the field lines far away from the particle jump forward later then the field lines close to the particle. This creates kinks in the electric field lines which travel away like waves on a string, and an electromagnetic wave is born.

    The key is that there are two kinds of fundamental types of acceleration, linear and rotational, and both lead to radiation. Linear acceleration of charge would be like the current driving charges forward and backward in a straight radio antenna. But forcing a charge to curve into a circular path even if its speed is constant is also a form of acceleration and leads to radiation. Oscillatory accelerations (like in a radio antenna) lead to a train of smooth "kinks" in the field lines, so the radiation is nearly single frequency. A more constant acceleration leads to a broader smear of frequencies in the emitted radiation. So bremstrahlung and synchrotron radiation are similar in that they are non-oscillatory decelerations, but bremstrahlung typically refers to that caused by a linear deceleration, whereas synchrotron radiation is caused by an angular acceleration (curving of the charged particles by the bending magnets). Note that radiation can also be achieved in synchrotron using wigglers.
     
  4. Sep 13, 2011 #3

    xts

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    Every electric charge emits radiation when accelerating. Magnetic flux has no direct importance - it just causes the beam to bend, thus to accelerate charged particles with centriprocal force.

    You are right - synchrotron radiation is a kind of Bremsstrahlung radiation.

    You should try really good classical (40 years old) article by Ginzburg http://cdsads.u-strasbg.fr/cgi-bin/nph-bib_query?bibcode=1969ARA&A...7..375G
    - no one may explain synchrotron radiation better in a quick response on the forum.
     
  5. Sep 14, 2011 #4
    Thanks very much guys. Excellent explanations that have cleared it up nicely.
     
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