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cljc
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Hi,
I'm a EE PhD student working a little bit out of my area, and have just gotten stumped trying to figure out the transient dymanics of a relativistic electron moving past a discontinuity. My little thought problem came up from wakefield interactions of a relativistic electron in a waveguide. Here's a general reference to the field: slac.stanford.edu/cgi-wrap/getdoc/slac-pub-4547.pdf. I tried to include an inline link, but the forum gave me the error: You are welcome to include a link only after reaching 10 posts. I'm not very welcome, I suppose :).
I'm trying to wrap my head around the energy flow into waveguide modes from a relativistic electron moving past a metallic (either resistive or PEC) discontinuity.
I made a quick little graphic in PDF form to attach as a descriptive aid.
judylab.org/lib/exe/fetch.php?id=people%3Ajere_harrison&cache=
cache&media=people:slide.pdf
(You'll need to put www . before that to get to the file because of how our server is set up. Sorry I couldn't attach it - same issue with the number of posts.)
When I think about this in the intertial frame of the waveguide, a Lorentz contracted electric field comes in contact with the scattering boundary at t_1, producing a propagating electromagnetic field. The electric field is essentially contained within a thin disk perpendicular to the direction of motion for γ >> 1. This scattered electromagnetic field catches up to the relativistic electron at t_2. Now, after the electron has been traveling down the waveguide for a while, the steady state field matching all makes sense to me and I can find the wakefield, energy conservation looks solid, etc. But I cannot figure out how the transient behavior of the fields between t_1 and t_2 fits with energy conservation.
I realize that there will be a little bit of electric field from the electron in the direction parallel to the electron velocity, but it is vanishingly small. The vast majority of the energy in the excited TM electromagnetic modes that interact with the electron comes from the transverse component of the electron's field, which doesn't get excited until the electron is right there. As soon as the fields in the waveguide are excited by surface currents in the metal, there's got to be energy flow. But the electron doesn't see the electromagnetic field from the metal wall until it's passed it by a ways.
And if the waveguide is short enough that the electron exits the other side before the wakefield catches back up to the electron... can you bend the electron away with a steering magnet? How will the wakefield catch back up to balance the energy? It just doesn't make sense to me, so I know I'm missing something here.
Thanks!
Jere
I'm a EE PhD student working a little bit out of my area, and have just gotten stumped trying to figure out the transient dymanics of a relativistic electron moving past a discontinuity. My little thought problem came up from wakefield interactions of a relativistic electron in a waveguide. Here's a general reference to the field: slac.stanford.edu/cgi-wrap/getdoc/slac-pub-4547.pdf. I tried to include an inline link, but the forum gave me the error: You are welcome to include a link only after reaching 10 posts. I'm not very welcome, I suppose :).
I'm trying to wrap my head around the energy flow into waveguide modes from a relativistic electron moving past a metallic (either resistive or PEC) discontinuity.
I made a quick little graphic in PDF form to attach as a descriptive aid.
judylab.org/lib/exe/fetch.php?id=people%3Ajere_harrison&cache=
cache&media=people:slide.pdf
(You'll need to put www . before that to get to the file because of how our server is set up. Sorry I couldn't attach it - same issue with the number of posts.)
When I think about this in the intertial frame of the waveguide, a Lorentz contracted electric field comes in contact with the scattering boundary at t_1, producing a propagating electromagnetic field. The electric field is essentially contained within a thin disk perpendicular to the direction of motion for γ >> 1. This scattered electromagnetic field catches up to the relativistic electron at t_2. Now, after the electron has been traveling down the waveguide for a while, the steady state field matching all makes sense to me and I can find the wakefield, energy conservation looks solid, etc. But I cannot figure out how the transient behavior of the fields between t_1 and t_2 fits with energy conservation.
I realize that there will be a little bit of electric field from the electron in the direction parallel to the electron velocity, but it is vanishingly small. The vast majority of the energy in the excited TM electromagnetic modes that interact with the electron comes from the transverse component of the electron's field, which doesn't get excited until the electron is right there. As soon as the fields in the waveguide are excited by surface currents in the metal, there's got to be energy flow. But the electron doesn't see the electromagnetic field from the metal wall until it's passed it by a ways.
And if the waveguide is short enough that the electron exits the other side before the wakefield catches back up to the electron... can you bend the electron away with a steering magnet? How will the wakefield catch back up to balance the energy? It just doesn't make sense to me, so I know I'm missing something here.
Thanks!
Jere
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