Speaker
Description
The Smith-Purcell effect is a well-known radiation emitted when an electron beam propagates the vicinity of a diffraction grating surface. Apparently, the surface current model* successfully interprets the process of Smith-Purcell radiation (SPR) generated through an Eshellet-type grating with a small blazing angle. According to the surface current model, the SPR intensity rapidly increases as the observing angle approaches the traveling direction of electrons. In fact, since the longitudinal formfactor of the surface current (charge) distribution is considered to be identical to that of the electron bunch, coherent SPR has been investigated as a candidate for a non-destructive tool of diagnosing bunch length.
We have investigated the distribution of surface current on the metal grating induced by the single electron employing a classical electromagnetism approach for electric field propagation. As a result, we found that the longitudinal distribution of surface current is not a delta-function and has a long tail, which mean the surface current formfactor is not 1 and much suppressed in entire frequency range. Considering the finite longitudinal distribution of electrons in a short bunch, a higher frequency component of coherent SPR is much suppressed. We will report the detailed calculation of the surface current with simple math. Effects of finite beam size are also discussed.
Footnotes
Smith, S.J.; Purcell, E.M. “Visible Light from Localized Surface Charges Moving across a Grating”. Phys. Rev. 1953, 92, 1069.
*Brownell, J.H.; Walsh, J.; Doucas, G. “Spontaneous Smith-Purcell radiation described through induced surface currents”. Phys. Rev. E 1998, 57, 1075.
Funding Agency
Work supported by
JSPS KAKENHI grant numbers 23K17306, 22K12660 and 18K11915.
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