Abstract
We have developed a novel method based on vector electromagnetic theory and Schellkunoff's principles to calculate the spectral and angular distributions of transtion radiation (TR) and diffraction radiation (DR) produced by a charged particle interacting with an arbitrary target. The vector method predicts the polarization and spectral angular distributions of the radiation at an arbitrary distance form the source, i.e. in both the near and far fields, and in any direction of observation. The radiation fields of TR and DR calculated with the commonly used scalar Huygens model are shown to be limiting forms of those predicted by the vector theory and the regime of validity of the scalar theory is explicitly shown. Calculations of TR and DR done using the vector model are compared to results available in the literature for various limiting cases and for cases of more general interest. Our theory has important applications in the design of TR and DR diagnostics particularly those that utilize coherent TR or DR to infer the longitudinal bunch size and shape. A new technique to determine the bunch length using the angular distribution of coherent TR or DR is proposed.
Highlights
Optical transition radiation (OTR) from metallic targets is widely used for the measurement of transverse size, divergence, and energy of electron and proton beams [1–5]
Huygens theory in the regime where this approach is applicable, i.e., high energy or normal incidence; second, we give an estimate of accuracy of our method in the near field zone; third, we theoretically compare the Huygens scalar and the vector solutions and demonstrate when the Huygens solution is valid; fourth, we apply the method to calculate the angular distribution (AD) to situations where the Huygens scalar method is inapplicable; and we show that it may be possible to use the AD of coherent TR and diffraction radiation (DR) to infer the beam bunch length
50 mm disk calculated from vector theory and a single Gaussian longitudinal beam distribution with full widths of 1, 1.5, and
Summary
Optical transition radiation (OTR) from metallic targets is widely used for the measurement of transverse size, divergence, and energy of electron and proton beams [1–5]. Optical transition radiation (OTR) from metallic targets is widely used for the measurement of transverse size, divergence, and energy of electron and proton beams [1–. Incoherent TR has the interesting property that, when the radiating foil is large, i.e., the radiation parameter =2 a the size of the radiator, the angular distribution (AD) of the radiation is independent of the frequency of the emitted photon out to the plasma frequency of the radiating material. When =2 a, TR can be considered, by application of Babinet’s principle [6,11], to be a form of diffraction radiation and in this case the far field AD of the radiation is frequency dependent even at frequencies much lower than the plasma frequency. For long wavelengths and/or at high energies, the far field angular distributions of DR and TR are both functions of the observed wavelength
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