Up to now an ideal electron beam was assumed, but in experiments a deficient electron beam
(tab. 1) affects the photon spectra, especially the collimated ones.
A finite beam spot size, characterised by the distribution
of
the impact positions
of the electrons on the radiator, has the same effect
like a collimator with a fuzzy edge and smears out the collimator cutoff in the photon spectra at x_{c} (eq. 3b).
The primary divergence of the electron beam, described by the distribution
,
has a similar effect
on x_{c} but causes in addition a variation of the crystal angles with
respect to their nominal values
changing the intensity due to the dependence of the
momentum transfer on these angles.
The deflection of the electron is not given by the beam divergence alone but is enhanced because the electron
undergoes many small angle scattering processes mainly due to Coulomb interaction with atoms
while traversing the radiator (thickness z_{R}).
This distribution is well represented by Molières theory[11], which uses a Gaussian approximation
for small angles defined by the variance
being a function of medium properties and pathlength z, the particle has travelled.
source | distr. | effect | influence |
diamond temperature | - | Debye Waller factor | |
BS: beam spot size | "fuzzy" collimator | x_{c} | |
BD: beam divergence | + variation of | x_{d} | |
MS: multiple scattering | increases BD | x_{d} | |
ES: beam energy spread | smears out peaks |