Beam energy absolute measurement using K-edge absorption spectrometers Page: 4 of 7
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The accuracy of the measurement depends on the angle of SR beam collimation, h/L,
and the absolute value of the intensity drop gradient AN5.,t/A6 between the upper and
lower points of the absorption curve.
To exclude from 6b the bend angle created by the short dipoles 66, these magnets have
opposite directions of the vectors of magnetic field strength.
For the spectrometers, ordinary EXAFS (extended x-ray absorption fine structure)
spectrometers can be used (see, for example, [4,5]). Double crystal monochromators which
are in use for these spectrometers have an angular resolution better than 1 arc sec. The
monochromator described in  consists of two non-dispersive Si(422) channel-cut crystals,
whose rocking curve width is e ~ 2.6 aresec, installed in a dispersive geometry (see Figure
2) having an energy resolution AE,/Eo better than 10-5 and permitting measurement
of the angle of about 5.6 arc deg from CuKa,2 to CuK# with an accuracy 60 better than
0.6 arc sec. This accuracy was stable in several sweeps over a period of several hours.
Figure 2 High-resolution crystal monochromator for EXAFS spectrometer.
Using this type of spectrometer the bend angle of the electron beam in the main
dipole (about 4.5 arc deg) will be measured with the accuracy 60/ better than 4 x 10-5.
The angular resolution of the K-edge spectrometer depends on the absolute value of
a gradient of the intensity drop within the upper and lower (Au and At) borders of K-edge
G-Nyl - Nyu(1
G = ,(1)
and the intensity fluctuation at the lower border of absorption Ny, = NvR7I, at a given
electron beam intensity, I,, and can be determined as follows:
64 x G = v/R. (2)
The gradient of intensity drop depends on a ratio between the intensities created at
A0 in the short and main dipoles too, because of the large divergence angle of radiation in
the main dipole. This ratio can be limited to a few units of 10-2.
The magnetic field intensity in the short dipole B. can be taken as 2 T and with a
bend angle of 2 x 10 5 rad.
A typical absorption curve of Cu at its K edge with an energy resolution about 2 eV
 having the ratio Nyu/Nl higher than 30 has a A equal to 4.25 x 10-4 rad (see Figure
3). For the following calculations these parameters were used.
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Karabekov, I.P. & Neil, G. Beam energy absolute measurement using K-edge absorption spectrometers, article, May 1, 1994; Newport News, Virginia. (digital.library.unt.edu/ark:/67531/metadc704165/m1/4/: accessed January 23, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.