Beam energy absolute measurement using K-edge absorption spectrometers Page: 3 of 7
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The concept of the method is the following. A beam of electrons passes through a
high-precision mapped and continuously monitored dipole magnet having a field average
intensity b = k f Bl and two short dipoles having opposite direction of field intensity
B, > Bb installed on its sides. The synchrotron radiation generated in the main dipole
and short magnets have different spectral distributions defined by. corresponding critical
wavelengths Ac, and At, which are chosen to satisfy the condition ac, > Ac,. So these short
magnets are working as magnetic targets generating wavelength A0, which is practically
not represented in the spectrum radiated from electrons in the main dipole.
The principle of the method is as follows. Two K-edge absorption spectrometers (see
Figure 1) having input collimators of width h and installed on the SR beam produced
by the first short magnet at distance L can be tuned up at a wavelength A0 between the
upper and lower borders of K-edge absorption of a chosen element. Scanning synchrotron
light by the input collimator one can find the higher intensity at chosen wavelength which
is the centroid of the SR beam generated in the first short magnet. This procedure will
lower the quantum fluctuation of output (after absorption) intensity, which is one of the
main sources of systematic errors. Then one of the spectrometers will be installed on
the second beam axis by moving in a direction perpendicular to the axis of the first SR
beam. The same wavelength Ao with the same output intensity can be registered in the SR
beam generated in the second short magnet by scanning this beam and rotating the second
spectrometer around the axis of its first crystal. When the same point of the absorption
curve is reached--i.e., when the output intensities Ny.nt of both spectrometers are equal
and the gradients AN-mut/A6 of both spectrometers are equal-the bend angle 66 in the
main dipole will be equal to the angle of rotation of the second spectrometer.
1st SR beam
2nd SR beam
Main dipole e' beam
calibration position Absorbers Spectrometer 1
. working position
slits ', Detector
Figure 1. The scheme of absolute energy measurement with the K-edge spectrometers.
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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/m1/3/: accessed December 10, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.