Beam energy absolute measurement using K-edge absorption spectrometers Page: 2 of 7
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Beam Energy Absolute Measurement Using
K-Edge Absorption Spectrometers*
Ivan P. Karabekovt and George R. Neilt
fYerevan Physics Institute
2 Alikhanian Brothers st., Yerevan, 375036, Republic of Armenia
tContinuous Electron Beam Accelerator Facility
12000 Jefferson Avenue, Newport News, Virginia 23606
A method is presented of absolute energy measurement with an accuracy of AE ~
104E0 by direct measurement of the bend angle in a high-precision magnetic dipole using
two opposite-direction short (about 2 mm long) high-field-intensity magnets (Bdpoie <
Bshort mag) installed at each end and two K-edge absorption spectrometers. Using these
spectrometers and the hard x-ray synchrotron radiation created by the short magnets, a
bend angle of 4.5 arc deg for the CEBAF energy bandwidth can be measured with an
accuracy of a few units of 10-6 rad, and the main sources of systematic errors are the
absolute measurement of the field integral and the determination of the centroid of the
synchrotron beam at a wavelength equal to the K-edge absorption of the chosen substance.
The use of magnetic spectrometers to determine absolute beam energy is well known.
The best performance of the method was the SLC energy measurement facility . This
facility measured the bending angle using two synchrotron radiation (SR) swaths created
in two short kicker magnets having magnetic field perpendicular to the field direction in the
main bending magnet and installed on its sides. The field integral f Bdl in the main dipole
was measured with an accuracy better than 10-4 and monitored by a special rotating coil
or NMR probes .
Two phosphorescent screens equipped with a system of fiducial wires and CCD video
cameras measured the distance between SR beams with an accuracy of ; 10-4.
The distance between the center of the main bending and the phosphorescent screen
equaling 15 m was measured with an absolute accuracy of 1.5 mm.
The main source of errors limiting the accuracy of energy determination at the level
of 5 x 104 is nonorthogonality of the vectors of the magnetic field strength in the kickers
and in the main bending dipole .
In this paper a new method of bend angle measurement using the K-edge absorption
technique is discussed. The application of the method to high-precision absolute energy
measurement at CEBAF is presented.
* Work supported by U.S. Department of Energy under contract DE-AC05-84ER40150.
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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/m1/2/: accessed December 13, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.