An electrostatic energy analyzer for longitudinal energymeasurements Page: 3 of 18
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The constant, 18.0 in., is called the dispersion coefficient.
The final important parameter is the spectral resolving power. The cen-
tral wire of the multiwire array of current collectors at the exit of the
analyzer could be activated by incident ions over a range of electrode vol-
tages even if the ions had a precisely defined energy. This effect is due to
the widths of the slit aperture and detector wire, as well as aberrations,
which give the image a nonzero width at the detector. This width is equiva-
lent to an apparent energy spread in the beam, if one makes use of equa-
tion 2. The analyzer is incapable of discerning real energy spreads in the
beam that are smaller than this apparent spread. A quantity of interest is
the spectral resolving power, R, defined as:
= dispersion coefficient/image width
where To = kinetic energy of ions on the central path (3)
ST = apparent energy spread in the beam
Values for R were calculated in the paraxial, zero space charge limit, and
are shown in Table I.
In the paraxial, zero space charge limit, the image plane should have
been 6.4 ins. above the exit of the cylindrical electrodes. However, in the
experiment using the 12mA ion beam of the SBTE it was discovered that a
sharper image was located at approximately 11 ins. above the electrodes. In-
terestingly, when the beam was attenuated to 3-1/2% of the 12mA, the best fo-
cus was achieved when the harp was located 6 to 7 ins. above the electrodes.
For this reason, two values for various parameters are given in Table I. The
values for the nonzero space charge case are not calculated from a derivation
taking space charge into consideration. All that has been
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Sato, A.H. An electrostatic energy analyzer for longitudinal energymeasurements, report, September 1, 1985; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc876366/m1/3/: accessed April 22, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.