THERMAL EMITTANCE MEASUREMENT DESIGN FOR DIAMOND SECONDARY EMISSION. Page: 4 of 5
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imaging more difficult. From simulation results in Figure
3, we choose the upper limit for each effect.
aode pinhole radis:
' B oooo
0. 0 0005
0 0.2 B.9 ..6
Thennal Energy [eV]
0.4eV hlenual energy --
100 nucron -u-
150 nucron -
200 ~ ~ ~ vca
Figure 3: Aberration and space charge effects on beam
spot size on screen.
The upper limit of the aperture and current is
determined by leading to a small change in the spot size.
From the simulation above, an aperture radius of 100 m
and a current of 10pA are chosen.
COMPARISON OF LENSES
The criterion of choosing the focusing lens is the
growth rate in beam waist spot size with respect to
thermal energy of the cathode. A large growth rate as a
function of temperature will minimize the system errors.
Results from simulation of different kinds of focusing
lenses are shown in Figure 4 and Figure 5. All curves in
both plots are simulated with same distance from anode to
lens (2cm) and from lens to screen (25.5cm) for
comparison. In both plots, the solenoid has a faster growth
rate compared to other lenses. In Figure 4, 0.5cm aperture
Einzel lens growth rate is comparable with solenoid, but
the nonlinear effect due to small aperture is significant,
and this will result large system error for spot size
measurement. The simulation also shows that the closer
the lens is to the anode and the further is the screen
location, the better is the resolution.
0.2 0.4 8.6
Tlennal Enoergy [eVI
Figure 5: Comparison of solenoid and two quadrupoles.
Solenoid is the final choice of focusing lens.
All components in the measurement setup have low
permeability. Shielding the solenoid is very important to
prevent a magnetic force on the electrons during
acceleration, which will reduce the resolution. Figure 6
shows the performance of a solenoid with and without
shielding, and compares with hard edge field.
bard edge soleojoid --
0 0.2 0.4 0.6
Thenmal Energy [eV]
Figure 6: Solenoid with different shielding.
solenoid, 989.5 69.400
eifl lmons. 2o, ap..-tur. 02002 -4--
0 8.3 1 1.5 2 P.5 9
Thiemnal Energy [eV]
1 Figure 4: Comparison of solenoid and two Einzel lenses.
magueic quadmpole -K-
soletnoid - --
- solenoid withoUt slueldig -x-
solenoid with shielding -r -
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WU,Q.; BEN-ZVI, I.; BURRILL, A.; CHANG, X.; KAYRAN, D.; RAO, T. et al. THERMAL EMITTANCE MEASUREMENT DESIGN FOR DIAMOND SECONDARY EMISSION., article, June 25, 2007; United States. (https://digital.library.unt.edu/ark:/67531/metadc897372/m1/4/: accessed April 19, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.