Synchrotron-based high-pressure research in materials science Page: 3 of 5
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2. Preliminary 1D Simulations.
A preliminary study was carried out with a one-dimensional PIC to explore the physics within the
beam path. It was desired to assess the distribution of the longitudinal voltage drop in the beam and
to observe if the converging beam could give rise to significant space-charge deneutralization. The
simplified model was done in a spherical geometry. It consisted of 2 concentric shells, with the radius
of the outer one equal to the radius of curvature of the converter electrode. The gap between the
shells was set equal to the distance between the converter and the exit aperture (- 7 cm). The gap
was filled with a constant H' particle density. The inner sphere acted as a perfectly absorbing
boundary, while the outer shell produced N and a whenever it was struck by an incoming H*. The
conversion efficiencies for K and e- were YH = 0.7 and ye = 1 respectively. When an H' was
absorbed by either boundary, it was regenerated within the volume with a simulated e impact
ionization. The results obtained for a low plasma density of 3 1014m3 are shown in Figure 2.
x 105 Plasma hydrogen phase space x Plasma electrons phase space
3 5
-2
1 r' a1 7
0
I
-1 - - - - - - 5- --- - - -- - - --
0.06 0.07 0.08 0.09 0.1 0.11 0.12 0.06 0.07 0.08 0.09 0.1 0.11 012
R (m) R (m)
x 10 Negafve hydrogen phase space x 10 Converter electrons phase space
0 . . .-0 ,
-0.5 2
1 2 -8
~LO
-2.5 - -1 j 10k.....-- ____-
-3 ' - - - -12
0.06 0.07 0.08 0.09 0.1 0.11 0.12 0.06 0.07 0.08 0.09 0.1 0.11 0.12
R (m) R (m)
Figure 2. Phase space of the particle species modelled with the 1D code. nH' = 3.1 o"m3.
The nH' - 3 104m"3 choice for these simulations was because at higher nH', the N and e
currents from the outer shell would cause significant heating of the plasma e-. This occurred because
the model did not include dissipative processes (i.e.: collisions with neutral particles). Nevertheless,
the ID simulations indicated the presence of a large sheath region surrounding the converter. This
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Synchrotron-based high-pressure research in materials science, article, Date Unknown; [Los Alamos, New Mexico]. (https://digital.library.unt.edu/ark:/67531/metadc929370/m1/3/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.