Technical Design Report Super Fragment Separator

DRAFT
per 50 ns impinged on a 7 cm thick liquid Li target. The beam spot was assumed to be Gaussian
with σx = σy = 1 mm. In the present 2-dimensional calculation the high power density deposited in
a column of liquid Li is predicted to lead to a fast vaporization of the Li contained in the volume
traversed by the beam and to a shock wave that travels orthogonal to the beam direction.
The finite velocity of sound in Li makes sure that during the interaction the target density is unchanged,
so that the probability of producing a fragment and its kinematical properties are unchanged.
Typical parameters of Li in the beam trajectory according to the BIG-2 calculation are a
temperature of 13,000 K, a pressure of 14 GPa, and an energy density of 42 kJ/g, see Figure 2.4.124
(left).
Figure 2.4.124: Calculated density of lithium - left: after the beam passage (after 50 ns) - right: 1µs after the
passage of beam. Along the beam trajectory the vaporized Li explodes, violet regions in the figure. Orthogonal
to the beam direction the shock front moves and within 1µs will travel by about 8 mm. For several
positions in the Li jet, the values of temperature (T), pressure (P) and energy density (E) are also given in the
plots.
The BIG-2 calculation predicts that the vaporized Li will explode in (positive and negative) beam
direction with velocities of about 10 km/s, with the central density being reduced rapidly (Figure
2.4.124, right). Orthogonal to the beam direction, temperature and density are not much higher than
normal, but a pressure wave travels outward with an initial velocity of about 1.5 km/s. After 1 µs
the shock front has moved by about 8 mm.
The above conditions are, obviously, not suitable for a fragmentation target. They were just used as
a benchmark to check if 3-dimensional hydro-dynamical calculations of the behaviour of the Li jet
yield similar results, i.e. if the less time-consuming 2-dimensional calculations are realistic enough
to use them to find suitable operating conditions for an actual Li-jet target. First 3-dimensional
calculations were performed at LLNL, Livermore, USA, using the code ALE3D [79].ALE3D is a
three-dimensional finite-element code that utilizes Arbitrary Lagrangian-Eulerian techniques to
simulate fluid dynamics and elastic-plastic response on an unstructured mesh. The code has a range
of equation-of-states and constitutive descriptions that are appropriate for modelling hydrodynamic
shock phenomena. The ALE3D numerical results for the scenario described above are very
similar to the results from BIG-2.
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