1. magnetic confinement - ENEA - Fusione

5. INERTIAL CONFINEMENT 125
5.3 Theory
density and laser rays are displayed. About 10 ps later the light is transmitted.
In the picture at left in figure 5.4 the density r is represented as function of the space
coordinates. The map in the center is the density as function of the calculation grid
indexes. At right is shown a detail of rays propagation, with different colors for
different incidence angle.
The situation near t s
is represented in figure 5.5. Rays are refracted in a sort of ring
as seen in the map at top of figure 5.5. In the same figure are also represented the
quantities Z k T e
(where Z is the average ion charge and T e
the electronic
temperature) and the average ion kinetic energy in the flow (that is 1/2 m i
n 2 , where
n is the flow velocity and m i
the ionic mass). Both are measured in °K. Kinetic energy
prevails only in a thin, dense layer destined to splash on the next one in a multi foil
target. From this follows that the flow energy is partially dissipated in a shock wave
driven in the next layer.
The last map shows the distribution of the flow velocity (U z is the component along
z, the positive axis pointing towards the laser).
The process of layer collision was produced in simulations for the interaction of a
three layer target with a light beam focused in such a way to initially reproduce, at the
first exposed surface, the conditions at surface of case 3.
Fig. 5.3 - Fraction of
absorbed light as function
of time for a single foil. A
fast drop in absorption
occurs when the target
becomes transparent.
At the time 0.65 ns the irradiated foil
impinges on the second foil. In figure
5.6 is shown the map of the velocity
along z at this time. Typical negative
velocity is about 2 (in units of 10 7
cm/s). In figure 5.7 is shown the
density map at the same time. The
propagation of the shock wave in the
second foil is clearly seen by the
representation of density in terms of
grid indexes.
-6 -5 -4 -3 -2 -1 0
Logr(g/cc)
Fig. 5.4 – Left: density (r) map 10 ps before light starts to be transmitted
through the target. Center: the figure is a representation of the density as
function of the grid coordinates. Details of ray propagation are shown in the
figure at right.