1. magnetic confinement - ENEA - Fusione

5. INERTIAL CONFINEMENT 123
5.1 Introduction
For the reference period we shall report on (i) the preparation of a new experimental
campaign on laser-foam interaction that implied the assembling and testing on a new
diagnostic line, (ii) the theoretical activity for the preparation of the new experiment
and for the implementation of a new package in the code COBRAN for the treatment
of the energy deposition of the nuclear products (charged particles and neutrons),
and (iv) the design of the diode pumped amplifier.
5.2 Diagnostic Upgrading
The diagnostic package shown in figure 5.1 was assembled for measurements of light
transmission through the target during the laser irradiation.
After the transmitted light conversion to 2ω the target is imaged on a camera and on
the photodiode phd2ω by the lenses 2 and 3. The photodiode phdω is used to register
the waveform of the incident laser beam. A mask was placed on the phd2ω image to
select the probed area where transmission will be measured (typically smaller than
the laser focal area, see figure 5.2).
5.3 Theory
5.3.1 Interaction of laser beams with multi-foil plastic structures
In the following we report on the 2D simulations performed with the lagrangian
code COBRAN to study the evolution of structured plastic targets irradiated by laser
beams1. The method used was to start with the simplest material assemblies to begin
a computational study of the interaction of laser beams with large pore foams.
We began with simulations relative to the irradiation of single thin foils, to frame the
Polarizers
Target
Lens 1 Lens 2
Polarizers
Beam A
phd
Array of 256
lenses
Camera
/4 plates
stop
SHG
Infrared absorber
Lens 3
Beam
splitter
phd2
Filter
Dump
Target images
Fig. 5.1 - Package for the measurement of the transmitted light and for target
imaging in transmitted light. The photodiode phdω is used to register the
waveform of the incident laser beam. After the transmitted light is converted
to 2 ω, the target is imaged on a camera and on the photodiode phd2ω by the
lenses 2 and 3. A mask is placed on the phd2ω image to select the probed area
where transmission is measured (typically smaller than the laser focal area). The
transmission coefficient is deduced by normalization with shots without target
(anything else unchanged) and taking in to account the dependence on intensity
of the conversion to 2ω. Since the bandwidth of the waveforms registering
system is 6 GHz, the method allows time-resolved measurements within the
laser waveforms.