One way to achieve fusion in laboratory consists in heating and compressing, by using a laser, a capsule
containing a deuterium - tritium mix. Achievement of such a project can be obtained only through the development of a
new generation of laser facilities. With this end in view, CEA is developing the "Laser Mega-Joule" (LMJ), a facility
made of 240 laser lines. The "Ligne d'Intégration Laser" (LIL) is a prototype of the LMJ made of a four laser lines
assembly. Presently operational, it must permit the validation of the technological choices that have been made.
Particular attention must be given in the achievement of the alignment of the target compared with the laser
beams: it must be positioned at the center of the target chamber with a precision better than fifty micrometers rms. The
quality of this alignment must be guaranteed in order to ensure the success of the physics experiments performed on the
facility.
We are presenting the device that has been devised to reach this objective: the "Système de Visualisation de
Cible" (SYVIC) or target viewing system. This device is made of two optical visors set on the target chamber, associated
with a complicated three-dimensional reconstruction algorithm. It permits to position an object at the center of the
chamber, rapidly and with the required orientation. It also makes possible the alignment of all the plasma diagnostics,
mounted on the chamber wall in order to study the plasma created by the laser-matter interaction.
The first plasma experiment using the SYVIC alignment device took place at the beginning of 2007 with a
specific target. Doing so we qualified the accuracy of this device and its implementation on LIL.
The CEA is currently developing the "Laser Mega Joule "(LMJ), a facility capable of concentrating an extremely
high quantity of energy from 240 laser beams on a micro target for a brief moment. The characteristics of the facility
have been defined to obtain the temperature and pressure conditions required to reach thermonuclear combustion.
The "Ligne d'Intégration Laser" (LIL) is a facility designed to validate the choices adopted for the LMJ. It consists
of a basic laser line from the MJL with four identical beams.
On the LIL, an experiment consists of a series of laser/material interaction firings. For a given firing, there is a
concatenation of the phenomena from the triggering of the physical mechanisms to the recording of the signals on
the recording instruments (diagnostics). The interaction gives rise to plasma.
One sure method to enable the reconstruction of the events in the course of the experiments involves recording an
optic time fiducial signal on the main instruments. This temporary marking makes it possible to reposition in time
the signals recorded on the measuring instruments against a point of reference.
We present here a prototype that has been developed for the time fiducial of the visible streak cameras : "SYMOD :
SYstème de Marquage Optique par Diode laser".
The original architecture of the bench is based on the use of one laser diode per diagnosis to be marked. Other
components, including synchronization equipment and two chronometry arrays, are arranged around this source
which constitutes the main component of the device.
Tests have been run to validate the technical choice of the source and to demonstrate that the main time
requirements concerning the fiducial are met (rise time < 50ps and time jitter < 16ps rms).
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