Search

Le projet Laser MegaJoule (LMJ) [1] initie en 1995 par le Commissariat a l’Energie Atomique a comme objectif d’etudier la fusion par confinement inertiel C’est un laser a verre dope au Neodyme et triple en frequence capable d’irradier avec 240 faisceaux des cibles a un niveau de 1.8 MJ / 500 TW a la longueur d’onde de 351 nm. La Ligne d’Integration Laser (LIL) est le prototype a l’echelle 1 d’une chaine du LMJ ; elle est constituee de 8 faisceaux regroupes par paquets de 4. Pendant les campagnes de qualification, une puissance de 2 TW et une energie de 9.5 kJ ont ete obtenus sur un seul faisceau, et la tache focale d’un quadruplet sur cible a ete completement caracterisee[2].

Following LIL single beamline commissioning in 2003, where performance in terms of power and energy required for LMJ was demonstrated, we spent year 2004 to qualify the quadruplet (or quad) performance at 1ω/3ω. Over that year, the first quad high power and high energy laser experiments took place on LIL facility. A careful set of test campaigns were conducted to safely ramp up laser performance. The main goal was to measure quad-specific features such as beam synchronization and focal spot (size, smoothing contrast ratio or irradiation nonuniformity σ rms ) versus the LMJ requirements. LIL Quad beam waist was recorded for various pulse durations, smoothing techniques and for a wide range of laser intensities up to LMJ-nominal ones. Now, LIL quad has been commissioned to the center of the target chamber and the first plasma experiments are made.

The Laser MegaJoule (LMJ) under construction at CESTA, a CEA laboratory located near Bordeaux, is designed to produce 240 beams, 1.8 MJ, 500 TW of ultraviolet light for high energy density physics experiments and thermonuclear burn of DT targets. The first step of LMJ program consisted in the construction of a full scale prototype the "Ligne d'Integration Laser" (LIL) which was developed to demonstrate LMJ performances and qualify all its components and systems as well as maintenance procedures. Commissioned in 2002, LIL facility mainly includes a laser bay which houses a bundle of 8 beamlines similar to the LMJ ones and a target bay where are located the 1ω-3ω conversion system, the focusing gratings and the 4.4-meter diameter target chamber equipped with plasma diagnostics. This paper describes the LIL facility as a tool for laser-matter interaction pointing out the laser system.

The LIL which is under construction at the French Atomic Energy Commission CESTA center is an 8 beam facility -- 60 kJ @ 0.35 μm -- dedicated to laser matter interaction experiments. This facility is now in the last construction phase and the first experiments have already been conducted in order to demonstrate the performances of both front end and multipath high energy section at 1.05 μm. The experiments that were recently conducted have demonstrated the efficiency of the 4 pass and L-turn amplification concept, and already show that the expected output intensity performance at 1w has been reached. Moreover, these experiments have confirmed the capability of our laser simulation code (Miro) to predict this laser output performance. We are currently implementing the 1w/3w conversion and focusing system, which combines for each beam a large 1w grating associated with KDP/DKDP frequency doubler and tripler and a large 3w (0.35 μm) focusing grating. Focal spot size will be available in the 0.5 to 4 mm range with either a circular or elliptical spatial profile. LIL will also support the beam smoothing capability (longitudinal or transverse). The 1w section is currently under tests at the kJ level, and 3w tests will be performed very soon. The LIL prototype facility is the first step of the French Atomic Energy Commission program toward the construction of the 240 beam Laser Megajoule (LMJ) facility which will enable us to conduct high energy density experimental program in the 640 TW @ 2 MJ range before the end of this decade.