Research On Laser Fusion Energy Driver Concept And Core Technology Exploration

Laser fusion energy research is the scientific frontier in the exploration and exploitation of new energy sources, which can totally get rid of energy shortages and develop safe, carbon-free, sustainable and ideal energy sources. To meet the high efficient, repetition rate operation requirement for the laser driver in the fusion energy application, the high energy, high average power diode-pumped solid-state lasers have gained more and more interest, and been expected to be a promising candidate for the driver of future commercial laser fusion power plant. However, amplified spontaneous emission and thermal effects in the amplifier which is the core element of the driver, and the design of the amplification configuration are still the critical challenges that encountered in the increase of energy conversion efficiency and repetition rate of the facility. Therefore, in this dissertation, based on the diode end-pumped multislab amplifier, research on the concept of the laser fusion driver are carried out in term of amplified spontaneous emission, thermal effects and the design of the amplification configuration.A three-dimensional numerical model for the optimization of energy storage, heat deposition and amplification processes in multislab laser amplifiers is firstly presented to analyze the impact of amplified spontaneous emission, based on the theory of quasi-three-level Yb3+ions and Cr4+:YAG saturable absorption, the Monte Carlo and ray-tracing methods. And then, two novel multislab amplifier architectures, namely the gradient doped amplifier and the interlayer-doped amplifier, are proposed to suppress amplified spontaneous emission and prevent unwanted parasitic oscillations. Improved lasing characteristics in the above two amplifiers are obtained with respect to gain medium volume requirement, energy storage capacity, heat distribution and output energy.For exploring the influence of thermal effects on the laser system performance, thermal effects and thermal management technique in the multislab amplifier are then investigated. According to the theory of thermal effects and the conjugate heat transfer between fluids and solids, two 3D models are built to optimize the cooling parameters to remove the waste heat efficiently and minimize the influence of thermal effects, which are a thermodynamic finite element model with homogeneous cooling condition and a thermo-hydro-mechanical coupled one with cryogenic helium flow forced cooling, respectively. The optimization parameters are determined which include the helium temperature, heat transfer coefficient, pressure and velocity. Additionally, thermally induced birefringence effect in the amplifier chain is compensated via the 90° rotator and the multi-layer Cr4+:YAG technique.In the end the concept of the laser fusion driver is investigated in regard to the amplifier element and the amplification configuration based on the limited conditions of the system design. The scalability of the multislab amplifier is discussed. The energy flow characteristics of LIFE architecture are compared with the bidirectional amplifying architecture with twin pulses, and the maximum output capability of the latter is analyzed. The results presented here illustrate that a substantially high extraction efficiency can be obtained for the bidirectional amplifying architecture with twin pulses while keeping the laser operation fluence at a low level, thus reducing the damage problems and the effects of nonlinear phase shift, and relaxing the requirement of the preamplifier, which is beneficial to system reliability and stability.