Application Of Thermal Wave Theory In Indirect-drive Laser Fusion

A laser delivers energy to the interior of a high Z hohlraum and is converted toX-rays in laser indirect-drive confinement fusion experiments. Thermal wave describethe ablative drive of target implosion by X-rays. Also radiation confinement inhohlraum targets is controlled by thermal wave, diffusing energy into the containingwall. Here we study on the interaction of thermal wave with high Z and low Z materialto find ways of improving capsule coupling efficiency, which is very important forinertial confinement fusion. The main research work and results are listed as follows:1. A self-similar solution of the radiation diffusion equation is admitted forradiation ablative heat wave. In this thesis we get the solution by dimensional analysis.The scaling relations of ablated mass and ablative pressure with time are given.Comparisons with numerical simulations and the work before show excellentagreement.2. Most of the X-rays energy is absorbed by hohlraum wall because of rarefactiondiffusion when thermal wave propagates. We find low density foam wall could restrainrarwith Hy akdre.s T choed es iimn urlaadtiivatei orens tuelmts psehroawtu rteh iTsr d=e n2s5it0y epVro cfilollne srad isdtaiiovanel. d~eT3nh0se%ity re i endm itshtribution toρ0(erf)a c=tion diffusion. Then we adjust initial hohlraum waite r awtiaoll rliosesssand capsule coupling efficiency can be improved by graded wall density profiles. Laserheat foam wall is also simulated with Multi code. The results show that the movementof laser absorption position is tamped in foam wall conditions, which is another way forsymmetric controlling.3. We present one dimensional (1D) plane radiation ablating characters of Be, CHand BC in this thesis. And the yields of capsule with three materials as ablator arecompared by1D spherical implosion simulation. Considering of energy couplingefficiency, preheat and symmetry, Be is the best. BC is not chosen because of the highalbedo. Non-Planckian frequency dependent radiation ablates low Z1D plane materialis calculated to compare with Planckian radiation. The results show the high frequencyof M-band increases the ablation pressure and mass ablation velocity, reduces thealbedo, and improves the temperature before thermal wave. The material is preheated, that is detrimental to nearly isentropic compress. A strong pressure increase is producedwhen x ray heated foam-solid target due to impedance mismatch at the foam-solidinterface. We evaluate the shock pressure amplified as a function of the density andadiabatic exponent based on strong wave assumption, and point out that the amplifiedpressure is a short high pressure pulse.4. The shock waves driven by thermal wave make fuel shell moving. We discussthe shell movement stage of acceleration, deceleration and stagnation with time, and theeffects of shock timing on implosion. We can conclude that a timing precision of50psis enough for ignition. Also the shock merger position is very important. The influenceto implosion of offsetting to DT ice is worse than to DT gas.