Hydrodynamic Process In Double-cone Ignition Scheme

In traditional inertial confinement fusion（ICF）,direct drive and indirect drive are two main methods.Professor Zhang proposed the double-cone ignition（DCI）which has combined the direct drive and the fast-ignition scheme,compress the fuel shells in symmetrically arranged golden cones to make them ejected out of the cones and collide with each other,then use the heating laser to increase the temperature,reduce the implosion symmetry requirements by separating the compression and heating process.This paper first introduced a model combines analytic calculations and one-dimensional simulations to estimate the Rayleigh-Taylor instability（RTI）growth.The result shows that in the later stage of the compression in cone,the out surface of the shell began to decelerate and expand,and we found the most dangerous time and perturbation modes in flight,then give some advices that could optimize the scheme.In experiment,we utilized a set of diagnose which was composed by a Kirkpatric-Baze microscope and a x-ray framing camera（KB-XFC）to observed the signal in stagnation process from double-cone ignition experiment,and calculate the temperature profile in collision areas.We also used the Ti-backlighter targets to get the back light images of ejective plasma from the cone,and get the information of their shapes and areal densities,which can help us to estimate the real compression performance in cones.The first part is introduction,the background and basic theory of ICF have been presented,along with the progress and difficulties in traditional central ignition schemes.Then is the explanation of the core concept in double-cone ignition scheme,that is using the collision and heating laser to improve the density and temperature of fuel assembly,and in this manner to separate compression process and ignition process,reduce the influence from implosion asymmetry.At the end of this part,the importance of the study in RTI growth and the significance of the observations on stagnation process have been clarified.In the second part,the author analyses the RTI growth rate when the shells are compressed in cones.Because the golden cones obstruct the detective path,it is hard to directly measure the hydrodynamic instabilities in cones,a quantitative theoretical model would help us to predict the integrality of the target and benefits the improvement of laser-target design.The author has considered the shock wave stacking influences on the adiabat of the shell,the ablation velocity changes caused by the compression of the shells in cone,and used the analytical formula of linear and weak nonlinear ARTI growth.Finally,the out-surface perturbation amplitudes at the end of the laser duration have been gotten,and one-dimensional simulation result have been used to verified the evolution of the critical physical quantities.The analytical model shows that the fuel experiences low adiabat compression under design parameters,and at the end of the acceleration phase,the shell thickness raised again because of the confinement of the golden cone,this could benefit to maintain the integrity of the shell.For 14 nm initial root mean square perturbation amplitude,the most dangerous moment is at 4 ns,the ratio between perturbation amplitudes and shell thickness reaches about 0.3,the shell is at risk of breaking.The third part shows the self-emission signals observed by KB-XFC in experiment,its intensity reflects the density and temperature information in the stagnated plasma,and according to the time evolution of the collided plasma signals which is detected by framing camera,we know that the duration of stagnation is about 800 ps,the Gaus-sian fitting gives 300 ps full width at half maximum.The plasma is ellipsoid,flattened over time,with 130μm diameters of the 17%maximum intensity contour of the self-emission area at the peak compression time on lateral direction,and 105μm on vertical direction,the Legendre polynomial modes analysis gives₂/₀≈17%.By using the two energy channels KB microscope and the density profile from Cu-Kdiagnosis,the temperature profile of plasma can be calculated by Abel inversion algorithms.The electron temperature within radius 65μm remains between 450⁵00 e V,this radius corresponding to the main self-emission area,and also close to the size of high-density regions.At outer locations,temperature and density rapidly decreases and the self-emission signals gradually disappears.In the next part,the author has extended the former works.The calculation method of the RTI growth has been improved,the perturbation growth under different wave-forms and targets in experiment has been compared,and we found that the waveform with pre-pulses could significantly reduce the Rayleigh-Taylor instability growth.Fast Fourier analysis of the laser spot overlap inhomogeneity has been performed,then cal-culate the RTI growth caused by the laser imprint,found that the overall RTI growths could be fast and the long wavelength modes are dominant.In the Ti-backlighter single cone target experiments,the plasma ejected out of the cone has been observed,with the analysis of its area density,we believe that the shell had broken in the cone which caused the dramatically drops in area density.The final part is the conclusion of the whole works in this article,and several im-provement advices have been proposed for the future double-cone ignition scheme.