Radiation Characteristics And Implosion Dynamics Of Tungsten Wire Array Z-Pinches And Dynamic Hohlraums

Store energy in pulsed power generators can be efficiently converted into X rays through high current Z-pinches,which are widely applied in inertional confinement(ICF)fusion and high energy density plasma physics.Wire array driven dynamic hohlraum based on fast pulses is regarded as one of promising approaches for X-ray indirect-drive ICF.Fusion ignition and high yield can in principle be achieved using enoughly intense X rays,which require that the pulsed power system can generate significantly high curren.On the other hand,the complexity of Z-pinches limited the understanding of corresponding fusion conditions.Therefore,the overarching goal of the Z-pinch driven ICF research is to develop predictive theorectical models and numerical simulations,by advancing the understanding of dynamic hohlraum and fusion conditions,to establish the reliable physical scaling law and to maximize the fusion gains and yields with the smallest possible pulsed-power driver.In the above context,this thesis provide a detailed description of the experiments conducted on high current facility,a self-developed high current pulsed power driver,using tungsten wire array Z-pinches and dynamic hohlraums with varied load configurations.A specific set of data provided by various high space-and time-resolved diagnostics,along with theorectical model calculations and analysis,are used to investigate the implosion dynamics and radiation characteristics of wire array Z-pinches and dynamic hohlraums,the shock formation and propagation,the radiation temperature and the optimization of hohlraum performance.Through researches on these key physics questions,we expect to advance the understanding of the basic physical discipline for wire array Z-pinches and dynamic hohlraum under specific pulsed power drive conditions,and to provide a basis for subsequent radiation-drive capsule implosion experiments and relative radiation source applications.The main works of this dissertation are as follows.1.We provided a detailed description of several phenomenological Z-pinch models,including the 0D Thin-shell model,the TheVenin equivalent circuit model and the ablation snowplow model.We also developed a set of calculation methodes and codes for a specific pulsed power facility.0D thinsell model was used to predict the stagnation time of wire arrays for known dive currents and load parameters.TheVenin equivalent circuit model,which consistently reproduced the array implosion and the circuit response of the driver,was used to investigate the driver-load coupling properties.Calculations within wide load parameters showed the dependancy and trendency of load currents and macro dynamic properites such as implosion time,velocities and kinetic energies on the load parameters.The ablation-snowplow model was utilized to fit the experimental implosion tajectories,which provided an investigation into effects of the wire ablation and traling mass on implosions.These models guided the load design on high current facility,and also presented useful methodes to analyze the experimental data and to understand the physics of wire array implosion.2.Multiple diagnostics for wire array Z pinches and dynamic hohlraum have been developed on high current facility,to provide high time and space resolved images of implosion and shock and quantitative or qualitative X-ray pulse radiation parameters.These diagnostics can reliablely operate in the high electromagnetic interference,intense radiation background,and strong shock envirement,with ns-time-resolution correlation and synchronization,thus a single shot can produce diverse measuremental data such as X-ray power waves,total radiation energy,and high resolution implosion images.New and innovative calibration methodes and data analysis procedures of those core diagnostics have been developed,enabling absolute measurement of the X-ray energy and power.Multiple analysis procedures were also used for extraction of the imploding plasma trajectories,velocities,pinched radius,instability perturbation amplitude,shock trajectories and velocities,and hohlraum temperature and its profile from various measured images.These diagnostics provided an abundance of quantitative or qualitative data for investigation of wire array and hohlraum implosion dynamics and radiation characteristics,and for analysis of shock formation and propagation,along with establishment of the corresponding physical pictures.(3)The implosion dynamics and radiation characteristics of wire arrays with drive current of 6-8 MA and implosion time of 80-130 ns systematically have been demonstrated on High-Current facility.It is shown that the implosion time can be well controlled by design of initial wire array mass and radius.Under above drive conditions,output current and its risetime increased as implosion time,the quality of pinched plasma along with X-ray power and energy trended to decrease with implosion time.The measured implosion times and load currents were consistent with the theoretical model calculation.Analysis of experimental data along with the driver circuit indicated the optimal implosion time were about 80-90 ns,which correspond with the linear load mass of 0.64?1.25 mg/cm.Peak X-ray power of 50 TW with total energy of 500 kJ was obtained from single arrays.Experiments demonstrated that nested array indeed improve the radial compression and uniformity of implosions,along with better stability.Peak power of 80 TW were obtained from nested arrays while the total radiation energy were comparable with that of single array.Experimental results showed that the trajectories of imploding wire array plasmas deviated from the 0D Thin-shell calculations,which also indicated that the wire array implosion on High-Current facility were dominated by wire ablation.For 10-mm radius wire arrays,the ablation phase corresponded with aboutTwo thirds of the experimentally measured implosion time,this feature can be taken as a peculiarity of high current facility wire array implosion and distinguished the High-Current facility from other pulsed power drivers.These experiments not only validated the drive level of High-Current facility and its capability of producing radiation,but also enriched the measuremental data and understanding of wire array implosion at the specific drive conditon of 6-8 MA and 80-130 ns implosion time.4.Dynamic hohlraums have been firstly domanstrated on High-Current facility,utilizing the impact of the tungsten wire array on low density foam.Systematically experimental study on the formation and properties of dynamic hohlraums with varied setup parameters of arrays and foam converters has been conducted on High-Current facility.The outer array implosion,interaction of outer and inner array,strike of plasmas on foam,stagnation of plasmas and the primary features of the radial and axial radiation pulses were observed and investigated.We also analyzed the shock propagation,the formation and evolution of the hohlraum radiation field.Experimental results displayed well controlled driver performance and reproducible implosion measurements.It demonstrated the improved stability of imploding plasma,uniformity and synchronization of impact onto foam along with hohlraum performance by using nested arrays to drive dynamic hohlraums.Typical shock duration of 5-8 ns,shock velocites of 200-300 km/s,and radiation temperature up to 120 eV were obtained on High-Current facility.Improved drive currents and plasma implosion quality and radiation temperatures have also been demonstrated by optimization of the load height and the configuration of feed electrodes,which increased the energy coupling in unit length of dynamic hohlraum.These above researches enriched the experimental data of dynamic hohlraum with 6-8 MA current level,and advance the understanding of the drive-target coupling and underlying physical disciplines of dynamic hohlraums,which are useful to develop corresponding simulation capability,and to establish the current scaling of the radiation performance in dynamic hohlraums.