Hypervelocity Loading Technology And Its Application To Ultrafast X-ray Diffraction Experiments

The two-stage gas gun is widely used in the hypervelocity launching field,and it is an important device for the study of dynamic materials properties under ultrahigh strain rate loading.The dynamic response of materials requires in situ,real-time,high spatial and temporal resolutions in measurements.Third generation synchrotrons offer opportunities to overcome such difficulties.Thus,it is highly desirable to combine a two-stage gas gun with synchrotron x-ray diagnostics.Here a mini two-stage gas gun is developed with helium as driving gas at the Advanced Photon Source(Argonne National Laboratory,IL)Ballistic simulation of two-stage light gas gun is performed through theoretical calculation and finite element modelling.The relation between piston,projectile and reservoir pressure,and pressure variations within two different chambers are explored and serve as the basis for the overall design.Considering experimental requirements,the final design parameters are determinedThe design of the two-stage gas gun is based on the gas gun theory and the finite element simulation results,including launch structure,gun structure and auxiliary system.The piston in the launch structure is sealed by itself and controlled by a solenoid valve.The gun structure consists of a pump tube,a conical high-pressure section,a launch tube and a sample chamber The simulation analysis on primary parts of the two-stage gas gun is conducted and the simulation results satisfy experimental requirements.In order to increase the reciprocal space covered by a small-area detector,a conventional target chamber is split into two chambers The distance between a diffraction detector and the sample under impact is about 80-100 mm,the diffraction angle(20)is up to 30°.A hypervelocity launch system is built at the APS based on the developed two-stage gas gun.And the two-stage gas gun impact is synchronized with synchrotron x-ray pulses and high-speed cameras.The experiments are performed on single-crystal magnesium.According to the analysis of two-dimensional x-ray diffraction patterns for single-crystal magnesium,extension twinning occurs upon shock compression along(1010)and(1120),but only upon release for loading along(0001).