Research On Magnetically Driven Isentropic Compression And Flyer Plates

The technique of magnetically driven isentropic compression and high-velocity flyer plates is a new experimental one for studying dynamics of materials developed abroad in nearly six or seven years,by which the quick(0.1～1.0μs)and ramp loading on materials with high pressure(10~2～10~3 GPa,"isentropic compression")can be attained,the macroscopic and complete flyer plates with super-velocity can be obtained,and the experimental domains of shock dynamics are extended largely.This technique can be used to study the dynamic behaviours of materials under isentropic and shock compression,and a new method or tool used to study high energy density physics is established.It is very important to develop the technique,which is an important tool used to determine the off-H(u|¨)goniot properties and study complete equation of state of materials for superhigh pressure,and which is with importantly practical significance and application prospects for the high energy density and nuclear weapon physics.The key technology of this new experimental tool is the technique of magnetic pressure loading(or magnetically driven technique),which is also the main aim of this paper in choosing topics.The principle,path and innovational design of magnetically driven loading technique are researched,and the experiments of magnetically driven isentropic compression and high velocity flyer plates for materials are done by designing and establishing an apparatus with 50GPa loading ability.Based on these,the advanced experimental technique is certified and mastered,and the firm foundations are established for future developments and applicationsThe contents of this paper are to surround the design and experiments of an apparatus for magneticallt driven isentropic compression and flyer plates under the pressure of 50 GPa,to solve the related design principle,key technologies,measurement technologies,insulation technology of high voltage and some theoretical questions,to provide an expeimental platform for studying the dynamic behaviours of materials under isentropic and shock compression and complete equations of states,and to establish and accumulate technology foundations and experiences for developing the experimental techniques of magnetically driven isentropic compression to higher pressure(50GPaμ℃100GPa)and higher velocity flyer plates on next stage.The main contents of this paper are composed of six chapters below:(1)Searching and analyzing the related references at home and abroad.(2)Fundamental theories of design of magnetically driven isentropic compression and flyer plates.(3)One-dimensional magnetohydrodynamic simulation of magnetically driven isentropic compression and flyer plates.(4)Design and establishment of expeimental apparatus for magnetically driven isentropic compression and flyer plates.(5)Analyses of discharging current pulse shaping techniques(6)Experimental study on magnetically driven isentropic compression and flyer plates in principle.The main results of this paper are:1.Magnetically Driven Loading Technique and Apparatus(1)By means of the circuit simulation software of OrCAD/Pspice,the whole design of magnetically driven experimental apparatus is carried out with parameters of rise time about 500ns and peaking current nearly 1.5 MA,and the parameter values of discharging circuit and key parts of the apparatus are determined.The results show that the whole storage energy ia 30～50kJ,and that the whole inductance is no more than 18nH,and that the charging voltage is 65～80kV.For the apparatus with single closing switch,it is composed of four capacitors in parallel,which can produced about 50GPa isentropic compression wave on the surface of the samples and accelerate Aluminum flyer plates to about 7km/s.(2)An explosive logic network closing switch with multi discharging channels is developed, which is with low inductance(about 4.5nH)and about 55ns synchronization,and can bear high voltage and large current,and is flat plate and easily connected with parallel-plate transmission lines.This switch can satisfy the requirements of the apparatus designed,and there are no other switches can get to them at home.And a physical model of this switch is put forward.With the function of analyzing static electromagnetic field of ANSYS software,quantitative relationship between the inductance and the discharging channels of the switch,and an optimal design thought is presented.(3)The magnetically experimental apparatuses CQ-0.6 with single capacitor and CQ-1.5 with four capacitors in parallel are designed and established.For CQ-0.6,a single detonator closing switch is used,and its rise time of discharging current is 400～450ns and peaking value about 0.65MA.With this apparatus,the insulation and safety problems under high voltage and discharging current measurement are solved.CQ-0.6 can be used to accelerate flyer plates to less than 4 km/s and produced nearly 10GPa loading pressure for isentropic compression experiments.For CQ-1.5,an explosive logic network closing switch with four discharging channels is used,and its rise time of discharging current is about 500ns and peaking value nearly 1.5MA.CQ-1.5 can be used to accelerate flyer plates to about 7 km/s and produced about 50GPa loading pressure for isentropic compression experiments.2.Magnetically Driven Isentropic Compression and Flyer Plates Experiments(4)With CQ-0.6 and CQ-1.5,the experiments of magnetically driven isentropic compression and flyer plates in principle are done.The results of isentropic compression experiments in CQ-1.5 show that the velocity curves of free surface of samples with different thickness are different for the same loading pressure,the sample more thicker and the velocity curve more steeper,which is agreement with the propagation property of compression waves inside the copper samples.The experimental compression isentropes below 35GPa are consistent with the theoretical one and shock Hugoniot,and the results of several shots are repeatable.The experimental error is less than 3%compared with the theoretical isentrope and shock Hugoniot.(5)The results of magnetically driven flyer plates in CQ-0.6 and CQ-1.5 show that the velocity histories of the flyer plates can reflect the process of magnetically driven flyer plates,and the macro metallic flyer plates with velocity more than 6.26km/s is attained.(6)The experimental results show that the apparatuses CQ-0.6 and CQ-1.5 can be used to do magnetically driven isentropic compression and flyer plate experiments.3.Theoretical Researches Related with Magnetically Driven Isentropic Compression and Flyer Plates(7)Based on the Gr(u|¨)eisen equation of state,the linear relationship between shock wave velocity U_S and particle velocity u_p and SESAME equation of state database,the isentropes,Lagrange sound velocity and temperature rise of copper and Aluminum under 150GPa are calculated with analytic theory.By means of multi-shock compression approximating single isentropic compression process and the calculation formula of temperature under shock compression,the temperature produced during the process of nearly isentropic compression loading,and further the entropy gain of nearly isentropic compression is discussed.The results can be used to determine the isentopic extent and predict the ideally loading pressure waveforms.(8)The design guide rules of samples are discussed and presented.A physical model is put forward which can approximately calculate the velocity of magnetically driven flyer paltes in the condition of the flyer plates without highly accumulated internal energy.(9)Based on the Lagrangian coordinates,equations of magnetohydrodynamics,resistivity equation,SESAME equation of state and magnetic diffusion theory,One-dimensional magnetohydrodynamic simulation of magnetically driven isentropic compression and flyer plates is done.The experimental and computed results from references are used to certify the feasibility of the programme.With this programme,the density and temperature profiles of Aluminum flyer plates at different times,the varying relationships between magnetic diffusion ratio and loading current density are obtained for magnetically driven flyer plates,and the density,pressure and particle velocity profiles and varying relationships with time of copper samples are also gained for magnetically driven isentropic compression.The threshold of forming shock inside copper samples is determined.These results redound to recognize the properties of samples and flyer plates during the process of magnetically driven isentropic compression and flyer plates,and provide basis to deisgn the samples and flyer plates.The resistivity equation chosed in this programme can be used before vaporization point.After that,it is necessary to choose an universal resistivity equation.(10)It is significant to shape the discharging current waveform of experimental apparatus. The proper discharging current waveform can delay shock forming inside the samples and increase the thickness of the samples,and can improve the experimental measuring precision and increase the amplitude of isentropic compression wave and the velocity of the flyer plates.At first,the ideally loading waveform is determined in theory,which rises slowly at original stage,concaves up in the middle part and rises fast at last stage.With OrCAD/Pspice software and a simple hydrodynamic code,the shaping modes are studied. The results show that the optimal shaping mode is the combination of programmed discharging and double peaking capacitors for this compact pulsed power experimental apparatus.The research contents of this paper are novel and first presented at home,the main innovations are:(1)An experimental platform("CQ-1.5")of magnetically driven isentropic compression and flyer plates is designed and developed with about 500ns rise time and 1.5MA peak current. By means of the software of circuit analysis,the method of realizing current pulse shaping is discussed well.(2)An explosive logic network closing switch with multi discharging channels is developed, which is with low inductance and can transfer large quantity of electric charge.A physical model used to analyze the electromagnetics properties is put forward,and the quantitative conclusions are gained.(3)Based on energy conservation principle,A model is put forward for approximately calculating the velocity of magnetically driven flyer plates,which is agreement with the experimental result in the wide range of current values.(4)With CQ-1.5,Very good experimental results are obtained by improving the experimental technologies:the experimental compression isentropes below 35GPa in Copper samples are consistent with the theoretical isentrope and the repeatability is good.The experimental error is less than 3%.A velocity of more than 6km/s is attained for magnetically driven Aluminum flyer plates.