Compact Pulsed Intense Magnetic Field Generator For Laser Plasma Experiments And Its Application

In recent years,the phenomenon of magnetized high energy density plasma in the laboratory has aroused widespread interest in academia.It has important application value in many research fields,such as astrophysics and space physics,inertial confinement fusion and laser acceleration.The mechanism of formation and collimation of high-speed jets in a magnetized disk during stellar evolution,the acceleration mechanism of high-energy particles in a magnetized interstellar medium,the reconnection of magnetic fields in the sun and the Earth's magnetosphere,various fluctuations in the Earth's magnetosphere,and magnetic fluids unstable structures and so on have always been very active research directions in astrophysics and space physics.The experimental study of magnetized laser plasma can help to understand these astrophysics and space physics phenomena.In the laser-driven inertial confinement fusion,the external magnetic field can suppress the radial heat conduction of the implosion target,thereby increasing the ion temperature and the neutron yield;the external magnetic field is expected to replace the indirect driving of the inflation chamber,suppressing the plasma expansion of the chamber wall while suppressing Laser stimulated scattering.In laser acceleration,the external magnetic field can stabilize the electron acceleration channel and improve the electron acceleration effect.Recently,the international academic community has begun to pay attention to the experimental study of magnetized laser plasma with strong magnetic fields.Pulsed strong magnetic Held devices are the key equipments for magnetized laser plasma experiments,but the development of pulsed magnetic field devices for laser plasma is still immature.It is necessary to develop suitable pulsed strong magnetic field devices according to their respective research needs.In order to carry out gas target magnetization laser plasma experiments on the small laser device of the University of Science and Technology of China,we have independently developed a compact pulse magnetic field device that can be used in low vacuum environments.It can output a peak current of 95 kA and produce a quasi-uniform magnetic field of 12 T in a volume of approximately 1 cm3.By improving the structural design,we successfully solved the technical problems of high voltage,low inductance and vacuum sealing.As a result,we developed the first compact pulse magnetic field device that works normally in a low vacuum environment.We have found that when the pulsed magnetic field device is operated in a low vacuum environment,in some intermediate pressure ranges,the induced electric field of the pulsed magnetic field ionizes the background gas and interferes with the effective plasma signal.Therefore,our experiments,theories and simulations studied the temporal characteristics and pressure dependence of background gas ionization,and provided a simple and practical analytical model for the experimental design of gas target laser plasma.The pulsed magnetic field device cooperated with the small laser device of the University of Science and Technology of China to complete the physics experiment of magnetized astrophysics jet with background gas.In order to carry out physical experimental research on the high driving energy such as magnetization shock wave,we need to use a large laser device such as the Shanghai Shenguang ? upgrade laser device.Therefore,we have developed a compact pulsed magnetic field device suitable for Shanghai Shenguang ? upgrade large laser device.We creatively designed a high-voltage and high-current flexible transmission line,and flexibly connected the magnetic field coil to other parts of the discharge system,so that the magnetic field coil can be precisely adjusted inside the target chamber through the electric translation stage;we also independently developed a high-voltage high-current electric trigger gas switch,replacing the original light-triggering gas switch.The device structure is more compact and the versatility is greatly improved;we have improved the grounding and electromagnetic shielding measures to reduce the influence of electromagnetic interference.The compact pulsed magnetic field generator was used in the large-scale laser device upgraded by Shanghai Shenguang ?to complete the magnetization laser plasma physics experiment,and the Hall magnetic fluid instability phenomenon at the interface between the magnetic field and the plasma was observed.In order to leave room for laser and diagnosis,compact pulsed magnetic field devices for laser plasma generally use small single coils or Helmholtz coils.The inductance of this small coil accounts for a small share of the total inductance of the discharge system.For example,the magnetic energy of the magnetic field of our existing device accounts for less than 15%of the total energy of the entire energy storage.If a transformer coil is used,the inductance of the coil portion can be greatly increased,thereby increasing the energy share of the magnetic energy,increasing the energy utilization rate,and increasing the magnetic field strength.And the secondary circuit of the transformer still uses a single coil,which does not block the optical path.Therefore,we have studied the transformer coil technology.Firstly,the design principle of the pulse transformer coil is given.The reflection impedance of the secondary circuit of the transformer to the primary circuit is considered in the formula.Then the numerical calculation is carried out in combination with the parameters of the current pulsed magnetic field device,and the design suitable for the existing device is given.In order to verify the correctness of the numerical calculation,we used the circuit simulation software to carry out the simulation comparison.The multi-physics coupling simulation software was used to jointly simulate the circuit,magnetic field,heat transfer and mechanics of the whole transformer coil,and further explore the heat transfer and structural mechanical properties of the coil.Finally,we fabricated a pulse transformer coil that can be used in experiments and conducted a discharge test.The test results are highly consistent with our previous theoretical analysis and simulation results.Experimental and theoretical simulation results show that when the primary winding diameter of the transformer is 25 mm and the primary coil turns 10,the peak magnetic field is increased by 120%compared to the single coil.Transformer coils significantly improve energy efficiency and have great application prospects in future device upgrades.In addition to the research and development of pulsed magnetic field devices,we used this device to carry out laser ablation physical experiments in conjunction with the small nanosecond laser of the University of Science and Technology of China.It was found for the first time that the applied pulsed strong magnetic field can significantly enhance laser ablation.We experimentally measured the laser ablation with or without an applied pulsed strong magnetic field.From the aspects of ion charge and pulsed laser deposition coating,it was confirmed that the applied pulsed strong magnetic field enhanced the laser ablation efficiency by more than one order of magnitude,and the coating area was larger.Large particle droplet contamination is significantly reduced,and high energy ion components are significantly suppressed.By measuring plasma luminescence,laser ablation pits,large particle droplet ejection,etc,it is found that enhanced laser ablation is derived from laser plasma re-ablative and pulsed magnetic field induced ablation from a steady-state magnetic field,and pulsed magnetic field induction ablation eliminates large Part of the large particle droplets are contaminated.The addition of a pulsed strong magnetic field to improve laser ablation can be used to improve the pulsed laser deposition coating technology.It can greatly suppress the contamination of large particle droplets,weaken the lattice defects caused by high-energy ionic components,significantly increase the size of the coatingoand increase the coating efficiency by orders of magnitude.As a result,it c.an greatly promote the development of pulsed laser deposition coating technology.