Plasma Opening Switch The Physical Mechanism Of Particle Simulation

Plasma Erosion Opening Switch(PEOS) is a critical device used in the pulsed power apparatus for modern radiation physics and inertial confinement fusion research. There is no perfect theoretical description or model for PEGS presently,and the switching phenomena differ from system to system. In addition,there is still much to do for the improvement of performance. The purpose of this dissertation is therefore to inspect possibly undiscovered factor and mechanism dominating the PEGS behavior,and to seek potential technical solution for better switch performance.Because that complex phenomena in PEGS involve kinetic effects of plasma and cathode emitted electrons,and evolution of electromagnetic fields,Particle-in-cell(PIC) code is chosen as study tool,and a two and half dimensional cylindrical fully electromagnetic PIC code CYLINDER2-1/2D,which is suitable for simulating the operation of the PEGS,has been established. In the CYLINDER2-1/2D code,Object-Oriented methodology is employed to increase flexibility and extensibility,a charge conserving current weighting algorithm and a multi-time-scale algorithm is used to enhance computational efficiency. Currently,CYLINDER2-1/2D includes boundary conditions for the electric and magnetic fields at the surface of ideal conductors,the cylindrical axis,the incoming wave ports. A new and simple model for explosion electron emission from cathode surfaces is described. The simple two dimensional diode emission problem is simulated by the PIC code and classical one-dimensional Child-Langmuir law is extended to two dimensions.Conduction and opening processes of low density(1012/cm3) PEGS are examined with the aid of PIC simulation. In simulations,all important Phenomena,such as non-neutral sheath widening near cathode,cathode electron emitting,current channel migrating to the load side of the plasma,ion accelerating toward cathode and magnetic insulation of cathode emitting electrons etc,have been observed and depict the internal physics of this device. Also presented is the influence of cathode emitted electrons on phenomena in the conduction processes of PEGS. The simulation results show,without cathode emitted electrons,rapid magnetic field penetration takes place only in region near the cathode,with cathode emitted electrons,magnetic field penetration takes place in all plasma region. The scaling relations of conduction time and opening time with the plasma density,which are computed by a series of simulation results,show that,influence of plasma density on conduction time is greater than opening time. Influence of cathode emitted electrons on conduction process,which is found to be more important when initial plasma density is low,is dependent of the initial plasma density.The penetration of a magnetic field into cylindrical middle-density(1013/cm3) C++ and H+ plasma with uniform and parabolic density profile,are examined with aid of PIC simulation. In regions where EMHD is expected to be dominant,the simulations showrapid axial penetration of magnetic field into plasma. However,the speed of penetration is equal to predicted value by fluid theory only in C++ plasma with uniform density profile. On other conditions,strong two-dimensional effects,electrostatic accelerating,magnetic pressure and plasma pressure should be included in the fluid analysis.The gap formation process,in the last stages of conduction phase of high density(1015/cm3) PEGS,is examined by PIC simulation. In simulations,evolution plots of plasma and current streamline are used to analyze the mechanism of gap formation. According to simulation result,new erosion model is suggested to reasonably describe the opening process of high density PEGS.PIC simulations are performed to determine gap scaling in a high density PEGS. Comparisons of simulation results with simply theory results and experiment results,indicate that the PEGS gap is always equal to the critical gap for magnetic insulted electron flow. It is important to note that,the vacuum electron flow to the anode causes current los...