Mechanism Investigation Of Laser Propulsion With Solid Propellant

Laser propulsion is a new concept propulsion technology by which the aircraft is promoted utilizing the counterforce generated during the injection of plasma with extremely high temperature and pressure which formed by interaction between high-power laser and propellant. Solid matter is the most promising state of propellants for its easy processing and maneuverability. In this dissertation, it focuses on the ablation mode laser propulsion with solid propellant. Physical and mechanism of this mode have been studied through numerical simulation and experiment. Some significant results are achieved.The energy consumption model for plasma formation in vapor through the dynamic ablation of solid propellants and laser energy absorption model introduced by beam tracing method are built in this dissertation. A program named LDAP-2D for 2D axis symmetrical hydrodynamic is made using WENO spatial difference scheme and Runge-Kutta temporal discretization scheme and combining the ideal state equations of plasma. The interaction between laser and monatomic solid matter could be studied by this program including the dynamic ablation of solid matter by laser, the formation and injection of vapour plasma, the evolution of flow field which is favorable to study the physical mechanism and mechanical efficiency of ablation mode laser propulsion. It will enhance the precision of numerial simulation for flow field.It is found that the absorption of laser by vapor plasma is coupled with the evolution of flow field and the oscillation of absorption shows up at pulse width inμs order. It is also found that short wavelength is beneficial to transform the laser energy to the dynamic energy of flow field, more energy deposited in condensed target favors propulsion efficiency and larger v_e makes against improving the propulsion efficiency.Study on that the laser energy and intensity effects on propulsion efficiency at laser intensity great than threshold intensity shows that the impulse gained by propelling target increases with the pulse energy, Cm decreases with the laser energy at the same intensity, while Isp increases with it. Cm is in exponential decay with laser intensity at the same energy, while Isp changes not much with it.Study on the wavelength of the four lasers candidates (1.06μm, 1.315μm, 3.8μm, 10.6μm) effect on propulsion efficiency shows that Cm decreases with the laser intensity at each wavelength and decreases with the wavelength at the same laser intensity. At the first three wavelengths, Isp decreases a little then increases back with laser intensity, and increases with wavelength, while it almost decreases linearly with intensity. So that the two wavelength 1.315μm, 3.8μm are better choice regarding to Cm and Isp synthetically.Study on C, Al, Cu, Fe propellants target shows that propellant which has moderate atom is good choice, pulse duration of tens or hundreds of ns benefit the synthetic propulsion efficiency, it will oscillate between innet energy and kinetic energy in flow field while not helping improving the propulsion efficiency.We record the emission spectrum of Al, copper Graphite, PVC, POM plasma. The space- resolved and the power density-depended spectrum are studied. Under the local thermo equilibrium supposition, we obtain the electron temperature and the electron density with regard to Al and copper from the relative intensity and broadening of characteristic spectrum. Their dependence on laser power-density and spacial variation are also studied. The obtained electron temperature of Al and Cu is in the range of (7.9-25)×10³K and electron density of Al is in the range of (4-9)×10¹⁷cm^-3. At the same time, we take the photos of instant ablation of the six materials in vacuum by the camera's B shutter and analyze the ejected matter.The propulsion efficiency of the six material in air is studied. The results show that all of the material have a little greater Cm under single pulse than two repeated pulses, Cm increases with laser intensity and then decreases after reaching the highest Cm, polymer material have sensitive variation with laser intensity and Delrin shows wonderful character for propulsion. Many related experiments are summarized in this dissertation and a database of the results of experiments is built.