Diagnosing Microwave Plasma Thruster's Plume By Holographic Interferometry

Microwave Plasma Thruster(MPT) of Electron thruster has so many advantages, such as high specific impulse, long longevity, small cubage and little pollution, it thus is attached great importance by astronautics to diagnose the plume. As holography interferometry has more outstanding strongpoints and better advantages for phasic field, such as all field, noncontact, and high precision and non-disturbance by plasma luminescence, it is an effective means in the plasma number density of electronic diagnosis and is very meaningful in diagnosing the MPT's plume. This dissertation has probed into diagnosing the MPT's plume of holographic interferometry and digital holographic from two pare of the fundamental theory and experiment , and the intervened stripe simulated by MATLAB program; two setups are designed to diagnose the MPT's plume in the vacuum box. The main content is as follows:(1) History, evolution, status quo and advantage of holographic and digital holographic are summarized, the basic information of MPT and methods of diagnosing plasma is presented. It is shown that the optical diagnosing plasma is an effective method for diagnosing MPT plasma's plume.(2) Foundation theory of holographic interferometry is presented, theory of double-exposed holographic interferometry is deduced by formula, and theory of recording and reappearance digital holography is introduced. Analytical foundations for numerical reconstruction of digital holography, namely discrete Fourier transform theory, is also showed in this dissertation. Digital holography is analyzed by MATLAB program. Lastly, the foundation theory of interferometry diagnosing plasma is presented.(3) Optical distance disturbed by the plasma's plume field is observed by Mach-Zehnder interference, double-exposed holography, and real time holography—all get the similar result. Holographic of the plasma's plume is recorded by double-exposed holographic experimentation, picture of digital holography is recorded by digital holographic interferometry, and phasic difference is directly gained by numerically reconstructing, from which the electron density is also calculated. By employing the phase multiplication method, the fringe density of the interference pattern obtained by digital hologram was multiplied to reveal the refractive index distribution of the plume field more intuitively. Base on the experiment on the optical table, two setups are designed to diagnose plume in vacuum box.(4) Foundation information of MATLAB program is presented. Light wave front and light wave linearity transfer are simulated by using MATLAB. And the pole, globosity and cone plasma field interference figures are simulated by MATLAB, and reference fringe is added to the interference. Graph user interface is programmed for the simulation of the optical experiment.