A Multi-frame Mach-Zehnder Interferometer For Measuring The Plasma Of Z-Pinch

This paper describes a multi-frame Mach-Zehnder (M-Z) interferometer (MFMZI) developed by ourselves. MFMZI was conducted on a small gas-puff Z-Pinch device, and three interferograms with an interpulse delay of 13 ns were obtained in one shot of Z-Pinch. MFMZI consists of a Nd:YAG laser, a beam-splitter, a M-Z interferometer and a image system. With double-frequency technique and Q switch technique the laser delivers a laser pulse of 532-nm in wavelength, 5-ns in pulse width, 35-mJ in energy and 2-cm in coherent length. The beam-splitter comprises three pairs of fully reflecting planar mirrors and partially reflecting planar mirrors. According to the workspace size and experimental requirement, they were placed with a distance of 195-cm between two mirrors. When passed through the beam-splitter, a pulsed laser beam was split into 3 beams with an interpulse delay of 13 ns. These 3 separated laser pulses reach the M-Z interferometer at different time and each laser pulse gave a snapshot of the implosion state. Thus three different-time interferograms can be obtained in one shot of Z-Pinch. The image system includes a positive lens with 40-cm focal distance, a prism with a angle,a receiving board and a CCD camera with 5.02 million pixels. The laser beams from M-Z interferometer will focus on three different dots after going through the positive lens, and the prisms were placed on these dots. Owing to the deviation of these prisms, three interferograms will be separated each other when they reach the image board. Then these separated interferograms can be recorded by CCD cameraThe experiments with the multi-frame interferometer was carried out on a small gas-puff z-pinch device with 23 kV working voltage and 210 kA peak current and about 2 risetime, and good results were obtained. According to the fringe shift of the interferograms, electron density and implosion velocity can be obtained. In the early period of plasma imploding,the averaged electron density is ,and the averaged implosion velocity is up to; Near the final focus, the smallest radium of plasma shell is about 0.49 mm, and the electron density was estimated to be more than, and the averaged implosion velocity is about ; In the collapsing period, the averaged collapsing velocity is about .