Multiframing Mach-Zehnder interferometer for spatiotemporal electron density measurement in a field-reversed configuration plasma

Interferometric measurement is used to establish the spatially and temporal ly resolved electron density distribution in high beta plasma experiments. However, a series of interferograms are recorded separately on different sh ots. In order to avoid shot-to-shot data variation, we have developed a mul tiframing Mach-Zehnder interferometer system to produce multiframe interfer ograms on a single field-reversed configuration (FRC) plasma shot. In this interferometer system, a continuous wave He-Ne laser is used to illuminate the interferometer and the interferograms at various instances are recorded photographically by a rotating mirror framing camera at framing rates of 0 .7-2.9 MHz. A simple electromechanically operated optical shutter with open ing time of 300 ms was developed in our lab to gate the laser light to prev ent both the considerable attenuation of laser light intensity and multiple exposure of the interferograms. The precise timing of the interferograms r elative to FRC plasma discharge is determined with two optical fiber glasse s pointed separately towards the first and the last microlenses in the fram ing camera to pick up their laser light pulse signals. Twenty-eight consecu tive FRC plasma interferograms were recorded successfully on Kodak T-MAX 40 0 film in the first half discharge period of 10 ms with this system. From t hese interferograms, the spatiotemporal evolution of plasma density can be evaluated. (C) 1999 American Institute of Physics. [S0034-46748(99)63501-8] .