Improved visualization of z-pinch dynamics from inversion of streak camera data into video format

Summary form only given. Streak cameras operate by scanning an image present on the photocathode across a recording device such as a film. Traditional operation preprocesses that image with a slit aperture. This slit is made as narrow as possible to improve the time resolution i.e. so as to minimize the overlap of optical data on the film from one moment to the next. This has the advantage of greatly simplifying the interpretation of the final data. We propose to open this aperture, allowing the full image of the scene to fall on the photocathode and pass through the system onto the film. The resulting overlap of images can be postprocessed to reveal the time-dependent image that must have been present on the photocathode. The temporal length of the final video is limited only by the fastest sweep speed of the streak camera. Reconstruction is accomplished by expressing the operation of the streak camera as a matrix transformation. This matrix transform maps the input scene at the photocathode onto the streak data at each moment in time. The equation takes the form G*m=d. Due to the operation of the streak camera, the number of points in the data is significantly smaller than the number of pixels in the video which results in an underdetermined system. To select from the infinite pool of possible solutions we assume that the most probable solution will be the video with highest entropy, as defined by information theory, under the constraint that it reproduces the data when transformed by the matrix G. We further assume that the streak data has been properly normalized so that the video pixel values range between zero and one. This greatly reduces the size of the solution space. Under these assumptions, our solver is able to converge to a single most probable solution vector m. This vector is then postprocessed to reveal the most probable video of the plasma scene. We present the mathematical representation of the system along with the algorithm used for arriving at the solution. Simulated streak data is generated by taking output from the enhanced MHD computer simulation code PERSEUS1 and applying the streak camera transform matrix. We display frames taken from the recovered video for comparison with the original PERSEUS output. We also examine the theoretical resolution limits in the final video.