Cameras

Ultra Fast Framing Cameras

Two types of framing camera have been developed each capable of framing rates of 3 frames per nanosecond with spatial resolution of 9 lppmm at a modulation transfer function greater than 0.1. The camera have static resolution of 18 lppmm.

Both cameras are based on image converter tubes and operate by successively moving and holding still the electron beam to produce a sequence of images at the screen. The main difference between the cameras is in the design of their electron beam deflection structures and the voltage wave forms required to drive them. Both are travelling wave deflection structures and the first, called type I, is a helical deflection structure formed in strip line construction with an electrical rise time (10% to 90%) of 70ps requiring a staircase voltage waveform to produce frames. The second, Type II, is a novel design which requires only a single voltage step to produce frames. It is formed in strip line and coaxial cable construction and also has an electrical rise time of 70ps.

The theory of deflection by such structures is given in the thesis as are the results of computer modelling and their detailed design considerations. The computer model agrees with experimental results fairly well and gives the theoretical limit on interframe time and resolution as 300ps and 9 lppmm at MTF = 0.1. The voltage wave forms for both cameras were produced using silicon Auston switches driven by short laser pulses.

The first type of camera was used to study the six beam laser compression of microballoon targets by framing x-ray shadowgraphy with an interframe of 500ps. The resolution at this interframe time was shown to be limited by the pinhole camera aperture to 10$\mu$m in the image plane (4 lppmm at the cathode). The photographs showed symmetrical structure commensurate with the non-uniform illumination of the target by the six beams. The results were compared with “Medusa” computer simulations and a critical comparison made between framing camerastudies and other methods of studying such compressions.