Combined Magnetic Deflection and Focusing in a Pick-up Tube with the Scanning Focus Coil

Abstract

This chapter discusses combined magnetic deflection and focusing in a pick-up tube with the scanning focus coil. Conventional coil units for deflecting and focusing the electron beam in camera pick-up tubes contain two pairs of deflection coils perpendicular to each other and a separate long coil providing the constant axial focusing field. In addition, a set of four alignment coils is necessary for proper operation of a pick-up tube with low-velocity target stabilization. The complexity of such a coil unit makes it rather expensive. Moreover, it is difficult to obtain adequate reproducibility. The scanning/focusing coil unit described in this chapter has a much simpler construction, resulting in a smaller diameter and less weight. The new concept is based on the idea that deflection of the electron beam in a pick-up tube can be achieved without separate deflection coils by changing the direction of the focusing field over the full length of the beam path. With the scanning focus coil, normal landing takes place without the need of a separate mesh or a flare field on the side of the target scanned, because there are neither radial nor tangential electron velocity components to be compensated.