Spiral accelerator
The spiral accelerator is a resistive helix painted on the inside of a cathode-ray tube (CRT) from near the deflection plates almost to the phosphor screen. It is designed to minimize beam compression in the post-deflection acceleration system by applying a gradually increasing acceleration voltage along the bulb's length.
The end of the helix near the deflection plates is held at the potential of the plates. This assures that the electrons do not see the high voltage at the phosphor screen and can travel between the plates relatively slowly, allowing them to be deflected easily. After passing though the plates, the resistive helix presents an increasing voltage that gives the electrons a much higher speed, resulting in a bright spot.
The spiral accelerator was first suggested in 1938 but not developed into a practical device.
In 1952, Howard Vollum revived the idea for the T51 CRT that Tektronix was developing for the 1953 model 535 scope.
The spiral accelerator displaced multi-band acceleration by the 1960s.
Literature
- Peter Keller, The Cathode-Ray Tube: Technology, History, and Applications, pp.110-114. Palisades Press, 1991. ISBN 0963155903, 9780963155900
- Oscilloscope Cathode-Ray Tube Concepts, Chuck Devere, 1969
