  This paper describes a helical deflector to perform circular sweeps of keV
electrons by means of radio frequency fields in a frequency range 500-1000 MHz.
By converting the time dependence of incident electrons to a hit position
dependence on a circle, this device can potentially achieve extremely precise
timing. The system can be adjusted to the velocity of the electrons to exclude
the reduction of deflection sensitivity due to finite transit time effects. The
deflection electrodes form a resonant circuit, with quality factor Q in excess
of 100, and at resonance the sensitivity of the deflection system is around
1~mm per V of applied RF input.
