  In this paper, we analyze electric deflection fields for polar molecules in
terms of a multipole expansion and derive a simple but rather insightful
expression for the force on the molecules. Ideally, a deflection field exerts a
strong, constant force in one direction, while the force in the other
directions is zero. We show how, by a proper choice of the expansion
coefficients, this ideal can be best approximated. We present a design for a
practical electrode geometry based on this analysis. By bending such a
deflection field into a circle, a simple storage ring can be created; the
direct analog of a weak-focusing cyclotron for charged particles. We show that
for realistic parameters a weak-focusing ring is only stable for molecules with
a very low velocity. A strong-focusing (alternating-gradient) storage ring can
be created by arranging many straight deflection fields in a circle and by
alternating the sign of the hexapole term between adjacent deflection fields.
The acceptance of this ring is numerically calculated for realistic parameters.
Such a storage might prove useful in experiments looking for an EDM of
elementary particles.
