  The implementation of log-pol transformation has recently introduced a new
boost in electron optics with charged matter vortices, allowing to map
conformally between linear and orbital angular momentum (OAM) states and to
measure them. That coordinate change belongs to the general framework of
Hossack's transformations and it has been recently realized efficiently by
means of electrostatic elements. In this letter we show that it is a general
property of those conformal transformations to be produced by harmonic phase
elements and therefore to admit an electrostatic implementation in the electron
optics scenario. We consider a new kind of conformal mapping, the
circular-sector transformation, which has been recently introduced for OAM
multiplication and division in optics, and discuss how it represents a general
solution of Laplace's equation, showing the analogy of the generating phase
elements with projected multipole fields and linear charge distributions.
Moreover, we demonstrate its capability to perform the sorting of multipole
wavefronts, discovering a novel and effective method to measure the strength
and orientation of a dipole field in a fast, compact and direct way.
