An ion trap comprising: a first array of magnetic elements arranged to generate a first magnetic field with a degree of homogeneity; and an array of electrodes arranged to generate an electrostatic field including a turning point in electrical potential at a location where the magnetic field has a substantially maximum degree of homogeneity; wherein the array of electrodes is planar and parallel to the direction of the magnetic field at the location; and wherein a primary first magnetic element is arranged to generate a first component of the first magnetic field and other first magnetic elements are arranged to generate compensating components of the first magnetic field that reduce the gradient, the curvature and higher order derivatives of the first component of the first magnetic field at the location where the first magnetic field has the substantially maximum degree of homogeneity.