Patent ID: 8198581

Claim:
An electrostatic ion trap for a mass spectrometer, comprising: an inner electrode and an outer electrode defining therebetween an ion trapping volume; the inner electrode and outer electrodes having surfaces that respectively approximate a first and second equipotential of a trapping field of the form U ⁡ ( r , φ , z ) = k 2 [ z 2 - r 2 2 ] + k 2 ⁢ ( R M ) 2 · ln ⁡ [ r R m ] where U(r,φ,z) is the potential at a point r,φ,z in cylindrical coordinates within the trap; k is the field curvature; and R m is the characteristic radius; wherein the inner electrode has a maximum diameter D 1 at z=0 which is smaller than the maximum of r at Z=0 defined by the first equipotential of U(r,φ,z); and wherein the outer electrode has a maximum inner diameter D 2 at z=0 which is larger than the maximum of r at z=0 defined by the second equipotential of U(r,φ,z).