An electrostatic linear ion trap for measuring induced current of one or more ions and reducing higher order frequency harmonics of the induced current by combining the induced current with measurements from reflecting reflectron plates, said electrostatic linear ion trap comprising: a first set of reflectron plates with holes in the center that are coaxially aligned along a central axis, wherein the first set of plates includes a first inlet plate followed by a first plurality of reflection plates (1212, 1213, 1214, 1215) followed by a first plurality of trapping plates (1216, 1217, 1218, 1219); a cylindrical pickup electrode positioned so that a first end of the pickup electrode is adjacent to the first inlet plate of the first set of plates and the pickup electrode is coaxially aligned with the first set of plates along the central axis; a second set of reflectron plates with holes in the center that are coaxially aligned with the pickup electrode along the central axis, wherein the second set of plates includes a second inlet plate followed by a second plurality of reflection plates (1222, 1223, 1224, 1225) followed by a second plurality of trapping plates (1226, 1227, 1228, 1229) and wherein the second set of plates is positioned so that the second inlet plate is adjacent to a second end of the cylindrical pickup electrode; a voltage power supply configured to apply separate voltages to one or more plates of the first set of reflectron plates and to one or more plates of the second set of reflectron plates in order to trap and oscillate one or more ions that have been received along the central axis through the holes of the first set of plates between the first set of plates and the second set of plates; and measurement circuitry configured to measure a first induced current from the cylindrical pickup electrode, a second induced current from one or more plates of the first set of reflectron plates, and a third induced current from one or more plates of the second set of reflectron plates and to combine the first measured induced current with the second measured induced current and the third measured induced current to determine an induced current of the one or more ions and reduce higher order frequency harmonics of the induced current. a first set of reflectron plates with holes in the center that are coaxially aligned along a central axis, wherein the first set of plates includes a first inlet plate followed by a first plurality of reflection plates (1212, 1213, 1214, 1215) followed by a first plurality of trapping plates (1216, 1217, 1218, 1219); a cylindrical pickup electrode positioned so that a first end of the pickup electrode is adjacent to the first inlet plate of the first set of plates and the pickup electrode is coaxially aligned with the first set of plates along the central axis; a second set of reflectron plates with holes in the center that are coaxially aligned with the pickup electrode along the central axis, wherein the second set of plates includes a second inlet plate followed by a second plurality of reflection plates (1222, 1223, 1224, 1225) followed by a second plurality of trapping plates (1226, 1227, 1228, 1229) and wherein the second set of plates is positioned so that the second inlet plate is adjacent to a second end of the cylindrical pickup electrode; a voltage power supply configured to apply separate voltages to one or more plates of the first set of reflectron plates and to one or more plates of the second set of reflectron plates in order to trap and oscillate one or more ions that have been received along the central axis through the holes of the first set of plates between the first set of plates and the second set of plates; and measurement circuitry configured to measure a first induced current from the cylindrical pickup electrode, a second induced current from one or more plates of the first set of reflectron plates, and a third induced current from one or more plates of the second set of reflectron plates and to combine the first measured induced current with the second measured induced current and the third measured induced current to determine an induced current of the one or more ions and reduce higher order frequency harmonics of the induced current.