Abstract: An ion mass spectrometer is described which detects and indicates the characteristics of ions received over a wide angle, and which indicates the mass to charge ratio, the energy, and the direction of each detected ion. The spectrometer includes a magnetic analyzer (18) having a sector magnet (24) that passes ions received over a wide angle, and an electrostatic analyzer (30) positioned to receive ions passing through the magnetic analyzer. The electrostatic analyzer includes a two dimensional ion sensor (32) at one wall of the analyzer chamber, that senses not only the lengthwise position of the detected ion to indicate its mass to charge ratio, but that also detects the ion position along the width of the chamber to indicate the direction in which the ion was travelling.