Mass spectrometer having a multichannel detector

A mass spectrometer comprising an ion source, an ion momentum analyzer, an electrostatic ion-energy analyzer and a multichannel detector locatable in the image focal plane of said electrostatic analyzer and capable of recording at least a portion of the mass spectrum of ions entering it, wherein said electrostatic analyzer comprises an upper and a lower group of spaced-apart electrodes respectively disposed above and below the ion beam passing through it, each said group of electrodes comprising a pair of electrodes between which one or more central electrodes are disposed, the potentials of one electrode of the pair being more positive and the other electrode of the pair being more negative than the potential at which ions comprised in said ion beam enter said electrostatic analyzer and the potentials of all the electrodes comprising each said group progressively increasing from one electrode to the next, thereby providing an electrostatic field in a central plane between said groups which is capable of deflecting said ions along different curved trajectories according to their energy, and wherein the potentials of said electrodes are further selected so that said image focal plane is coincident with said multichannel detector over at least a substantial portion of the length of said detector.