GB1233812A - - Google Patents

Abstract

1,233,812. Mass spectrometers. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. 14 April. 1970 [16 May, 1969], No. 25109/69. Heading H1D. [Also in Divisions H3-H5] In a mass spectrometer of the type wherein an ion beam passes through an analyser and the shape of the beam is distorted by fringing fields from the analyser, such distortion is corrected by means of a six-pole electrostatic device. The device shown in Fig. 6 comprises six parallel rods, of which four 13-16 are shown, preferably equally spaced around the beam path and extending parallel to the path. Each rod is supported by a pair of insulating members 22, and the members 22 are screened by conductive cylinders at each end of the device. Each rod is connected to an individual potential which is the sum of a number of components, each adapted to produce a different effect. Thus the rods may be paired in different ways with equal and opposite voltages applied to each pair; one pairing producing or correcting curvature of a rectangular beam, another pairing rotates the beam, and a third pairing focuses the beam in one direction. In one arrangement, Fig. 1 (not shown), the ion beam passes through an electrostatic analyser and then through a magnetic analyser, and correction devices are disposed at points where the beam has minimum width adjacent the output slits of the two analysers. Alternatively the devices may be positioned in the entry and exit planes of the magnetic analyser in order to minimize the length of time for which the beam travels in a distorted state. Energizing circuits.-Potentials -V o and V o proportional to the ion accelerating voltage are applied to opposite ends of a number of potentiometers (Fig. 7, not shown), three of which are adapted to produce equal and opposite output voltages. Each potentiometer effects a particular function (e.g. curvature of the beam, focusing in one direction, trimming, deflection) and the outputs of the potentiometers are fed to six summing circuits which supply the final output potentials to the six electrostatic poles.