Patent ID: 6078043
Filing Date: 2000-06-20
Classification: H01J

Abstract:
A mass selector for separating particles in a particle beam according to mass, said selector including a pair of first electrodes between which is defined an elongate first path for the passage of the particle beam; means for focusing the particle beam so that, in use, a focused particle beam passes along the elongate first path; a pair of second electrodes spaced from the pair of first electrodes in a direction transversely of the direction of extent of the first path, said pair of second electrodes defining therebetween an elongate second path for separated particles, said second path being parallel to said first path; first voltages-applying means for applying a first voltage pulse across said first electrodes so that, in use, the particles in a portion of the beam which is in said elongate first path are accelerated transversely of their direction of movement along said first path towards said second path, second voltage-applying means for applying a second voltage pulse across said second electrodes so that, in use, particles which have been accelerated by said first voltage pulse and which have entered said second path are decelerated transversely of their direction of movement along said second path; and controlling means for controlling the first and second voltage-applying means so that said first voltage pulse accelerates the particles in said portion of the beam with substantially constant momentum acceleration and the second voltage-applying means applies said second voltage pulse with substantially constant momentum deceleration a pre-selected time interval after said first voltage pulse so that particles of the selected mass pass along said second paths in substantially the same mutual dispositions as they travelled along said first path.