GB1134490A - Particle velocity sorter using an r.f. tranverse electric space harmonic and a transverse bias field - Google Patents

Abstract

1,134,490. Particle spectrometers. VARIAN ASSOCIATES. 10 April, 1967 [19 April, 1966], No. 16330/67. Heading H1D. A charged particle velocity sorter comprises means 13 for forming and projecting charged particle beam, means 3, 4 for producing along the beam a spacially periodic R.F. electric field transverse to the beam and a second transverse field having an equal and opposite effect on particles having a velocity synchronous with the phase velocity of an even number spacial harmonic of the R.F. field to allow such particles to pass through the sorter and deflect non-synchronous particles out of the beam. In a mass spectrometer for analysing the charge to mass ratio a ribbon beam of gas, ionized by an electron beam (26), passes between comb members 3, 4 across which an R.F. source 7 and a D.C. source are connected. The R.F. source is operated in the 2# space harmonic mode so that all ions except synchronous ions with velocity V 1 =f 0 # are deflected out of the beam where f 0 is the frequency and X the distance between teeth of members 3, 4. The D.C. source is obtained from a rectifier (38) supplied from the R.F. source. A scan voltage (35) is applied to a beam voltage control electrode (34). Synchronous ions reach a collector electrode 11, behind a secondary electron suppressor (42) and connected to an electrometer (44) whose output is fed to a recorder (45) together with the scan voltage. An alternative ion sorter comprises a pair of slotted plates (51), Fig. 8 (not shown), between outer plates (52) across which the fields are applied, the slotted plates and electrode (34) being at the same potential. The D.C. source may be replaced by a square wave audio frequency supply. The sorter may be used with negative ions or electrons.