GB709842A - Improvements in apparatus comprising means for concentrating beams of charged particles - Google Patents

Abstract

709,842. Electron lenses; particle accelerators. PHILIPS ELECTRICAL INDUSTRIES, Ltd. Jan. 1, 1952 [Jan. 4, 1951], No. 36/52. Class 39(1) [Also in Group XL(c)] In a discharge tube employing a focused beam of electrons or ions focusing is effected by two coaxial conductive helices having the same pitch and diameter and carrying unequal D.C. potentials, each turn of each helix being midway between two turns of the other helix. In one form, Fig. 1, designed as a travelling wave tube, two helices 5, 6 of equal pitch and diameter are intermeshed as shown and are maintained at 930 and 1400 volts respectively with respect to the cathode. Their capacity to cylinder 4, which also serves as accelerating anode, provides strong high frequency coupling between them. In another form, Fig. 2, serving as a signal delay device, electron pulses produced by positive pulses applied to grid 12 are deflected by magnetic field 13 perpendicular to the plane of the paper to pass through two coaxial helices 14, 15, are reflected by electrode 16 and retraverse the helices, finally being collected at 17. The pulses may be replaced by a modulated signal. In another form, Fig. 3 (not shown) serving as an oscillator the transit time from the control grid to the collector is an odd number of half cycles of the oscillations generated. The control grid and collector are coupled by a capacitor, the grid is earthed via a high resistance and the collector is earthed via an antiresonant circuit. In another form, Fig. 4 (not shown), serving as an amplifier one helix (at higher D.C. potential) has a number of spaced tappings connected alternately to opposite sides of an oscillatory circuit, the collector also being connected to one side of the circuit. The electron transit time between two adjacent tappings is one half period of the wave and the input is applied to the control grid. In all forms the ratio of the D.C. voltages applied to the helices is at least 3:2, preferably 2:1 or 3:1, and the lower voltage may or may not be zero i.e. equal to cathode voltage. The two helix system may be wound as a whole into an arbitrary curved shape e.g. a helix, provided that the radius of curvature of the curved axis is several times greater than the diameter of each helix, and the beam path is correspondingly curved. The invention may also be applied to klystrons, two beam space charge wave tubes and ion accelerators.