GB817283A - Improvements relating to electron discharge devices - Google Patents

Abstract

817,283. Velocity modulated tubes. GENERAL ELECTRIC CO. Dec. 29, 1955 [Jan. 20, 1955], No. 37269/55. Class 39(1). An electron discharge interaction device comprises a suppressor electrode and an electron collector and means for applying a potential difference between the collector and the suppressor electrode so as to produce an electric field for decelerating electrons passing to the collector, the collector being of tubular form and having a tapered end. As applied to a travelling wave tube having a helical wave structure 18, Fig. 1, the suppressor electrode 16 is maintained at a potential of about 1000 volts above that of the collector 17 and is located at least in part within a bucking coil 30 which shields the electrode 16 and the collector 17 from the field H of the focusing coil 29 and which has also a radial field component 31. The field H<SP>1</SP> of the bucking coil and the lower potential of electrode 16 relative to the structure 18 causes the beam to spiral and spread as at 32 on entering the collector 17 so that the majority of the secondary electrons emitted travel inwards into the collector. Any secondary or reversed primary electrons re-entering the electrode 16 are deflected thereon by the ringing electric field and the magnetic field 31. If is is desired to collect all electrons in the collector 17 the field of coil 29 is arranged to include the electrode 16 and the coil 30 is located around the cylindrical portion of the collector 17. In lieu of the bucking coil 30 or in addition thereto, the deflection of the electrons may be affected by a cross magnetic field. The collector 17 may be provided with a central metal post extending into the electrode 16 to provide therein an electric field which also deflects electrons from the main beam. A secondary electron collector at a potential between that of the electrode 16 and that of the collector 17 may be located intermediately of the suppressor and the collector. In the embodiment shown in Fig. 3 the electron beam between a suppressor electrode 16 and a collector 41 is deviated by means of a cross magnetic field 45 and a further electrode 47 at the same potential as that of the suppressor 16 is located as shown to provide a decelerating gap 46 at the entrance to the collector. Reversed primaries or escaping secondaries are deviated by the field 45 on to a collector 43 whose potential is higher than that of the electrode 16.