GB696058A - Improvements in electron discharge tubes - Google Patents

Abstract

696.058. Travelling-wave tubes. NATIONAL RESEARCH DEVELOPMENT CORPORATION. Oct. 11, 1950 [July 15, 1949], No. 18764/49. Class 39(i) In a travelling wave amplifier there is interposed between the gun and main helix 8 an auxiliary helix 7 unconnected to any external source of waves, which has the same wave velocity as the main helix but a different D.C. potential or, as preferred, a different wave velocity as by making the pitch or diameter different but the same or nearly the same D.C. potential, so that the wave and beam velocities are unequal in the auxiliary helix; it is stated that random noise fluctuations in the beam induce a noise wave on the auxiliary helix which reacts back on the beam to induce a bunching modulation and that the voltage induced in the main helix 8 by random noise fluctuations and by the modulation component are out of phase and can be made to cancel. Exact cancellation can be achieved by varying the D.C. potential of the auxiliary helix 7 and the total beam current. The helices may be replaced by waveguides. Helix 7 is much shorter than helix 8 by a definite fraction in terms of wavelength. The molybdenum helices 7, 8 are supported by glass rods 10, and input and output guides 11, 12 associated with flanges 13 and chokes 14 are coupled to the ends of helix 8; a drift tube 15 connected to helix 7 is interposed between the two helices. The helix 8 may be copper plated to reduce losses, and the glass rods 10 may be coated with colloidal graphite at the vicinity of the centre portion of helix 8 to inhibit oscillation. The Provisional Specification states in addition that the voltage of the auxiliary helix may be less than that of the main helix for example 100 volts less. The auxiliary helix or guide may be replaced by a resonator detuned from the signal frequency.