GB1010163A - Improvements in or relating to accelerometer utilizing electron beams - Google Patents

Abstract

1,010,163. Accelerometers; generating waveforms photo-electrically. J. J. MASCUCH. May 1, 1963, No. 17255/63. Headings G1A and G1N. [Also in Divisions H1 and H3] Apparatus for determining the acceleration of a moving body comprises an electron discharge tube in which a bunched electron beam follows a helical path in a longitudinal magnetic field along a drift tube to generate, in virtue of the inertia of the helical beam, a signal whose frequency is dependent upon the movement of the tube. This signal is combined with the modulating signal bunching the beam and, as the frequency of the modulating signal is unaffected by the movement of the tube, the difference frequency gives an indication of the acceleration. In Fig. 1 where 22 is the drift tube, 24 a magnet coil, 30 an annular output electrode and 26 the helical electron beam, the beam is generated in bunches at a photocathode 20 by the coherent light beam of a laser 15. The laser beam passes through the photocathode where it is modulated when the bunches of electrons are emitted, and is reflected by mirror 33 along the drift tube 22 to a photocathode 34, Fig. 2, at the centre of the electron beam output target 30. Signal currents due to the electron and light beams then flow in the conductive cap 31 and conductor 32. The photocathodes 20, 34 each comprise a one molecule thick monolithic silver backing layer deposited on a thin quartz disc and a one molecule thick caesium layer. The drift tube 22 is of quartz and with the magnet coil 24 is encased in a grounded metallic shield 25. In Fig. 3 the electron beam 26 generated by gun 45 is velocity modulated by cavity resonator 50, the resonator being fed by ammonia gas maser 15. The outputs of the drift tube anode 30 and the gas maser 51 are rectified at 38, 38a and combined to produce a difference frequency. An axial electric field is also produced in the drift tube between electrode 49 and 30. With suitable integrating output circuits velocity and distance travelled may be determined as well as the acceleration.