| 摘要 |
787,181. Travelling wave tubes. STANDARD TELEPHONES & CABLES, Ltd. June 17, 1955 [June 21,1954], No. 18181/54. Class 39(1). In a travelling wave tube provided with noise reducing means comprising at least two successive accelerating gaps in the gun followed by a field free " drift tube " connected between the final anode and helix, the magnetic focusing field is made divergent in the gun region so as to reduce the noise space charge waves still further. The divergent magnetic field is obtained by reversing the position of the magnetic pole piece 28 so that it projects forwardly instead of backwardly from the magnetic end plate 16, and the cathode is placed inside the pole piece tunnel one inch from the left hand end. The axial field is zero in the plane of the end plate due to the shielding effect of the pole piece and increases to a maximum at the right hand end of the pole piece tunnel, thereafter decreasing to a constant value along the helix. The magnetic field will therefore diverge from behind the cathode and become parallel at the right hand end of the pole piece. Alternatively the current in the first solenoid coil 17 can be made greater than in the remaining coils. The accelerating gaps are formed between cathode and anodes C, A 1 , A 2 , A 3 , Fig. 1, at D.C. potentials of 0, 55, 115 and 950 volts respectively, anode As being connected to one end of drift tube 7 which is of such length that its end adjacent the helix is a point of A.C. noise velocity minimum. 3 is a cathode shield electrode. The spacing between A 1 and A 2 is twice that between the cathode and A 1 but equal to the spacing between A 2 and A 3 . The probe 9, connected between " drift tube " 7 and helix 8, and about one turn of the helix, lie within input wave-guide 10. Focusing coils 17- 22 are clamped by tie bars 23 of magnetic material between magnetic end plates 14, 16. The magnetic field may vary from 600 gauss ¢ inch behind the cathode to 320-330 gauss 3 inches in front of the cathode, and the spacings of A1, A2 and A3 from the cathode are respectively 0À053 inch, 0À170 inch and 0À320 inch. A prior art arrangement is referred to in which the gun has two accelerating gaps to reduce noise as in the present invention but in which the magnetic field is uniform ; the potentials of the gun electrodes and beam current may be so adjusted that the beam diverges between the cathode and first anode, and this is stated to further reduce the noise by 2dB. |
