Trochotron


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Trochotron

 

a multielectrode electron-beam device with a trochoidal sheet electron beam, used mainly as a switching device. The electron beam is formed by two crossed fields, namely, a constant magnetic field produced by an external magnet and a variable electric field generated by the electrodes of the device. The beam travels essentially along an equipotentiat surface with a potential near the cathode potential Vc. Beam switching is accomplished by varying the potential Vs of special electrodes, which are called spades, and results from the controlled shift of the equipotential surface and, consequently, the electron beam.

In the most widely used device—the linear decade trochotron (see Figure 1)—a constant potential VSc, which is equal to 50–100 volts (V) and negative with respect to Vc, is supplied to the screen, and a constant potential VAVT ≈ 100 V, which is positive with respect to Vc, is supplied to the anode and each of the targets. If the potentials of all the spades are near VA, the electron beam, which represents a current of a few milliamperes, enters the first array of the trochotron; this array is formed by the edge of the screen, the first target, and the spade adjacent to the first target. Upon reaching the target, the electron beam closes the circuit between the target and the cathode. If the potential of the first spade is now reduced to approximately VSc, the beam reaches the second array, that is, the second target, and so on. Thus, the beam can be directed to any of the targets.

Figure 1. Schematic diagram of a linear decade trochotron: (A) anode, (C) cathode, (Sc) screen, (T1–T10) targets, (S1–S9) spades. The dotted line illustrates the trochoidal trajectory of the electrons for the case where the potential of the spades is near the anode potential. The magnetic field is perpendicular to the plane of the figure.

The major types of trochotrons are distinguished mainly by the arrangement of the arrays and the shape of the electrodes forming an array. For example, in a two-dimensional trochotron the electron beam is controlled by two independent groups of arrays. In a binary trochotron, spades of different lengths are grouped in a specific way. In an annular trochotron the arrays are situated on the circumference of a circle at whose center a cylindrical cathode is located.

Trochotrons provide flexible control of currents. They are used in various electric circuits, mainly pulse circuits, to switch circuits, count pulses, and measure time intervals; they are also used, for example, as electronic delay lines.

REFERENCE

Lozhnikov, A. P., and A. M. Kharchenko. Impul’snye ustroistva no trokhotronakh. Moscow, 1963.

M. V. TSEKHONOVICH