Experimental Study of High-Voltage and High-Frequency Electromagnetic Processes Using a Rogowski Cathode Oscillograph (W. Rogowski, Naturwis. 16, 161, 1928). In recent years the development of electrical engineering has been devoted to the theoretical and experimental solution of the problem of the so-called transient regime, i.e., the phenomena accompanying the switching on and switching off of voltage. Interruptions in the operation of high-voltage electric stations are explained chiefly by the insufficiency of our knowledge in this relatively new field of electrical engineering. If, on an open circuit—for example Volkhovstroy–Leningrad—we apply at its beginning a voltage of approximately 50,000 V, then this voltage, for a line length of 100 kilometers, will propagate not instantaneously, but over the course of

\[ \frac{1}{3000}\ \text{sec}; \]

if we take the propagation velocity of electromagnetic disturbances to be 300,000 km/sec, such a voltage wave, having reached the free end of the network,

will be reflected and, as a result of interference with the initial one, will produce a standing wave already with an amplitude of 100,000 V. We shall have a phenomenon quite analogous to hydraulic shock, investigated in detail in its time by Prof. N. E. Zhukovsky. Thus we see that the resulting voltage will be twice the initial one. The theory also gives the form of the wave; namely, in the case of an undamped process we would obtain a wave in the form of rectangles alternating with lines of zero potential. In reality, owing to ohmic losses, the steep rectangular wave will gradually decrease, and at the end of the charging process the entire network will be under a voltage of 50,000 V.

If we imagine that, instead of a constant voltage, we have an alternating voltage of ordinary frequency—50 periods per second—and that in Leningrad we connect the network to a transformer, then, as the theory indicates, because of the steepness of the wave the voltage will be imposed only on the first few turns of our transformer; electrotechnical practice has fully confirmed the theoretical conclusions: it is always precisely the first turns of the transformer that are punctured. The facts cited above show with sufficient clarity the necessity of laboratory investigations of all the details of unsteady electromagnetic processes; and it is also clear that, in a laboratory setting, where the length of the network under test is measured not in kilometers but only in meters, the duration of the processes described above will be measured in millionths of a second. Of course, no mechanical instruments will be suitable for recording processes of such short duration.

Only the cathode beam, which in practice is an electric current devoid of mechanical mass and which directly follows all oscillations of the magnetic and electric field, can satisfy our requirements; in other words, the solution of the problem was closely connected with the improvement of the Braun tube, which had already long been used for the investigation of electric and magnetic fields as well as of high frequency (thousandths of a second).

Let us recall in a few words its construction: the electrons emitted by the cathode pass through a diaphragm, bored in the anode, in the form of a thin cylindrical beam. This beam falls on a screen coated with zinc blende and forms on it a phosphorescent spot. To obtain voltage curves on the screen, we deflect the cathode beam by means of electrostatic forces. Namely, inside the tube there is placed a capacitor consisting of two metal plates situated approximately at a distance of 1 centimeter from one another. The electrons flying between the plates of the capacitor are deflected with forces proportional to the voltage under investigation. In this way we obtain the ordinate of our phosphorescent curve. To obtain a deflection parallel to the time axis, we pass our beam through a second capacitor, perpendicular to the first, to which there is applied a ris—

voltage, increasing from zero to a maximum at the end of the period, proportional to the time.

Dufour and Rogowski introduced into the Braun tube, in place of the phosphorescent screen, a photographic plate. With the aid of the Braun tube thus improved, it became possible to study objectively processes with durations from one hundred-thousandth to one millionth of a second. By reducing the scattering of electrons to a minimum, Rogowski thereby increased the effective intensity of the Braun tube a thousandfold and obtained the possibility of photographically recording processes with durations of one billionth of a second. At present Rogowski is working on replacing the cold cathode of the ordinary Braun tube with an incandescent cathode, which will increase the emission of electrons to an extraordinary degree.

A billionth of a second is at present the limit of the “resolving” power of the cathode oscillograph: however small the apparent mass of the electron may be, in processes of still shorter duration its inertia nevertheless begins to make itself felt. If the old Braun tube may be called an electromagnetic loupe, then Rogowski compares the improved tube with a microscope of enormous resolving power.

Yu. Barats.