[en] Criteria are described which must be considered in the application of solid brushes to current collection in fast-discharge homopolar machines. A typical design is described in which brushes carry a peak current density of 15.5 MA/m² in a 30 ms pulse. Initial experimental results are described for a unit of the brush system design

No abstract available

No abstract available

[en] The device consists of an articulated folding arm whose one part is pivoted on a plate attached to the radiation source column while the other is provided with springs and with a stirrup and a recess between the springs. The extended pin on the tomographic part is slidably fitted in the stirrup with recess. The pin is provided with an adjustable contact linked to the microswitch contact. In tomography, the operator mechanically connects the tomography bar fitted in a sleeve to the source, thus disconecting the articulated folding arm from the extended pin of the tomograph. The disconnected arm will then be folded in the vertical position by the action of gravity. At the same time, the microswitch contact displaying the arm position breaks. The double-sided stirrup design makes it possible to use the device in both right-hand and left-hand operation. (J.B.). 2 figs

[en] Audio frequency noise density measurements were performed on weakly superconducting proximity effect bridges on using a cooled transformer and room temperature low noise preamplifier. The noise temperature of the measuring system is approximately 4⁰K for a 0.9 Ω resistor. Noise density was measured as a function of bias current and temperature for the bridges. Excess noise above that expected from Johnson noise for a resistor equal to the dynamic resistance of the bridges was observed in the region near the critical current of the device. At high currents compared to the critical current, the noise density closely approaches that given by Johnson noise

No abstract available

[en] A linear displacement transducer, or extensometer, has been designed and constructed to measure displacements over a range of 0--150 mm. The transducer works by electromagnetic induction and consists of a bifilar coil coaxial with two conducting cylinders, one inside and the other outside the coil. The induction extensometer has been designed to eliminate errors caused by temperature changes from 0⁰ to 1000⁰C. Experimental measurements show an error of 1 mm over the 150-mm displacement range for a temperature change of 500⁰C, and the error should not be larger over the full 1000⁰C temperature range. The displacement range can be varied from 2.5 to 250 mm by scaling the entire experiment up or down, and the temperature compensation can be made for any temperature range that is compatible with the constructional materials

[en] Either of two distinctively different surface flashover mechanisms may lead to the electrical breakdown of an insulator under high voltage stress in vacuum. While the more familiar cathode-initiated mechanism propagates toward the anode and depends on secondary electron multiplication on the insulator surface, anode-initiated flashover propagates in the opposite direction and appears to involve processes related to bulk breakdown. The study of anode-initiated flashover may therefore help to elucidate the physics of the treeing mode of insulation failure. In addition, anode-initiated flashover very likely limits the electric field that can be withstood by conventionally designed insulators having surfaces inclined to avoid electron multiplication. In the work reported here, a variety of dielectric materials were subjected in vacuum (10^-3 to 10^-4 Pa pressure) to high voltage steps having 3 ns risetime. Damage patterns on the insulator surface characteristic of anode-initiated flashover occurred with various experimental arrangements having in common high electric fields directed into the surface of the insulator. The flashover mechanism was studied by detecting emission current from the insulator and by examining the surface damage with the aid of scanning electron microscopy. A model of the flashover mechanism based on these observations is proposed

[en] In the development of fast RF amplitude measurement systems the accuracy is limited above all by the statistical errors of measurement. This limitation is smaller in a non-d.c. measurement technique as compared with a d.c. technique and is constituted by the thermal noise of the equivalent resistances. This is the first report on such a measuring system utilizing the non-linear capacity characteristic of a varactor diode to demodulate the RF amplitude. An accuracy of the amplitude measurement of 10^-5 was achieved in the S band (2.7 GHz) at room temperature and a bandwith of 100 kHz. (orig.)

No abstract available