High-speed Stroboscope Research Articles

Combined time-resolved magnetooptical and electrical flux detection in thin-film superconductors

The dynamic behavior of the current-induced dissipative flux-flow state in a thin-film type I superconductor was studied by simultaneous stroboscopic magnetooptical flux detection and direct recording of the time-resolved flux-flow voltage. Employing high-resolution magnetooptical flux detection with a high-speed stroboscope, it was possible to visualize globally individual multiquantum flux tubes during their rapid motion across the superconducting Pb film, yielding spatial and temporal resolution of better than 1 µm and 0.1 µsec, respectively. Simultaneously, the temporal structure of the flux-flow voltage was recorded using a highly sensitive signal-averaging procedure, thereby yielding a voltage resolution of about 30 nV at a time resolution of 10 nsec (corresponding to a recording bandwidth of 25 MHz). The recorded temporal voltage structures agreed well with the voltages expected from the velocity profiles of all flux tubes existing simultaneously obtained from the magnetooptical data. The experiments are the first to demonstrate full agreement between both independent flux-detection measurements, clearly confirming the existing theory.

Current-induced flux motion in type-I superconducting films studied at 100-ns time resolution

Abstract The motion of magnetic flux tubes in the current-induced resistive state of superconducting Pb films several microns thick has been studied with magnetooptical flux detection in conjunction with a high-speed stroboscope, permitting the time-resolved observation of rapid flux-tube dynamics. A computer model of flux-tube motion has been developed which, when suitably modified, is in reasonable agreement with the experimental results. By measuring the flux-tube velocity directly, it has been determined that the phenomenological expression for the viscous drag coefficient is inadequate and can account for only about 20% of the observed drag force. A recalculation of the viscous drag including quasiparticle diffusion and relaxation effects is offered as an explanation of this disparity.

An Interferometric Technique for Measuring Binary Diffusion Coefficients

An accurate interferometric technique for the measurement of Fick binary diffusion coefficients is described. The technique employs a Mach-Zehnder interferometer together with a high-speed stroboscope and flash-tube light source and a drum camera as a recording system. Successive concentration profiles are recorded in a modified, transient, one-dimensional Arnold diffusion model. A relative-time, relative-position method is used to analyze the interferograms, thus eliminating the uncertainties regarding the absolute diffusion time and exact position above the liquid surface in the diffusion cell as well as the overall mass transfer rate. This technique yields experimental values of the diffusion coefficient with an estimated accuracy of 1/2 percent and reproducibility of approximately ±1 percent. The binary diffusion coefficients for ten materials, four polar and six nonpolar, diffusing in air are presented. Of these, five have been studied by other investigators. The other five have not been previously reported in the literature.

A new stroboscopic light source for precision timing applications

A repetitive light source with reasonably fast rise time and high intensity was required in order to transmit a timing pulse into the high voltage terminal of a d.c. accelerator. A suitable source has been developed which provides all the required features using a special type of stroboscopic tube. The main advantage is that the `jitter' or variation in time delay is extremely small and the system could be developed for nanosecond timing applications. The light source may also be used as a high speed stroboscope.

The measurement of velocities for solid-fluid flow in a pipe

When a stream of particles is conveyed by air or water in a glass pipe two photographs of a portion of the stream are superimposed on the same photographic negative. The pictures are taken by the light from a pair of discharge lamps, the time interval between the flashes being variable and measured by a rotating disk. A more satisfactory light source is a high speed stroboscope, the interval between flashes being predetermined by a setting of a multivibrator. The velocity of a particle is obtained from its displacement measured on the photograph. The method is illustrated by its application to the movement of gravel by air and coal by water.

Stroboscopic-Light Source

A description of a high-speed stroboscope is given. A blocking-oscillator circuit is used to produce short pulses of several amperes of anode current in a high-vacuum tube, the anode of which is coated with fluorescent material.