Moshe Sinvani

HT-SMES operating at liquid nitrogen temperatures for electric power quality improvement demonstrating

We have developed and tested a laboratory scale High-T/sub C/ Superconducting Magnetic Energy Storage (HT-SMES) system with storage capacity of up to 1.2 kJ. It was designed to improve the power quality for a consumer supplied by 3-phase standard commercial electric power grid at a consumer power of up to 20 kW. This SMES is based on a high-T/sub C/ superconducting coil with a ferromagnetic core, immersed in liquid nitrogen at 65 K to provide efficient thermal contact with the coolant. We also developed a cryogenic DC-DC converter based on low resistance power MOSFET transistors, providing low losses in the stored energy and high operational efficiency. The power conditioning capability of our HT-SMES was proved, and compensation of voltage drops in the electric grid was successfully demonstrated.

Effect of external magnetic field on the critical current in single and bifilar Bi-2223 tapes

We report on measurements of the critical current in a single and bifilar multifilamentary Bi-2223/Ag tapes, at 77 K, under various DC magnetic fields applied perpendicular to the tape plane. At low applied fields the bifilar tape exhibits higher critical current, as expected. However, above ∼50 G the situation is reversed, i.e., the critical current of the single tape is higher. These results are attributed to the different spatial distribution of the self-field in these two configurations. Our data and analysis imply that, in terms of critical current, the bifilar configuration has over advantage over the single tape configuration only in a limited range of external magnetic fields.

Magneto-optical system for high speed real time imaging

A new magneto-optical system has been developed to expand the range of high speed real time magneto-optical imaging. A special source for the external magnetic field has also been designed, using a pump solenoid to rapidly excite the field coil. Together with careful modifications of the cryostat, to reduce eddy currents, ramping rates reaching 3000 T/s have been achieved. Using a powerful laser as the light source, a custom designed optical assembly, and a high speed digital camera, real time imaging rates up to 30 000 frames per seconds have been demonstrated.

AC-induced DC voltage in HTS coil

Abstract The interplay between AC and DC currents in a High- T c Superconducting (HTS) coil, made of multifilamentary silver-sheathed Bi-2223 tape, was investigated. We observed that the application of a small sinusoidal current in the frequency range of 50–500 Hz into the coil, while it is already carrying a DC current in the range of 16–22.5 A, caused an increase in the coil DC voltage. The DC voltage increment due to the AC signal is found to increase linearly with frequency and quadratically with amplitude. The DC voltage increment increases as the coil current grows towards its critical value of 22.2 A. This result may be important in some power applications such as fault current limiters (FCL) and superconducting magnet energy storage (SMES) based on HTS coils.

Direct current voltage increment due to ac coupling in a high Tc superconducting coil

The voltage–current characteristics of a superconducting coil, made of multifilamentary silver-sheathed Bi2Sr2Ca2Cu3O10+δ tape, are investigated. We find that a small ac current Iac superimposed on a relatively large dc current Idc causes a significant increase in the coil dc voltage, approximately proportional to Idc, Iac2, and the ac frequency. We attribute this effect to the nonlinear magnetoresistance of the coil, and discuss its significance in power applications of high Tc superconducting coils, such as fault current limiters and superconducting magnetic energy storage devices.

All optical modulator based on silicon resonator

In this paper we present an all-optical silicon modulator, where a silicon slab (450 μm) thick is coated on both sides to get a Fabry-Perot resonator for laser beam at wavelength of 1550nm. Most of the modulators discussed in literature, are driven by electrical field rather than by light. We investigate new approaches regarding the dependence of the absorption of the optical signal on the control laser pulse at 532 nm having 5nm pulse width. Our silicon based Fabry-Perot resonator increases the intrinsic c-Si finesse to >10, instead of the uncoated silicon with natural finesse of 2.5. The improved finesse is shown to have significant effect on the modulation depth using a pulsed laser. A modulation of 12dB was attained. The modulation is ascribed to two different effects - The Plasma Dispersion Effect (PDE) and the Thermo- Optic Effect (TOE). The PDE causes increase in the signal absorption in silicon via the absorption of the control laser light. On top of that, the transmission of the signal can decrease dramatically in high finesse resonators due to change in the refractive index due to TOE. The changes in the signals absorption coefficient and in the refractive index are the result of incremental change in the concentration of free carriers. The TOE gives rise to higher refractive index as opposed to the PDE which triggers a decrease in the refractive index. Finally, tradeoff considerations are presented on how to modify one effect to counter the other one, leading to an optimal device having reduced temperature dependence.

Usage of Laser Timing Probe for Sensing of Programmed Charges in EEPROM Devices

A method to measure programmed charges in EEPROM devices is presented. The measurement of the charges was made with subtraction of images captured using a laser timing probe. The effect of the charges is expressed over the captured images due to the plasma dispersion effect.

Improved Margins Detection of Regions Enriched with Gold Nanoparticles inside Biological Phantom

Utilizing the surface plasmon resonance (SPR) effect of gold nanoparticles (GNPs) enables their use as contrast agents in a variety of biomedical applications for diagnostics and treatment. These applications use both the very strong scattering and absorption properties of the GNPs due to their SPR effects. Most imaging methods use the light-scattering properties of the GNPs. However, the illumination source is in the same wavelength of the GNPs’ scattering wavelength, leading to background noise caused by light scattering from the tissue. In this paper we present a method to improve border detection of regions enriched with GNPs aiming for the real-time application of complete tumor resection by utilizing the absorption of specially targeted GNPs using photothermal imaging. Phantoms containing different concentrations of GNPs were irradiated with a continuous-wave laser and measured with a thermal imaging camera which detected the temperature field of the irradiated phantoms. By modulating the laser illumination, and use of a simple post processing, the border location was identified at an accuracy of better than 0.5 mm even when the surrounding area got heated. This work is a continuation of our previous research.

Magnetic flux oscillations in partially irradiated Bi2Sr2CaCu2O8+δ crystals

We report on generation of spatiotemporal oscillations of magnetic flux in a Bi2Sr2CaCu2O8+δ crystal irradiated in part with 2.2 GeV Au ions. Flux oscillations are spontaneously excited after exposing the sample to a steady magnetic field near the order-disorder vortex phase transition line. The oscillations originate at the border between the irradiated and nonirradiated parts of the sample and propagate into the nonirradiated region toward the sample edge. Previously reported flux oscillations were observed in the vicinity of undefined defects in as grown Bi2Sr2CaCu2O8+δ crystals. Observation of spontaneous oscillations in partially irradiated samples present the first attempt to generate such oscillations in a controlled manner.

Initiatory concept of localized CO2 laser-based tapering rig for realization of in-fiber devices

We present the development procedure as well as preliminary fabrication results for a CO 2 laser-based tapering rig allowing one stage tapering of optical fibers. Our aim is to develop in-fiber devices constructed from fibers filled with various materials, which can be drawn from thick preforms using the presented procedure. The constructed tapering rig consists of a CO 2 laser as the heating source, ellipsoid-based mirror optics, and computer-controlled high-precision motors.