A magnetic current sensor with SQUID readout

Luca Callegaro, Bruno Trinchera, Luca Roncaglione

Abstract

A cryogenic magnetic current sensor has been constructed and tested for operation and sensitivity in the ac regime. The sensor is based on a ferromagnetic-core current transformer, coupled to a superconducting-quantum-interferencedevice (SQUID) current detector. The SQUID electronics provides a voltage output that can be coupled to roomtemperature signal recovery electronics, such as a lock-in amplifier. Working in liquid helium (4.2K) the sensor transresistance is about 1.8M in the audio frequency range; the equivalent input current noise of the sensor, at the frequency of 1 kHz, is a few pAHz−1/2 per unit primary winding turn. A major contribution to the detector noise is the thermal noise of the ferromagnetic core; however, an important excess noise contribution at low frequency is also present. The experiment is intended as a feasibility test towards the realization of high-sensitivity electromagnetic devices, such as current comparators, to be employed in primary current and impedance metrology setups working in the audio frequency range.

Keywords

SQUID; current sensor; current detector; current comparator; current transformer

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DOI

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IMEKO TC

TC4 - Measurement of Electrical Quantities

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