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Eddy Currents

Eddy Currents

Since eddy currents occur only in conductors, magnets can separate metals from other materials. For example, in a recycling center, trash is dumped in batches down a ramp, beneath which lies a powerful magnet. Conductors in the trash are slowed by eddy currents, while nonmetals in the trash move on, separating from the metals. This works for all metals, not just ferromagnetic ones.
Other major applications of eddy currents appear in metal detectors and the braking systems of trains and roller...

Torque On A Current Loop In A Magnetic Field

Torque On A Current Loop In A Magnetic Field

The most common application of magnetic force on current-carrying wires is in electric motors. These consist of loops of wire, which are placed between the magnets with a magnetic field. When current flows through the loops, the magnetic field applies torque, which causes the shaft to rotate, thus converting electrical energy to mechanical energy.
Consider a rectangular current-carrying loop containing N turns of wire, placed in a uniform magnetic field. The net force on a current-carrying loop...

Magnetic Field Of A Current Loop

Magnetic Field Of A Current Loop

Consider a circular loop with a radius a, that carries a current I. The magnetic field due to the current at an arbitrary point P along the axis of the loop can be calculated using the Biot-Savart law.

Magnetic Field Due to Two Straight Wires

Magnetic Field Due to Two Straight Wires

Consider two parallel straight wires carrying a current of 10 A and 20 A in the same direction and separated by a distance of 20 cm. Calculate the magnetic field at a point "P2", midway between the wires. Also, evaluate the magnetic field when the direction of the current is reversed in the second wire.

Toroids

Toroids

A toroid is a closely wound donut-shaped coil constructed using a single conducting wire. In general, it is assumed that a toriod consists of multiple circular loops perpendicular to its axis.
When connected to a supply, the magnetic field generated in the toroid has field lines circular and concentric to its axis. Conventionally, the direction of this magnetic field is expressed using the right-hand rule. If the fingers of the right hand curl in the current direction, the thumb points in...

Magnetic Field Due To A Thin Straight Wire

Magnetic Field Due To A Thin Straight Wire

Consider an infinitely long straight wire carrying a current I. The magnetic field at point P at a distance a from the origin can be calculated using the Biot-Savart law.

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Related Experiment Video

Updated: Mar 11, 2026

Quantifying the Relative Thickness of Conductive Ferromagnetic Materials Using Detector Coil-Based Pulsed Eddy Current Sensors

Quantifying the Relative Thickness of Conductive Ferromagnetic Materials Using Detector Coil-Based Pulsed Eddy Current Sensors

Published on: January 16, 2020

The eddy current probe array for Keda Torus eXperiment.

Zichao Li¹, Hong Li¹, Cui Tu¹

¹CAS Key Laboratory of Geospace Environment, Department of Modern Physics, University of Science and Technology of China, Hefei 230026, People's Republic of China.

The Review of Scientific Instruments

|December 3, 2016

Summary

A new eddy current probe array accurately measures eddy currents in reversed field pinch devices, crucial for controlling plasma instabilities and improving high-parameter operation. This diagnostic tool enhances understanding of plasma-wall interactions.

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Last Updated: Mar 11, 2026

Quantifying the Relative Thickness of Conductive Ferromagnetic Materials Using Detector Coil-Based Pulsed Eddy Current Sensors

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Published on: January 16, 2020

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Published on: June 28, 2018

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Published on: January 4, 2011

Area of Science:

Plasma physics
Fusion energy research
Electromagnetism

Background:

Conductive shells in reversed field pinch devices are critical for plasma stability.
Plasma instabilities like resistive wall and tearing modes are influenced by eddy currents in the shell.
External coil-induced eddy currents also impact active instability control.

Purpose of the Study:

To develop and validate a diagnostic tool for measuring eddy currents in composite shells.
To assess the impact of eddy currents on plasma stability in reversed field pinch devices.
To enable precise control of plasma instabilities through real-time eddy current monitoring.

Main Methods:

Utilized an eddy current probe array combined with magnetic probes to detect eddy currents.
Measured currents through copper bolts connecting poloidal shield copper shells for comprehensive coverage.
Validated measurements against a 3D electromagnetic model using a 1/4 vacuum vessel bench test.
Recorded eddy current data during discharges in the Keda Torus eXperiment (KTX) device.

Main Results:

Achieved high resolution for magnetic field (2 G) and eddy current (6 A) measurements.
Demonstrated sensitivity to vortex electric fields with a resolution of 0.2 mV/cm.
Observed typical toroidal and poloidal eddy currents reaching 3.0 kA and 1.3 kA, respectively, during KTX discharges.
Preliminary data showed good agreement with simulation results.

Conclusions:

The developed eddy current probe array is a sensitive and effective diagnostic for reversed field pinch devices.
Accurate eddy current measurement is vital for understanding and controlling plasma instabilities.
This technology supports advancements in achieving high-parameter plasma operation in fusion devices.