Other applications of superconductors

1. In high energy physics experiments.

2. In NMR imaging.

3. In magnetohydrodynamic power generation.

4. In magnetic separation for refining ores and chemicals.

5. As memory storage element in computers.

6. In superconducting generators and motors.

7. In superconducting fuses, switches and cables.

SQUID

It consists of a ring of superconducting material with two side arms Aand B. P and Q are the Josephson junctions (insulating layers) of
different thickness. Let p and q represent the phase differencebetween the input current and output current while passing through theinsulator junctions P and Q respectively. In the absence of magneticfield, these two phases are equal. i.e. p = q = 0.When a magnetic field is applied, the phase difference between thereunited currents is directly proportional to the magnetic flux passing through the ring. It can be shown that total current comingout of the ring, I = 2I0 sin0 cos(e/hc)This expression indicates that the output current varies with theapplied magnetic flux and shows oscillations.SOUID is used as a very sensitive magnetometer which can measure veryweak magnetic fields of the order of 10-13 Tesla.

Josephson effect

This effect was first predicted by Josephson in 1962. The experimentalarrangement was a Josephson junction which consists of a thininsulator sandwiched between two superconductors as shown:If the insulator layer is very thin, of the order of 10-50 Å inthickness, a tunneling phenomenon called Josephson tunneling(Josephson effect) takesplace through the insulator. Thus theinsulator turns into a superconductor.With no applied voltage, a dc current (ic) will flow across thejunction. This is called dc Josephson effect. When a small voltage isapplied across the junction, current oscillates with a frequency This is called ac Josephson effect. If the applied voltage isincreased beyond the critical voltage (vc), the current attains anohmic behaviour.If a magnetic field is applied perpendicular to the junction, thevalue of critical supercurrent drops to zero whenever flux through thejunction is a multiple of flux quantum 0. This property is used inSQUID (Superconducting QUantum Interference Device).