Superconducting switch

An electrical switch comprising:

• a loop of superconducting material,
• wherein the loop comprises a first branch and a second branch, the first and second branches being electrically connected in parallel between a first terminal and a second terminal, and wherein the loop has an axis which is substantially normal to the plane of the loop, and
• wherein the loop is configured to carry a transport current between the first terminal and the second terminal;
• and
• a magnetic field generator,
• wherein the magnetic field generator is configured to generate a time-varying magnetic field through the loop with the direction of the magnetic field through the loop being generally parallel to, or having a component which is generally parallel to, the axis of the loop,
• wherein the magnetic field generator is configured to be selectively activated and de-activated to switch the electrical switch between a low-resistance state and a higher-resistance state, and
• wherein, in the low-resistance state, the magnetic field generator does not generate the varying magnetic field through the loop and the transport current flows through the loop between the two terminals, and, in the higher-resistance state, the magnetic field generator generates the varying magnetic field through the loop, inducing a screening current in the loop, such that the sum of the transport current and the screening current in one or more of the first branch and second branch approaches the critical current, is substantially equal to the critical current or is greater than the critical current of the superconducting material.