Uses and limitations of Superconductors

#### Introduction

• It is no surprise that all major uses for superconductors rely on two major properties:
• Yet their limitations are also very straightforward:
• Low critical temperatures are difficult, expensive and energy intensive to maintain.
• The materials are usually brittle, not ductile and hard to shape.
• They are also chemically unstable in some environments.
• It cannot function with AC electricity, as the switching in AC destroys Cooper pairs.
• There is a "limit" to the current passing through the material before it loses its superconducting properties.

#### Power Transmission

• The lack of resistance means it can transmit electricity without losing power in heat.
• This allows for large current densities (up to about 5 times more) to be conducted in thin wires with no power loss.
• This would also reduce the demand for new power stations & reduce the cost of power.
• However the brittleness of the material in the high temperature superconductors (G2) makes superconducting wires impossible.
• Also since only DC can be used, the voltages cannot be transformed easily.

#### Power Generation

• Using the Meissner effect, a very powerful magnetic field could be generated with the use of superconductors.
• This means a smaller magnet can be used as a rotor/stator in a motor/generator, meaning less mass has to be moved to generate the same amount of power.
• This then leads to an increase in efficiency and thus a decrease in the amount of fossil fuels required to make electricity.

#### Power Storage

• Currently, electricity cannot be stored for long periods of time.
• However with superconductors, this becomes possible with the use of Superconducting Magnetic Energy Storage.
• This is a system that "traps" electricity within it by forcing it to flow inside the SMES until it is necessary to be used.
• Since it's using superconductors, no energy loss occurs during the storage.
• Of course this is used with DC instead of AC.
• This also opens the way to renewable energy sources such as solar power and wind energy as the energy can be stored rather than used immediately.

#### Electronics

• Research is still being done in this field, but there's an almost unlimited scope here.
• In integrated circuits, further miniaturisation is prevented by generation of heat due to resistance (less area, more resistance)
• The speed that signals can be transmitted are also limited by current standards due to resistance.
##### The Josephson Effect
• It was found that if two superconducting layers are separated by an insulator, it is possible for Cooper pairs to pass the barrier without any resistance.
• This is because of a quantum tunnelling effect, and its consequences are that:
• a current will flow through this Josephson function without any Voltage applied
• when a Voltage IS applied, the current oscillates at a constant frequency
• This superconducting film has achieved extremely fast switching speeds ($9 \times 10^{-12}s$), which means that superfast computers can be created.
• It also allows very precise measurements of magnetic flux, allowing for better magnetometers used in geological surveys.

#### Medical Diagnoses

• To diagnose patients, doctors sometime perform Magnetic Resonance Imaging (MRI).
• The process requires extremely strong magnetic fields.
• To generate such fields without superconductors, massive solenoids and large amounts of energy are needed.
• With the use of superconductors and the Meissner effect, the device could be smaller and much more efficient.
• It should be noted that when the desired current level is reached in the SC, it runs in a ''persistent current mode'
• This means it DOES NOT NEED FURTHER INPUT as electricity becomes trapped inside it, flowing with no energy loss.
• Also the ability for it to detect magnetic flux precisely allows the electrical signals sent out by nerves to be analysed
• This is done using a Superconducting Quantum Interference Device (SQUID) which can detect fields as small as $1 \times 10^{-13}$T.

#### Transport

• Mentioned later, the Meissner effect allows for Magnetic levitation, and the ability to travel at high speeds safely due to a lack of friction.
page revision: 1, last edited: 03 Oct 2011 12:16