5. Superconductors: Conductors and Applications Flashcards Preview

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Flashcards in 5. Superconductors: Conductors and Applications Deck (17)
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1
Q

What are the basic material requirements for a superconducting wire?

A
  • Ductile/easy to form into a wire
  • Large Hc2 (field at which superconductivity disappears)
  • Large Jc (Critical current)
2
Q

What force interaction occurs at the critical current?

A

At the critical current point, the Lorentz force on the vortex lines cause them to start moving (it exceeds the pinning force)

3
Q

Why is the transition to higher resistances not a sudden change with straight lines at the critical current?

A

Because of thermal fluctuations, the random vibrations can cause breakdown of superconductivity at a range of currents

4
Q

According to the bean critical state model, what happens in a constant magnetic field to a superconductor?

A

A constant current density Jc is established up to some depth in the superconductor

5
Q

What happens to Jc if Temp increases, and thus the penetration depth

A

It decreases, so thus the penetration depth must increase

6
Q

What is ‘quenching’ in superconductors?

A

It is the cascade process where an initial temperature increase in a superconductor causes Jc to fall, the penetration depth to increase to make up for this, the moving of flux lines to do this is dissipative and releases heat, causing a knock on further temperature rise and so on.

7
Q

What are the methods to improve the stability of superconductors and reduce ‘quenching’?

A
  • Add conductive metal eg copper (improves cooling of superconductor, called cryogenic stabilisation)
  • Adiabatic stabilisation (find a critical thickness from the critical state model)
8
Q

Is superconductivity resistance-less for both AC and DC?

A

No, just DC as AC moves flux lines when it reverses direction

9
Q

Why is there a limit to the amount of copper you can put around a superconductive cable?

A

As if it is too conductive you’ll get eddy current losses

10
Q

What does the AC losses in a type 2 superconductor depend on?

A

The frequency and the thickness of the conductor

11
Q

Why is it beneficilal to use a phase diagram to process a material such that it grows a precipitate?

A

THe precipitation phase will act as pinning centres for magnetic flux lines

12
Q

What differentiates intermetallic materials from metals?

A

They have covelent bonds rather than metalic, which makes them brittle and hard to deal with

13
Q

What are the 3 practical methods for producing Nb3Sn wires (intermetallic)?

A

Bronze process
Internal Tin
Powder in tube (PIT)

14
Q

What are the two main issues processing the ceramic High temperature superconductors into practical wires?

A
  • Theyre too brittle
  • Crystaline misorientation drastically reduces Jc (therfore they need to processed in a way to ensure crystalign allignment)
15
Q

What industries are high temperature superconducting wires aimed at?

A

Industries willing to pay alot for small increases in performance eg Military, aviation, medicine

16
Q

What is the largest market for superconducting magnets?

A

In Magnetic Resonance Imaging (MRI)(Medical)

17
Q

Name uses of superconducting magnets

A

MRI, HIgh field solenoids (up to 20T, used in scientific research)