Unit 6 - Superconductor stability and margin

<!--HTML--><p>This unit belongs to the third part of the course, which is focussed on&nbsp;providing some elements of superconductivity. Here we outline the main reasons requiring a very peculiar layout for a high current density superconducting wires, namely (i) fine filaments and (ii) a copper matrix.</p> <p>We will first discuss the magnetization in a superconductor, the Bean theory and the conditions for&nbsp;full penetration of the magnetic field. This mechanisms generates&nbsp;the conditions for stability of the superconductor: a bulk superconductor cannot transport large current densities, but it must be split in fine filaments. The relation between filament size, current density and temperature margin is therefore derived.</p> <p>The second part is dedicated to prove that a copper matrix is needed to enhance the tolerance to transitions to normal conducting state induced by local deposition of heat.</p> <p>Finally we will discuss the concept of margin for a superconducting magnets: we will start with the&nbsp;loadline&nbsp;margin, an empirical concept widely used in the magnet design. We will translate the loadline margin into a temperature and enthalpy margin for both Nb3Sn and Nb-Ti.</p>