Flux flow in high-temperature type II superconductors governed by the activation of Frank-Read sources and the resultant motion of core dislocations

The functional form of the volume pinning force F p for high-temperature type II superconductors is derived as the degree of distortion in the flux-line lattice changes. A single mechanism operates in both NbTi and Nb 3 Sn, namely the activation of Frank-Read sources where F p =(1/100)( mu 0 H 2 c2 /DK 2 )b(1-b/0.95) for 0.3<or=b<or=0.9 and F p =(1/21)( mu 0 H 2 c2 /DK 2 )b 1 2/(1-b) 2 for 0.1<or=b<or=0.9 respectively. Above the critical state, flux flow is first characterised by the motion of core dislocations.