Speaker
Description
REBCO tapes are promising material for the
construction of high field magnets because of large engineering
critical current densities at high field, however, the slow normal zone propagation velocity (NZPV) makes the protection against
quenches a critical issue. Stability margin of REBCO cables is
two or three orders of magnitude greater than that of lowtemperature superconducting cables, which leads to a much
slower quench propagation in REBCO cables. On the other hand, heat treatment is a key process to ensure stability of the high
temperature superconductor (HTS) cable. Thus, the main aim of
this article is to analyse the quench behaviors of graded REBCO
tapes with different critical current after heat treatment. To
control the critical current of graded REBCO tapes precisely, heat treatment is taken for 4-mm-wide REBCO conductors under different temperature gradients while maintaining the
same heating time in a vacuum tubular furnace and tested them
to get the relation between heating time and critical current in 77
K. Besides, NZPV of these tapes with various critical current was
investigated at the same current margin (80% Ic) the finding is
that it was more affected by the transport current than the margin. When heated for 60 minutes, the NZPV of the tapes was 1.2 times larger than that of without heat treatment, independent of the temperature. Afterwards heating time has changed, realizing the velocity was positively related to heating time. A
conclusion is drawn that the reason of this tendency is the change of the interlayer resistance of the tape by heating.
