STABILITY IN Nb[sub 3]Sn CONDUCTORS; MAGNETIC AND SELF-FIELD INSTABILITY CONSIDERATIONS AT 4 K AND 2 K

Abstract

Stability in Nb 3 Sn conductors and cables is an important issue for Nb 3 Sn magnets generally, and High Energy Physics (HEP) magnets specifically. Substantial understanding of the instabilities has been gained in recent years, by adapting and applying well known models to the conductors of the present day. In this work, the results of an investigation of the roles of Residual Resistance Ratio (RRR), d eff , and strand diameter in regimes of both magnetic and self-field instabilities at 4 K as well as 2 K are described. Simple analytic models are used to compare the relative strengths of these effects in various field regimes at 4 K and 2 K. The sensitivity of the instabilities to RRR, d eff , and strand diameter are then described. The influence of the simultaneous changing of external field and strand transport (as would be present in a magnet) on the relative strengths of the self-field and the magnetization based current distributions is then discussed.

Nb3Sn High Field Magnets for the High Luminosity LHC Upgrade Project

“…In order to address the above mentioned question, many authors have developed models [19]- [21] and have performed tests on strands [22]- [25] and cables [26]- [27]. Nonetheless magnet tests have shown a level of complexity not yet reproduced in conductor tests.…”

Influence of heat treatment temperature and Ti doping on low-field flux jumping and stability in (Nb-Ta)3Sn strands

“…In the mid 2000s, conductor instabilities manifested themselves anew in a generation of Nb 3 Sn developmental magnets [13,14]. These instabilities were not of the simple flux jump variety; they included current distribution effects either from transport current redistribution of magnetization [15], or from self-field effects [16][17][18]. Indeed, these effects, well known in NbTi conductors [9,19,20], had re-emerged with high performance Nb 3 Sn.…”

Critical current densities and microstructures in rod-in-tube and tube type Nb3Sn strands—present status and prospects for improvement

“…The goal of internal-Sn strand processing is to achieve high J c in association with a small subelement diameter, d eff , since a small J c d eff product is necessary for the low field stability essential for most applications of Nb 3 Sn [2,3,4]. A small J c d eff product is also very important in multi-pole magnets for improving field quality at the bore because reduction in persistent current magnetization at low fields calls for a reduction in J c d eff product [5].…”

“…The present record of above 3000 A mm −2 (at 4.2 K, 12 T) is held by distributed barrier internal-Sn (or rod-in-tube, alternatively restacked-rod-process, RRP) strands; thus these are one of the favored advanced conductors for near-term HEP machine development and machine upgrades. The goal of internal-Sn strand processing is to achieve a high J c in association with a small subelement diameter, d eff , since a small J c d eff product is necessary for the low-field stability essential for most applications of Nb 3 Sn [2][3][4]. A small J c d eff product is also very important in multi-pole magnets for improving field quality at the bore, because reduction in persistent current magnetization at low fields calls for a reduction in the J c d eff product [5].…”