Test results of TQS03: a LARP shell-based Nb3Sn quadrupole using 108/127 conductor Page: 2 of 13
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Technology Quadrupole (TQ), a 1-meter long 90 mm aperture quadrupole, was the first step toward
this goal. This series of magnets was developed in parallel between FNAL and LBNL, using the same
coils in two different mechanical structures. In this paper, we focus only on magnets which were
tested in the TQS shell-based structure (Technology Quadrupole Shell) relying on the "key and
bladder" technology -. This structure imparts a low preload to the coils at room temperature by
the use of interference keys inserted by water-pressurized bladders which are removed before cool-
down. The differential thermal contraction between the outside Aluminum (7075 T6) shell and the
Iron yoke (1018 steel) completes the full pre-loading of the coil during cool-down. This technique
prevents any pre-stress overshoot of the strain sensitive Nb3Sn conductor since the required
operational preload is attained after cool-down.
Since 2006, nine TQS magnets have been tested (TQSOla/b/c, TQS02a/b/c/d and TQS03a/b). In
all of them, the same mechanical structure was used with various degrees of preloads. Only the coils
exhibited differences in terms of conductor and pole piece material. The change of pole piece material
from Aluminum Bronze in TQS01 to Titanium Alloy (Ti6Al4V) in the TQS02 and TQS03 series was
done for mechanical reasons detailed in ,  and . In addition, the change from the OST
Modified Jelly Roll (MJR) strand (Jc of 1800 A/mm2 at 4.2 K and 12 T) to the OST RRP (Restacked
Rod Process) 54/61 strand  (Jc of 2800 A/mm2 at 12 T and 4.2 K) allowed an increase of the
calculated short-sample gradient at 4.2 K from 215 T/m to 243 T/m in the quadrupole aperture. The
detailed comparison between these two series can be found in .
The TQSO2 series exhibited unstable behavior at 1.9 K with erratic and reduced quench current
with respect to the more stable 4.3 K plateaus. Studies conducted (-) to understand this issue
led to the development of a new conductor: the OST RRP 108/127 strand (-) with smaller
filaments, more copper and lower Jc. This new conductor has been used to fabricate four TQ coils (30,
31, 32 and 33) - first assembled in the TQSO3a magnet. The objective of the first test (TQSO3a) was to
evaluate the performance of the new OST 108/127 conductor at 4.3 K and at 1.9 K. In the second test
(TQSO3b), the purpose was to retest and study the magnet performance with an adjusted increase in
After describing the conductor and the magnet design in the first section, the second part of this
article reports on the mechanical behavior of the TQSO3 magnets during assembly, cool-down and
excitation. In the last section, the quench performance of these magnets is analyzed and compared
with results from TQSO2c; a magnet using 54/61 conductor.
2. Magnet design
2.1. Conductor parameters and magnetic design
This article is focused on the TQSO3 series. Nevertheless, for comparison, we need to refer to the
TQSO2 series and in particular to the TQSO2c magnet. As mentioned in the introduction, the TQSO2
series had a reduced performance at 1.9 K with quenches occurring at a lower short sample current
percentage than at 4.3 K .
(a) n*" (b) =C
Figure 1. TQSO2 and TQSO3 strand cross-sections: 0.7 mm
OST RRP strand with 54/61 stack (a) and 0.7 mm OST RRP
strand with 108/127 stack (b)
This behavior is attributed to instabilities in superconducting strands. Several theories are under
investigation. One of the theories includes "flux jump" instabilities in superconductor driven by the
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Felice, H.; Ambrosio, G.; Bajko, M.; Barzi, E.; Bordini, B.; Bossert, R. et al. Test results of TQS03: a LARP shell-based Nb3Sn quadrupole using 108/127 conductor, article, September 13, 2009; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc1014234/m1/2/: accessed July 23, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.