The Resistance and Strength of Soft Solder Splices between Conductors in MICE Coils Page: 1 of 4
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MICE Note 308
The Resistance and Strength of Soft Solder
Splices between Conductors in MICE Coils
H. Wu, H. Pan, M. A. Green Member IEEE, D. Dietderich Member IEEE, T. E. Gartner,
H. C. Higley, M. Mentink, D. G. Tam, F. Y. Xu, F. Trillaud, X. K. Liu, L. Wang, and S. X. ZhengAbstract- Two of the three types of MICE magnets will have
splices within their coils. The MICE coupling coils may have as
many as fifteen one-meter long splices within them. Each of the
MICE focusing coils may have a couple of 0.25-meter long
conductor splices. Equations for the calculation of resistance of
soldered lap splices of various types are presented. This paper
presents resistance measurements of soldered lap splices of
various lengths. Measured splice resistance is shown for
one-meter long splices as a function of the fabrication method.
Another important consideration is the strength of the splices.
The measured breaking stress of splices of various lengths is
presented in this paper. Tin-lead solders and tin-silver solders
were used for the splices that were tested. From the data given in
this report, the authors recommend that the use of lead free
solders be avoided for low temperature coils.
Index Terms-Conductor Splice Resistance and Strength.
I. INTRODUCTION
Splices are common occurrence in superconducting
magnets of all types [1]. Splices fall into two general
categories superconducting splices and normal splices.
Magnets that must run in persistent mode generally have
splices that are superconducting. Normal splices involve
connecting the normal stabilizer metal of one conductor with
the normal metal of the second conductor. In a normal splice
the current flow from the superconductor of the first conductor
through normal metal to the superconductor of the second
conductor. This paper discusses normal splices between
conductors that can be wound into a superconducting coil.
The magnets for the muon ionization cooling experiment
(MICE) [2] cooling channel are a case in point. Two types of
these coils contain splices because the available conductor
piece lengths are too short. Because the coil currents are low
(<300 A) and the splices are not cooled with helium directly,
the splice resistance must also be low (<10 nQ). MICE coil
splices must have the following characteristics; 1) the splice
must be less than one turn length, 2) the longitudinal or radial
space occupied by an insulated splice must be less than the
space occupied by two turns within the coil.
Manuscript received 3 August 2010. This work was supported by funds of
the cryogenic and superconductivity technology innovation project under the
"985-2" plan of Harbin Institute of Technology. This work was also supported
by the Office of Science, United States Department of Energy under contract
DE-AC-02-05CH 1231.
H. Wu, H. Pan, F. Y. Xu, X. K. Liu, and S. X. Zheng are with the Institute
of Cryogenics and Superconductive Technology, HIT, Harbin 150001, China.
L. Wang, is with the Shanghai Institute of Applied Physics, Shanghai 201204,
China. M. A. Green is with Lawrence Berkeley National Laboratory,
Berkeley CA, 94720 USA (e-mail: magreenglbl.gov). D. Diederich, T.
Gartner, H. Higley, M. Mentik D. Tam, and F. Trillaud are also with LBNL.Cold Welded Butt Splice
L a Si
Soft Soldered Lap SpliceUp-down Lap Splice
(Layer-to-layer Splice)Sieb-ie Lap Splce
(witi ae pieFig. 1. Cold Welded Butt Splice and Two Types of Lap Splices
Fig. 1 shows the three types of normal splices were studied;
cold welded butt splices, soldered up-down lap splices, and
soldered side-by-side lap splices [3], [4]. The fabricators for
the coupling magnet [5] and the AFC magnet [6] have chosen
to make their splices at the ends of a layer, so that the splice is
a transition from one layer to the next. Therefore, the
measurements presented here are for up-down soldered lap
splices, which can be used at the ends of a coil layer.
II. CALCULATION OF SPLICE PARAMETERS
A. Calculation of the Splice Resistance
The resistance for a butt splice can be expressed as follows;R = pLr (r+1)
Ac1 r(1)
where Rj is the resistance of the splice; pj is the electrical
resistivity of the weld material in the splice; Lj is the length of
the fused region within the splice; r is the copper to
superconductor ratio for the conductor; and Acj is the
cross-sectional area of the conductor. For a MICE conductor
butt splice, p1 = 1.6x10-9 Qm, Lj = 100 [um, and Acj = 1.5x10-6
m2. The calculated resistance of this splice is 106 nQ, which
is too high for MICE magnets [7].
The calculated resistance of a lap splice is divided into two
terms, the copper resistance and the solder resistance. The
un-insulated MICE coupling coil conductor has a width w =
1.6 mm and a thickness t = 0.95 mm. The coupling coil
conductor has rounded corner R, = 0.2 mm. The resistance of
up-down lap splices is given by the following expression;R = 2Pcutc" + soltsol
L(w-2Rc) L(w -2Rc)(2)
1
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Wu, Hong; Pan, Heng; Green, Michael A.; Dietderich, Dan; Gartner, T. E.; Higley, Hugh C. et al. The Resistance and Strength of Soft Solder Splices between Conductors in MICE Coils, article, August 3, 2010; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc1012448/m1/1/: accessed April 18, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.