IEC 61788-4:2011

Superconductivity - Part 4: Residual resistance ratio measurement - Residual resistance ratio of Nb-Ti composite superconductors

IEC 61788-4:2011 covers a test method for the determination of the residual resistance ratio (RRR) of composite superconductors comprised of Nb-Ti filaments and Cu, Cu-Ni or Cu/Cu-Ni matrix. This method is intended for use with superconductors that have a monolithic structure with rectangular or round cross-section, RRR less than 350, and cross-sectional area less than 3 mm2. All measurements are done without an applied magnetic field. The method described in the body of this standard is the "reference" method and optional acquisition methods are outlined in Clause A.3. This third edition constitutes a technical revision which adds two new annexes: "Uncertainty considerations" (Annex B) and "Uncertainty evaluation in test method of RRR for NbTi" (Annex C). Copper is used as a matrix material in multifilamentary superconductors and works as an electrical shunt when the superconductivity is interrupted. It also contributes to recovery of the superconductivity by conducting heat generated in the superconductor to the surrounding coolant. The cryogenic-temperature resistivity of copper is an important quantity, which influences the stability of the superconductor. The residual resistance ratio is defined as a ratio of the resistance of the superconductor at room temperature to that just above the superconducting transition.

Supraconductivité - Partie 4: Mesure du rapport de résistance résiduelle - Rapport de résistance résiduelle des supraconducteurs composites de Nb-Ti

La CEI 61788-4:2011 spécifie une méthode d'essai pour la détermination du rapport de résistance résiduelle (RRR) de supraconducteurs composites constitués de filaments de Nb-Ti et d'une matrice de Cu, Cu-Ni ou Cu/Cu-Ni. Cette méthode est destinée à être utilisée avec des supraconducteurs présentant une structure monolithique avec une section rectangulaire ou circulaire, un rapport RRR inférieur à 350 et une surface de section inférieure à 3 mm2. Toutes les mesures sont effectuées sans appliquer de champ magnétique. La méthode décrite dans le corps de texte de la présente norme est la méthode de "référence" et des méthodes d'acquisition facultatives sont présentées à l'Article A.3. Cette troisième édition constitue une révision technique qui ajoute deux nouvelles annexes: "Considérations relatives à l'incertitude" (Annexe B) et "Evaluation de l'incertitude de la méthode d'essai de RRR (rapport de résistance résiduelle) de NbTi" (Annexe C). Le cuivre est utilisé comme matériau de matrice dans les supraconducteurs multifilamentaires et fonctionne comme une dérivation électrique lorsque la supraconductivité est interrompue. Il contribue également à la reprise de la supraconductivité en dirigeant la chaleur générée dans le supraconducteur vers le fluide de refroidissement environnant. La résistivité à la température cryogénique du cuivre est une grandeur importante qui influe sur la stabilité du supraconducteur. Le rapport de résistance résiduelle est défini comme le rapport entre la résistance du supraconducteur à température ambiante et celle immédiatement supérieure à la transition supraconductrice.

General Information

• Status: Published
• Publication Date: 10-Jul-2011
• ICS: 17.220.20 - Measurement of electrical and magnetic quantities
• ICS: 29.050 - Superconductivity and conducting materials
• Technical Committee: TC 90 - Superconductivity
• Drafting Committee: WG 4 - TC 90/WG 4
• Current Stage: DELPUB - Deleted Publication
• Completion Date: 19-Jan-2016

Standards Content (Sample)

IEC 61788-4
®

Edition 3.0 2011-07
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside


Superconductivity –
Part 4: Residual resistance ratio measurement – Residual resistance ratio of
Nb-Ti composite superconductors

Supraconductivité –
Partie 4: Mesure du rapport de résistance résiduelle – Rapport de résistance
résiduelle des supraconducteurs composites de Nb-Ti

IEC 61788-4:2011

---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC 61788-4
®

Edition 3.0 2011-07
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside


Superconductivity –
Part 4: Residual resistance ratio measurement – Residual resistance ratio of
Nb-Ti composite superconductors

Supraconductivité –
Partie 4: Mesure du rapport de résistance résiduelle – Rapport de résistance
résiduelle des supraconducteurs composites de Nb-Ti

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX U
ICS 17.220.20; 29.050 ISBN 978-2-88912-554-8

® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale

---------------------- Page: 3 ----------------------
– 2 – 61788-4  IEC:2011
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 7
4 Requirements . 8
5 Apparatus . 8
5.1 Material of measuring mandrel or of measuring base plate . 8
5.2 Diameter of the measuring mandrel and length of the measuring base plate . 8
5.3 Cryostat for the resistance, R , measurement . 9
2
6 Specimen preparation. 9
7 Data acquisition and analysis . 9
7.1 Resistance (R ) at room temperature . 9
1
7.2 Resistance (R *) just above the superconducting transition . 9
2
7.3 Correction on measured R * for bending strain . 11
2
7.4 Residual resistance ratio (RRR) . 12
8 Uncertainty and stability of the test method . 12
8.1 Temperature . 12
8.2 Voltage measurement. 12
8.3 Current . 12
8.4 Dimension . 12
9 Test report. 13
9.1 RRR value . 13
9.2 Specimen . 13
9.3 Test conditions . 13
Annex A (informative) Additional information relating to the measurement of RRR . 15
Annex B (informative) Uncertainty considerations . 21
Annex C (informative) Uncertainty evaluation in test method of RRR for Nb-Ti . 25

Figure 1 – Relationship between temperature and resistance. emperature T * is that at
c
the intersection point . 8
Figure 2 – Voltage (U) versus temperature (T) curves and definitions of each voltage . 10
Figure A.1 – Definition of voltages . 16
Figure A.2 – Bending strain dependency of RRR for pure Cu matrix of Nb-Ti composite
superconductors (comparison between measured values and calculated values) . 18
Figure A.3 – Bending strain dependency of RRR for round Cu wires . 18
Figure A.4 – Bending strain dependency of normalized RRR for round Cu wires . 19
Figure A.5 – Bending strain dependency of RRR for rectangular Cu wires . 19
Figure A.6 – Bending strain dependency of normalized RRR for rectangular Cu wires . 20
Figure C.1 – Distribution of observed RRR of Cu/Nb-Ti composite superconductor . 28

Table B.1 – Output signals from two nominally identical extensometers . 22
Table B.2 – Mean values of two output signals . 22

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61788-4  IEC:2011 – 3 –
Table B.3 – Experimental standard deviations of two output signals. 22
Table B.4 – Standard uncertainties of two output signals . 22
Table B.5 – Coefficient of variations of two output signals. 23
Table C.1 – Uncertainty of each measurement . 27

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– 4 – 61788-4  IEC:2011
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________

SUPERCONDUCTIVITY –

Part 4: Residual resistance ratio measurement –
Residual resistance ratio of Nb-Ti composite superconductors


FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61788-4 has been prepared by IEC technical committee 90:
Superconductivity.
This third edition cancels and replaces the second edition published in 2007. It constitutes a
technical revision. The main revisions are the addition of two new annexes, "Uncertainty
considerations" (Annex B) and "Uncertainty evaluation in test method of RRR for NbTi"
(Annex C).

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61788-4  IEC:2011 – 5 –
The text of this standard is based on the following documents:
FDIS Report on voting
90/263/FDIS 90/275/RVD

Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts of the IEC 61788 series, published under the general title Superconductivity,
can be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.

IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.

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– 6 – 61788-4  IEC:2011
INTRODUCTION
Copper is used as a matrix material in multifilamentary superconductors and works as an
electrical shunt when the superconductivity is interrupted. It also contributes to recovery of
the superconductivity by conducting heat generated in the superconductor to the surrounding
coolant. The cryogenic-temperature resistivity of copper is an important quantity, which
influences the stability of the superconductor. The residual resistance ratio is defined as a
ratio of the resistance of the superconductor at room temperature to that just above the
superconducting transition.
In this International Standard, the test method of residual resistance ratio of Nb-Ti composite
superconductors is described. The curve method is employed for the measurement of the
resistance just above the superconducting transition. Other methods are described in
Clause A.3.

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61788-4  IEC:2011 – 7 –
SUPERCONDUCTIVITY –

Part 4: Residual resistance ratio measurement –
Residual resistance ratio of Nb-Ti composite superconductors



1 Scope
This part of IEC 61788 covers a test method for the determination of the residual resistance
ratio (RRR) of composite superconductors comprised of Nb-Ti filaments and Cu, Cu-Ni or
Cu/Cu-Ni matrix. This method is intended for use with superconductors that have a monolithic
structure with rectangular or round cross-section, RRR less than 350, and cross-sectional
2
area less than 3 mm . All measurements are done without an applied magnetic field.
The method described in the body of this standard is the “reference” method and optional
acquisition methods are outlined in Clause A.3.
2 Normative references
The following referenced document is indispensable for the application of this document. For
dated references, only the edition cited applies. For undated references, the latest edition of
the referenced document (including any amendments) applies.
IEC 60050-815, International Electrotechnical Vocabulary (IEV) – Part 815: Superconductivity
3 Terms and definitions
For the purpose of this document, the terms and definitions given in IEC 60050-815 and the
following apply.
3.1
residual resistance ratio
RRR
the ratio of resistance at room temperature to the resistance just above the superconducting
transition
NOTE In this standard for Nb-Ti composite superconductors, the room temperature is defined as 293 K (20 °C),
and the residual resistance ratio is obtained in Equation (1) below, where the resistance (R ) at 293 K is divided by
1
the resistance (R ) just above the superconducting transition.
2
R
1
RRR= (1)
R
2
Figure 1 shows schematically a resistance versus temperature curve acquired on a specimen while measuring the
cryogenic resistance. Draw a line in Figure 1 where the resistance sharply increases (a), and draw also a line in
Figure 1 where the temperature increases but the resistance remains almost the same (b). The value of resistance
at the intersection of these two lines at T=T *, A, is defined as resistance (R ) just above the superconducting
2
c
transition.

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– 8 – 61788-4  IEC:2011

Temperature T * is that at the intersection point.
c
Figure 1 – Relationship between temperature and resistance
4 Requirements
The resistance measurement both at room and cryogenic temperatures shall be performed
with the four-terminal technique.
The target relative combined standard uncertainty of this method is defined as an expanded
uncertainty (k = 2) not to exceed 5 % based on the coefficient of variation (COV) of 2,5 % in
the intercomparison test (see Clause C.2).
The maximum bending strain, induced during mounting the specimen, shall not exceed 2 %.
5 Apparatus
5.1 Material of measuring mandrel or of measuring base plate
Material of the measuring mandrel for a coiled specimen or of the measuring base plate for a
straight specimen shall be copper, aluminium, silver, or the like whose thermal conductivity is
equal to or better than 100 W/(m⋅K) at liquid helium temperature (4,2 K). The surface of the
material shall be covered with an insulating layer (tape or a layer made of polyethylene
terephthalate , polyester, polytetrafluoroethylene , etc.) whose thickness is 0,1 mm or less.
5.2 Diameter of the measuring mandrel and length of the measuring base plate
Diameter of the measuring mandrel shall be large enough to keep bending strain of the
specimen less than or equal to 2 %.
The measuring base plate shall be at least 30 mm long in one dimension.

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61788-4  IEC:2011 – 9 –
5.3 Cryostat for the resistance, R , measurement
2
The cryostat shall include a specimen support structure and a liquid helium reservoir for the
resistance, R , measurement. The specimen support structure shall allow the specimen,
2
which is mounted on a measurement mandrel or a measurement base plate, to be lowered
and raised into, and out of, a liquid helium bath. In addition, the specimen support structure
shall be made so that a current can flow through the specimen and the resulting voltage
generated along the specimen can be measured.
6 Specimen preparation
The test specimen shall have no joints or splices, and shall be 30 mm or longer. The distance
between two voltage taps (L) shall be 25 mm or longer. A thermometer for measuring
cryogenic temperature shall be attached near the specimen.
Some mechanical method shall be used to hold the specimen against the insulated layer of
the measurement mandrel or base plate. Special care shall be taken during instrumentation
and installation of the specimen on the measurement mandrel or on the measurement base
plate so that no excessive force, which may cause undesired bending strain or tensile strain,
shall be applied to the specimen.
The specimen shall be instrumented with current contacts near each end of the specimen and
a pair of voltage contacts over a central portion of the specimen. The specimen shall be
mounted on a measurement mandrel or on a measurement base plate for these measure-
ments. Both resistance measurements, R and R , shall be made on the same specimen and
1 2
the same mounting.
7 Data acquisition and analysis
7.1 Resistance (R ) at room temperature
1
The mounted specimen shall be measured at room temperature (T (K)), where T satisfies
m m
the following condition, 273 ≤ T ≤ 308. A specimen current (I (A)) shall be applied so that
m 1
2 2
the current density is in the range of 0,1 A/mm to 1 A/mm based on the total wire cross-
sectional area, and the resulting voltage (U (V)), I and T shall be recorded. Equation (2)
1 1 m
below shall be used to calculate the resistance (R ) at room temperature. The resistance (R )
m 1
at 293 K (20 °C) shall be calculated using equation (3) for a wire with Cu matrix. The value of
R shall be set equal to R , without any temperature correction, for wires that do not contain
1 m
a pure Cu component.
U
1
R = (2)
m
I
1
R
m
R = (3)
1
[1 + 0,00393× (T – 293)]
m
7.2 Resistance (R *) just above the superconducting transition
2
Under a strained condition of the specimen, the measured cryogenic resistance, R *, is not a
2
correct value for R . The corresponding correction of the strain effect will be described in 7.3.
2
7.2.1 The specimen, which is still mounted as it was for the room temperature measurement,
shall be placed in the cryostat for electrical measurement specified under 5.3. Alternate
cryostats that employ a heating element to sweep the specimen temperature are described in
Clause A.2.

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– 10 – 61788-4  IEC:2011
7.2.2 The specimen shall be slowly lowered into the liquid helium bath and cooled to liquid
helium temperature over a time period of at least 5 min.
7.2.3 During the acquisition phases of the low-temperature R * measurements, a specimen
2
2
current (I ) shall be applied so that the current density is in the range of 0,1 A/mm to
2
2
10 A/mm based on the total wire cross-sectional area, and the resulting voltage (U(V)), I (A),
2
and specimen temperature (T (K)) shall be recorded. In order to keep the ratio of signal to
noise high enough, the measurement shall be carried out under the condition that the
absolute value of the resulting voltage above the superconducting transition exceeds 10 µV.
An illustration of the data to be acquired and its analysis is shown in Figure 2.

Voltages with subscripts + and – are those obtained in the first and second measurements under positive and
negative currents, respectively, and U and U are those obtained at zero current. For clarity, U is not
0rev
20+ 20–
shown coincident with U . Voltages U * and U * with asterisk are those at the intersection points.
0– 2+ 2–
Figure 2 – Voltage (U) versus temperature (T) curves and definitions of each voltage
7.2.4 When the specimen is in superconducting state and test current (I ) is applied, two
2
voltages shall be measured nearly simultaneously: U (the initial voltage recorded with a
0+
positive current polarity) and U (the voltage recorded during a brief change in applied
0rev
current polarity). A valid R * measurement requires that excessive interfering voltages are not
2
present and that the specimen is initially in the superconducting state. Thus, the following
condition shall be met for a valid measurement:
U − U
0+ 0 rev
< 1 % (4)
U
2
where U is the average voltage for the specimen in the normal state at cryogenic
2
temperature, which is defined at 7.2.10.
7.2.5 The specimen shall be gradually warmed so that it changes to the normal state
completely. When the cryostat for the resistance measurement specified under 5.3 is used,

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61788-4  IEC:2011 – 11 –
this can be achieved simply by raising the specimen to an appropriate position above the
liquid helium level.
7.2.6 The specimen voltage versus temperature curve shall be acquired with the rate of
temperature increase maintained between 0,1 K/min and 10 K/min.
7.2.7 The voltage versus temperature curve shall continue to be recorded during the
transition into the normal state, up to a temperature somewhat less than 15 K. Then, the
specimen current shall be decreased to zero and the corresponding voltage, U , shall be
20+
recorded at a temperature below 15 K.
7.2.8 The specimen shall then be slowly lowered into the liquid helium bath and cooled to
the same temperature, within ±1 K, where the initial voltage signal U was recorded. A
0+
specimen current, I , with the same magnitude but negative polarity (polarity opposite that
2
used for the initial curve) shall be applied and the voltage U shall be recorded at this
0–
temperature. The procedural steps 7.2.5 to 7.2.7 shall be repeated to record the voltage
versus temperature curve with this negative current. In addition, the recording of U shall be
20–
made at the same temperature, within ±1 K, where U was recorded.
20+
7.2.9 Each of the two voltage versus temperature curves shall be analyzed by drawing a line
(a) through the data where the absolute value of voltage sharply increases with temperature
(see Figure 2) and drawing a second line (b) through the data above the transition where the
voltage is nearly constant with temperature. U * and U * in Figure 2 shall be determined at
2+ 2–
the intersection of these two lines for the positive and negative polarity curves respectively.
7.2.10 The corrected voltages, U and U , shall be calculated using the following
2+ 2–
equations, U = U *– U and U = U *– U . The average voltage, U ,shall be defined

2+ 2+ 0+ 2– 2– 0– 2
as
| U − U |
2+ 2
−
U =   (5)
2
2
7.2.11 A valid R * measurement requires that the shift of thermoelectric voltage be within
2
acceptable limits during the measurements of the U and U . Thus, the following condition
2+ 2–
shall be met for a valid measurement,
|∆ −∆ |
+ −
< 3% (6)
U
2
where ∆ and ∆ are defined as ∆ = U – U and ∆ = U – U . If the R * measurement
+ – + 20+ 0+ – 20– 0– 2
does not meet the validity requirements in 7.2.4 and this subclause, then improvement steps
either in hardware or experimental operation shall be taken to meet these requirements
before results are reported.
*) just above the
7.2.12 Equation (7) shall be used to calculate the measured resistance (R
2
superconducting transition.
U
2
*
R =  (7)
2
I
2
7.3 Correction on measured R * for bending strain
2
If there is no pure Cu component in the superconductor, then R shall be set equal to R *.
2 2

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– 12 – 61788-4  IEC:2011
For a specimen with a pure Cu component, the bending strain shall be defined by
ε = 100 × (h/r) (%), where h is a half of the specimen thickness and r is the bending radius. If
b
the bending strain is less than 0,3 %, then no correction is necessary, and R shall be set
2
equal to R *.
2
If neither of the above two situations applies, then the resistance R just above the
2
superconducting transition under the strain-free condition shall be estimated by
L
*
R = R −∆ρ× (8)
2
2
S
Cu
∆ρ is defined below and S and L are defined in 8.4. The increase in the resistivity of
where
Cu
pure copper at 4,2 K due to tensile strain, ε(%), is expressed by
–12 –14 2;
∆ρ (Ωm) = 6,24 × 10 ε − 5,11 × 10 ε ε ≤ 2 % (9)
The calculation of equation (9) shall be carried out assuming that the equivalent tensile strain
ε is (1/2) ε and (4/3π) ε for rectangular and round wires, respectively. The bending strain
b b
dependency of residual resistance ratio for pure
...