Superconductivity - Part 17: Electronic characteristic measurements - Local critical current density and its distribution in large-area superconducting films

IEC 61788-17:2013 describes the measurements of the local critical current density (Jc) and its distribution in large-area high-temperature superconducting (HTS) films by an inductive method using third-harmonic voltages. The most important consideration for precise measurements is to determine Jc at liquid nitrogen temperatures by an electric-field criterion and obtain current-voltage characteristics from its frequency dependence. Although it is possible to measure Jc in applied DC magnetic fields, the scope of this standard is limited to the measurement without DC magnetic fields. This technique intrinsically measures the critical sheet current that is the product of Jc and the film thickness d. The range and measurement resolution for Jcd of HTS films are from 200 A/m to 32 kA/m, with a measurement resolution of 100 A/m.

Supraleitfähigkeit - Teil 17: Messungen der elektronischen Charakteristik - Lokale kritische Stromdichte und deren Verteilung in großflächigen supraleitenden Schichten

Supraconductivité - Partie 17: Mesures de caractéristiques électroniques - Densité de courant critique local et sa distribution dans les films supraconducteurs de grande surface

La CEI 61788-17:2013 décrit les mesures de la densité de courant critique local (Jc) et sa distribution dans les films supraconducteurs à haute température (HTS) de grande surface par une méthode inductive utilisant les tensions de troisième harmonique. La considération la plus importante pour effectuer des mesures précises consiste à déterminer Jc aux températures de l'azote liquide au moyen d'un critère de champ électrique et obtenir des caractéristiques courant-tension d'après sa dépendance vis-à-vis de la fréquence. Bien qu'il soit possible de mesurer Jc dans des champs magnétiques en courant continu appliqués, le domaine d'application de la présente norme est limité à la mesure sans champ magnétique en courant continu. Cette technique mesure de façon intrinsèque le courant de feuille critique, qui est le produit de Jc par l'épaisseur d du film. La plage et la résolution de mesure pour Jcd des films HTS est de 200 A/m à 32 kA/m avec une résolution de mesure de 100 A/m.

Superprevodnost - 17. del: Meritve elektronskih karakteristik - Krajevno kritična tokovna gostota in njena porazdelitev po površinsko obširnih razsežnih superprevodnih plasteh

Ta del IEC 61788 opisuje meritve lokalne kritične tokovne gostote (Jc) in njene porazdelitve na obsežnih visokotemperaturnih superprevodnih (HTS) filmih z induktivno metodo s pomočjo tretje-harmonskih napetosti. Najpomembnejši del pri natančnosti meritev je določiti Jc pri temperaturah tekočega nitrogena s kriterijem električnega polja in pridobiti lastnosti trenutne napetosti iz frekvenčne odvisnosti. Čeprav je mogoče Jc izmeriti v uporabljenih enosmernih magnetnih poljih [20, 21]2, se ta standard nanaša le na meritve brez enosmernih magnetnih polj. Ta tehnika meri kritični tok plasti, ki je rezultat Jc in debeline filma d. Obseg in ločljivost meritve za Jcd filmov HTS sta naslednja:
– Jcd: od 200 A/m do 32 kA/m (glede na rezultate, ne omejitve);
– Ločljivost meritve: 100 A/m (na podlagi rezultatov, ne omejitve).

General Information

Status
Published
Publication Date
04-Apr-2013
Technical Committee
Drafting Committee
Current Stage
6060 - Document made available
Due Date
20-May-2013
Completion Date
05-Apr-2013

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SLOVENSKI STANDARD
SIST EN 61788-17:2013
01-julij-2013

6XSHUSUHYRGQRVWGHO0HULWYHHOHNWURQVNLKNDUDNWHULVWLN.UDMHYQRNULWLþQD

WRNRYQDJRVWRWDLQQMHQDSRUD]GHOLWHYSRSRYUãLQVNRREãLUQLKUD]VHåQLK
VXSHUSUHYRGQLKSODVWHK

Superconductivity - Part 17: Electronic characteristic measurements - Local critical

current density and its distribution in large-area superconducting films

Supraleitfähigkeit - Teil 17: Messungen der elektronischen Charakteristik - Lokale

kritische Stromdichte und deren Verteilung in großflächigen supraleitenden Schichten

Supraconductivité - Partie 17: Mesures de caractéristiques électroniques - Densité de

courant critique local et sa distribution dans les films supraconducteurs de grande

surface
Ta slovenski standard je istoveten z: EN 61788-17:2013
ICS:
17.220.20 0HUMHQMHHOHNWULþQLKLQ Measurement of electrical
PDJQHWQLKYHOLþLQ and magnetic quantities
29.050 Superprevodnost in prevodni Superconductivity and
materiali conducting materials
SIST EN 61788-17:2013 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

---------------------- Page: 1 ----------------------
SIST EN 61788-17:2013
---------------------- Page: 2 ----------------------
SIST EN 61788-17:2013
EUROPEAN STANDARD
EN 61788-17
NORME EUROPÉENNE
April 2013
EUROPÄISCHE NORM
ICS 17.220.20; 29.050
English version
Superconductivity -
Part 17: Electronic characteristic measurements -
Local critical current density and its distribution in large-area
superconducting films
(IEC 61788-17:2013)
Supraconductivité - Supraleitfähigkeit -
Partie 17: Mesures de caractéristiques Teil 17: Messungen der elektronischen
électroniques - Charakteristik -
Densité de courant critique local et sa Lokale kritische Stromdichte und deren
distribution dans les films Verteilung in großflächigen supraleitenden
supraconducteurs de grande surface Schichten
(CEI 61788-17:2013) (IEC 61788-17:2013)

This European Standard was approved by CENELEC on 2013-02-20. CENELEC members are bound to comply

with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard

the status of a national standard without any alteration.

Up-to-date lists and bibliographical references concerning such national standards may be obtained on

application to the CEN-CENELEC Management Centre or to any CENELEC member.

This European Standard exists in three official versions (English, French, German). A version in any other

language made by translation under the responsibility of a CENELEC member into its own language and notified

to the CEN-CENELEC Management Centre has the same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus,

the Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany,

Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland,

Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom.

CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
Management Centre: Avenue Marnix 17, B - 1000 Brussels

© 2013 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.

Ref. No. EN 61788-17:2013 E
---------------------- Page: 3 ----------------------
SIST EN 61788-17:2013
EN 61788-17:2013 - 2 -
Foreword

The text of document 90/310/FDIS, future edition 1 of IEC 61788-17, prepared by IEC TC 90,

"Superconductivity" was submitted to the IEC-CENELEC parallel vote and approved by CENELEC as

EN 61788-17:2013.
The following dates are fixed:
• latest date by which the document has (dop) 2013-11-20
to be implemented at national level by
publication of an identical national
standard or by endorsement
(dow) 2016-02-20
• latest date by which the national
standards conflicting with the
document have to be withdrawn

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. CENELEC [and/or CEN] shall not be held responsible for identifying any or all such patent

rights.
Endorsement notice

The text of the International Standard IEC 61788-17:2013 was approved by CENELEC as a European

Standard without any modification.
---------------------- Page: 4 ----------------------
SIST EN 61788-17:2013
- 3 - EN 61788-17:2013
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications

The following documents, in whole or in part, are normatively referenced in this document and are

indispensable for its application. For dated references, only the edition cited applies. For undated

references, the latest edition of the referenced document (including any amendments) applies.

NOTE When an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD

applies.
Publication Year Title EN/HD Year
IEC 60050 Series International electrotechnical vocabulary - -
---------------------- Page: 5 ----------------------
SIST EN 61788-17:2013
---------------------- Page: 6 ----------------------
SIST EN 61788-17:2013
IEC 61788-17
Edition 1.0 2013-01
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Superconductivity –
Part 17: Electronic characteristic measurements – Local critical current density
and its distribution in large-area superconducting films
Supraconductivité –
Partie 17: Mesures de caractéristiques électroniques – Densité de courant
critique local et sa distribution dans les films supraconducteurs de grande
surface
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX X
ICS 17.220.20; 29.050 ISBN 978-2-83220-583-9

Warning! Make sure that you obtained this publication from an authorized distributor.

Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé.

® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
---------------------- Page: 7 ----------------------
SIST EN 61788-17:2013
– 2 – 61788-17 © IEC:2013
CONTENTS

FOREWORD ........................................................................................................................... 4

INTRODUCTION ..................................................................................................................... 6

1 Scope ............................................................................................................................... 8

2 Normative reference ......................................................................................................... 8

3 Terms and definitions ....................................................................................................... 8

4 Requirements ................................................................................................................... 9

5 Apparatus ......................................................................................................................... 9

5.1 Measurement equipment ......................................................................................... 9

5.2 Components for inductive measurements .............................................................. 10

5.2.1 Coils .......................................................................................................... 10

5.2.2 Spacer film ................................................................................................ 11

5.2.3 Mechanism for the set-up of the coil .......................................................... 11

5.2.4 Calibration wafer ....................................................................................... 11

6 Measurement procedure ................................................................................................. 12

6.1 General ................................................................................................................. 12

6.2 Determination of the experimental coil coefficient .................................................. 12

6.2.1 Calculation of the theoretical coil coefficient k ........................................... 12

6.2.2 Transport measurements of bridges in the calibration wafer ...................... 13

6.2.3 U measurements of the calibration wafer ................................................. 13

6.2.4 Calculation of the E-J characteristics from frequency-dependent I

data ........................................................................................................... 13

6.2.5 Determination of the k’ from J and J values for an appropriate E .......... 14

ct c0

6.3 Measurement of J in sample films ........................................................................ 15

6.4 Measurement of J with only one frequency ........................................................... 15

6.5 Examples of the theoretical and experimental coil coefficients ............................... 16

7 Uncertainty in the test method ........................................................................................ 17

7.1 Major sources of systematic effects that affect the U measurement ..................... 17

7.2 Effect of deviation from the prescribed value in the coil-to-film distance ................ 18

7.3 Uncertainty of the experimental coil coefficient and the obtained J ....................... 18

7.4 Effects of the film edge .......................................................................................... 19

7.5 Specimen protection .............................................................................................. 19

8 Test report ...................................................................................................................... 19

8.1 Identification of test specimen ............................................................................... 19

8.2 Report of J values ................................................................................................ 19

8.3 Report of test conditions ........................................................................................ 19

Annex A (informative) Additional information relating to Clauses 1 to 8 ................................ 20

Annex B (informative) Optional measurement systems ......................................................... 26

Annex C (informative) Uncertainty considerations ................................................................ 32

Annex D (informative) Evaluation of the uncertainty ............................................................. 37

Bibliography .......................................................................................................................... 43

Figure 1 – Diagram for an electric circuit used for inductive J measurement of HTS

films ...................................................................................................................................... 10

Figure 2 – Illustration showing techniques to press the sample coil to HTS films ................... 11

Figure 3 – Example of a calibration wafer used to determine the coil coefficient ................... 12

---------------------- Page: 8 ----------------------
SIST EN 61788-17:2013
61788-17 © IEC:2013 – 3 –

Figure 4 – Illustration for the sample coil and the magnetic field during measurement ........... 13

Figure 5 – E-J characteristics measured by a transport method and the U inductive

method ................................................................................................................................. 14

Figure 6 –Example of the normalized third-harmonic voltages (U /fI ) measured with

3 0

various frequencies ............................................................................................................... 15

Figure 7 – Illustration for coils 1 and 3 in Table 1 .................................................................. 16

Figure 8 – The coil-factor function F(r) = 2H /I calculated for the three coils ........................ 17

0 0

Figure 9 – The coil-to-film distance Z dependence of the theoretical coil coefficient k ........ 18

Figure A.1 – Illustration for the sample coil and the magnetic field during measurement ....... 22

Figure A.2 – (a) U and (b) U /I plotted against I in a YBCO thin film measured in

3 3 0 0

applied DC magnetic fields, and the scaling observed when normalized by I (insets) .......... 23

Figure B.1 – Schematic diagram for the variable-RL-cancel circuit ........................................ 27

Figure B.2 – Diagram for an electrical circuit used for the 2-coil method ............................... 27

Figure B.3 – Harmonic noises arising from the power source ................................................ 28

Figure B.4 – Noise reduction using a cancel coil with a superconducting film ........................ 28

Figure B.5 – Normalized harmonic noises (U /fI ) arising from the power source ................. 29

3 0

Figure B.6 – Normalized noise voltages after the reduction using a cancel coil with a

superconducting film ............................................................................................................. 29

Figure B.7 – Normalized noise voltages after the reduction using a cancel coil without

a superconducting film .......................................................................................................... 30

Figure B.8 – Normalized noise voltages with the 2-coil system shown in Figure B.2 ............. 30

Figure D.1 – Effect of the coil position against a superconducting thin film on the

measured J values .............................................................................................................. 41

Table 1 – Specifications and coil coefficients of typical sample coils ..................................... 16

Table C.1 – Output signals from two nominally identical extensometers ................................ 33

Table C.2 – Mean values of two output signals ..................................................................... 33

Table C.3 – Experimental standard deviations of two output signals ..................................... 33

Table C.4 – Standard uncertainties of two output signals ...................................................... 34

Table C.5 – Coefficient of variations of two output signals .................................................... 34

Table D.1 – Uncertainty budget table for the experimental coil coefficient k’ ......................... 37

Table D.2 – Examples of repeated measurements of J and n-values ................................... 40

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SIST EN 61788-17:2013
– 4 – 61788-17 © IEC:2013
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SUPERCONDUCTIVITY –
Part 17: Electronic characteristic measurements –
Local critical current density and its distribution
in large-area superconducting films
FOREWORD

1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising

all national electrotechnical committees (IEC National Committees). The object of IEC is to promote

international co-operation on all questions concerning standardization in the electrical and electronic fields. To

this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,

Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC

Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested

in the subject dealt with may participate in this preparatory work. International, governmental and non-

governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely

with the International Organization for Standardization (ISO) in accordance with conditions determined by

agreement between the two organizations.

2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international

consensus of opinion on the relevant subjects since each technical committee has representation from all

interested IEC National Committees.

3) IEC Publications have the form of recommendations for international use and are accepted by IEC National

Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC

Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any

misinterpretation by any end user.

4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications

transparently to the maximum extent possible in their national and regional publications. Any divergence

between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in

the latter.

5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity

assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any

services carried out by independent certification bodies.

6) All users should ensure that they have the latest edition of this publication.

7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and

members of its technical committees and IEC National Committees for any personal injury, property damage or

other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and

expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC

Publications.

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.

International Standard IEC 61788-17 has been prepared by IEC technical committee 90:

Superconductivity.
The text of this standard is based on the following documents:
FDIS Report on voting
90/310/FDIS 90/319/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 the parts of the IEC 61788 series, published under the general title

Superconductivity, can be found on the IEC website.
---------------------- Page: 10 ----------------------
SIST EN 61788-17:2013
61788-17 © IEC:2013 – 5 –

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.
---------------------- Page: 11 ----------------------
SIST EN 61788-17:2013
– 6 – 61788-17 © IEC:2013
INTRODUCTION

Over twenty years after their discovery in 1986, high-temperature superconductors are now

finding their way into products and technologies that will revolutionize information

transmission, transportation, and energy. Among them, high-temperature superconducting

(HTS) microwave filters, which exploit the extremely low surface resistance of

superconductors, have already been commercialized. They have two major advantages over

conventional non-superconducting filters, namely: low insertion loss (low noise characteristics)

and high frequency selectivity (sharp cut) [1] . These advantages enable a reduced number of

base stations, improved speech quality, more efficient use of frequency bandwidths, and

reduced unnecessary radio wave noise.

Large-area superconducting thin films have been developed for use in microwave devices [2].

They are also used for emerging superconducting power devices, such as, resistive-type

superconducting fault-current limiters (SFCLs) [3–5], superconducting fault detectors used for

superconductor-triggered fault current limiters [6, 7] and persistent-current switches used for

persistent-current HTS magnets [8, 9]. The critical current density J is one of the key

parameters that describe the quality of large-area HTS films. Nondestructive, AC inductive

methods are widely used to measure J and its distribution for large-area HTS films [10–13],

among which the method utilizing third-harmonic voltages U cos(3ωt+θ) is the most popular

[10, 11], where ω, t and θ denote the angular frequency, time, and initial phase, respectively.

However, these conventional methods are not accurate because they have not considered the

electric-field E criterion of the J measurement [14, 15] and sometimes use an inappropriate

criterion to determine the threshold current I from which J is calculated [16]. A conventional

th c

method can obtain J values that differ from the accurate values by 10 % to 20 % [15]. It is

thus necessary to establish standard test methods to precisely measure the local critical

current density and its distribution, to which all involved in the HTS filter industry can refer for

quality control of the HTS films. Background knowledge on the inductive J measurements of

HTS thin films is summarized in Annex A.

In these inductive methods, AC magnetic fields are generated with AC currents I cosωt in a

small coil mounted just above the film, and J is calculated from the threshold coil current I ,

c th

at which full penetration of the magnetic field to the film is achieved [17]. For the inductive

method using third-harmonic voltages U , U is measured as a function of I , and the I is

3 3 0 th

determined as the coil current I at which U starts to emerge. The induced electric fields E in

0 3

the superconducting film at I = I , which are proportional to the frequency f of the AC current,

0 th

can be estimated by a simple Bean model [14]. A standard method has been proposed to

precisely measure J with an electric-field criterion by detecting U and obtaining the n-value

c 3

(index of the power-law E-J characteristics) by measuring I precisely at various frequencies

[14, 15, 18, 19]. This method not only obtains precise J values, but also facilitates the

detection of degraded parts in inhomogeneous specimens, because the decline of n-value is

more remarkable than the decrease of J in such parts [15]. It is noted that this standard

method is excellent for assessing homogeneity in large-area HTS films, although the relevant

parameter for designing microwave devices is not J , but the surface resistance. For

application of large-area superconducting thin films to SFCLs, knowledge on J distribution is

vital, because J distribution significantly affects quench distribution in SFCLs during faults.

The International Electrotechnical Commission (IEC) draws attention to the fact that it is

claimed that compliance with this document may involve the use of a patent concerning the

determination of the E-J characteristics by inductive J measurements as a function of

frequency, given in the Introduction, Clause 1, Clause 4 and 5.1.

IEC takes no position concerning the evidence, validity and scope of this patent right.

The holder of this patent right has assured the IEC that he is willing to negotiate licenses free

of charge with applicants throughout the world. In this respect, the statement of the holder of

this patent right is registered with the IEC. Information may be obtained from:
___________
Numbers in square brackets refer to the Bibliography.
---------------------- Page: 12 ----------------------
SIST EN 61788-17:2013
61788-17 © IEC:2013 – 7 –
Name of holder of patent right:
National Institute of Advanced Industrial Science and Technology
Address:
Intellectual Property Planning Office, Intellectual Property Department
1-1-1, Umezono, Tsukuba, Ibaraki Prefecture, Japan

Attention is drawn to the possibility that some of the elements of this document may be

subject to patent rights other than those identified above. IEC shall not be held responsible for

identifying any or all such patent rights.

ISO (www.iso.org/patents) and IEC (http://patents.iec.ch) maintain on-line data bases of

patents relevant to their standards. Users are encouraged to consult the data bases for the

most up to date information concerning patents.
---------------------- Page: 13 ----------------------
SIST EN 61788-17:2013
– 8 – 61788-17 © IEC:2013
SUPERCONDUCTIVITY –
Part 17: Electronic characteristic measurements –
Local critical current density and its distribution
in large-area superconducting films
1 Scope

This part of IEC 61788 describes the measurements of the local critical current density (J )

and its distribution in large-area high-temperature superconducting (HTS) films by an

inductive method using third-harmonic voltages. The most important consideration for precise

measurements is to determine J at liquid nitrogen temperatures by an electric-field criterion

and obtain current-voltage characteristics from its frequency dependence. Although it is

in applied DC magnetic fields [20, 21] , the scope of this standard is
possible to measure J
limited to the measurement without DC magnetic fields.

This technique intrinsically measures the critical sheet current that is the product of J and the

film thickness d. The range and measurement resolution for J d of HTS films are as follows:

– J d: from 200 A/m to 32 kA/m (based on results, not limitation);
– Measurement resolution: 100 A/m (based on results, not limitation).
2 Normative reference

The following documents, in whole or in part, are normatively referenced in this document and

are indispensable for its application. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60050 (all parts), International Electrotechnical Vocabulary (available at
)
3 Terms and definitions

For the purposes of this document, the definitions given in IEC 60050-815:2000, some of

which are repeated here for convenience, apply.
3.1
critical current
maximum direct current that can be regarded as flowing without resistance
Note 1 to entry: I is a function of magnetic field strength and temperature.
[SOURCE: IEC 60050-815:2000, 815-03-01]
___________
Numbers in square brackets refer to the Bibliography.
---------------------- Page: 14 ----------------------
SIST EN 61788-17:2013
61788-17 © IEC:2013 – 9 –
3.2
critical current criterion
I criterion

criterion to determine the critical current, I , based on the electric field strength, E or the

resistivity, ρ
-13

Note 1 to entry: E = 10 µV/m or E = 100 µV/m is often used as electric field criterion, and ρ = 10 Ω · m or

-14

ρ = 10 Ω · m is often used as resistivity criterion. (“E = 10 V/m or E = 100 V/m” in the current edition is mistaken

and is scheduled to be corrected in the second edition).
[SOURCE: IEC 60050-815:2000, 815-03-02]
3.3
critical current density

the electric current density at the critical current using either the cross-section of the whole

conductor (overall) or of the non-stabilizer part of the conductor if there is a stabilizer

Note 1 to entry: The overall current density is called in English, engineering current density (symbol: J ).

[SOURCE: IEC 60050-815:2000, 815-03-03]
3.4
transport critical current density
critical current density obtained by a resistivity or a voltage measurement
[SOURCE: IEC 60050-815:2000, 815-03-04]
3.5
n-value (of a superconductor)

exponent obtained in a specific range of electric field strength or resistivity when the

voltage/current U (l) curve is approximated by the equation U ∝ I
[SOURCE: IEC 60050-815:2000, 815-03-10]
4 Requirements

The critical current density J is one of the most fundamental parameters that describe the

quality of large-area HTS films. In this standard, J and its distribution are measured non-

destructively via an inductive method by detecting third-harmonic voltages U cos(3ωt+θ). A

small coil, which is used both to generate AC magnetic fields and detect third-harmonic

voltages, is mounted just above the HTS film and used to scan the measuring area. To

measure J precisely with an electric-field criterion, the threshold coil currents I , at which U

c th 3

starts to emerge, are measured repeatedly at different frequencies and the E-J characteristics

are determined from their frequency dependencies.

The target relative combined standard uncertainty of the method used to determine the

absolute value of J is less than 10 %. However, the target uncertainty is less than 5 %

...

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