ASTM_B_714_-_82_1997e1.pdf

Designation:B 714 82(Reapproved 1997)e1Standard Test Method forD-C Critical Current of Composite Superconductors1This standard is issued under the fixed designation B 714;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon(e)indicates an editorial change since the last revision or reapproval.e1NOTEEditorial changes were made throughout in March 1997.1.Scope1.1 This test method covers the procedure for the determi-nation of the d-c critical current of composite superconductors.1.2 This method is intended for use with superconductorshaving a critical current of less than 600Aunder test conditionsand at magnetic fields of less than 0.8 of the upper criticalmagnetic field.1.3 This standard does not purport to address all of thesafety concerns,if any,associated with its use.It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.Specific hazardstatements are given in Section 6.2.Referenced Documents2.1 ASTM Standards:B 713 Terminology Relating to Superconductors23.Terminology3.1 Refer to Terminology B 713 for general terminology forthe field of superconductivity.4.Summary of Test Method4.1 A direct current is applied to the superconductor speci-men and the voltage generated along a section of the specimenis measured.The current is increased from zero and thevoltage-current characteristic is generated.The critical currentis defined as the current at which a specified electric field isexceeded in the specimen.5.Significance and Use5.1 The critical currends of composite superconductors areused to establish design limits for applications of supercon-ducting wires.The operating conditions of superconductors inthese applications determine much of their behavior and testsmade with this method may be used to provide part of theinformation needed to determine the suitability of a specificsuperconductor.5.2 Results obtained from this method can also be used fordetecting changes in the superconducting properties of acomposite superconductor due to processing variables,han-dling,aging,or other application or environmental conditions.This method is useful for quality control,acceptance,orresearch testing if the precautions below are observed.5.3 The critical current of composite superconductors de-pends on many variables.These variables need to be consid-ered in both the testing and the application of these materials(1).35.3.1 Test conditions such as magnetic field,temperatureand relative orientation of specimen,current and magnetic fieldare determined by the particular application.5.3.2 The test configuration may be determined by theparticular conductor through the tolerances required by 8.1 and8.4.5.3.3 The specific critical current criterion may be deter-mined by the particular application.5.3.4 It may be appropriate to measure a number of testspecimens if there are irregularities in testing.5.4 A precaution is needed in the interpretation of resultswhen the reference line of the V-I curve(8.5,8.5.1)has a finiteslope.The current transfer correction is to be used to correct fora true current transfer.Voltages may occur from other sources.5.4.1 A current transfer voltage will result from having avoltage tap near(near is determined by resistivity of the matrixand electrical field criterion)to a current contact,or having agradient in the magnetic field near the region between voltagetaps,or having a field-sample orientation change near theregion between voltage taps(1,2,3).6.Hazards6.1 Very large direct currents with very low voltages do notnecessarily provide a direct personal hazard,but accidentalshorting of the leads with another conductor,such as tools ortransfer lines,can release significant amounts of energy andcause arcs or burns.Care must be taken to isolate and protectcurrent leads from shorting.Also the stored energy in super-conducting magnets commonly used for the background mag-netic field can cause similar large current pulses or deposit1This test method is under the jurisdiction of ASTM Committee B-1 onElectrical Conductors and is the direct responsibility of Subcommittee B01.08 onSuperconductors.Current edition approved Dec.31,1982.Published February 1983.2Annual Book of ASTM Standards,Vol 02.03.3The boldface numbers in parentheses refer to the list of references at the end ofthis test method.1AMERICAN SOCIETY FOR TESTING AND MATERIALS100 Barr Harbor Dr.,West Conshohocken,PA 19428Reprinted from the Annual Book of ASTM Standards.Copyright ASTMNOTICE:Thisstandardhaseitherbeensupersededandreplacedbyanewversionordiscontinued.ContactASTMInternational(www.astm.org)forthelatestinformation.large amounts of thermal energy in the cryogenic systemscausing rapid boil off or even explosive conditions.6.2 The use of cryogenic liquids