IEC 61788-4:2020 pdf free download – superconductivity
5.3Cryostat for the resistance ( R ) measurement
The cryostat shall include a specimen support structure and a liquid helium reservoir formeasurement of the resistance R,.The specimen support structure shall allow the specimen,which is mounted on a measurement mandrel or a measurement base plate, to be lowered intoand raised out of a liquid helium bath. In addition, the specimen support structure shall be madeso that a current can flow through the specimen and the resulting voltage generated along thespecimen can be measured.
6 specimen preparation
The test specimen shall have no joints or splices with a length of 30 mm or longer.The specimenshall be instrumented with current contacts near each of its ends and a pair of voltage contactsover its central portion.The distance between two voltage taps ( L ) shall be 15 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 themeasurement mandrel or base plate.Special care should be taken during instrumentation andinstallation of the specimen on the measurement mandrel or base plate so that no excessiveforce，which may cause undesired bending strain or tensile strain，would be applied to thespecimen.ldeally, the Nb,Sn specimen is intended to be as straight as possible; however, thisis not always the case, thus care should be taken to measure the specimen in its as receivedcondition.
7.1 Resistance (R) at room temperature
The mounted specimen shall be measured at room temperature (Tm(K)), where rm satisfiesthe following condition:273 K≤ Tm ≤ 308 K.A specimen current ( 1,(A)) shall be applied so thatthe current density is in the range of 0,1 A/mm2 to 2 A/mm2 based on the total wire cross-sectional area,and the resulting voltage(U,(V)), and rm shall be recorded.Formula (2)below shall be used to calculate the resistance ( R ) at room temperature.The resistance ( R,)at 293 K (20 °C ) shall be calculated using Formula (3) for a wire with Cu matrix. For wires thatdo not contain a pure Cu component,the value of R shall be set equal to Rm, without anytemperature correction.
7.2.2Data acquisition of cryogenic resistance
The specimen,which is still mounted as it was for the room temperature measurement, shallbe placed in the cryostat for electrical measurement specified in 5.3.Horizontal mounting of thespecimen is recommended in Clause A.1.Alternative cryostats that employ a heating elementto sweep the specimen temperature are described in Clause A.2.The specimen shall be slowlylowered into the liquid helium bath and cooled to liquid helium temperature over a time periodof at least 5 min.
During the acquisition phases of the low-temperature R measurements, a specimen current(1 ) shall be applied so that the current density is in the range 0,1 A/mm2 to 10 A/mm2 basedon the total wire cross-sectional area,and the resulting voltage (U(V))，12(A), and specimentemperature (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 resultingvoltage above the superconducting transition exceeds 10 uV.An illustration of the data to beacquired and its analysis is shown in Figure 2.