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IEC 61788-7-2020 pdf free download
IEC 61788-7-2020 pdf free download.Superconductivity — Part 7: Electronic characteristic measurements — Surface resistance of high-temperature superconductors at microwave frequencies
Supraconductivité — Partie 7: Mesurages des caractéristiques électronique — Résistance de surface
des supraconducteurs haute temperature critique aux hyperfréquences.
The technique as described assumes that single- and triple-height sapphire rods can be fabricated with the same tan ö. However, the variation of the tan ô between nominally identical rods, cut from the same boule and polished by the same technique, may be as large as two orders of magnitude. To date, the smallest variation in tan öbetween nominally identical sapphire rods has been a factor of four. Therefore, the uncertainty in the measured tan Ô is large. The variation of tan dot the present sapphire rod causes an additional uncertainty up to at least 10 % in the surface resistance measurement. This limits the target uncertainty of the present technique at 5 %. If reproducibility of sapphire rods is improved, or a selection method for standard sapphire rods is established, a target uncertainty can be improved.
The measurement apparatus is cooled down to the specified temperature by any means during testing. An easy choice would be to immerse the apparatus into a liquid cryogen. This technique is quick and simple and yields a known and stable temperature. Unfortunately, most HTS materials are damaged by the condensation of moisture that occurs when removing the sample from the cryogen. In addition, uncertainties generated by the presence of a gas/liquid mixture within the cavity, and the inability to measure R as a function of temperature support the use of other cooling methods. These limitations can be circumvented by the immersion of a vacuum can into a liquid cryogen. If the vacuum can is backfilled with gas, then rapid cooling and uniform temperatures occur. If heaters are attached to the apparatus, then the temperature dependence of the HTS material can be measured. A third and equally good choice is the use of a cryocooler. In this case, the resonator is under vacuum and cooled by conduction through the metallic package. Temperature gradients with the apparatus shall be avoided.
A cryostat shall be provided with the necessary environment for measuring R and the specimen shall be measured while in a stable and isothermal state. The specimen temperature is assumed to be the same as the sample holder temperature. The holder temperature shall be reported to an accuracy of ±0,5 K, measured by means of an appropriate temperature sensor.
The difference between the specimen temperature and the holder temperature shall be minimized by using shields with good thermal conductivity.IEC 61788-7-2020 pdf free download.
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