在小型制冷机中测量薄片交流磁化率以决定超导转变温度的装置

本文介绍了一种利用电磁感应原理和超导磁效应,在小型制冷机中测量超导体转变温度的装置.本装置包括密闭的真空室、压缩制冷机、真空泵、真空计、锁相放大器、温控仪、计算机、线圈绕组.其中,线圈绕组置于真空室内,由初级线圈和次级线圈组成,初级线圈和次级线圈分别绕制在两个线圈骨架上;被测超导薄片材料放置于初级线圈和次级线圈之间;压缩制冷机用来为超导材料制冷;真空泵用来对真空室抽真空;温控仪用来测量和控制真空室内的温度;锁相放大器为初级线圈提供交流电压信号,并测量次级线圈的电信号以得到交流磁化率值;计算机记录温控仪测得的温度数据和锁相放大器测得的次级线圈的电压信号,并显示锁相放大器测得的次级线圈的电压信号随温度变化的曲线.实验证明该装置可以通过测量超导体交流磁化率的变化测得超导转变温度,具有自动化测量及测试成本低等特点.

A DEVICE FOR MEASURING SUPERCONDUCTING TRANSITION TEMPERATURE BY AC SUSCEPTIBILITY MEASUREMENT OF SUPERCONDUCTING FILM IN SMALL CRYOCOOLER

In this paper,a device for measuring superconducting transition temperature in small cryocooler,based on principles of electromagnetic induction and superconducting magnetic effect,is introduced.This device consists of a vacuum chamber,a small cryocooler,a vacuum pump,a vacuum gauge,a lock-in amplifier,a temperature controller,a computer and a coil pancake and so on.The coil pancake,which is fixed in the vacuum chamber,contains a primary coil and secondary coil,the primary coil and secondary coil are respectively wound onto two coil formers.The measured superconducting thin film is put between the primary coil and the secondary coil.The small cryocooler is used to cool superconducting thin film,the vacuum pump is used to pump gas in the vacuum chamber,and the temperature controller is used to measure and control the temperature of superconducting thin film.The internal oscillator of the lock-in amplifier is connected to the primary coil to provide an excitation field exerted to the superconducting film.At the same time,the lock-in amplifier is used to measure the response of the secondary coil.In our system,the sample temperature datum and the voltage output of the secondary coil are transmitted and saved in the computer;then these datum can be drawn into V～T lines displayed on the computer screen at real time.Experiments show that this device can be used to obtain superconducting transition temperature automatically by measuring ac susceptibility with a lower cost.