Development of New-Type Detector of Magnetic Monopole by Using Metastable Superconducting Granules

某种尺寸的I型超导体颗粒通过热成核或磁成核从亚稳态过热状态转变为正常状态。这种转变可以在温度和外加磁场下颗粒的相图中追踪。当入射粒子在粒子中失去能量时，温度升高，就会形成热成核中心。由于温度的升高强烈依赖于颗粒的大小，因此该过程在直径小于5 <mu> m的颗粒集合中有效实现。另一方面，磁成核是通过一个磁单极子通过它所引起的通量变化2 <phi>的触发而发生的。这一过程在直径为20-30 μ m的颗粒集合中占主导地位。在过去的两年里，我们的目的是：为了确定处于过热状态的颗粒是否可以用作反应物质，我们在亚稳态超高温状态下获得了实验基础数据。然后我们试探性地在检测器中构造一个目标部件。构建了SQUID磁力计，在温度为1.5K ~ 4.2K、磁场强度为1500高斯的条件下测量单个颗粒的磁性能。克服了样品传递机构中振动引起的噪声问题。测量得到相图。一个低温恒温器已经完成，其中的温度和磁场可以控制，以获取颗粒探测器上的数据。探测器的目标部分将在两个月内完成。提出了一种与相图制作并行的原型检测器读出系统。在此基础上，建立了半无限介质下金兹堡-朗道方程数值解的求法。在亚稳态超导状态下，对穿透深度、相干长度等不同值进行了数值计算。我们打算研究几种样品在不同温度下，通过实验和计算得到的过热临界场的差异。少

A granule in some size of a type I superconductor changes phase from a metastable superheated state to a normal state by virtue of either thermal or magnetic nucleation. Such transitions can be traced in a phase diagram of the granule on temperature and applied magnetic field. Thermal nucleation centers are formed with a rise in temperature when an incident particle loses its energy in a granule. Because the rise in temperature is strongly dependent on its size, this process is effectively realized in a collection of granules smaller than 5 <mu> m in diameter. On the other hand, magnetic nucleation takes place through a trigger of flux change 2 <phi> induced by a monopole passing through it. This process becomes dominant in a collection of granules as large as 20-30 <mu> m in diameter.Our purpose in past two years is as follow:In order to confirm whether granules in superheated states can be used as reactive matter or not, we take experimentally fundamental data on a metastable superhe … More ated state. Then we construct tentatively a target part in a detector.A SQUID magnetometer was constructed to measure magnetic properties of a single granule at temperatures from 1.5K to 4.2K in magnetic field up to 1500 Gauss. We overcome difficulty with noise which was induced by vibration in a sample transfer mechanism. Measurements are making to get a phase diagram. A cryostat was already completed in which temperature and magnetic field can be controlled to take data on a granule detector. The target part of detector will be accomplished in two months. We carry forward read-out system of a pototype detector in parallel with making the phase diagram.Furthermore, we have established a method to get numerical solutions of Ginzburg-Landau equation in the case of a semi-infinite medium. Numerical calculations in metastable superconducting states were made for various values in penetration depth, coherent length, etc.. We intend to study differnce of superheated critical fields obtained from experiment and calculation for several kinds of samples at several temperatures. Less