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

在一定尺寸的I型超导体中，颗粒通过热成核或磁成核将相从亚稳态过热状态转变为正常状态。这种转变可以在颗粒的温度和外加磁场的相图中追踪到。当入射粒子在颗粒中失去能量时，随着温度的升高，形成热成核中心。由于温度的升高强烈地依赖于其大小，因此这一过程可以在直径小于5微米的颗粒集合中有效地实现。另一方面，磁成核是通过单极通过它而引起的磁通变化2&lt；Phi&gt；的触发而发生的。这一过程在直径20-30微米的颗粒集合中占主导地位。我们在过去两年中的目的是：为了证实过热状态的颗粒是否可以用作反应物质，我们采用了亚稳态超氦…的实验基础数据更加紧张的状态。搭建了一台SQUID磁强计，在1.5K到4.2K的温度范围内测量了单个颗粒在1500高斯磁场下的磁学性质。我们克服了样品输送机构中由振动引起的噪音。正在进行测量，以得到相图。一个可以控制温度和磁场的低温恒温器已经完成，可以在颗粒探测器上获取数据。探测器的目标部分将在两个月内完成。我们将光子型探测器的读出系统与相图并行地向前推进，进而建立了半无限介质情况下Ginzburg-Landau方程的数值解方法。在亚稳态超导态下，对穿透深度、相干长度等参数进行了数值计算。我们打算研究几种样品在不同温度下由实验和计算得到的过热临界场的差异。较少

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