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

点击翻译按钮获取中文摘要

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