Measurements and analysis of magnetic noises arising from the second-stage pulse-tube refrigerator for the development of liquid helium less LTS-SQUID biomagnetic fields measurement system

用于开发无液氦LTS-SQUID生物磁场测量系统的第二级脉冲管制冷机产生的磁噪声的测量和分析

基本信息

批准号：
15206048
负责人：
SASADA Ichiro
金额：
$ 30.28万
依托单位：
KYUSHU UNIVERCITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (A)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2006
项目状态：
已结题

项目摘要

We have developed a second-stage pulse-tube refrigerator (hereafter PT) with a cooling power greater than 0.1 W at 4.2 K. Its unique aspect is that the PT and a valve motor is separated by about 2 m with three extended flexible hoses to avoid strong low- frequency magnetic interferences from the motor. We have characterized magnetic noises arising from the PT in operation with the temperature, T, of the second stage. In order to perform this, several key issues have been addressed : cleaning conducted EMI from an inverter to the PT that destroys the operation of the SQUID, fabrication of highly stable and sensitive (20 nT【square root】Hz) orthogonal fluxgate magnetometers (hereafter FG) of a miniature-size, and fabrication of a CFRP composited cylindrical magnetic shield of high shielding factor to reduce static environment magnetic field around the PT. A miniature FG was installed on the inner wall of an Aluminum Dewar so that the FG should not vibrate and be kept at the room temperatu … More re. From the measurements of the 1.8 Hz (pumping frequency of the He-gas) component of the magnetic noise with FG, we found that there are two components : one becomes prominent below about T=10 K and increases with 1/T and the other is smaller than the first and almost constant over wide range of the temperature above about 10 K. The former is attributed to the periodical variation of the magnetic susceptibility of the paramagnetic regenerative materials such as Er3Ni and HoCu2, on the other hand the latter is attributed to any mechanical variation of the constructing parts made of stainless steel. We further characterized by using a planar gradiometer of DROS (double relaxation oscillation SQIUD prepared by KRISS) attached to the second-stage. The 1.8 Hz component observed was as large as 0.5 nT and followed by the second and the third harmonics. It would be interesting to note that the harmonics of the magnetic noises gradually disappear beyond the orders of 5 and 6 and appear again around 20 Hz (near 10th order) which may be due to mechanical vibration of the SQUID in the static magnetic field. Less

我们开发了二级脉冲管制冷机（以下简称 PT），在 4.2 K 时制冷功率大于 0.1 W。其独特之处在于 PT 和阀门电机相距约 2 m，通过三根延伸的柔性软管避免来自电机的强低频磁干扰。我们已经描述了 PT 在第二阶段的温度 T 下产生的磁噪声。为了实现这一点，我们解决了几个关键问题：清除来自第二级的传导 EMI。一个破坏 SQUID 运行的 PT 逆变器，制造高度稳定和灵敏的（20 nT【平方根】Hz）微型正交磁通门磁力计（以下简称 FG），以及制造 CFRP 复合圆柱形磁屏蔽高屏蔽系数，以减少 PT 周围的静态环境磁场。在铝杜瓦瓶的内壁上安装了微型 FG，使 FG 不会振动。通过使用 FG 对磁噪声的 1.8 Hz（氦气泵浦频率）分量进行测量，我们发现有两个分量：其中一个在 T= 左右变得突出。 10 K 并随 1/T 增加，另一个小于第一个，并且在 10 K 以上的大温度范围内几乎恒定。前者归因于顺磁再生材料磁化率的周期性变化例如 Er3Ni 和 HoCu2，另一方面，后者归因于由不锈钢制成的结构部件的任何机械变化，我们通过使用连接到第二个的 DROS（由 KRISS 制备的双弛豫振荡 SQIUD）平面梯度计进一步表征。观察到的 1.8 Hz 分量高达 0.5 nT，随后是二次和三次谐波。噪声在 5 和 6 阶以上逐渐消失，并在 20 Hz 左右（接近 10 阶）再次出现，这可能是由于 SQUID 在静磁场中的机械振动所致。