Ultracryostat and frigidity supplying apparatus

Abstract

A ultracryostat is provided with a frigidity supplying member to supply frigidity to the ultracryostat which uses cryogen such as liquid helium, wherein the frigidity supplying member comprises a heat pipe and one end of the heat pipe is connected to a frigidity generating member of a cryocooler and the other end of the heat pipe is connected to a thermal anchor of a cryostat.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention relates to an apparatus for extending low temperature retention time of a cryostat using a superconducting quantum interference device (SQUID) for biomagnetism measurement. In more detail, the present invention relates to an ultracryostat and a frigidity supplying apparatus to reduce evaporation of helium. Further, the present invention relates to an ultracryostat and a frigidity supplying apparatus applicable not only to an ultracryostat for biomagnetism measurement but also to the other cryostat, for example a helium cryostat for MRI (magnetic resonance imaging system) using superconductive magnet and one used in physicality study. [0003] 2. Description of Related Art [0004] As shown in FIG. 2, an ultracryostat in earlier development is such that a freezer 106 is connected to an upper part of an cryostat 105 installed in a magnetic shield room 104 (for example, JP Tokukai 2004-116914A (page 4...

AI Technical Summary

Benefits of technology

The present invention provides a solution to the problem of heat flowback when a freezer is not in operation for a cryostat connected with a freezer for biomagnetic measurement. The invention provides a means to avoid heat flowback by using a frigidity supplying member, such as a heat pipe, which supplies frigidity to the cryostat when connected to a cryocooler. The heat pipe is made of stainless steel and has a controllable thermal conductivity that is controlled in conjunction with the switching of the cryocooler. The frigidity supplying apparatus may also include a gas regulating member to take in and out gas in the heat pipe. The invention provides a solution to the problem of heat flowback and allows for the operation of the cryostat with small noise as same as an ordinary cryostat.

Problems solved by technology

However, a common problem in the ultracryostat described in description of related art, i.e. a cryostat for biomagnetism measurement is that sufficient heat shield cannot be obtained because vacuum heat insulation layer is structurally thin.

This problem is caused by a purpose of measurement.

That is, sufficient SN (a ratio of signal to noise) cannot be obtained unless a measurement is performed in a condition that a sensor under ultra low temperature is placed as close as possible to a feeble magnetic signal source.

When volume of the cryostat is made larger, structural distortion becomes large and the thin vacuum heat insulation layer may brake to cause a thermal short.

Therefore, it cannot be made larger blindly.

However, it has not been into practical use due to the following problems regarding magnetic noise.

In view of the foregoing, it is difficult to attach a cryocooler directly onto a cryostat in a field of biomagnetic measurement.

However, because of large magnetic noise derived from a freezer, it is difficult to use any of the above devices for measurement when the freezer is in operation.

Further, when the freezer is not in operation during a measurement, heat flows back immediately.

Thus, noise increases in SQUID due to instability of the internal temperature as well as evaporation rate of helium extremely increases.

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