JPH0241591Y2 - - Google Patents

Description

[Detailed description of the invention] (a) Industrial application field The present invention relates to a liquid helium container for calibrating a superconducting magnetometer (SQUID).

(b) Prior art To operate a superconducting magnetometer, it is necessary to maintain the temperature of its probe below the temperature of liquid helium.
Therefore, when calibrating the sensitivity of the magnetometer, as shown in FIG. The magnetometer probe 6 is immersed in the liquid helium, and its temperature is usually maintained at the liquid helium temperature. A normal electromagnetic shield 4 is provided inside the container surrounding the probe 6, and the static magnetic field necessary for calibration is applied from outside the container. However, since superconducting magnetometers are extremely sensitive measurement devices, when calibrating their sensitivity, the influence of fluctuations in the earth's magnetic field may be large and the test location must be considered, especially if there are electromagnetic devices nearby. In such environments, no matter how strict the electromagnetic shield 4 is, as long as the above method is used, it will not be possible to completely prevent the intrusion of external noise magnetic fields.
Precise calibration of magnetometers is almost impossible.

(C) Purpose The purpose of this invention is to eliminate the above-mentioned drawbacks when calibrating a superconducting magnetometer by blocking external noise magnetic fields even in a normal field environment where leakage magnetic flux from nearby electromagnetic equipment exists. An object of the present invention is to provide a liquid helium container for calibrating a superconducting magnetometer, which can ensure accurate calibration of the magnetometer.

(d) Structure In order to achieve the above object, the liquid helium container according to the present invention includes a double shield case consisting of a shield case made of a normal conductive material and a shield case made of a superconducting material in a thermos for liquid helium made of reinforced plastic. The shield case further includes a coil for generating a magnetic field for calibration.

(e) Examples Examples of the present invention will be described below based on the drawings.

FIG. 2 is a sectional view of a liquid helium container for calibrating a superconducting magnetometer according to an embodiment of the present invention. In the figure, parts corresponding to the conventional container shown in FIG. 1 are given the same reference numerals as in FIG.
Their explanation has been omitted. In the figure, inner container 2
Inside, there is provided a double shield case consisting of a shield case 4 made of a normal conducting metal (for example, brass, copper) and a shield case 7 made of a superconducting metal (for example, lead, niobium). The superconducting magnetometer probe or pick-up coil to be calibrated is
Three pairs of Helmholtz coils winding with superconducting wire are inserted into the double-shielded case up to a predetermined position, and surrounding that position, the coil axes are orthogonal to each other. however,
In the figure, only cross sections of coil pairs 8 and 9 whose coil axes are orthogonal to each other on the paper are shown, and the coil pairs whose coil axes are orthogonal to the paper are not shown.

In the above configuration, with the probe or pick-up coil of the superconducting magnetometer inserted in the above predetermined position, the liquid level of the liquid helium in the container can be maintained at a height such that at least the inner superconducting shield case 7 is completely immersed. For example, the shield case 7 exhibits complete diamagnetic properties and completely shields external magnetic fields below a predetermined strength determined by the material. The magnetic field necessary for calibrating the magnetometer is generated by energizing the three Herzholtz coils mentioned above from the outside, but since the coil windings are also made of superconducting material, there is no generation of Joule heat. There is no evaporation of liquid helium when the coil is energized. Note that the shield case 4 made of normal conductive metal is used to further ensure shielding performance, and particularly prevents the intrusion of non-static magnetic fields or electromagnetic waves.

(f) Effects As is clear from the above explanation, according to the liquid helium container for superconducting magnetometer calibration according to the present invention, external electromagnetic fields including static magnetic fields are completely shielded.
Accurate calibration of superconducting magnetometers is possible not only in the earth's magnetic field but also in environments where leakage magnetic fields from electromagnetic equipment exist.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a state in which a magnetic field meter probe is inserted into a liquid helium container having a conventional structure. Second
The figure is a configuration diagram of an embodiment of the present invention. 1... Outer container, 2... Inner container, 3... Heat insulating layer, 4... Normal conducting shield case, 7... Superconducting shield case, 8, 9... Helmholtz coil.

Claims (1)

[Scope of utility model registration request] This is a thermos flask for liquid helium made of reinforced plastic to keep the superconducting magnetometer at a predetermined low temperature, and inside is a shield case made of a normal conducting material and a superconducting material surrounding the space holding the superconducting magnetometer. Furthermore, within this double shield case, there are three pairs of superconducting magnetometers whose axes are orthogonal to each other, centered at the holding position of the superconducting magnetometer. A liquid helium container for calibrating a superconducting magnetometer, characterized by being equipped with a Helmholtz coil.