JPH0727725A - Measuring device for colorimetric detection of alternating magnetic field loss of superconductor - Google Patents

Abstract

PURPOSE: To provide a measuring device which can measures alternate current losses of several superconductors in a short time. CONSTITUTION: A cylindrical ring 11 has an axial length which is equal to at least the axis length of a holder 1 to be checked, and an another cylindrical zone 2 is continued on the other side of a center cylindrical zone 3, having a diameter in a range of a minimum diameter and a maximum diameter of the holder 1 to be checked, and a ring space 22 opened at one side is present in a condition in which the ring 11 is fitted. Further, the ring space 22 is charged therein with a dielectric fluid which does not chemically react with a material to be made into contact therewith. The thermal resistance is given by fluid which is present in the holder 1 to be checked, the ring 11 and the ring space 22.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a measuring device for colorimetrically detecting an alternating magnetic field loss of a superconductor in an alternating magnetic field having an arbitrary frequency. The specimen is mounted on a specimen holder, the specimen holder is a cylinder, the material of the cylinder has a low thermal conductivity, and the specimen holder has a central cylindrical region more than other cylinder regions. Has a small diameter, an electric heating device is placed on the jacket surface of the cylindrical body, and at least one layer of the test object to be measured is wound around the heating device,
A temperature measuring device and a thermal resistance are arranged in the immediate vicinity of the subject holder, and the thermal resistance relates to the measuring device connected to the subject by a cooling bath liquid.

[0002]

BACKGROUND OF THE INVENTION Measuring the energy dissipation of superconductors in alternating magnetic fields is very important for the use of superconductors.

There are various measurement techniques based on the electromagnetic characteristic of the subject. The colorimetric method described therein is particularly sensitive because it is very sensitive and the thermal conditioning time is very short. The colorimetric method of the present invention is substantially different from the conventionally known colorimetric method in that the evaporation rate of the liquid helium bath liquid is measured.

In this measurement, evaporation of helium is not measured, but a slight temperature rise of the object is measured. This temperature rise is a measure for loss. For this purpose, the specimen is placed in a vacuum chamber and brought into contact with the liquid helium bath liquid via a thermal resistance.

Rev. Sci. Instrum. 61
(3), March 1990, C.I. Schmidt and E. S
pecht, pp. 988-992, "ac loss.
measurements on supercond
uctors in thematicattrattra
nge "describes the principle of the measurement method and the measurement configuration shown in FIG.

This measurement method was first used to measure cable loss. This measurement method shows sufficient accuracy. The equilibrium time constant is only a few seconds.

The main advantage of the method according to the invention is the large measuring area. By simply changing the value of thermal resistance, the measurement area can be changed over multiple orders.

NbTi / Cu for 50 Hz AC applications
The Ni superconductor could be measured with a sensitivity of 10E-8W or less.

Preparation of the subject is time consuming and can cause vacuum problems. Although the measurement itself can be performed quickly, accurately and easily, the preparatory work for the subject is extremely time-consuming when a large number of subjects should be measured.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide a measuring device capable of measuring a large number of superconductor test objects with respect to their AC loss in a short time.

[0011]

According to the present invention, a temperature measuring device is fitted to a jacket surface,
The temperature measuring device is planarly coupled to the jacket surface, and a cylindrical region having a diameter larger than that of the subject coil is connected to one side of the central cylindrical region, and a cylindrical shape is formed on the cylindrical region. The ring is tightly fitted, the material of the ring contracts to the same or stronger than the material of the ring under test due to the cooling action, and the cylindrical ring has an axial length. The directional length has at least the axial length of the subject holder, and another cylindrical region continues to the other side of the central cylindrical region, the other cylindrical region being the minimum diameter and the maximum diameter of the subject holder. Has a diameter between and, and in the fitted state of the ring, there is an open ring space on one side, which is filled with a dielectric fluid that does not chemically react with the material in contact. , The thermal resistance is Configuration to be solved so that the fluid present in the grayed space.

Therefore, the subject is wound around a cylindrical body having a small thermal conductivity. Immediately below the subject is a coil of electrically heated wire. The coil allows the subject to be heated in a predetermined manner, which is used for calibration. Heating is controlled via the temperature measuring device of the subject. For geometric reasons, the carbon resistance is located below the heating coil. However, errors due to this configuration are acceptable. Measuring the temperature of the object itself raises the structural cost extremely,
Due to the great complexity of the operation, it is no longer possible to carry out continuous measurements in an acceptable time.

The subject, heating coil and temperature measuring device are conventionally arranged in a central cylindrical area having a relatively small diameter.

A hollow cylindrical ring having at least the height of the coil body is fitted into the wound body. The coil body is in close contact with the cylindrical jacket surface at the lower part of the main body due to the strong cooling shrinkage of the material, and forms a ring space with the central part and the upper part of the main body. This ring space is filled with a fluid that is chemically and physically suitable for the measurement. The body or subject holder, the liquid and the hollow cylindrical ring form the thermal resistance between the subject and the liquid helium bath. The analyte, the contracted ring and the liquid filled for the measurement are surrounded on their free surface by liquid helium.

The materials as claimed in the dependent claims are intended for use in measuring devices and represent advantageous configurations of measuring devices.

The subject holder is made of fiberglass-epoxide. A carbon resistance prepared as a temperature measuring device is fitted and bonded just below the jacket surface in the central cylindrical portion. To avoid eddy current loss,
Alternatively, in order to suppress it at least to a negligible level, the carbon resistance copper line is removed, and a thin manganin wire is directly bonded to the resistance layer by a conductive epoxy resin. In order to avoid the induced voltage, the manganin wire is twisted at the notch of the subject body and guided to the connection socket. Similarly, the heating wire consists of manganin wire having a given diameter. The connecting wires are also twisted together at the notches and guided to the socket. The socket is arranged on a tube, which is fixedly connected concentrically with the subject body and is used as a mechanical holder for the measuring device.

The hollow cylinder and the ring space between the central cylindrical region and the upper cylindrical region of the subject holder are filled with liquid and mechanical oil of low viscosity. This mechanical oil meets the chemical and physical ambient conditions for the measurement. The specimen is in all cases completely immersed in the oil. This configuration eliminates the need for a unique vacuum container, and thus significantly reduces the measurement cost.

The winding of the subject only takes a few minutes. The actual measurement according to the measurement method shown in the above-mentioned document proceeds rapidly. If the superconducting solenoid concentrically surrounding the measuring device is fitted to the carrier can, the alternating magnetic field loss measurement can be carried out on this conventional carrier for liquid helium. Said solenoid forms an alternating magnetic field with a uniform magnetic field superimposed for the measurement.

For conventional applications where measurements need not be performed at high background magnetic fields, no inherent cryostat is required. The solenoid used (discussed below) has an outer diameter of 48 mm and produces a magnetic field of up to 2.5T. Since the entire measuring panel has a very small mass, the cooling of liquid helium to the temperature takes place in a few minutes. The object can be continuously measured in a short time with sufficient sensitivity.

Compared to conventional colorimetric measurements, the amount of helium used is significantly reduced by the simple instrumental measurement arrangement. Therefore, the cost is significantly reduced.

An embodiment of the invention is shown in the drawings and will be described below.

[0022]

The subject has heretofore been exclusively the conductor part for high-current superconductor technology. Thus, an alternating magnetic field having a normal frequency in the energy supply network (ie 50 or 60 Hz) or a normal frequency band in the power device is formed in the measuring device for detecting the alternating magnetic field loss. Particular realization of the equipment with specific planning and superconductors is the group of components such as generators, motors, power converters, current limiters and the group of electronic signal components or communication technology components. The latter is measured with a relatively high frequency superimposed alternating magnetic field, depending on the intended use.

The subject holder 1 or body 1 of FIG. 1 consists of three cylindrical regions 2, 3, 4 having different diameters.
These cylindrical regions have a common axis 5. The central region 2 has the smallest diameter 3. Immediately below the jacket surface, the temperature measuring device 6 is fitted and glued in the notch 26 (FIG. 2). The temperature measuring device 6 is a carbon resistance that has been prepared and processed (see FIG. 4), and will be described later in detail.

A heating device 7 is provided on the treated cylindrical jacket surface after the incorporation of the carbon resistor 6. The heating device consists of a layer of wound heating wire with a diameter of 0.1 mm. The heating wire is made of manganin, impregnated with epoxide, and cured while rotating. This gives the heating coil 7 a completely flat surface towards the outside. The two lines 8 of the heating coil 7 are twisted together,
The inside of the notch is guided in the direction of the axis 5 of the subject holder 1. From here the line is guided concentrically to the 4-pole socket 9 and is brazed to it.

The subject 10 is wound in a single layer or a plurality of layers through the central region 3. This covers the entire axial length of this area 3. The lower region 4 has a diameter 4 which is at least the same as the wound holder region. The cylindrical tube member 11 is placed on this. This tube member is made of Teflon, is in close contact with the subject holder 1 in the lower region 4, and extends upward to at least the end of the main body 1. A ring-shaped space 22 is formed by the remaining region, and this space is filled with low-viscosity mechanical oil. In this way, the subject 10 is completely immersed in it anyway.

A tube member 12 made of a non-metallic material having a low thermal conductivity is in contact with the object holder 1 concentrically, and its free end is closed by a 4-pole socket 9. At the same time, the tube member is used as a mechanical holding portion for the subject holder 1. In the pipe member, two electric lines 8 each,
13 is led to the socket 9, where it is brazed to the corresponding pin of the socket 9. These lines are for the current sources of the signal processing and heating device 7, not shown. A further temperature measuring device 18 for measuring the temperature of liquid helium is provided on the outer tube wall. Both temperature measuring devices 6, 18 measure the important temperature difference between liquid helium and the analyte.

The measuring device thus prepared is then slid inwards onto a base 25 for measurement, where it is held in place on the bottom of the subject holder via a concentric recess 24. It The base 25 is made of glass fiber reinforced plastic for the superconductor solenoid 14 (see FIG. 3). The solenoid 14 is connected to the current supply unit via the current lead wire 5. It remains connected during sample exchange and therefore does not need to be disassembled. The magnet 14 can form a uniform magnetic field having an alternating magnetic field component in a predetermined waveform or a predetermined frequency range. For that purpose the entire device is immersed in a can 16 with liquid helium. FIG. 3 only shows the base of the can 16 with its closure 17. For the required space of the measuring device, important outer dimensions are shown in FIGS. 3 and 1.

FIG. 4 shows a carbon resistor 6 prepared for the measuring device. The right half shows the original state, and the left half shows the state where the commercially available carbon resistor 6 is prepared and processed. This is an Allen-Bradley carbon resistor with a nominal resistance of 100Ω. This resistance is about 1000Ω at 4.2K.
Has a resistance value of. For use in the measurement, the ceramic outer skin 19 and a part of the carbon layer 20 are chamfered into segments in a flat shape over the entire length (see FIG. 4). The original tinned copper wire terminal 21 has been replaced by a 0.1 mm diameter manganin wire. This is because tin-plated copper wire terminals produce large losses in alternating magnetic fields. The remaining tin is completely removed by etching. The ends of the two manganin wires are adhered to the respective end faces of the carbon layer 20 with a conductive epoxy resin. The two manganin wires 13 provided with a thin insulating layer are then twisted together so that the surface surrounding the conductor is not as perpendicular as possible to the applied alternating magnetic field. This is because an induced voltage can be formed by this surface.

The carbon resistor 6 thus prepared and processed has the flat end face outside and the central region 3 of the subject holder 1.
Placed in the notch 26 and glued to fix the position.

The performance of the measuring device will be described below based on the measuring method (see also FIG. 5).

A calibration curve is recorded in the first experimental step. This curve shows the ohmic resistance profile of the temperature sensor 6 on the sample support 1 as a function of the heating capacity. Helium temperature T
Since 1 is likewise known, it is possible to plot the course ΔT of the important temperature difference.

The temperature sensor 6 itself does not need to be calibrated.
The approximate course of the resistance value as a function of temperature is only necessary to ensure that the temperature of the subject 10 remains within the tolerance zone.

The original measurement is to apply an alternating magnetic field having a desired frequency and amplitude and measure the respective resistance values of the carbon resistance 6 of the sample holder 1. A corresponding loss power is calculated from these values using a calibration curve previously determined. This method provides a region accuracy of about 2 to 5% depending on the measurement region.

If the measuring accuracy is to be increased, this point must be recorded for each measuring point recording by means of an alternating magnetic field without a magnetic field, but by heating with a heating device 7 to a corresponding temperature or a corresponding resistance value of the temperature sensor 6. I have to. The measurement accuracy achieved by this is an error of 1% or less.

The usable measuring area of the measuring device is defined by the thermal resistance and the maximum and minimum measurable temperature difference allowed. When the minimum measurable temperature difference is 10 mK and the measurable maximum temperature difference is 1 K, the measurement area is 2
It is a digit order. Even larger temperature differences can be measured, but this is no longer usable. The maximum temperature difference allowed depends on how much variation in the sample temperature is allowed in the actual measurement. In general, AC losses are only slightly temperature dependent and can be calculated and corrected.

Basically, the sample temperature T2 can be kept constant even if the temperature T1 of the helium bath liquid changes.
It can be easily lowered to 4.2 K or less by exhausting the helium bath liquid to a predetermined pressure. This pressure, and consequently the helium temperature, is adjusted so that the sample temperature always remains the same. However, in most cases this measure, which would increase the measurement costs, is not necessary.

The structure of the measuring device is important for pouring measurements. The temperature profile within the subject holder will not be exactly the same if the same power is dissipated in the heating device or subject.

FIG. 2b shows the radial temperature profile in the central cylindrical region 3 of the measuring device both for the energy dissipation due to the alternating magnetic field at the same power and for the energy dissipation when the heater 7 is switched on and off. The measured temperature is slightly higher than for the calibration measurement at the same power. This is because the position of the heat source is different. Therefore, correction is necessary.

In an additional experiment, the superconducting sample was replaced by a 0.4 mm copper wire wrapped with a thin heating wire. Therefore, in this case, the sample was heated by ohmic heating instead of the alternating magnetic field. The required correction amount can be obtained by comparing the power loss of this sample with the power of the heating coil incorporating the same power temperature. This correction amount is 2.1% ± 0.3%
Met. That is, the alternating magnetic field loss is 2.1% higher than in the case of ohmic heating adjusted to the same temperature.

Optimization of the measuring device can only be carried out for a given sample format for which the measuring device is designed. Different samples require different sensitivities of the device or different minimum sample diameters. This is because a thick sample cannot be bent to a small radius.

Device sensitivity ΔT / Q = Rth (Rth = thermal resistance) is an important parameter. The sensitivity defines the measurable area. The sensitivity is 55 K / W in the example. For a given sample, it is advantageous if ΔT / Q is relatively large or small.

The smaller the loss the sample has, the greater the ΔT / Q must be. For that purpose, a material having a low thermal conductivity such as nylon must be used. Similarly, reducing the sample diameter increases ΔT / Q. Coefficient 10 or ΔT / Q is about 500K
/ W is possible.

It is easy to reduce ΔT / W for samples with high loss. To this end, a material having a relatively high conductivity, a relatively large diameter sample support and a relatively thin outer cylinder may be used.

The sensitivity can be varied to some extent for a given sample support. That is, different materials are used for the outer sleeve or ring 11. Two materials were detected, nylon and Teflon.

Nylon sleeve Thickness 6 mm: ΔT / Q = 94K / W Teflon sleeve Thickness 0.6 mm: ΔT / Q = 34K
/ W This means a change of a factor of 3.

Even if the core of the sample support can be taken out, the sensitivity can be lowered. This allows a relatively good heat release to the shaft.

In the example, an output resolution of ΔQ = ΔT / Rth = 5 μW was obtained. Here, Rth = 55K / W, and the temperature resolution is ± 0.25 mK.

The heat adjustment time is obtained from the time constant for temperature conversion when the heating output is applied or cut off. This heat conditioning time is important for exponentially dropping to the temperature of liquid helium after removing the constant heating power.

In the embodiment, this time constant is about 2.5 seconds. With the five time constants after the application of the alternating magnetic field, the temperature reaches the final value with an error of 1% or less. This means recording the measuring points at very short intervals.

For comparison, refer again to the colorimetric method for measuring the evaporation rate of a helium bath solution. The corresponding time constant in this case lies in the region of a few minutes or more. This means that it is very time consuming.

[0051]

According to the present invention, there can be obtained a measuring device capable of measuring a large number of superconductor analytes with respect to their AC loss in a short time.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a central cylindrical region of the present invention and a diagram showing a temperature profile in a radial direction.

FIG. 3 is a schematic view of a measuring device.

FIG. 4 is a schematic diagram of carbon resistance.

FIG. 5 is a diagram showing the basics of measurement.

[Explanation of symbols]

 1 Subject Holder 2, 3, 4 Region 5 Axis 6 Temperature Measuring Device 7 Heating Device 9 Socket 10 Subject

Claims (6)

[Claims] 1. A measuring device for colorimetrically detecting an alternating magnetic field loss of a superconductor in an alternating magnetic field of an arbitrary frequency, comprising a superconducting object (10), said superconducting object being an object to be detected. Mounted on a specimen holder (1), the specimen holder is a cylinder, the material of the cylinder has a low thermal conductivity, the specimen holder (1) being in the central cylindrical region (3) An electric heating device (7) is mounted on the jacket surface of the cylindrical body having a smaller diameter than in other cylindrical regions, and the heating device has at least one object (10) to be measured.
The layers are wrapped and the temperature measuring device (6) is placed in the immediate vicinity of the subject holder (1).
And a thermal resistance are arranged, and the thermal resistance is measured by a temperature measuring device (6) fitted in the jacket surface in a measuring device connected to the subject (10) by a cooling bath liquid. The device is planarly connected to the jacket surface, with a cylindrical region (4) having a larger diameter (4) than the subject coil (10) leading to one side of the central cylindrical region (3). , The cylindrical ring (11) is tightly fitted in the cylindrical region (4), and the material of the ring contracts by the cooling action to be the same as the material of the ring to be inspected or stronger than that, The cylindrical ring (11) has an axial length, the axial length being at least the axial length of the subject holder (1), and the other on the other side of the central cylindrical region (3). Cylindrical region (2)
The second cylindrical region (2) has a diameter between the minimum diameter and the maximum diameter of the subject holder (1) and is open on one side in the fitted state of the ring (11). A ring space (22) is present, and the ring space (22) is filled with a dielectric fluid that does not chemically react with the contacting material, and the thermal resistance is the subject holder (1) and the ring (11). And a measuring device comprising a fluid present in the ring space (22). 2. The object holder (1) is a glass fiber
The measuring device according to claim 1, which is made of epoxy resin, nylon, or other non-metallic material. 3. The temperature measuring device (6) is a carbon resistance (6), and the jacket surface of the carbon resistance has a carbon layer (2) in a partial region.
0) is chamfered to be flat, and the carbon resistance (6) is located in the subject holder (1), and the flat region of the jacket surface is located in the central cylindrical region (3) of the subject holder (1). The two manganin wires (13) each having a predetermined thickness are attached by a heat conductive epoxy resin, and the inductive voltage component due to the alternating magnetic field applied to the outside directly from the carbon layer (20). 3. The measuring device according to claim 2, wherein is drawn so as to be held so small that it can be ignored. 4. The heating device (7) provided in the central cylindrical region (3) consists of a manganin wire wrapped in a jacket surface and filled with epoxy resin or another resistance wire of non-ferromagnetic material. 3. The measuring device according to 3. 5. Two lead wires (8, 13) each twisted together have a carbon resistance (6) and a heating device ((7)).
Is adhered to the groove from the groove and guided in the direction of the axis (5) of the subject holder (9) and brazed with at least a 4-pole socket (9), the socket being assembled to the tube (12), The measuring device according to claim 4, wherein is firmly connected to the object holder (1) in the axial direction. 6. The fluid used to fill the ring space ((22) is a low viscosity oil, which has a low thermal conductivity at the temperature of liquid helium, and which requires special care during sample exchange. The measuring device according to claim 5, which does not need to be handled as a unit.