JP2014085276A - Superconductive current meter - Google Patents

Abstract

By simultaneously acquiring and processing a plurality of SQUID outputs with different magnetic flux biases without using a feedback loop in FLL, a current to be measured is measured with high sensitivity regardless of its value.
When the same current to be measured I ₁ is supplied to input coils 103 and 106, SQUID_A and SQUID_B extract outputs that repeat with the same period Φ ₀ / M ₁ with respect to the current to be measured I ₁ . Further, the output b of SQUID_B is shifted from the output a of SQUID_A by the magnetic flux bias due to the constant bias current I ₂ supplied to the magnetic flux bias coil 107. The signal processing circuit 109, instead of the estimated value of the unknown M ₁ I ₁ / Φ _0, among the noise included in the estimate for each M ₁ I ₁ / Φ ₀ from SQUID_A and SQUID_B, and more noise-less An estimated value from the possible SQUID is selected and output as a measured current value.
[Selection] Figure 1

Description

  The present invention relates to a superconducting ammeter, and more particularly to a superconducting ammeter having a configuration in which two or more superconducting quantum interference devices (SQUIDs) are combined.

FIG. 7A shows a circuit diagram of an example of a superconducting ammeter. The superconducting ammeter shown in FIG. 6A is the simplest example, and includes a SQUID 10 and an input coil 13 and measures a current I ₁ flowing through the input coil 13. The SQUID 10 is a superconducting closed circuit composed of one or more Josephson junctions 11 and a coil 12, and functions as a highly sensitive magnetometer that operates in a cryogenic environment. The input coil 13 is coupled to the coil 12 of the SQUID 10 with a mutual inductance M ₁ .

When a current I ₁ to be measured is passed through the input coil 13 and a magnetic field proportional to the current I ₁ to be measured is created between the coil 12 and the coil 12, Φ ₀ / An output that changes with period M ₁ is taken out. Here, Φ ₀ is a magnetic flux quantum of 2.0678 × 10 ⁻¹⁵ Wb. Therefore, if the value of current M ₁ I ₁ / Φ ₀ normalized by Φ ₀ / M ₁ is used as an input, the output can be in the range of 0 to 1 as shown in FIG. Is good. The output is voltage, inductance, etc. depending on the method.

The SQUID is an element that works as a highly sensitive magnetometer that operates at a cryogenic temperature, and can be used as a highly sensitive ammeter by combining it with a coil that creates a magnetic field proportional to the current. In particular, it is considered indispensable as a high-sensitivity, low-noise ammeter for reading a detector operating at a very low temperature. In order to use as an ammeter, the characteristics shown in FIG. 7B are acquired in advance, and the input measured current is estimated from the output during actual current measurement. However, since the output characteristic of the SQUID is a periodic response, a high sensitivity, that is, a range where the output change is large with respect to the change in the current to be measured is limited. In particular, since the characteristics are turned back during the Φ ₀ period, a region having no sensitivity is generated in the vicinity thereof.

  Here, considering that noise from an amplifier or the like is added to the output of the SQUID 10, the input conversion noise (resolution) greatly varies depending on the input current to be measured as shown in FIG. 7C. For example, if the required resolution corresponds to the value “1” on the vertical axis indicated by the dotted line in FIG. 7C, the input range in which the noise becomes smaller than this is limited to about 2/3 of the whole.

In order to overcome this limitation, a conventional superconducting ammeter generally uses a technique called FLL (Flux-Locked Loop) as shown in the circuit diagram of FIG. 1). In FIG. 8A, the same components as those in FIG. 7A are denoted by the same reference numerals. The superconducting ammeter shown in FIG. 8A is provided with a feedback coil 15 coupled to the coil 12 of the SQUID 10 by a mutual inductance M ₂ separately from the input coil 13, and the output of the SQUID 10 is fed back via the negative feedback circuit 16. In this configuration, negative feedback is input to the coil 15. In this superconducting ammeter, the SQUID 10, the input coil 13 and the feedback coil 15 are operated in a cryogenic environment, and the current to be measured I ₁ supplied to the input coil 13 is estimated.

In the superconducting current meter determines the operating point changes to the input, as shown in FIG. 8 (b) is an output X _F in steep range, the output in the change in the measurement current I ₁ is shifted from X _F Occasionally, a current I ₂ is passed through the feedback coil 15 so as to cancel it, and negative feedback is applied so that the magnetic flux linked to the closed circuit of the SQUID 10 is always kept at the operating point. Assuming that the flux linkage at this operating point is Φ _F , the following equation M ₁ I ₁ + M ₂ I ₂ = Φ _F
Is always true. Therefore, by measuring the negative feedback current I ₂ at room temperature, it is possible to know a change in the measured current I ₁ input to the SQUID 10 in a cryogenic environment. At this time, the SQUID 10 is always at the operating point, and the measured current I ₁ can be measured with low noise regardless of the value as shown by a black circle in FIG. Conventionally, a superconducting ammeter using the FLL technology has been used.

R.P.Giffard, tR.A.Webb.and J.C.Wheatley, Journal of Low Temperature Physics, vol.6, p.533,1972

  However, the above-described conventional superconducting ammeter has two problems, that is, an increase in the number of wires and a limitation in response speed when the number of channels is increased.

First, an increase in the number of wirings when the number of channels is increased will be described. There is a TES (Transition Edge Sensor) as a high-performance detector that operates at extremely low temperatures, which is analyzed because it maintains a very high energy resolution for electromagnetic waves with energy higher than visible light, for example. Application to devices is expected. This TES is a low impedance current source of 1 ohm or less when viewed from the output side, and is always operated in combination with a superconducting ammeter for its low noise readout. That is, for the conventional superconducting ammeter shown in FIG. 8A, a TES (not shown in FIG. 8A) is used as a cryogenic detector for supplying the current I ₁ to be measured to the input coil 13. ) Is provided.

  However, this TES has a trade-off relationship between size and energy resolution in principle, and has a weak point that a single element has a smaller detection area than a semiconductor detector or the like. Therefore, in order to realize a practical analyzer, it is considered essential to increase the effective detection area by arraying a large number (100 or more) of elements and operating them simultaneously. In that case, if a large number of pairs of superconducting ammeters and TESs shown in FIG. 8A are simply prepared, a large number of signal lines are connected between the negative feedback circuit 15 at room temperature and the superconducting ammeter in a low temperature environment. If the scale of the number of detectors (TES) is several hundred or more, it becomes difficult to realize due to heat inflow from the signal line. Specifically, when there are 1000 pairs of the conventional superconducting ammeter and TES shown in FIG. 8 (a), it is between the negative feedback circuit 15 at room temperature and the superconducting ammeter in a low temperature environment. Since 4000 wires are required, it is extremely difficult to realize.

  To solve this problem of heat inflow, a method is known in which a plurality of signals are multiplexed and input / output to reduce the number of wires, and in particular, multiplexing of SQUID outputs in the microwave band is known. (JABMates. GCHilton, KDIrwin, LRVale, KWLehnert, Applied Physics Letters, 92, 023514, 2008.). According to this document, it is technically possible to take out an output signal from several hundred SQUIDs to a frequency in the microwave band and frequency-multiplex them to room temperature with a single signal line. Has been. In this case, for example, a signal having a band of 100 kHz can be modulated by modulating a carrier frequency that is different by 1 MHz and multiplexed in a band of 1 GHz by 1000. However, it is difficult to achieve the same scale of multiplexing for the feedback current. Therefore, the FLL method cannot be adopted in an application in which reading of a detector array having a scale such that the total signal band is 100 MHz or more is performed.

  Next, the response speed limitation will be described. Some TESs that require a superconducting ammeter are those that require a fast response speed and a signal bandwidth of 10 MHz or more (D. Fukuda, RMT Damayanthi, A. Yoshizawa, N. Zen, H. Takahashi, K. Amemiya, and M. Ohkubo, IEEE Transactions on Applied Superconductivity, vol. 17, p. 259, 2007). On the other hand, the bandwidth of the superconducting ammeter using the FLL is limited by the time delay due to the negative feedback loop, and when the negative feedback circuit 16 is placed in a room temperature environment, the room temperature negative feedback circuit 16 and the cryogenic environment. It is considered that the upper limit of the signal band is about 10 MHz due to the wiring length between the lower superconducting ammeter and the TES pair. Therefore, in order to read out a TES signal at a higher speed, a superconducting ammeter that does not use a negative feedback loop is required.

  The present invention has been made in view of the above points, and by simultaneously acquiring and processing a plurality of SQUID outputs with different magnetic flux biases without using a feedback loop in the FLL, the current to be measured can be increased regardless of its value. An object is to provide a superconducting ammeter capable of measuring sensitivity.

  In order to achieve the above object, a superconducting ammeter according to a first aspect of the present invention includes a first input coil and a second input coil to which the same current to be measured is supplied, and a first input coil connected to the first input coil. A first superconducting quantum interference device coupled with a mutual inductance; a second superconducting quantum interference device coupled with the second input coil with the first mutual inductance; and the second superconducting quantum device. A magnetic flux bias coil coupled to the interference element with a second mutual inductance, and a constant bias current is supplied to the magnetic flux bias coil, so that the output of the first superconducting quantum interference element is compared with the second superconducting quantum interference element. A bias current source for giving a magnetic flux offset to the output of the conduction quantum interference device; a first noise included in an estimated value expressed by a linkage magnetic flux / flux quantum of the output of the first superconducting quantum interference device; The second super transmission Signal processing for selecting an estimated value with less noise from the second noise included in the estimated value represented by the interlinkage magnetic flux / flux quantum of the output of the quantum interference element, and outputting this as a measured current value Means.

  In order to achieve the above object, the superconducting ammeter according to the second invention includes a plurality of the second input coil, the second superconducting quantum interference device, the magnetic flux bias coil, and the bias current source. And the signal processing means includes a first noise included in an estimated value represented by an interlinkage magnetic flux / flux quanta of an output of the first superconducting quantum interference device, and the plurality of second superconducting elements. An estimated value with the least noise is selected from the second noise included in a plurality of estimated values represented by interlinkage magnetic flux / flux quanta of the output of the quantum interference element, and this is output as a measured current value It is characterized by.

  In order to achieve the above object, the superconducting ammeter of the third invention is provided with a plurality of superconducting ammeters of the first invention, and each superconducting ammeter of the plurality of superconducting ammeters is provided. The first and second input coils are supplied with different currents to be measured, and the bias current source of each superconducting ammeter supplies the same bias current to the magnetic flux bias coil of each superconducting ammeter. It is characterized by doing.

In order to achieve the above object, a superconducting ammeter according to a fourth aspect of the present invention includes a first input coil and one or more second input coils to which the same current to be measured is supplied, A first superconducting quantum interference element coupled to the input coil with a first mutual inductance and one or more second superconducting elements coupled to the one or more second input coils with the first mutual inductance. A quantum interference element, one or more magnetic flux bias coils coupled to the one or more second superconducting quantum interference elements with a second mutual inductance, and a pre-assigned first resonance frequency comprising: The first resonance circuit that changes in accordance with the output of the superconducting quantum interference device and the one or more second resonance frequencies assigned in advance correspond to the output of the one or more second superconducting quantum interference devices. One or more second covariants that vary independently Circuit and, n sets of current meter portion to set a more becomes configured with (n is 2 or more desired natural number) provided in parallel,
N sets of the ammeter parts are connected in series, bias current supplying means for supplying the same bias current to the flux bias coils, and n sets of the ammeter parts Multiplexed signal supply means for commonly supplying a multiplexed signal in which the frequencies corresponding to the first and second resonance frequencies different from each other in the ammeter portion are multiplexed via one cable; and n sets The n sets of n sets of ammeter portions are output from the multiplexed signal that is output with the phase and amplitude changed according to changes in the n sets of first and second resonance frequencies through the ammeter portions of the n sets. Demodulating means for outputting n-channel demodulated signals output from the first and second superconducting quantum interference devices, and the first and second channels for each channel of the n-channel demodulated signals supplied from the demodulating means. 2 An n-channel signal that selects an estimated value with the least noise from among the noises included in the estimated value represented by the flux linkage / flux quanta of the output of the superconducting quantum interference device and outputs it as the measured current value of that channel And a processing means.

  Here, the n sets of ammeter portions may be fabricated on a single substrate with the characteristics of the first and second superconducting quantum interference devices being made uniform by an integrated circuit process.

  According to the present invention, since there is no feedback loop in the FLL, it is possible to perform high-speed current measurement with the signal band expanded to the upper limit of the response speed of the superconducting quantum interference device. Further, according to the present invention, when a multi-channel ammeter is configured, output multiplexing can be easily performed.

It is a circuit diagram of a first embodiment of a superconducting ammeter of the present invention. It is a figure explaining the operation | movement of the normalized input current of FIG. 1, a SQUID output, and a signal processing circuit. It is a circuit diagram of 2nd Embodiment of the superconducting ammeter of this invention. It is a figure explaining the operation | movement of the normalized input current of FIG. 3, a SQUID output, and a signal processing circuit. It is a circuit system diagram of one Example of the multichannel superconducting ammeter of the present invention. It is a circuit diagram of the modification of the superconducting ammeter of the present invention. It is a circuit diagram of an example of a superconducting ammeter, and a characteristic diagram of standardized input current, SQUID output, and input conversion noise. It is a circuit diagram of other examples of a superconducting ammeter, and a characteristic figure of standardized input current, SQUID output, and input conversion noise.

Next, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
FIG. 1 shows a circuit diagram of a first embodiment of a superconducting ammeter of the present invention. The superconducting ammeter 100 of the present embodiment includes a first superconducting quantum interference device SQUID_A, a second superconducting quantum interference device SQUID_B, input coils 103 and 106, a magnetic flux bias coil 107, and a magnetic flux bias source. 108 and a signal processing circuit 109. The magnetic flux bias source 108 and the signal processing circuit 109 are in a room temperature environment, and the other SQUID_A and SQUID_B, the input coil 103, the input coil 106, and the magnetic flux bias coil 107 are in a cryogenic environment.

SQUID_A is superconducting closed circuit consisting of Josephson junctions 101 and coil 102. are coupled in mutual inductance M ₁ to the coil 102 is input coil 103. Further, SQUID_B is superconducting closed circuit consisting of the Josephson junction 104 and the coil 105., with the input coil 106 to the coil 105 is coupled by mutual inductance M _1, flux bias coil 107 is coupled by mutual inductance M ₂ Has been.

The input coil 103 and the input coil 106 are connected in series, and the same measured current I ₁ is supplied. The magnetic flux bias source 108 supplies a constant bias current I ₂ to the magnetic flux bias coil 107. The signal processing circuit 109 selects and outputs the output with the lower noise out of the output a of SQUID_A and the output b of SQUID_B.

Next, the operation of the superconducting ammeter 100 of the present embodiment will be described. When the same measured current I ₁ is supplied to the input coils 103 and 106, the measured currents are obtained from the SQUID_A and SQUID_B having the coils 102 and 105 coupled to the input coils 103 and 106 with the same mutual inductance M _1. An output which is repeated with the same period Φ ₀ / M ₁ with respect to I ₁ is taken out. Here, Φ ₀ is the flux quantum as described above, and is 2.0678 × 10 ⁻¹⁵ Wb. The SQUID_B coil 105 is also coupled to the magnetic flux bias coil 107 with a mutual inductance M ₂ , and the output b of the SQUID_B is a magnetic flux with respect to the output of SQUID_A by a constant bias current I ₂ supplied to the magnetic flux bias coil 107. The bias is shifted.

Therefore, a current normalized by Φ ₀ / M ₁ (ie, flux linkage / flux quantum) M ₁ I ₁ / Φ ₀ is used as an input, and the range from “0” to “1” is shown in FIG. ), The output a of SQUID_A has the characteristic indicated by the dotted line I in FIG. The output b of SQUID_B is shifted in the input axis direction by M ₂ I ₂ / Φ _{0 in the} same period as the output a and converted to magnetic flux with respect to the output a, as indicated by the broken line II in FIG. (Magnetic flux offset).

When the input measured current I ₁ is estimated from these two outputs a and b in the same manner as the superconducting ammeter shown in FIG. 7A, the input conversion noise calculated under the same assumption as in FIG. The output a of SQUID_A has a characteristic indicated by a dotted line III in FIG. 2B, and the output b of SQUID_B has a characteristic indicated by a broken line IV in FIG. 2B. As can be seen from FIG. 2B, the input conversion noises of the two SQUID_A and SQUID_B strongly depend on the input range. In the present embodiment, these characteristics are acquired prior to actual current measurement and stored in the signal processing circuit 109.

Actual current measurement is performed by the following procedure using the signal processing circuit 109.
First, the value of M ₁ I ₁ / Φ ₀ corresponding to the input measured current I ₁ is estimated from the outputs a and b of the two SQUID_A and SQUID_B (use of the characteristics shown in FIG. 2A). Next, from the periodicity of the estimated values, there are two estimated values of M ₁ I ₁ / Φ ₀ from SQUID_A and SQUID_B in the range of 0 to ₁ , but the estimated values from these two SQUIDs are compared. By selecting one having a close value, it is uniquely determined in the range of 0 to 1 except for a special case such as a bias current I ₂ = 0. For example, when the estimated values IA1 and IA2 from SQUID_A are the estimated values IB1 and IB2 from SQUID_B, if IA1 is close to either IB1 or IB2 (assuming this is IB1), the value IA1 ~IB1 becomes the estimated value of I _1, IA2 and IB2 if I ₂ is appropriate will be different values.

That is, the magnitude relation of the noise included in the estimated values of M ₁ I ₁ / Φ ₀ from SQUID_A and SQUID_B varies depending on the input range, as indicated by characteristics III and IV in FIG. Therefore, the signal processing circuit 109, instead of the unknown estimate of M ₁ I ₁ / Φ _0, among the noise included in the estimate for each M ₁ I ₁ / Φ ₀ from SQUID_A and SQUID_B, more noise An estimated value from the SQUID considered to be small is selected and output as a measured current value. At this time, the input conversion noise included in the selected estimated value has the characteristic of α (thin solid line) in FIG. In FIG. 2B, range A indicates a range in which the noise included in the estimated value from SQUID_A is smaller than the noise included in the estimated value from SQUID_B, and range B is included in the estimated value from SQUID_B. The range of noise is smaller than the noise included in the estimated value from SQUID_A.

The following procedure can also be applied as a processing method for further reducing noise. Similarly to the above, the signal processing circuit 109 obtains an estimated value of M ₁ I ₁ / Φ ₀ from two SQUIDs from FIG. 2A, and then based on the expected noise shown in FIG. 2B. (To minimize the included noise) and output as a measured current value. The input conversion noise included at this time has a characteristic indicated by β (bold solid line) in FIG. 2B, and it can be expected that the noise is reduced from the characteristic α when the selection based on the above range is performed. Therefore, it can be expected that low noise measurement can be performed over the entire input region by selecting the value of the magnetic flux offset so that the regions where the noises of the two SQUID_A and SQUID_B are large do not overlap.

  As described above, according to the superconducting ammeter 100 of the present embodiment, the one with less noise included in the estimated output value of the two SQUID outputs SQUID_A and SQUID_B is provided without providing a feedback loop in the FLL. By selecting, it is possible to measure current with high sensitivity, low noise and high sensitivity up to the upper limit of the response speed of the SQUID.

(Second Embodiment)
FIG. 3 shows a circuit diagram of a second embodiment of the superconducting ammeter of the present invention. In the figure, the same components as those in FIG. In the superconducting ammeter 100 of the first embodiment using two SQUIDs, the sensitivity may be insufficient even if the value of the magnetic flux offset is adjusted. In that case, low noise current measurement can be performed using three or more SQUIDs and using the same method as when two SQUIDs are used. The superconducting ammeter 200 of the second embodiment shown in FIG. 3 is a superconducting ammeter that performs low-noise current measurement using three SQUIDs and the same technique as when two SQUIDs are used. is there.

  A superconducting ammeter 200 shown in FIG. 3 includes a first superconducting quantum interference device SQUID_A, a second superconducting quantum interference device SQUID_B, a third superconducting quantum interference device SQUID_C, input coils 103 and 106, and 112, magnetic flux bias coils 107 and 113, magnetic flux bias sources 108 and 114, and a signal processing circuit 115. The magnetic flux bias sources 108 and 114 and the signal processing circuit 115 operate in a room temperature environment, and other SQUID_A, SQUID_B, and SQUID_C, the input coils 103, 106, and 112, and the magnetic flux bias coils 107 and 113 operate in a cryogenic environment. To do.

SQUID_C is superconducting closed circuit consisting of Josephson junctions 110 and the coil 111., the coil 111 with the input coil 112 is coupled by mutual inductance M _1, flux bias coil 113 is coupled by mutual inductance M ₃ ing. Input coil 103, input coil 106 and the input coil 112 are connected in series, the same current to be measured I ₁ is supplied. The magnetic flux bias source 108 supplies a constant bias current I ₂ to the magnetic flux bias coil 107. The magnetic flux bias source 114 supplies a constant bias current I ₃ to the magnetic flux bias coil 113. The signal processing circuit 115 selects and outputs the output with the lowest noise among the output a of SQUID_A, the output b of SQUID_B, and the output c of SQUID_C.

Next, the operation of the superconducting ammeter 200 of the present embodiment will be described. When the same measured current I ₁ is supplied to the input coils 103, 106, and 112 connected in series, the coils 102, 105, and 111 coupled to the input coils 103, 106, and 112 with the same mutual inductance M ₁ are connected. From SQUID_A, SQUID_B, and SQUID_C, the output that is repeated with the same period Φ ₀ / M ₁ for the current I ₁ to be measured is extracted. Here, Φ ₀ is the flux quantum as described above, and is 2.0678 × 10 ⁻¹⁵ Wb.

The SQUID_B coil 105 is also coupled to the magnetic flux bias coil 107 with a mutual inductance M ₂ , and the output b of the SQUID_B is a magnetic flux with respect to the output of SQUID_A by a constant bias current I ₂ supplied to the magnetic flux bias coil 107. The bias is shifted. Similarly, the coil 111 of the SQUID_C is also coupled to the magnetic flux bias coil 113 with a mutual inductance M ₂ , and the output c of the SQUID_C is compared with the output of SQUID_A by a constant bias current I ₃ supplied to the magnetic flux bias coil 113. It is shifted by the magnetic flux bias. Therefore, the current normalized by Φ ₀ / M ₁ (that is, the flux linkage / flux quantum) M ₁ I ₁ / Φ ₀ is used as an input, and the range from “0” to “1” is shown in FIG. ), The output c of SQUID_C is input in the same period as the output a and by M ₂ I ₃ / Φ _{0 in} terms of magnetic flux with respect to the output a, as indicated by the alternate long and short dash line V in FIG. It has a characteristic with a deviation (magnetic flux offset) in the axial direction.

When the input measured current I ₁ is estimated from these three outputs a, b, and c, the input conversion noise calculated under the same assumption as in FIG. 7C is shown for the output a of SQUID_A and the output b of SQUID_B. Similar to 2 (b), the characteristics shown by the dotted line III and the broken line IV in FIG. 4 (b) are obtained. Further, the output c of SQUID_C has a characteristic indicated by a one-dot chain line VI in FIG. As can be seen from FIG. 4B, the input conversion noise of the three SQUIDs strongly depends on the input range. In the present embodiment, these characteristics are acquired prior to actual current measurement and stored in the signal processing circuit 115. Then, the estimation from the SQUID considered to be the least noise among the noises included in the estimated values of M ₁ I ₁ / Φ ₀ from SQUID_A, SQUID_B, and SQUID_C by the same method as the first embodiment Select a value and output it as the measured current value. At this time, the input conversion noise included in the selected estimated value has the characteristic of γ (thin solid line) in FIG.

As a processing method for further reducing noise, the signal processing circuit 115 obtains an input M ₁ I ₁ / Φ ₀ estimated value from three SQUIDs from FIG. ) And a weighted average based on the expected noise shown in FIG. The input conversion noise included at this time has a characteristic indicated by δ (bold solid line) in FIG. 4B, and it can be expected that the noise is reduced from the characteristic γ when the selection is performed according to the above range. Therefore, it can be expected that low noise measurement can be performed over the entire input region by selecting the value of the magnetic flux offset so that the regions where the noises of the three SQUIDs are large do not overlap. As described above, the superconducting ammeter 200 according to the present embodiment also acquires and processes a plurality of SQUID outputs to which different magnetic flux biases are applied without using a feedback loop in the FLL, similarly to the superconducting ammeter 100. The current to be measured can be measured at high speed and with high sensitivity regardless of the value.

  Note that the number of wires between room temperature and cryogenic temperature is 4 in total, 2 inputs and 2 outputs in the conventional superconducting ammeter shown in FIG. 8A using FLL. On the other hand, the superconducting ammeter 100 of the first embodiment shown in FIG. 1 has a total of six inputs with two inputs and four outputs, and the superconductivity of the second embodiment shown in FIG. The ammeter 200 has 7 inputs, 3 inputs and 4 outputs. When a multi-channel ammeter system is constructed using these superconducting ammeters 100 and 200, the method of efficiently performing frequency multiplexing as described above is known for the output, and they are combined into one wiring. Is possible.

  On the other hand, in the conventional superconducting ammeter using the FLL shown in FIG. 8 (a), a signal that varies for each channel and changes with time is given. It is difficult to reduce On the other hand, in the superconducting ammeters 100 and 200 of the present invention that do not use the FLL, the input is a constant bias current and can be made the same in each channel. The superconducting ammeter 100 shown in FIG. 3 can be grouped into two, and the superconducting ammeter 200 shown in FIG.

  First, an example of integration on a substrate will be described. In the superconducting ammeter of the present invention, it is desirable that the characteristics of two or more SQUIDs to be combined are uniform. Since an SQUID having a large number of characteristics can be manufactured on a single substrate by an integrated circuit manufacturing process similar to that used in a semiconductor, the technology of the present invention can be easily achieved by adopting this technology. A SQUID with uniform characteristics used for a conduction ammeter can be produced.

  Next, an embodiment of a multichannel superconducting ammeter in which the number of wires is suppressed by microwave band multiplexing will be described.

  FIG. 5 shows a circuit diagram of one embodiment of a multi-channel superconducting ammeter. In the figure, a multi-channel superconducting ammeter multiplexes and outputs an n-channel superconducting ammeter chip 300 arranged in an ultra-low temperature environment and m (m is an arbitrary natural number) microwave band frequencies. It comprises a microwave signal generation source 390, a microwave signal generation source 390 arranged in a room temperature environment, a bias current source 391 that outputs a constant bias current, a multiplexed signal demodulation circuit 392, and a signal processing circuit 393. . FIG. 5 shows a configuration of an n-channel superconducting ammeter (where n is a natural number of 2 or more that satisfies m = 2n).

  The n-channel superconducting ammeter chip 300 includes m SQUIDs, n first input coils 321-32n, n second input coils 331-33n, and n magnetic flux bias coils 341-. 34n, n cryogenic detectors 351 to 35n, m coplanar lines 361 to 36m having different lengths, m capacitors 371 to 37m, and m + 1 lines 380 to 38m This is an ammeter portion that is created by aligning the characteristics of m SQUIDs on a single substrate by an integrated circuit creation process, and is connected to a microwave signal generation source 390 with a single microwave cable, and is also a multiplexed signal demodulation circuit It is connected to 392 with a single microwave cable and operates in a cryogenic environment.

Among the total of n sets of SQUIDs that are two adjacent (a pair of) SQUIDs, each set of SQUIDs is supplied with the current to be measured from the same cryogenic detector among the cryogenic detectors 351 to 35n. . For example, among the input coils 321 and 331 to which the same current to be measured is supplied from the cryogenic detector 351, a superconducting closed circuit including a coil 311 coupled to the input coil 321 with a mutual inductance M ₁ and a Josephson junction 301. And a second SQUID constituting a superconducting closed circuit composed of a coil 312 coupled to the input coil 322 with a mutual inductance M ₁ and a Josephson junction 302 constitute a set of SQUIDs. To do.

The first SQUID is connected to a connection point between the lines 380 and 381 through a coplanar line 361 and a capacitor 371 in series. The second SQUID is connected to a connection point between the lines 381 and 382 through a coplanar line 362 and a capacitor 372 in series. The inductance of the input coil 311 of the first SQUID, the mutual inductance M ₁ , the coplanar line 361, the capacitor 371, etc. constitute a first resonance circuit, and the resonance frequency of the first resonance circuit is the output of the first SQUID. Accordingly, it changes within a slight frequency range. Then, the phase and amplitude of the signal having the same frequency as the resonance frequency of the first resonance circuit in the m frequency multiplexed signals of the microwave band supplied from the microwave signal generation source 390 are the first resonance. It changes according to the change of the resonant frequency of the circuit.

Similarly, the inductance of the input coil 312 of the second SQUID, the mutual inductance M ₁ , the coplanar line 362, the capacitor 372, etc. constitute a second resonance circuit, and the resonance frequency of the second resonance circuit is the second SQUID. It changes within a slight frequency width according to the output of. Then, the phase and amplitude of the signal having the same frequency as the resonance frequency of the second resonance circuit in the m frequency multiplexed signals of the microwave band supplied from the microwave signal generation source 390 are the second resonance. It changes according to the change of the resonant frequency of the circuit. The remaining n-1 sets (m-2) of SQUIDs have the same configuration, and are set in the multiplexed signals of m frequencies in the microwave band supplied from the microwave signal source 390. M-2 resonance circuits that resonate with the frequency are formed. The phase and amplitude of the signal having the same frequency as the resonance frequency of the remaining m-2 resonance circuits in the m-frequency multiplexed signal in the microwave band depend on the output of the remaining m-2 SQUIDs. It changes according to a slight change of each resonance frequency of the resonance circuit.

  The microwave signal generation source 390 frequency-division multiplexes frequency signals in m microwave bands that are the same as the resonance frequencies of m microwave bands assigned to m resonance circuits connected to m SQUIDs. Generated multiplexed signals. The multiplexed signal in the microwave band from the microwave signal generation source 390 is input to the n-channel superconducting ammeter chip 300 through one cable. The n-channel superconducting ammeter chip 300 outputs a frequency division multiplexed signal in which the phase and amplitude of the corresponding frequency signal are changed among the m frequency signals in accordance with the outputs of the m SQUIDs.

  The multiplexed signal demodulation circuit 392 specifies which of the 2n SQUID outputs from the frequency in the frequency division multiplexed signal taken out from the n-channel superconducting ammeter chip 300 through one microwave cable. The SQUID output is demodulated according to a predetermined rule from the phase and amplitude of the frequency signal. The signal processing circuit 393 has a configuration in which n signal processing circuits having a configuration similar to that of the signal processing circuit 109 in FIG. 1 are provided in parallel, and 2n SQUIDs of n channels supplied from the multiplexed signal demodulation circuit 392 are provided. Detecting n cryogenic temperatures by performing signal processing to select the estimated value with the least noise from the noise included in the estimated value represented by the flux linkage / flux quantum for each channel of the demodulated signal Current measurement values of n-channel currents output independently from each other from the devices 351 to 35n are output in parallel.

In addition, it is easy to make the mutual inductances of each channel (M ₁ and M _{2 in} FIG. 5) the same by the integrated circuit fabrication process on a single substrate, and the same magnetic flux offset is applied to all m SQUID pairs. The same low noise measurement becomes possible by giving. Therefore, in FIG. 5, the magnetic flux bias coils 341 to 34n of all the SQUID pairs can be connected in series to allow the same bias current to flow. As a result, the DC input / output lines connected to the bias current source 391 can also be reciprocated. A book would be enough. Therefore, in the configuration of FIG. 5, the wiring between the room temperature environment and the low temperature environment is not limited to the number n of the cryogenic detectors 351 to 35 n whose current is to be measured. There are a total of four DC input / output lines, and the problem of heat inflow does not occur (the wiring for driving the cryogenic detectors 351 to 35n is not included).

  In the above-described embodiment, two or three SQUIDs are used, but it is of course possible to use four or more SQUIDs and to have the same configuration as that of the embodiment. Further, FIG. 5 shows a configuration in which each set of SQUIDs consists of two SQUIDs as shown in FIG. 1, but the present invention can be similarly applied to a configuration in which each set of SQUIDs consists of three or more SQUIDs. . Further, the present invention provides two superconducting ammeters having the configurations of FIGS. 1 and 3 as shown by 401 and 402, like a superconducting ammeter 400 of a modification of the circuit diagram of FIG. The first and second input coils of the superconducting ammeters 401 and 402 are supplied with different currents to be measured, and the magnetic flux bias source 403 of each superconducting ammeter 401 and 402 is a magnetic flux of each superconducting ammeter. A common configuration for supplying the same bias current to the bias coil may be used. In FIG. 6, two superconducting ammeters 401 and 402 are provided.

  In X-ray spectroscopy, there is a high resolution analyzer called a wavelength dispersion method, but it has a weak point that the detection efficiency is low and the measurement time is long. On the other hand, an analyzer using a semiconductor detector has high detection efficiency and high speed, but low energy resolution. On the other hand, by using the superconducting ammeter of the present invention, it is possible to realize a high-resolution and high-speed analyzer having an effective detection area equivalent to that of a semiconductor detector using a TES for X-ray detection. In addition, there is no detector with a resolution higher than TES in the gamma ray region, and if the effective detection area can be increased, it is possible to realize an unprecedented analyzer such as a device that can quantitatively analyze radioactive substances without chemical treatment. Be expected.

100, 200, 400, 401, 402 Superconducting ammeter 101, 104, 110, 301-30m Josephson junction 102, 105, 111, 311-31m Coil 103, 106, 112, 321-32n, 331-33n Input coil 107, 113, 341-34n Flux bias coil 108, 114, 403 Flux bias source 109, 115 Signal processing circuit 300 n-channel superconducting ammeter chip 351-35n Cryogenic detector 361-36m Coplanar line 371-37m Capacitor 380 38m line 390 Microwave signal generation source 391 Bias current source 392 Multiplex signal demodulation circuit 393 Signal processing circuit SQUID_A, SQUID_B, SQUID_C Superconducting quantum interference device (SQUID)
I ₁ Current to be measured I ₂ , I ₃ Bias current

Claims (5)

A first input coil and a second input coil to which the same measured current is supplied;
A first superconducting quantum interference device coupled to the first input coil with a first mutual inductance;
A second superconducting quantum interference device coupled to the second input coil with the first mutual inductance;
A magnetic flux bias coil coupled to the second superconducting quantum interference device with a second mutual inductance;
A bias current source for supplying a constant bias current to the magnetic flux bias coil so that the output of the second superconducting quantum interference device has a magnetic flux offset with respect to the output of the first superconducting quantum interference device;
The first noise included in the estimated value represented by the flux linkage / flux quantum of the output of the first superconducting quantum interference device, and the flux linkage / flux of the output of the second superconducting quantum interference device A signal processing means for selecting an estimated value with less noise from the second noise included in the estimated value represented by quantum, and outputting the selected value as a measured current value;
A superconducting ammeter characterized by comprising: A plurality of the second input coil, the second superconducting quantum interference device, the magnetic flux bias coil, and the bias current source are provided,
The signal processing means includes a first noise included in an estimated value represented by a flux linkage / flux quantum of an output of the first superconducting quantum interference device, and the plurality of second superconducting quantum interference devices. The second noise included in the plurality of estimated values represented by the interlinkage magnetic flux / flux quantum of the output is selected and the estimated value with the least noise is selected and output as a measured current value. The superconducting ammeter according to claim 1.   A plurality of superconducting ammeters according to claim 1 are provided, and different measured currents are supplied to the first and second input coils of each superconducting ammeter of the plurality of superconducting ammeters, The bias current source of each superconducting ammeter supplies the same bias current to the magnetic flux bias coil of each superconducting ammeter. A first input coil and one or more second input coils to which the same current to be measured is supplied;
A first superconducting quantum interference device coupled to the first input coil with a first mutual inductance;
One or more second superconducting quantum interference devices coupled to the one or more second input coils with the first mutual inductance;
One or more flux bias coils coupled with one or more second superconducting quantum interference elements with a second mutual inductance;
A first resonance circuit in which a pre-assigned first resonance frequency changes according to an output of the first superconducting quantum interference device;
One or more second resonance circuits in which one or more pre-assigned second resonance frequencies change independently according to the output of the one or more second superconducting quantum interference elements;
N units (n is a desired natural number greater than or equal to 2) in parallel are provided in parallel with an ammeter portion having a configuration consisting of:
bias current supply means for connecting the magnetic flux bias coils of the n sets of ammeter portions in series and supplying the same bias current to the magnetic flux bias coils;
A multiplexed signal in which frequencies corresponding to all the first and second resonance frequencies different from each other in the n sets of ammeter portions are multiplexed with respect to the n sets of ammeter portions via one cable. Multiplexed signal supply means for supplying in common,
From the multiplexed signals that are output with the phase and amplitude changed according to changes in the first and second resonance frequencies of the n sets through the n sets of ammeter parts, demodulating means for outputting an n-channel demodulated signal of the outputs of the n sets of first and second superconducting quantum interference devices;
For each channel of the n-channel demodulated signal supplied from the demodulating means, the noise contained in the estimated value represented by the interlinkage magnetic flux / flux quantum of the output of the first and second superconducting quantum interference devices Among them, an n-channel signal processing means that selects an estimated value with the least noise and outputs it as a measured current value of the channel;
A multichannel superconducting ammeter characterized by comprising:   5. The super set according to claim 4, wherein the n sets of ammeter portions are formed by aligning the characteristics of the first and second superconducting quantum interference devices on a single substrate by an integrated circuit process. Conduction ammeter.

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