JP2009180677A - Magnetic field stabilizing mechanism, magnetic resonance apparatus, and electron spin resonance apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an externally-locking magnetic field stabilization technology for accurately stabilizing the magnetic field of an NMR apparatus, or the like. <P>SOLUTION: In a magnetic field stabilization mechanism for measuring the magnetic field from a NMR signal of a locking sample, disposed separated from a measurement sample and stabilizing the magnetic field generated from an NMR magnet, based on the measured magnetic field, a correction quantity calculating section, is provided so as to calculate the correction current values required for the magnetic field correction coil for suppressing the magnetic field fluctuations in a NMR measurement sample position, based on the strength of the magnetic field in a locking sample position. Since stabilization can be obtained, even if the magnetic field fluctuation is large, the magnetic field can be stabilized accurately, even if a current is carried from an external power supply to the NMR magnet. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a lock mechanism for stabilizing a magnetic field of a magnetic resonance apparatus or an electron spin resonance apparatus.

  An NMR (nuclear magnetic resonance) apparatus is an apparatus for measuring the resonance frequency of a sample placed in a static magnetic field, and is used for measuring a wide range of samples ranging from organic substances and solids to biopolymers. In the NMR apparatus, a high-sensitivity and high-resolution spectrum can be obtained by increasing the magnetic field. In particular, in solid-state NMR, almost all elements can be analyzed in principle, but due to lack of sensitivity and resolution, it is difficult to measure quadrupole nuclei. If the sensitivity and resolution of quadrupole nucleus measurement are improved by increasing the magnetic field, it becomes possible to analyze many elements and materials that have not been analyzed in the past. Therefore, increasing the magnetic field is particularly effective in solid-state NMR.

By the way, a low-temperature superconducting wire such as NbTi or Nb ₃ Sb is used for a magnet of a conventional NMR apparatus. Such a magnet is composed of several tens of coils, and the coils are connected by superconductive connection. Then, after excitation, the circuit is short-circuited by a permanent current switch and operated in a permanent current mode separated from the excitation power source. Such a superconducting magnet has a magnetic field stability of 10 ⁻⁸ / h in the permanent current mode. Since a solution NMR apparatus requires a magnetic field stability of 10 ⁻¹⁰ / h or less, a magnetic field lock apparatus is usually provided to achieve this level.

In solution NMR, an internal lock is used. Internal lock dissolved in containing the species for locking the sample for measurement ^{(2 H} is often used) solvent, it observed separately from the NMR signal of the measurement sample an NMR signal of the locking nuclide. Then, the current of the magnetic field correction coil for locking is adjusted so that the frequency of the NMR signal for locking becomes constant. Thereby, the magnetic field is stabilized. This method is called an internal lock because the lock sample is measured at the same location as the measurement sample.

  The internal lock device uses a detector. A detector is a device that can see the difference in frequency between a reference signal and a measurement signal. This method is very sensitive and can detect a frequency difference with high accuracy. And by always correcting this deviation, the magnetic field of the superconducting magnet can be stabilized with high accuracy.

A method of measuring the lock sample at a place different from the place of the measurement sample is called an external lock. The external lock is a method used when the internal lock cannot be used as in solid state NMR. In solid-state NMR, since the line width of a spectrum is thicker than that in solution NMR (that is, frequency resolution is low), the magnetic field stability as high as solution NMR is not required. Therefore, a magnetic field stability of 10 ⁻⁸ / h realized in the permanent current mode is sufficient, and there has not been much research on an external lock system that can obtain a higher degree of stability.
U.S. Pat. No. 4,101,681 U.S. Pat. No. 4,171,511 JP 62-222179 A US Pat. No. 6,037,775 JP 2006-38570 A Japanese Patent Laid-Open No. 2007-3458

When trying to realize NMR exceeding 1 GHz (the magnitude of the magnetic field is expressed by a nuclear magnetic resonance frequency of ¹ H. Corresponding to 23.5 T), the low-temperature superconducting wire cannot be used in the high magnetic field portion. This is because the critical current density of the low-temperature superconducting wire is small in a high magnetic field exceeding 20T. Due to the problem of the critical current of this low-temperature superconducting wire, it is difficult to achieve a high magnetic field of about 1 GHz or more by the conventional method.

Therefore, it is necessary to use a high-temperature superconducting wire for the high magnetic field part of the magnet of the NMR apparatus. When a high-temperature superconducting wire is used at a superfluid helium temperature, a high critical current can be obtained even in a high magnetic field, so that a high magnetic field of 1 GHz or more can be achieved. However, the high-temperature superconducting wire generates a small amount of resistance when a large current flows. In addition, since it is impossible to connect the coils by superconducting connection, a slight resistance is generated at the connection portion. For this reason, when used in a permanent current mode like an NMR magnet using a low-temperature superconducting wire, this resistance attenuates the current at a rate of 10 ⁻⁴ / h to 10 ⁻⁶ / h, which is required for NMR. Sufficient magnetic field stability cannot be achieved.

Therefore, it is necessary to always supply current from an external power source instead of using an NMR magnet made of a high-temperature superconducting wire in the permanent current mode. Thereby, magnetic field attenuation can be suppressed. However, when an external power source is used, there arises a problem that the magnetic field fluctuates due to current fluctuation of the external power source. Although the amount of current fluctuation depends on the performance of the power source, even when a highly stabilized power source is used, it is about 10 ⁻⁶ to 10 ⁻⁵ , which is in comparison with the permanent current energization used in the conventional NMR apparatus. This is much larger, which modulates the NMR spectrum, making it impossible to make precise measurements.

  Thus, when a current is supplied to the NMR magnet from an external power source, it is essential to stabilize the magnetic field.

The internal lock method is effective when the rate of magnetic field fluctuation is relatively small as in the permanent current mode, but may not be able to cope with a large fluctuation in magnetic field as in the external power supply energization mode. When the frequency difference is detected by the detector, the output of the dispersion signal is proportional to the frequency difference only when the frequency difference is small. When the frequency difference (magnetic field fluctuation) increases, the correction accuracy deteriorates. End up. In solid NMR using a solid sample, it is difficult to mix a lock sample (such as ² H) into the measurement sample, and the internal lock method cannot be applied to solid NMR.

  On the other hand, the conventional external lock method has a large allowable range of magnetic field fluctuations, but there is a limit to high-accuracy stabilization.

  That is, until now, there has been no means for stabilizing the high-temperature superconducting wire with the required accuracy of NMR measurement when the magnetic field fluctuation is large, such as when an external power source is energized.

  The present invention has been made in consideration of such problems, and an object thereof is to provide an external lock type magnetic field stabilization technique for stabilizing the magnetic field of a magnetic resonance apparatus or an electron spin resonance apparatus. .

  In order to achieve the above object, the magnetic field stabilization mechanism according to the present invention stabilizes the magnetic field generated by the magnetic field generation unit of the magnetic resonance apparatus or the electron spin resonance apparatus by the following means.

The magnetic field stabilization mechanism according to the present invention includes a locking sample disposed in the vicinity of a measurement sample, a locking resonance signal receiving unit that receives a resonance signal by irradiating the locking sample, and a magnetic field generation unit. A magnetic field correction coil for correcting the magnetic field is included. The magnetic field stabilization mechanism according to the present invention is a magnetic field stabilization mechanism based on a so-called external lock method that corrects a magnetic field based on a resonance signal obtained from a lock sample located at a position different from the measurement sample.

  In the magnetic field stabilization mechanism according to the present invention, the current value to the magnetic field correction coil to be applied to suppress the magnetic field fluctuation at the position of the measurement sample is calculated based on the fluctuation of the resonance signal obtained from the resonance signal receiver for locking. A correction amount calculation unit to calculate is included.

  According to the magnetic field stabilization mechanism according to the present invention, in the external lock method, the magnetic field is stabilized in consideration of the non-uniformity of the magnetic field generated by the magnetic field correction coil. ), But the magnetic field at the measurement sample position can be stabilized with higher accuracy. Thereby, highly accurate measurement is possible.

  The correction amount calculation unit can calculate a correction current value to be applied by the following process, for example. That is, first, the relationship between the current value applied to the correction coil and the strength of the magnetic field at the lock sample position and the measurement sample position (characteristics of the magnetic field correction coil) is acquired in advance. Then, the magnetic field value at the lock sample position is measured from the resonance signal obtained from the lock resonance signal receiver, and the measurement sample position is calculated from the measured value, the characteristics of the magnetic field correction coil and the correction current value currently applied. Calculate (estimate) the strength of the magnetic field at. Then, a correction current value applied to the magnetic field correction coil is calculated by feedback control or the like so that the strength of the magnetic field at the measurement sample position is constant.

  The characteristics of the magnetic field correction coil are obtained, for example, by applying various current values to the coil and measuring the strength of the magnetic field generated at that time at both the lock sample position and the measurement sample position. Alternatively, representative current values may be measured, and current values during the measurement may be obtained by interpolation. Alternatively, by utilizing (assuming) that the magnetic field intensity is proportional to the current value, the magnetic field fluctuation amount when the unit current is applied to the magnetic field correction coil may be obtained at the lock sample position and the measurement sample position.

  In this way, it is possible to stabilize the magnetic field strength at the measurement sample position based on the magnetic field strength at the lock sample position.

  The correction amount calculation unit preferably measures the strength of the magnetic field at the lock sample position by measuring the frequency of the resonance signal obtained from the lock resonance signal receiving unit using a frequency counter. As the signal input to the frequency counter, the signal received by the lock resonance signal receiving unit may be input as it is, or may be input after being converted to a low frequency.

  By using the frequency counter in this way, even when the magnetic field to be measured has a large fluctuation (the frequency fluctuation of the resonance signal is large), the fluctuation amount can be accurately measured. Therefore, the correction current value applied to the magnetic field correction coil can be obtained with high accuracy, and the stability of the magnetic field is increased.

  The magnetic field stabilization mechanism according to the present invention is applicable even when the magnetic field fluctuation is large. Therefore, the present invention is preferably applied to a magnetic resonance apparatus or an electron spin resonance apparatus having a large magnetic field fluctuation. Such a measuring apparatus with a large magnetic field variation includes a magnetic resonance apparatus and an electron spin resonance apparatus having a magnet that applies a current from an external power source to a coil of a high-temperature superconducting wire or a normal conducting wire as a magnetic field generating means.

In addition, the magnetic field stabilization mechanism according to the present invention is preferably applied to a solid-state NMR apparatus that cannot employ an internal lock method. However, even with a solution NMR apparatus, the magnetic field fluctuation is large,
It is also suitable to apply to an NMR apparatus in which a conventional lock method cannot be used.

  The present invention can be understood as a magnetic field stabilization mechanism of a magnetic resonance apparatus or an electron spin resonance apparatus including at least a part of the above means. Further, the present invention can be understood as a magnetic resonance apparatus or an electron spin apparatus including the magnetic field stabilization mechanism. Further, the present invention can be understood as a magnetic field stabilization method of a magnetic resonance apparatus or an electron spin resonance apparatus, a measurement method in these apparatuses, or a program for realizing such a method, including at least a part of the above processing. it can. Each of the above means and processes can be combined with each other as much as possible to constitute the present invention.

  According to the present invention, it is possible to stabilize the magnetic field of the magnetic resonance apparatus or the electron spin resonance apparatus with higher accuracy by the external lock method.

(First embodiment)
The NMR apparatus according to this embodiment will be described with reference to FIG. The NMR magnet in this embodiment is composed of a plurality (several to several tens) of superconducting coils. A high-temperature superconducting wire such as Bi2223 is used for the innermost layer coil, and a low-temperature superconducting wire such as NbTi or Nb ₃ Sn is used for the other layers. This is because the critical current density of the low-temperature superconducting wire becomes small in a high magnetic field as shown in FIG. On the other hand, when a high-temperature superconducting wire is used at a superfluid helium temperature (4K), a high critical current density can be obtained even in a high magnetic field. The high-temperature superconducting wire is commercially available in the form of a tape and may be used. Depending on the strength of the magnetic field, high-temperature superconducting wires may be used not only for the innermost coil but also for other layers.

The high-temperature superconducting wire generates a slight resistance when a large current is passed. In addition, because of the shape and properties of the wire, it is difficult to make a superconducting connection between the superconducting coils. Therefore, when used in the permanent current mode, the current is attenuated at a speed of 10 ⁻⁶ / h to 10 ⁻⁴ / h by resistance. Therefore, in this embodiment, the current is always supplied from the external power source 2 to the NMR magnet 1 to suppress the attenuation of the magnetic field.

  Inside the probe 3 is a measurement sample tube into which a measurement sample 4 is placed, and a measurement coil 5 for detecting an NMR signal is provided around the measurement sample tube. In solid state NMR, the measurement sample 4 is rotated at a magic angle (54.74 °) in order to cancel the anisotropic interaction.

  The NMR spectrometer 6 is normally used, and outputs a high-frequency pulse for exciting the NMR signal to the measurement coil 5 and receives the NMR signal from the measurement sample 4 by the measurement coil 5. Then, the chemical property of the measurement sample 4 is observed by a chemical shift of the NMR signal.

In order to accurately observe the NMR signal, it is necessary to make the magnetic field applied to the measurement sample 4 constant. When the external power supply 2 is used as in this embodiment, it is affected by the current fluctuation. The characteristics of the external power supply are shown in FIG. FIG. 3A shows the current fluctuation of a normally used power source for excitation, and has a fluctuation width of about 15 ppm in 30 minutes. FIG. 3B shows the current fluctuation of the highly stabilized power supply, and there is a fluctuation width of about 1 ppm in 30 minutes. All of these current fluctuations are much larger than the fluctuations in the permanent current mode (10 ⁻⁸ ) used in ordinary NMR magnets, which modulates the NMR spectrum and makes it impossible to make precise measurements. Become.

  Therefore, in the present embodiment, the magnetic field during energization of the external power supply is stabilized to a level necessary for NMR measurement by the external lock mechanism described below. As the external power source 2, it is preferable to use a highly stabilized power source having a fluctuation range of about 1 ppm as shown in FIG. 3B, but a power source having a fluctuation of about 15 ppm as shown in FIG. It doesn't matter.

In order to be able to measure the magnetic field generated by the NMR magnet 1, the NMR signal generated from the magnetic field measurement lock nucleus sample (lock sample) 7 is detected by the magnetic field measurement coil 8 separately from the measurement sample 4. . In the present embodiment, a solution sample containing ⁷ Li nuclei such as a lithium chloride solution is employed as the lock nucleus sample 7. The lock nucleus sample 7 may be a solution sample containing nuclei such as ² H, ¹ H, and F. In order to avoid interference with the NMR signal for measurement, it is preferable to use a nuclide having a large difference in resonance frequency from the measurement sample 4.

Since the location of the lock core sample 7 is far from the center of the magnet and the uniformity of the magnetic field is not sufficient, the NMR signal tends to be broad due to the influence. In order to prevent this, the lock nuclear sample 7 and the magnetic field measuring coil 8 are limited because of the limitation of the installation space (the probe is about 40 mm in diameter and the inside is narrow).
Is as small as possible. Conversely, if it is too small, the sensitivity will deteriorate. In the present invention, the lock core sample 7 is placed in a PTFE tube or glass tube having a diameter of about 1 mm, and a magnetic field measuring coil 8 is wound around the PTFE tube. The magnetic field measuring coil 8 is used for both the purpose of applying a high frequency pulse for excitation to the lock nuclear sample 7 and for receiving the NMR signal excited from the lock nuclear sample 7. The magnetic field measuring coil 8 is a solenoid coil having a diameter of 1.5 mm or less and a number of turns of 40 or less. The solenoid coil wire is assumed to be copper, aluminum, or silver or gold plated on these. Alternatively, in order to cancel the residual magnetism, the copper surface may be coated with aluminum, or the aluminum surface may be coated with copper or gold. The wire may be surface-insulated or not insulated. A tube is desirable for containing the sample, but a hollow sphere or spheroid may be used.

  If the magnetic field becomes non-uniform only by winding the solenoid around the sample tube and the NMR signal spectrum of the lock nucleus becomes broad, the entire solenoid is preferably immersed in grease or oil. By this processing, the Q value of the solenoid coil can be increased, and the spectrum of the NMR signal becomes sharper.

  The sample tube containing the lock core sample 7 was installed at a position 15 mm below the position of the NMR measurement sample 4 (the magnetic field center of the NMR magnet 1). Although this sample tube is preferably installed on the central axis of the NMR magnet 1 and the magnetic field correction coil 9 as in the measurement sample 4, it may be installed at a position different from the central axis. The sample tube containing the lock core sample 7 may be at a position not less than 5 mm and not more than 30 mm from the position of the NMR measurement sample 4.

  The locking NMR signal excitation circuit including the pulse transmitter 10, the power amplifier 11, and the like generates an excitation pulse for exciting the lock nuclear sample 7 via the magnetic field measurement coil 8. By this excitation pulse, an NMR signal having a Larmor frequency (resonance frequency) corresponding to the nuclide and the static magnetic field is generated from the lock nuclear sample 7. Since the nuclide of the lock nucleus is known, measuring the Larmor frequency of the NMR signal is equivalent to measuring the strength of the static magnetic field applied to the lock nucleus.

  The magnetic field correction coil 9 is provided in the room temperature shim, and corrects the magnetic field based on the magnetic field measured by the magnetic field measurement coil 8 so that the magnetic field at the position of the measurement sample 4 is constant. A specific correction amount (current value applied to the magnetic field correction coil 9) will be described in detail later.

The switch 12 periodically switches between high-frequency pulse output and NMR signal input. The NMR signal generated from the lock nuclear sample 7 is amplified by a low noise amplifier (LNA) 13, is made low frequency so that the local oscillator 14 and the mixer 15 can be easily processed later, and is filtered by a band pass filter (BPF) 16. Add processing.

  The NMR signal dropped to a low frequency is input to the frequency counter 17 and its frequency is measured. A reciprocal counter is used as the frequency counter 17 in order to accurately measure the frequency with a short gate time. From the frequency of the local oscillator 14 and the measurement result of the frequency counter 17, the frequency (resonance frequency) of the original NMR signal is obtained.

  The measured value of the frequency counter 17 is input to a PC (personal computer) 18. The PC 18 calculates the current value for stabilizing the magnetic field fluctuation of the NMR magnet 1 by feedback control. The PC 18 corresponds to an arithmetic circuit that controls the magnitude of the correction coil current. However, this arithmetic circuit may be realized by a dedicated circuit. Hereinafter, the PC 18 is referred to as the calculation unit 18.

  In the correction current calculation process, the value of the correction current is obtained based on the measurement value of the frequency counter 17 so that the magnetic field at the position of the measurement sample 4 is constant. The correction current is not calculated so that the measured value of the frequency counter 17 is constant. That is, the magnetic field strength at the magnetic field measurement position of the lock nuclear sample 7 is not made constant.

  As a comparative example, FIG. 4 shows the result of locking when the correction current is obtained so that the magnetic field at the magnetic field measurement position is constant. FIG. 4 shows the fluctuation of the NMR signal spectrum of the measurement sample 4. As shown in the figure, when the correction current is calculated so that the magnetic field at the magnetic field measurement position (the lock nuclear sample 7 + the magnetic field measurement coil 8) is constant, the resonance frequency of the measurement sample 4, that is, the measurement sample 4 position. It can be seen that the magnetic field strength fluctuates with a fluctuation range of about 0.2 ppm.

  It is considered that the fluctuation range at the position of the measurement sample 4 is increased due to the magnetic field inhomogeneity of the magnetic field correction coil 9 as described above. That is, since the fluctuation due to the external power source is large, it is necessary to increase the correction magnetic field by the magnetic field correction coil 9, and the influence of the nonuniformity of the correction magnetic field cannot be ignored. FIG. 5 shows the intensity distribution of the magnetic field generated by the magnetic field correction coil 9. As shown in the figure, the magnetic field is strongest at the center position of the magnetic field correction coil 9 (position of the measurement sample 4) and decreases as the distance from the center position increases.

  As can be seen from the results in the above comparative example, the calculation unit 18 needs to obtain the correction current in consideration of the influence of the magnetic field nonuniformity of the correction coil 9. The correction current value calculation process performed by the calculation unit 18 will be described with reference to FIGS. FIG. 6 is a flowchart of the correction current value calculation process, and FIG. 7 is a diagram for explaining how to obtain the correction current value. In the following description, processing is performed on the resonance frequency, but since it is the resonance frequency of a known lock nucleus sample, that is, it is the same as processing on the magnetic field strength.

  First, the characteristics of the correction coil 9 are examined in advance. Here, how many Hz the resonance frequency fluctuates per 1 mA of the correction current is examined for each of the NMR measurement position (hereinafter referred to as the center position) and the external lock magnetic field measurement position (hereinafter referred to as the external lock position). deep. The amount of change at the center position is ΔFc [Hz / mA], and the amount of change at the external lock position is ΔFb [Hz / mA]. These changes that have been examined in advance are stored in the calculation unit 18.

  Next, the resonance frequency Fb [Hz] at the external lock position is measured (S1). Based on the resonance frequency Fb at the external lock position, the current correction current value I [mA], and the correction coil characteristics (ΔFc, ΔFb), the resonance frequency Fc at the center position is calculated (S2). That is, the resonance frequency Fc at the center position is calculated by Fc = Fb + I × (ΔFc−ΔFb) (see FIG. 7).

Then, feedback control is performed using this Fc (S3). Here, the target value of the resonance frequency to be kept constant is assumed to be Ftarget [Hz]. Then, the correction current change amount dI [mA] is determined according to the PI control. Specifically, dI is determined by dI = kp × (Ftarget−Fc) / ΔFc (where kp is a control parameter and 0 <kp <1). In this way, a new correction current Inew is obtained as Inew = I + dI.

  In the above description, the magnetic field fluctuation amount (ΔFc, ΔFb) per unit current is obtained as the characteristic of the magnetic field correction coil 9, but the present invention is not limited to this. For example, the magnetic field strength at the center position created by the magnetic field correction coil and the external lock position may be obtained for various correction current values. That is, the magnetic field strength distribution Fc (I) at the center position and the magnetic field strength distribution Fb (I) at the external lock position are obtained. The magnetic field calculation (estimation) at the center position in step S1 may be performed by Fc = Fb−Fb (I) + Fc (I).

  The correction current amount obtained by the calculation unit 18 is supplied to the magnetic field correction coil 9 via the DA converter 19.

FIG. 8 shows the fluctuation of the magnetic field at the position of the measurement sample 4 (center position) when the magnetic field is stabilized by the external lock mechanism according to this embodiment. FIG. 8 shows the fluctuation of the NMR signal spectrum of the measurement sample 4. As can be seen from the figure, the magnetic field at the center position is stabilized with high accuracy by using the above external locking mechanism. The fluctuation range of the magnetic field is suppressed to 10 ⁻⁸ (0.01 ppm) or less required for solid-state NMR.

  FIG. 9 is a diagram showing the time change of the measured value obtained by measuring the resonance frequency at the center position with the frequency counter, the estimated magnetic field value at the center position by the arithmetic circuit, and the correction current value during the measurement shown in FIG. It is. It can be seen that the magnetic field at the center position is stabilized by applying the correction current.

  According to the external lock mechanism according to the present embodiment, even when the NMR magnet is used in the external energization mode, it is possible to suppress the magnetic field fluctuation accompanying the current fluctuation of the external power source. As a result, the high-temperature superconducting wire in the external energization mode can be used as an NMR magnet, and a high magnetic field can be achieved.

  In particular, instead of making the magnetic field at the sample position for external locking constant, the calculation to estimate the magnetic field at the center position based on the measured value of the magnetic field at the sample position for external locking is added. The magnetic field at the center position can be stabilized with high accuracy. As a result, it is possible to achieve a high degree of stabilization that cannot be obtained simply by stabilizing the measurement magnetic field at the sample position for locking as in the comparative example described above. Since the stability of the magnetic field at the center position (NMR measurement position) contributes to the accuracy of NMR measurement, NMR measurement can be performed with high accuracy.

  The above advantages can also be understood as the magnetic field generated by the correction coil does not need to be uniform in a wide space. That is, it is not necessary to make the magnetic field generated by the correction coil uniform, and the correction coil can be easily designed and manufactured.

Moreover, the internal lock mechanism using the conventional detector may become difficult to apply when the fluctuation of the magnetic field increases. This is effective in the case of a magnetic field with relatively small fluctuations such as a permanent current mode because the range in which the output of the dispersion signal and the frequency difference are proportional is relatively narrow, but may not be able to cope with large magnetic field fluctuations. Because there is. In other words, the external locking mechanism in the present embodiment is not only applicable to the solid-state NMR apparatus using the high-temperature superconducting wire in the external energization mode described above. Applicable. For example, the present invention can also be applied to an NMR apparatus that externally energizes a hybrid magnet that combines a normal conducting wire (such as a copper wire) and a superconducting wire. Further, the present invention is applicable not only to an NMR apparatus that handles a high magnetic field of 20 T or more (a low-temperature superconducting wire cannot be used), but also to an NMR apparatus that performs external energization that handles a lower magnetic field.

  In the above description, the NMR apparatus is described as an example. However, since the MRI (magnetic resonance imaging) apparatus and the ESR (electron spin resonance) apparatus have basically the same configuration as the NMR apparatus, the magnetic field of this embodiment is used. A stabilization mechanism can be applied.

(Second Embodiment)
In the first embodiment, the magnetic field strength (resonance frequency) is obtained using a frequency counter. In the present embodiment, the magnetic field strength is obtained by a different method. In the present embodiment, a single-frequency high frequency (NMR excitation signal) is used, and the frequency is periodically changed up and down (for example, in a triangular wave shape). Then, the reference signal of the detector or the LO frequency of the mixer is linked to it. In this method, since the NMR signal is generated only when the frequency of the NMR excitation signal matches the resonance frequency of the lock nuclear sample, the magnetic field at the magnetic field measurement sensor position is determined based on the frequency of the NMR excitation signal when the NMR signal is generated. Can be measured. Even if it does in this way, the same effect is acquired.

It is a figure which shows the outline | summary of a structure of the NMR apparatus provided with the external lock system which concerns on 1st Embodiment. It is a figure which shows the relationship between the strength of the magnetic field of a high-temperature superconducting wire, and a low-temperature superconducting wire, and a critical current density. It is a figure which shows the electric current fluctuation | variation of the stabilized power supply ((a) normal excitation power supply, (b) highly stabilized power supply). It is a figure for showing the fluctuation | variation of the magnetic field intensity (resonance frequency) in a measurement sample position at the time of applying correction | amendment electric current so that the strength of the magnetic field in a lock | rock nucleus position may be made constant. The time change of the NMR signal spectrum at the center position is shown. It is a figure which shows distribution of the magnetic field intensity produced | generated by a magnetic field correction coil. It is a flowchart which shows the flow of a correction current calculation process. It is a figure explaining the process which calculates correction | amendment electric current. It is a figure for showing the fluctuation | variation of the magnetic field intensity (resonance frequency) in the measurement sample position at the time of applying correction | amendment electric current by the external lock by this embodiment. The time change of the NMR signal spectrum at the center position is shown. It is a figure which shows the time change of the measured value of the magnetic field of a center position, the estimated value of the magnetic field of a center position, and a correction electric current value in the measurement of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 NMR magnet 2 External power supply 4 Measurement sample 5 NMR measurement coil 6 NMR spectrometer 7 Lock nuclear sample 8 Magnetic field measurement coil 9 Magnetic field correction coil 17 Frequency counter 18 PC (calculation part)

Claims (6)

A magnetic field stabilization mechanism for stabilizing a magnetic field generated by a magnetic field generation unit of a magnetic resonance apparatus or an electron spin resonance apparatus,
A locking sample arranged in the vicinity of the measurement sample;
A locking resonance signal receiving unit that irradiates the locking sample with a high frequency and receives a resonance signal from the locking sample;
A magnetic field correction coil for correcting the magnetic field by the magnetic field generation means;
A correction amount calculation unit that calculates a current value to the magnetic field correction coil to be applied in order to suppress magnetic field fluctuations at the position of the measurement sample based on fluctuations in the resonance signal obtained from the resonance signal reception unit for locking;
A magnetic field stabilization mechanism. The correction amount calculation unit includes:
The relationship between the value of the current applied to the magnetic field correction coil and the strength of the magnetic field generated at that time at the lock sample position and the measurement sample position (hereinafter referred to as the characteristics of the magnetic field correction coil) is acquired in advance.
From the resonance signal obtained from the lock resonance signal receiver, the magnetic field strength at the lock sample position is measured,
From the measured magnetic field strength at the lock sample position, the characteristics of the magnetic field correction coil, and the correction current value currently applied, the magnetic field strength at the measurement sample position is calculated,
2. The magnetic field stabilization mechanism according to claim 1, wherein a current value to be applied to the magnetic field correction coil is calculated so that a magnetic field strength at the measurement sample position is constant. The magnetic field stabilization mechanism according to claim 2, wherein the correction amount calculation unit measures the strength of the magnetic field at the lock sample position using a frequency counter. The magnetic field stabilization mechanism according to any one of claims 1 to 3, wherein the magnetic field generation unit is a unit in which a current from an external power source is applied to the coil.   The magnetic resonance apparatus provided with the magnetic field stabilization mechanism in any one of Claims 1-4.   An electron spin resonance apparatus comprising the magnetic field stabilization mechanism according to claim 1.

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