JP2007051882A - Nmr system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an NMR system equipped with an amplifier of cooling type of small and low cost, without being affected by the heat generated from duplexer section at NMR measurement. <P>SOLUTION: The NMR equipment is constituted so that the NMR detector is transmitted with the high frequency via the duplexer, and the NMR signal detected by the NMR detector is received via the duplexer and is amplified by the preamplifier. The duplexer part, the preamplifier or the power resistor and the others are mutually heat insulated and cooled, respectively, with individual cooling systems. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an NMR apparatus, and more particularly to an NMR apparatus in which the detection portion is cooled to a very low temperature with low-temperature helium gas to increase the detection sensitivity of NMR signals.

  An NMR device applies a strong static magnetic field to a sample, causes precession about the static magnetic field direction to occur in the magnetic moment of the nucleus with nuclear spin in the sample, and is orthogonal to the static magnetic field direction. Transmit and apply a high-frequency magnetic field in the direction to excite the precession of the nuclear magnetic moment, and then emit an NMR signal that is emitted when the precession of the nuclear magnetic moment returns from the excited state to the ground state. This is a device that receives and observes a high-frequency magnetic field having a frequency specific to a sample.

  Since the NMR signal is usually very weak, in order to increase its detection sensitivity, an NMR probe with a built-in detection unit is provided with a pipe for circulating a low-temperature gas, and the detection unit is cooled to a very low temperature. It has been practiced to reduce the thermal noise of the apparatus and increase the sensitivity of the NMR apparatus (Patent Documents 1 to 3).

  The positional relationship between a conventional NMR probe and a superconducting magnet that generates a static magnetic field is shown in FIG. In the figure, A is a superconducting magnet. Inside the superconducting magnet A, a main coil B is wound by a superconducting wire. The main coil B is usually placed in a heat insulating container (not shown) that can store liquid helium and the like, and is cooled to a cryogenic temperature. The nuclear magnetic resonance probe C is composed of a bowl-shaped base portion arranged outside such a magnet and a cylindrical portion inserted inside the magnet, and the cylindrical portion is usually a superconducting magnet. It is inserted upward from the lower opening toward the inside of the cylindrical hole D penetrated along the central axis of A.

  Next, the structure of a conventional NMR probe is shown in FIG. This example shows the case of a low temperature probe called a cooling probe. In the figure, 8 is a probe container. The probe container 8 is connected to the refrigerator 14 by a transfer line 9. Each is evacuated inside for heat insulation from the outside. Inside the probe container 8, a detection unit 1 including a detection coil and a tuning matching circuit is placed. The detection unit 1 is in thermal contact with the heat exchanger 2 and can be cooled. In order to perform temperature control of the detection unit 1, a heater 100 is provided in the vicinity of the detection unit 1.

  A nuclear magnetic resonance detection signal detected by the detection unit 1 is input to the transmission / reception switching unit 3 with a built-in preamplifier via the cable 6 and amplified. The amplified signal (head amplifier output) is sent to a spectroscope (not shown) via the cable 7. The preamplifier built-in transmission / reception switching unit 3 is in thermal contact with the heat exchanger 4 and can be cooled. In order to control the temperature of the preamplifier built-in transmission / reception switching unit 3, a heater 5 is provided in the vicinity of the preamplifier built-in transmission / reception switching unit 3.

  Although the detection unit 1 has a structure for putting a sample from the outside of the probe container 8, it is not shown because it is not necessary for explanation of the cooling method.

  A refrigerator main body 19 such as a Gifford-McMahon (GM) system having a first cooling stage 20 and a second cooling stage 22 is attached to the refrigerator 14. The first cooling stage 20 and the second cooling stage 22 are provided with a heat exchanger 21 and a heat exchanger 23, respectively. Further, a heat exchanger 24 and a heat exchanger 25 are provided in the middle of the pipe 15 and the pipe 16. The refrigerator main body 19 is connected with piping 17 and piping 18 for supplying working gas. Further, inside the transfer line 9, there are a pipe 10, a pipe 11, a pipe 12 and a pipe 13, which are connected to the heat exchanger 2 and the heat exchanger 4, respectively.

  Next, the operation will be described. A working gas (helium gas) is supplied from an external compressor (not shown) through the pipe 17 and the pipe 18 to operate the refrigerator main body 19. Separately, the refrigerant helium gas is supplied from the pipe 16, passes through the heat exchanger 24, and is cooled by the heat exchanger 21 of the first cooling stage 20. Further, the helium gas passes through the heat exchanger 25 and is further cooled by the heat exchanger 23 of the second cooling stage 22. The gas temperature at this time is 10K.

  The cooled helium gas is supplied to the heat exchanger 2 through the pipe 10 in the transfer line 9 to cool the detection unit 1. The gas temperature immediately before entering the heat exchanger 2 is 15K, and the gas temperature immediately after leaving the heat exchanger 2 is 23K. This temperature rise is due to the fact that the heat of the detection unit 1 has been received, and at the same time, because the heater 100 is activated and heated by the heater 100 for the temperature control of the detection unit 1.

  When the detection coil and the tuning matching circuit housed in the detection unit 1 are cooled, the Q value is improved and the thermal noise is reduced, and the sensitivity is improved. The helium gas returns to the refrigerator 14 via the pipe 11, and the helium gas in the forward path is precooled by the heat exchanger 25 and the gas temperature is raised to 40 K. Then, the preamplifier built-in transmission / reception switching unit 3 is cooled to improve the NF (noise figure) of the preamplifier built-in transmission / reception switching unit 3.

  Thereby, the detection signal from the detection unit 1 can be transmitted to the spectroscope (not shown) via the cable 7 without deteriorating the S / N.

  The preamplifier built-in transmission / reception switching unit 3 is maintained at an appropriate temperature by the heater 5. The gas temperature immediately before entering the heat exchanger 4 is 40K, and the gas temperature immediately after leaving the heat exchanger 4 is 90K. This temperature rise is due to the reception of heat from the preamplifier built-in transmission / reception switching unit 3, and at the same time, the heater 5 is activated and heated by the heater 5 for temperature control of the preamplifier built-in transmission / reception switching unit 3. It is also because of the damage.

  The helium gas is returned to the refrigerator 14 through the pipe 13 in the transfer line 9, and after the forward helium gas is pre-cooled by the heat exchanger 24, the helium gas is returned to the external compressor (not shown) through the pipe 15 and circulated.

  FIG. 3 shows an NMR apparatus equipped with a low-temperature probe in which the detection unit is cooled to a very low temperature to reduce thermal noise. In the figure, reference numeral 101 denotes a probe which irradiates a sample with a high frequency and incorporates a transmission / reception coil (not shown) for detecting a weak high frequency signal (NMR signal) emitted from the sample. The probe 101 includes a switching means (not shown) configured by a duplexer for switching between a transmission mode and a reception mode, and a preamplifier (not shown) that quickly amplifies a weak NMR signal emitted from the sample. And a built-in cryoamplifier 102 are connected.

  A high-power high-frequency pulse sent from the transmitter 104 of the NMR spectrometer 103 passes through the transmission means 105 such as a coaxial cable, passes through the switching means of the cryoamplifier 102 in the transmission mode, and is built in the probe 101. Applied to a transmitted / received coil (not shown). As a result, the observation nucleus in the sample placed in the transmission / reception coil is excited by the applied high-frequency pulse magnetic field. When the excited observation nucleus returns from the excited state to the ground state, a weak high-frequency signal (NMR signal) is emitted. This NMR signal is detected by a transmission / reception coil (not shown) built in the probe 101, passes through the switching means (not shown) of the cryoamplifier 102 in the reception mode, and then provided in the cryoamplifier 102. Amplified by a preamplifier (not shown) and sent to a receiver 106 in the NMR spectrometer 103 via a transmission means 105 such as a coaxial cable.

  Switching between the reception mode and transmission mode of the switching means in the cryoamplifier 102 is performed in synchronization with the output of a high-power high-frequency pulse from the transmitter 104 of the NMR spectrometer 103, and the trigger signal from the NMR spectrometer 103 is used. Based on this, it is controlled by the cryoamplifier control unit 107.

  The probe 101 and the cryoamplifier 102 are placed in a vacuum vessel 109 evacuated by a vacuum pump 108, insulated from the outside, and sent from a refrigerator 110 placed outside the vacuum vessel 109. It is cooled by a refrigerant such as low-temperature helium gas, and is maintained at an extremely low temperature of about 10K, for example. As a result, thermal noise of the transmitting / receiving coil in the probe 101, the switching means in the cryoamplifier 102, the preamplifier, and the like is reduced to a significantly lower level than that at room temperature. Thereby, it is possible to improve the S / N ratio of the NMR signal and increase the sensitivity of the NMR apparatus.

  Although details are omitted in the figure, the cylindrical portion 111 from the upper end of the probe 101 toward the inside communicates with the outside of the vacuum vessel 109, and the measurement sample is in a normal temperature and normal pressure state. The probe 101 is configured to be inserted from the upper end toward the inside.

JP-A-10-307175 Japanese Patent Laid-Open No. 10-332801 JP 2001-153938 A

  FIG. 4, FIG. 5, and FIG. 6 show the structural schematic diagram of the current low temperature probe, the structural schematic diagram of the cooling type amplification unit used in the low temperature probe, and the electrical structural schematic diagram of the cooling type amplification unit.

  At present, the cooling type amplifying unit of the low-temperature probe is uniformly cooled by placing the duplexer unit and the preamplifier unit constituting the cooling type amplifying unit on the same heat exchanger in terms of electrical performance. However, in fact, the heat generation of the cooling type amplification unit of the low temperature probe is not uniform. In particular, the duplexer unit switches between transmission and reception of RF signals by a control signal from the NMR apparatus, and there is a large difference in heat generated by the power resistance before and after this switching.

  As shown in FIG. 6, in the RF power transmission mode in which the RF pulse from the NMR apparatus is transmitted to the low temperature probe side, the duplexer section generates a large amount of heat, but the mode is switched and the NMR probe detects and amplifies the NMR signal. In the RF power reception mode for sending to the receiver in the NMR apparatus, the duplexer section hardly generates heat.

  Therefore, before and after the mode switching of the duplexer unit, temperature imbalance occurs in the entire cooling type amplification unit, and the temperature stability of the preamplifier unit is lacking. This problem may adversely affect the NMR observation accuracy and the lifetime of the cooled amplification unit itself.

  Further, the heat generated by the power resistance of the duplexer unit accounts for most of the heat generated by the entire cooling type amplification unit. Currently, due to the structure of the cooling type amplification unit, the duplexer unit and the preamplifier unit are cooled together, so in order to cool the cooling type amplification unit, the maximum total heat generation in anticipation of the heat generation of the duplexer unit It is necessary to determine the cooling capacity from the quantity, and the cooling capacity must be set larger than when only the preamplifier section is cooled. For this reason, there has been a problem that the equipment for cooling the cooling type amplifying unit is increased in size and cost.

  In view of the above points, an object of the present invention is to provide an NMR apparatus including a small and low-cost cooling-type amplification unit that is not affected by heat generated by a duplexer unit during NMR measurement.

In order to achieve this object, the NMR apparatus according to the present invention comprises:
In the NMR apparatus configured to transmit the high frequency to the NMR detector via the duplexer, and to receive the NMR signal detected by the NMR detector via the duplexer and to amplify it by the preamplifier,
The duplexer unit and the preamplifier unit are insulated from each other and cooled by separate cooling mechanisms.

  Further, the cooling mechanism for cooling the preamplifier unit is a system using helium, and the cooling mechanism for cooling the duplexer unit is a system not using helium.

Further, in the NMR apparatus configured to transmit the high frequency via the duplexer to the NMR detector, and to receive the NMR signal detected by the NMR detector via the duplexer and amplify the preamplifier,
It is characterized in that the power resistance of the duplexer and the other are insulated from each other and cooled by separate cooling mechanisms.

  The cooling mechanism that cools the power resistance of the duplexer is a system that does not use helium, and the cooling mechanism that cools the other is a system that uses helium.

According to the NMR apparatus of the present invention,
In the NMR apparatus configured to transmit the high frequency to the NMR detector via the duplexer, and to receive the NMR signal detected by the NMR detector via the duplexer and to amplify it by the preamplifier,
The duplexer unit and preamplifier unit, or the power resistor of the duplexer and the others are insulated from each other and cooled by separate cooling systems, so they are not affected by the heat generated in the duplexer unit and are small in size. Thus, it is possible to provide a low-cost NMR apparatus including a cooling type amplification unit.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 7 shows an embodiment of the NMR apparatus according to the present invention. In the figure, 201 is a duplexer unit. The duplexer unit 201 includes a power amplifier port 202 that inputs an RF pulse transmitted from a power amplifier (not shown), and a probe port 203 that outputs the input RF pulse to the NMR probe side (not shown). In the example of this figure, there are three duplexer unit power resistors 204 in the duplexer unit, each of which is provided with a heat exchanger 206 via a heat conduction plate 205 for the duplexer unit power resistor. The heat exchanger 206 is connected to a refrigerant pipe 208 dedicated to the duplexer section that has passed through the external heat exchanger 207 so as to cool only the power resistance 204 of the duplexer section.

  On the other hand, the preamplifier unit 210 adjacent to the duplexer unit 201 amplifies the NMR signal input from the probe port 203 of the duplexer unit 201 and accommodates the multistage preamplifier 212 that outputs the amplified signal to the receiver port 211. Has been. The preamplifier 212 is structured to be cooled by a heat exchanger 214 dedicated to the preamplifier unit via a heat conduction plate 213 dedicated to the preamplifier. Inside the heat exchanger 214, a refrigerant pipe 215 dedicated to the preamplifier unit is communicated, and is structured to be cooled independently of the duplexer unit 201. That is, the duplexer section and the preamplifier section are insulated so that heat is not directly transferred.

  Each part operates as follows. First, liquid helium, which has finished cooling the detection coil of the NMR probe, is transferred through the refrigerant pipe 215 dedicated to the preamplifier, and passes through the heat exchanger 214 dedicated to the preamplifier, and the heat conduction plate 213 dedicated to the preamplifier. Is kept cool and the preamplifier 212 is cooled. Aside from the preamplifier cooling, there is a refrigerant pipe 208 dedicated to the duplexer section, through which a suitable refrigerant of gas or liquid such as air or nitrogen passes.

  The heat generated from the duplexer power resistor 204 is passed through a refrigerant pipe 208 dedicated to the duplexer, and the NMR probe passes through the heat exchanger 206 for the duplexer power resistor and the heat conduction plate 205 for the duplexer power resistor. To the outside.

  The duplexer unit 201 and the preamplifier unit 210 are electrically connected on the same printed circuit board. The duplexer power resistor 204 is also incorporated on the circuit as a part of the duplexer unit 201. However, the duplexer power resistor 204, the heat conductive plate 205 for the duplexer power resistor, and the heat exchanger 206 for the duplexer power resistor. These three are independent from the heat conduction plate 213 dedicated to the preamplifier section, and eliminate heat flow by increasing heat insulation or thermal resistance from the surroundings.

  Further, to the duplexer unit 201 and the preamplifier unit 210, a duplexer unit power / signal cable 220, an RF cable 221 for RF signal transmission, and a preamplifier unit power cable 222 are connected, respectively. However, heat flow is increased between the duplexer power resistor 204, the duplexer power / signal cable 220 connected to the duplexer power resistor 204, and the heat conduction plate 205 for the duplexer power resistor by increasing heat insulation or thermal resistance. It is lost.

  FIG. 8 shows another embodiment of the NMR apparatus according to the present invention. In the figure, reference numeral 301 denotes a cooling type amplification unit substrate. The cooling type amplification unit substrate 301 is placed on the heat conduction plate 302 for the cooling type amplification unit while keeping thermal contact. One end of the cooling type amplification unit heat conduction plate 302 is in contact with a cooling type amplification unit heat exchanger 304 through which the cooling type amplification unit cooling helium pipe 303 passes. On the cooling type amplification unit substrate 301, a duplexer unit power resistor 305 is provided so as to be insulated from the cooling type amplification unit substrate 301 while maintaining electrical connection. The duplexer power resistor 305 is connected to the low-temperature probe vacuum container housing 307 through the heat conductive material 306.

  Each part operates as follows. First, liquid helium that has finished cooling the detection coil of the NMR probe is transferred through the cooling type amplifying unit cooling helium pipe 303, and the cooling type amplifying unit heat is passed through the cooling type amplifying unit heat exchanger 304. The conductive plate 302 is kept at a low temperature, and the cooling type amplification unit substrate 301 is cooled. The duplexer power resistor 305 mounted on the cooling type amplification unit substrate 301 is configured as a circuit element of the cooling type amplification unit, and is kept in electrical contact with the circuit.

  On the other hand, the low-temperature probe vacuum container casing 307 and the duplexer power resistor 305 are thermally connected via a heat conductive material 306. The duplexer power resistor 305 and the cooling amplifier substrate 301 are insulated from each other or connected by a large thermal resistance. As a result, the heat generated from the duplexer power resistor 305 is hardly transmitted to the cooling amplification unit substrate 301, and the thermal load on the cooling amplification unit is reduced.

  Since the duplexer unit power resistor 305 is insulated from the cooling type amplifier unit substrate 301 and is placed in the cryogenic probe vacuum container casing 307, the heat generated by the duplexer unit power resistor 305 itself is not naturally radiated. This heat is conducted to the low-temperature probe vacuum container casing 307 by the heat conducting material 306 that is in thermal contact with the duplexer power resistor 305, and is radiated to the atmosphere using the casing as a radiator. With this cooling method via the housing, it is not necessary to use helium having a small heat capacity to cool the duplexer power resistor 305.

  It can be widely used in NMR apparatus equipped with a cooling probe.

It is a figure which shows the conventional NMR apparatus. It is a figure which shows the structure of the conventional low-temperature probe. It is a figure which shows the NMR apparatus provided with the conventional low-temperature probe. It is a figure which shows the structure schematic of the conventional low-temperature probe. It is a figure which shows the structure schematic of the cooling type amplification part currently used for the conventional low temperature probe. It is a figure which shows the electrical structure schematic of the conventional cooling type amplification part. It is a figure which shows one Example of the NMR apparatus concerning this invention. It is a figure which shows another Example of the NMR apparatus concerning this invention.

Explanation of symbols

A: Superconducting magnet, B: Main coil, C: Nuclear magnetic resonance probe, D: Hole, 1: Detection unit, 2: Heat exchanger, 3: Preamplifier built-in transmission / reception switching unit, 4: Heat exchanger, 5 : heater (main heater), 5 ^': sub heater, 6: cable, 7: cable, 8: probe container, 9: transfer line, 10: piping 11: pipe, 12: pipe, 13: pipe, 14: frozen 15: piping, 16: piping, 17: piping, 18: piping, 19: refrigerator main body, 20: first cooling stage, 21: heat exchanger, 22: second cooling stage, 23: heat exchanger, 24: Heat exchanger, 25: Heat exchanger, 100: Heater, 101: Probe, 102: Cryoamp, 103: NMR spectrometer, 104: Transmitter, 105: Transmission means, 106: Receiver, 107: Cryoamp Control unit 108: Vacuum pump 09: Vacuum container, 110: Refrigerator, 111: Cylindrical part, 201: Duplexer part, 202: Power amplifier port, 203: Probe port, 204: Duplexer part power resistance, 205: Heat conduction for duplexer part power resistance Plate, 206: heat exchanger, 207: external heat exchanger, 208: refrigerant pipe, 210: preamplifier section, 211: receiver port, 212: preamplifier, 213: heat conduction plate, 214: heat exchanger 215: Refrigerant piping, 220: Duplexer power / signal cable, 221: RF cable, 222: Preamplifier power cable, 301: Cooling amplifier board, 302: Heat conduction plate for cooling amplifier, 303: Cooling type amplification unit cooling helium piping, 304: cooling type amplification unit heat exchanger, 305: duplexer unit power resistance, 306: heat conduction material, 307 Cryoprobe vacuum container housing

Claims (4)

In the NMR apparatus configured to transmit the high frequency to the NMR detector via the duplexer, and to receive the NMR signal detected by the NMR detector via the duplexer and to amplify it by the preamplifier,
An NMR apparatus characterized in that a duplexer section and a preamplifier section are insulated from each other and cooled by separate cooling mechanisms. 2. The NMR apparatus according to claim 1, wherein the cooling mechanism for cooling the preamplifier unit uses helium, and the cooling mechanism for cooling the duplexer unit does not use helium. In the NMR apparatus configured to transmit the high frequency to the NMR detector via the duplexer, and to receive the NMR signal detected by the NMR detector via the duplexer and to amplify it by the preamplifier,
An NMR apparatus characterized in that the power resistance of the duplexer and the other are insulated from each other and cooled by separate cooling mechanisms. 4. The NMR apparatus according to claim 3, wherein the cooling mechanism for cooling the power resistance of the duplexer is a system that does not use helium, and the cooling mechanism that cools the other is a system that uses helium.

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