JP3942434B2 - NMR cryoprobe - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an NMR cryoprobe in which thermal noise generated from a transmission / reception coil, a preamplifier, and the like is reduced by cooling the transmission / reception coil, a preamplifier, and the like to a cryogenic temperature using a temperature lowering unit.
[0002]
[Prior art]
In general, in NMR measurement, after irradiating a sample with a high-frequency magnetic field, a weak high-frequency signal (NMR signal) emitted from the sample is detected and amplified, and a Fourier transform operation is performed on the amplified NMR signal. Above, the NMR spectrum is obtained. Compared to various other analyzers, the NMR device has a lower detection sensitivity of the sample. Therefore, the NMR device integrates the signals and reduces the thermal noise by cooling the detector to a very low temperature. It is normal for the device to be raised.
[0003]
FIG. 1 shows an NMR apparatus mounted with an NMR probe of a type called a cryoprobe in which a detection unit is cooled to a very low temperature to reduce thermal noise. In the figure, reference numeral 1 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 1 includes a switching means (not shown) composed of 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. Is connected to a cryoamplifier 2 having a built-in circuit.
[0004]
The high-power high-frequency pulse sent from the transmitter (not shown) of the NMR spectrometer 3 passes through the switching means of the cryoamplifier 2 in the transmission mode via the transmission means 4 such as a coaxial cable, It is applied to a transmission / reception coil (not shown) built in the probe 1. 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 1, passes through the switching means (not shown) of the cryoamplifier 2 in the reception mode, and then provided in the cryoamplifier 2. The signal is amplified by a preamplifier (not shown) and sent to a receiver (not shown) in the NMR spectrometer 6 via a transmission means 4 such as a coaxial cable.
[0005]
Switching between the reception mode and transmission mode of the switching means in the cryoamplifier 2 is performed in synchronization with the output of a high-power high-frequency pulse from a transmitter (not shown) of the NMR spectrometer 3. Is controlled by the cryoamplifier control unit 5 based on the trigger signal.
[0006]
The probe 1 and the cryoamplifier 2 are placed in a vacuum vessel 7 evacuated by a vacuum pump 6, insulated from the outside, and sent from a cooler 8 placed outside the vacuum vessel 7. 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, the thermal noise of the transmission / reception coil in the probe 1, the switching means in the cryoamplifier 2, the preamplifier, and the like is lowered to a significantly lower level than at normal temperature. Thereby, it is possible to improve the S / N ratio of the NMR signal and increase the sensitivity of the NMR apparatus.
[0007]
Although details are omitted in the figure, the cylindrical portion 9 from the upper end of the probe 1 toward the inside communicates with the outside of the vacuum vessel 7, and the measurement sample is in a state of normal temperature and pressure. The probe 1 is configured to be inserted from the upper end toward the inside.
[0008]
[Problems to be solved by the invention]
FIG. 2 shows an example of a current NMR cryoprobe. As shown in FIG. 2, the conventional NMR cryoprobe is provided between the cryoamplifier 2 installed in the vacuum vessel 7 and the NMR spectrometer 3 installed outside the vacuum vessel 7, and in the vacuum vessel 7. An airtight connector 10 is provided on the wall of the vacuum vessel 7 in order to connect the cryoamplifier 2 installed in the vacuum vessel and the cryoamp control unit 5 installed outside the vacuum vessel 7. 10, a high-frequency pulse from outside the vacuum vessel 7 and a control signal for switching means are transmitted into the vacuum vessel 7 and an NMR signal in the vacuum vessel 7 is taken out from the vacuum vessel 7.
[0009]
At that time, since the external cables 4 and 11 are always exposed to room temperature, the coaxial cables 12 and 12 in the vacuum vessel 7 are connected from the conductor portions made of metal of the external cables 4 and 11 through the airtight connector 10. There is a problem in that heat is transmitted to a conductor portion made of metal of the signal transmission cable 13 and unnecessary heat is supplied to the cryoamplifier 2 kept at an extremely low temperature. As a result, the temperature of the cryoamplifier 2 increases, leading to an increase in thermal noise, and the NMR cryoprobe cannot provide a predetermined performance or needs to use a more powerful cooler 8 in order to obtain a predetermined performance. Sex comes out.
[0010]
An object of the present invention is to provide a high-performance NMR cryoprobe that suppresses the inflow of heat through an external cable as much as possible in view of the above-described points.
[0011]
[Means for Solving the Problems]
In order to achieve this object, a nuclear magnetic resonance apparatus according to the present invention provides:
In the NMR cryoprobe that reduces the thermal noise from the probe or cryoamplifier by cooling the probe or cryoamplifier placed in the vacuum vessel to a cryogenic temperature using the temperature lowering means,
Connect the room temperature unit placed outside the vacuum vessel and the cryogenic probe or cryoamp placed inside the vacuum vessel via optical communication means ,
The optical communication means includes an optical conversion circuit on the room temperature side and a demodulation circuit on the cryogenic side .
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. FIG. 3 shows an embodiment of the NMR cryoprobe according to the present invention.
[0017]
In the figure, reference numeral 1 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 1 includes a switching means (not shown) configured by a duplexer for switching between a transmission mode and a reception mode, and a preamplifier that quickly amplifies a weak high-frequency signal (NMR signal) emitted from the sample. A cryoamplifier 2 incorporating an amplifier (not shown) is connected.
[0018]
The probe 1 and the cryoamplifier 2 are placed in a vacuum vessel 7 evacuated by a vacuum pump 6, insulated from the outside, and sent from a cooler 8 placed outside the vacuum vessel 7. It is cooled by a refrigerant such as cryogenic helium gas, and is maintained at a cryogenic temperature of about 10K, for example.
[0019]
Although details are omitted in the figure, the cylindrical portion 9 from the upper end of the probe 1 toward the inside communicates with the outside of the vacuum vessel 7, and the measurement sample is in a state of normal temperature and pressure. The probe 1 is configured to be inserted from the upper end toward the inside.
[0020]
A high-power high-frequency pulse sent from a transmitter 14 in the NMR spectrometer 3 passes through a transmission means 4 such as a coaxial cable exposed to room temperature, passes through an airtight connector 10 on the vacuum vessel wall, and passes through a transformer. Reach 15 In this case, as the transformer 15 at this time, it is preferable to adopt a transformer composed of one core in order to increase the degree of coupling between the input side and the output side. Since the transformer 15 is electrically insulated from the input-side conductor and the output-side conductor, the transformer 15 has an extremely excellent interruption characteristic with respect to heat transfer. Therefore, by relaying the transformer 15 between the airtight connector 10 and the cryoamplifier 2, it is possible to allow only high-frequency pulses to pass while blocking inflow of heat from the outside of the vacuum vessel. Thus, the high-frequency pulse that has passed through the transformer 15 passes through the switching means (not shown) of the cryogenic cryoamplifier 2 in the transmission mode, and is applied to the transmitting / receiving coil (not shown) in the cryogenic probe 1. The 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.
[0021]
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 cryogenic transmitter / receiver coil (not shown), passes through the switching means (not shown) of the cryogenic cryoamplifier 2 in the reception mode, and then provided in the cryoamplifier 2. Amplified by a cryogenic preamplifier (not shown) and reaches another transformer 16. As the transformer 16 at this time, like the transformer 15, it is preferable to adopt a type composed of one core in order to increase the degree of coupling between the input side and the output side. Since the transformer 16 is electrically insulated from the input-side conductor and the output-side conductor, the transformer 16 has an extremely excellent interruption characteristic with respect to heat transfer. Therefore, by relaying the transformer 16 between the airtight connector 10 and the cryoamplifier 2, it is possible to allow only high-frequency pulses to pass while blocking inflow of heat from the outside of the vacuum vessel. Thus, the NMR signal that has passed through the transformer 16 reaches the receiver 17 in the NMR spectrometer 6 through the airtight connector 10 on the vacuum vessel wall and the transmission means 4 such as a coaxial cable exposed to room temperature. To do.
[0022]
In this case, the switching between the reception mode and the transmission mode of the switching means in the cryoamplifier 2 is performed in synchronization with the output of a high-power high-frequency pulse from the transmitter of the NMR spectrometer 3. Is controlled by the cryoamplifier control unit 5 placed outside the vacuum vessel.
[0023]
FIG. 4 shows another embodiment of the NMR cryoprobe according to the present invention. In the figure, reference numeral 1 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 1 includes a switching means (not shown) configured by a duplexer for switching between a transmission mode and a reception mode, and a preamplifier that quickly amplifies a weak high-frequency signal (NMR signal) emitted from the sample. A cryoamplifier 2 incorporating an amplifier (not shown) is connected.
[0024]
The probe 1 and the cryoamplifier 2 are placed in a vacuum vessel 7 evacuated by a vacuum pump 6, insulated from the outside, and sent from a cooler 8 placed outside the vacuum vessel 7. It is cooled by a refrigerant such as cryogenic helium gas, and is maintained at a cryogenic temperature of about 10K, for example.
[0025]
Although details are omitted in the figure, the cylindrical portion 9 from the upper end of the probe 1 toward the inside communicates with the outside of the vacuum vessel 7, and the measurement sample is in a state of normal temperature and pressure. The probe 1 is configured to be inserted from the upper end toward the inside.
[0026]
The high-power high-frequency pulse sent from the transmitter 14 of the NMR spectrometer 3 passes through the switching means (not shown) of the cryoamplifier 2 in the transmission mode via the transmission means 4 such as a coaxial cable. , Applied to a transmitting / receiving coil (not shown) in the probe 1. 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.
[0027]
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), passes through the switching means (not shown) of the cryoamplifier 2 in the reception mode, and then is a preamplifier (shown in FIG. (Not shown) and sent to the receiver 17 in the NMR spectrometer 3 via the transmission means 4 such as a coaxial cable.
[0028]
Switching between a receiving mode and a transmitting mode of switching means (not shown) in the cryoamplifier 2 is performed in synchronization with the output of a high-power high-frequency pulse from the transmitter 14 of the NMR spectrometer 3. Is controlled by a cryoamplifier control unit 5 placed outside the vacuum vessel 7 based on a trigger signal from. The switching electrical signal from the cryoamplifier control unit 5 is once converted from an electrical signal to an optical signal by the optical conversion circuit 18 in the cryoamplifier control unit 5.
[0029]
This optical signal is transmitted from the cryoamplifier control unit 5 through an optical cable 19 made of plastic or the like having a lower thermal conductivity than a metal conductor, through an airtight optical connector 20 provided on the vacuum vessel wall, The light is again input to the cryogenic amplifier 2 via the optical cable 21. As the optical connector 20 at this time, it is preferable to employ one in which the terminal of the core connecting portion is made of a material having a small thermal conductivity. In this way, by utilizing the optical communication means having a smaller thermal conductivity than the electrical communication means as the relay means, the flow of heat from the outside of the vacuum vessel 7 is blocked and only the switching signal is passed. It becomes possible. Thus, the optical signal input to the cryoamplifier 2 is demodulated into an electrical signal by the demodulation circuit 22 provided in the cryoamplifier 2 and input to switching means (not shown) configured by a duplexer or the like. Control from the outside of the vacuum vessel 7 of the switching means is executed.
[0030]
【The invention's effect】
As described above, according to the NMR cryoprobe of the present invention, between the room temperature unit placed outside the vacuum vessel and the cryogenic transmission / reception coil or preamplifier placed inside the vacuum vessel, Since it is connected via a relay means for heat insulation, such as a transformer or optical communication means, it has become possible to greatly suppress the inflow of heat from outside the vacuum vessel into the vacuum vessel via an external cable. .
[Brief description of the drawings]
FIG. 1 shows a conventional NMR cryoprobe.
FIG. 2 is a view showing a conventional NMR cryoprobe.
FIG. 3 is a diagram showing an example of an NMR cryoprobe according to the present invention.
FIG. 4 is a diagram showing an example of an NMR cryoprobe according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Probe, 2 ... Cryoamp, 3 ... NMR spectrometer, 4 ... Coaxial cable, 5 ... Cryoamp control part, 6 ... Vacuum pump, 7 ... Vacuum container , 8 ... cooler, 9 ... cylindrical portion, 10 ... airtight connector, 11 ... signal transmission cable, 12 ... coaxial cable, 13 ... signal transmission cable, 14 ...・ Transmitter 15 ... Transformer 16 ... Transformer 17 ... Receiver 18 ... Optical conversion circuit 19 ... Optical cable 20 ... Optical connector 21 ... Optical cable 22: Demodulation circuit.

Claims (1)

In the NMR cryoprobe that reduces the thermal noise from the probe or cryoamplifier by cooling the probe or cryoamplifier placed in the vacuum vessel to a cryogenic temperature using the temperature lowering means,
Connect the room temperature unit placed outside the vacuum vessel and the cryogenic probe or cryoamp placed inside the vacuum vessel via optical communication means ,
An NMR cryoprobe characterized in that the optical communication means comprises an optical conversion circuit on the room temperature side and a demodulation circuit on the cryogenic side .

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