Pulsed Electron Paramagnetic Resonance Spectrometer

Abstract

A pulsed electron paramagnetic resonance spectrometer includes: a microwave excitation generating unit generating at least one microwave pulse; a microwave conducting unit including a resonant cavity and a microwave transmission line transmitting microwaves, the microwave transmission line being connected between the microwave excitation generating unit and the resonant cavity, the resonant cavity being configured to place a sample; a refrigerator and a magnet unit including a refrigerator for realizing ultra-low temperature cooling of the microwave resonant cavity, the microwave transmission line being arranged to pass through the refrigerator and connect the resonant cavity; the refrigerator and magnet unit also includes a magnet providing a magnetic field for reaching the sample magnetic resonance test, the resonant cavity being arranged in a room temperature gap of the magnet. The device disclosed in the present invention has the characteristics of ultra-low sample temperature (0.1 Kelvin level), and the instrument is fully functional and easy to operate.

Description

Technical Field

[0001] The present disclosure relates to the field of magnetic resonance spectrometers, and in particular to a pulsed electron paramagnetic resonance spectrometer capable of operating at ultra-low temperatures. Background Art

[0002] Electron paramagnetic resonance (EPR) is a device that studies unpaired electrons in matter. Its basic principle is the Zeeman effect of paired electron spins: a single electron has a spin quantum number of s = 1 / 2, so it can be in the m s = +1 / 2 or m s = -1 / 2 spin quantum state, when there is an external magnetic field, the energy of these two spin states will be split. Further applying a microwave field to detect the resonance signal of the energy level splitting can obtain the internal information of the material system, including the nuclear type around the electron, the magnetic field environment, the electron spin distance, etc.

[0003] EPR is a highly sensitive, non-invasive detection method with a wide range of applications in physics, chemistry, biology, medicine, engineering, and other fields. Some typical uses include detection of impurities or defects in materials in engineering and safety fields, quantitative analysis of specific elements in chemical reactions, tissue imaging in the biological field, quantitative analysis of radiation doses in the medical field, research on multi-body correlation and phase transition problems in condensed matter physics, and realization of quantum computing and quantum storage in the field of quantum information.

[0004] The standard EPR system mainly includes the following modules: microwave source, microwave pulse modulation and demodulation module, microwave amplifier, microwave bridge, sample rod, three-dimensional microwave resonant cavity, and super-uniform magnet. When the incident microwave of the EPR system is a continuous wave, this continuous wave EPR system can only be used for transition resonance signal detection. The incident microwave of the EPR system can also be set as a complex microwave pulse sequence. This pulsed EPR system has richer functions and can be used for other spin dynamics analysis such as spin population lifetime and coherence lifetime. Taking the application in the field of quantum information as an example, the existing technology generally requires a pulsed EPR system to realize functions such as spin quantum state manipulation, controlled quantum logic gates, microwave quantum state storage, etc.

[0005] At present, the main manufacturers that can produce pulsed EPR systems in the world are Germany's BRUKER. Considering the EPR analysis of solid materials, a low-temperature environment is generally required to cool the electron-phonon interaction inside the material. The lowest sample temperature that can be reached by commercial EPR systems is about 3K. However, this temperature cannot meet the demand for long coherent lifetimes of solids in the field of quantum information. To give a typical example, in recent years, rare earth ion-doped crystals have achieved high-fidelity storage of single photon quantum states, which is a quantum storage system with practical potential. The ultimate limitation of its storage life is the coherent lifetime of the electron spin and nuclear spin of the ion. The analysis results of a pulsed EPR system of the prior art show that as the temperature decreases, the coherent lifetimes of the sample electron spin and nuclear spin both increase significantly as the temperature decreases. When the system reaches the lowest temperature of 5K, the coherent lifetimes of the sample electron spin and nuclear spin reach the order of 0.1ms and 1ms respectively [Phys. Rev. Lett. 114.170503 (2015)]. However, practical quantum memory generally requires a storage life of the order of seconds. Continuing to lower the sample temperature in this experiment will obviously lead to a longer coherent lifetime, but the research group has no way to obtain further data because all current commercial EPR systems cannot reach temperatures below 3K. There is even a common view in the international academic community that it is impossible for an EPR system with a three-dimensional resonator to reach a sample temperature below 3K. For example, the document [Appl.Phys.Lett.106.193505(2015)] clearly points this out in the second paragraph on the first page. If a transmission line resonant cavity is used, it is easy to achieve cooling, but the AC magnetic field generated by this resonant cavity is only distributed in a scale range of tens to hundreds of microns near the transmission line. The magnetic field decays dramatically with distance, and its disadvantages are that the sample scale is limited and the magnetic field uniformity is very poor. Summary of the invention

[0006] In view of this, the purpose of the present disclosure is to provide an electron paramagnetic resonance spectrometer, whose sample temperature reaches the order of 0.1 K and has various test functions of a conventional electron paramagnetic resonance spectrometer.

[0007] The present disclosure provides a pulsed electron paramagnetic resonance spectrometer, comprising:

[0008] a microwave excitation generating unit for generating at least one microwave pulse;

[0009] A microwave conducting unit, comprising a resonant cavity and a microwave transmission line for transmitting microwaves, wherein the microwave transmission line is connected between the microwave excitation generating unit and the resonant cavity, and the resonant cavity is configured to place a sample;

[0010] The refrigerator and magnet unit comprises a refrigerator for realizing ultra-low temperature cooling of a microwave resonant cavity at the order of 0.1 Kelvin, wherein the resonant cavity is arranged in the refrigerator, and the microwave transmission line is arranged to penetrate into the refrigerator and be connected to the resonant cavity; the refrigerator and magnet unit also comprises a magnet for providing a magnetic field for reaching the sample magnetic resonance test, and the resonant cavity is arranged in a room temperature gap of the magnet.

[0011] In a further embodiment, the microwave conduction unit comprises a sample insert, one end of the sample insert is mounted with the resonant cavity, and the other end of the sample insert is fixed to the refrigerator.

[0012] In a further embodiment, the refrigerator comprises a plurality of cold plates arranged along a direction in which the microwave transmission line passes, so as to cool the microwave transmission line step by step.

[0013] In a further embodiment, the microwave resonant cavity is a microwave resonant cavity including multiple working bands of L, S, and X and double resonance of electrons and nuclei.

[0014] In a further embodiment, the conductive medium of the microwave transmission line is silver-plated stainless steel, silver-plated CuNi and NbTi superconductor.

[0015] In a further embodiment, the refrigerator and magnet unit further comprises:

[0016] An electric guide rail is used for carrying and positioning the magnet.

[0017] In a further embodiment, the refrigerator tail end is cylindrical, the outer diameter of which is compatible with the magnet gap, and the inner diameter of which is compatible with the resonant cavity.

[0018] In a further embodiment, the microwave transmission line is equipped with heat sinks and adapters at various cold plates to fully cool the outer shell and inner core of the microwave transmission line cable.

[0019] In a further embodiment, the sample insert comprises a thermally conductive metal material.

[0020] In a further embodiment, each stage of the cold plate is provided with a heat radiation shielding cover.

[0021] It can be seen from the technical solution provided by the present disclosure that by combining the EPR system with the refrigerator and the microwave transmission line, a sample temperature of the order of 0.1K can be obtained, thereby realizing EPR detection in the ultra-low temperature region. The electric guide rail can be used to conveniently realize the docking and assembly operation of the EPR system and the refrigeration system; the equipment used in the above process is easy to operate and has high stability, the sample temperature is low and is compatible with all functions of the conventional EPR system. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present disclosure. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0023] Figure 1 A framework diagram of a pulsed electron paramagnetic resonance spectrometer provided in an embodiment of the present disclosure;

[0024] Figure 2 A schematic diagram of a partial assembly of a pulsed electron paramagnetic resonance spectrometer provided in an embodiment of the present disclosure;

[0025] Figure 3 Applications provided for embodiments of the present disclosure Figure 2 The resonance spectrometer shown in Figure 6 shows the Nd in YSO crystal at 6.5K. 3+ Schematic diagram of ion scanning electron spin echo (ESE);

[0026] Figure 4A and Figure 4B Applications provided for embodiments of the present disclosure Figure 2 The resonance spectrometer shown in the figure shows Nd in YSO crystal at ultra-low temperature. 3+ The temperature dependence of the electron spin echo (ESE) of an ion. Figure 4A The time domain signals of the measured electron spin echo at different sample temperatures are given; Figure 4B The relationship between the relative size of the electron spin echo and the sample temperature is given. DETAILED DESCRIPTION

[0027] The following is a clear and complete description of the technical solutions in the embodiments of the present disclosure in conjunction with the drawings in the embodiments of the present disclosure. Obviously, the described embodiments are only part of the embodiments of the present disclosure, rather than all of the embodiments. Based on the embodiments of the present disclosure, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present disclosure.

[0028] The “ultra-low temperature” mentioned in the present disclosure refers to a temperature on the order of 0.1K (Kelvin).

[0029] As mentioned above, the EPR spectrometer in the ultra-low temperature region is an important basic instrument urgently needed in the field of quantum information and quantum storage. For example, at an ultra-low temperature of 0.1K, the population of electron spins in the X-band EPR spectrometer can achieve an initialization level of more than 95%, which directly makes the signal-to-noise ratio of the electron spin echo (that is, the signal-to-noise ratio of the instrument) compared to the test conditions of 3K temperature, one to two orders of magnitude. The improvement of the signal-to-noise ratio is the fundamental indicator of all measuring instruments, so the ultra-low temperature EPR system is also expected to be more widely used in other fields.

[0030] According to the basic concept of the present disclosure, a pulsed electron paramagnetic resonance spectrometer is provided, including: a microwave excitation generating unit for generating at least one microwave pulse; a microwave conduction unit, including a resonant cavity and a microwave transmission line for transmitting microwaves, the microwave transmission line is connected between the microwave excitation generating unit and the resonant cavity, and the resonant cavity is configured to place a sample; a refrigerator and a magnet unit, including a refrigerator for realizing ultra-low temperature cooling of the microwave resonant cavity, the microwave transmission line is arranged to pass through the refrigerator and connect the microwave resonant cavity; the refrigerator and magnet unit also includes a magnet for providing a magnetic field for reaching the sample magnetic resonance test, and the resonant cavity is arranged in the room temperature gap of the magnet. A microwave detection unit for collecting and analyzing microwaves emitted by the microwave conduction unit may also be included. Through the above-mentioned configuration, the EPR system is combined with a refrigerator to obtain an ultra-low sample temperature of the order of 0.1K.

[0031] Figure 1 This is a schematic diagram of the system framework provided by the first embodiment of the present disclosure. Figure 1 As shown, the device mainly includes:

[0032] A microwave excitation generating unit 11 , a microwave conducting unit 12 , a microwave detecting unit 13 and a refrigerator and a magnet unit 14 .

[0033] Wherein, the microwave excitation generating unit 11 is used to generate various high-energy microwave pulses;

[0034] The microwave conducting unit 12 is used for directional transmission of microwave pulses, installation of samples and realization of microwave emission and collection;

[0035] The microwave detection unit 13 is used for collecting and analyzing microwave signals;

[0036] The microwave excitation generating unit 11, the microwave conducting unit 12 and the microwave detecting unit 13 have complete testing functions such as field scanning paramagnetic resonance detection, electron spin echo, electron and nuclear double resonance, etc.

[0037] The refrigerator and the magnet unit 14 are used to realize ultra-low temperature cooling of the microwave resonant cavity and provide a highly uniform magnetic field to achieve magnetic resonance test conditions.

[0038] Furthermore, the microwave excitation generating unit 11 includes: a microwave source 111, a microwave modulation module 112, a microwave frequency conversion module 113, and a microwave amplifier 114;

[0039] Wherein, the microwave source 111 is used to generate a single-frequency microwave signal of a specific frequency;

[0040] The microwave modulation module 112 is used to generate microwave pulses of various sizes, phases and frequencies from single-frequency continuous microwaves;

[0041] The microwave frequency conversion module 113 is used to expand the test frequency band of microwaves;

[0042] The microwave amplifier 114 is used to amplify the microwave pulses to achieve high energy pulses required for pulse EPR.

[0043] Furthermore, the microwave conducting unit 12 includes: a microwave circulator 121, a microwave transmission line 122 and a microwave resonant cavity 123;

[0044] The microwave circulator 121 is used for directional transmission of microwaves, guides the microwaves of the microwave excitation unit 11 into the sample, and transmits the sample signal into the microwave detection unit 13;

[0045] The microwave transmission line 122 is used for microwave conduction between the microwave circulator 121 and the microwave resonant cavity 123; different from conventional microwave transmission cables, considering the ultra-low temperature cooling requirements of the device, the material selection of the microwave transmission line should take into account both conductivity and thermal insulation requirements, and typical conductive media can be silver-plated stainless steel, silver-plated CuNi and NbTi superconductors.

[0046] The microwave resonant cavity 123 is used to install samples and realize microwave emission and collection. The microwave resonant cavity 123 disclosed in the present invention is a three-dimensional resonant cavity. The AC magnetic field generated by the three-dimensional resonant cavity is evenly distributed and can test large-sized samples, and has richer testing functions.

[0047] Furthermore, the track microwave detection unit 13 includes: a protection gate 131, a mixer 132, a low-pass filter and amplifier 133 and an oscilloscope 134;

[0048] The protection door 131 is used to close the detection system when a high-energy microwave pulse is incident, and to open the detection system when a signal is detected;

[0049] The mixer 132 is used to mix the microwave signal collected by the microwave conduction module with the local oscillator microwave to extract the signal; the local oscillator microwave comes from the microwave excitation generating unit 11

[0050] The low-pass filter and amplifier 133 is used to perform low-pass filtering and amplification on the mixed signal output by the mixer 132 to achieve pulse demodulation; and is used to amplify the demodulated pulse signal;

[0051] The oscilloscope 134 is used to store and display signals.

[0052] Furthermore, the refrigerator unit 14 includes: a refrigerator 141, a refrigerator cavity 142, a super-uniform magnet 143, and an electric guide rail 144;

[0053] The refrigerator 141 is used to provide cooling capacity to cool the target system; the sample temperature of the instrument can reach 0.1K level through the refrigerator;

[0054] The refrigerator cavity 142 is used for installing the microwave transmission line 122 and the microwave resonant cavity 123 and isolating external heat radiation;

[0055] The super-uniform magnet 143 is used to generate a highly uniform and stable magnetic field; it can be a room temperature electromagnet or a superconducting magnet.

[0056] The electric guide rail 144 is used to transport and position the magnet when performing sample replacement; the electric guide rail is equipped with a jack that moves up and down for transporting and positioning the magnet, and the horizontal stroke exceeds the outer dimensions of the magnet.

[0057] The disclosed embodiment combines a refrigerator with a conventional EPR system to achieve ultra-low temperature EPR testing and helps to significantly improve the signal-to-noise ratio of the test; the equipment used in the above process is easy to operate, and the system has high stability and complete testing functions.

[0058] In order to further introduce the present disclosure, the embodiments of the present disclosure will list specific values ​​and introduce the component parameters in the device; it should be noted that the listed component parameter values ​​are only for facilitating the understanding of the present disclosure and do not constitute a limitation; in actual applications, users can use components with different parameters according to needs or experience.

[0059] Figure 1 Each module in the system can be purchased and assembled separately, or a subsystem assembled from multiple modules can be provided from the existing technology. Based on such a subsystem, it is easier to build a pulsed electron paramagnetic resonance spectrometer. For example, a commercial EPR spectrometer can provide a microwave excitation unit, a circulator and a microwave cavity in a microwave conduction unit, a microwave detection unit, and an ultra-uniform magnet in a refrigerator and a magnet unit. Figure 2 FIG. 1 is a schematic diagram of a system assembly of an EPR spectrometer provided by an embodiment of the present disclosure. The figure omits the multi-layer radiation shielding shell in the cryogenic chamber and the matching compressor unit of the cryogenic chamber, and only shows the important details of the system docking.

[0060] It mainly includes:

[0061] 1) Pulsed multi-band EPR system (the EPR system here includes a microwave excitation generation unit, a microwave circulator in a microwave conduction unit, a microwave resonant cavity, a microwave detection unit, and a magnet in a refrigerator and magnet unit)

[0062] It mainly includes: L / S / X-band microwave bridge, L / S / X-band microwave amplifier, microwave modulator based on arbitrary waveform generator, L / S / X-band microwave resonant cavity, X-band microwave detection system, electronic and nuclear double resonance (ENDOR) module and super-uniform magnet.

[0063] In this embodiment, the parameters of the X-band microwave bridge can be: frequency range 9.0~10.0GHz. The L / S-band microwave bridge mainly realizes the function of frequency conversion. It realizes the frequency conversion of X-band and L / S-band signals based on a mixer with a fixed local oscillator frequency. This frequency conversion method is the most economical way to achieve frequency band expansion. Multiple bands can share the X-band microwave detection module. Microwave bridges of the three bands are built-in microwave circulators to realize directional transmission of microwaves.

[0064] In this embodiment, the X-band microwave amplifier is a 300W solid-state amplifier, and the output power of the L / S-band amplifier is about 100W.

[0065] In this embodiment, the parameters of the microwave modulator based on the arbitrary waveform generator may be: sampling rate 5 GS / s, modulation bandwidth 500 MHz, and arbitrary waveform modulation of frequency, phase, and amplitude.

[0066] In this embodiment, the parameters of the L / S / X band microwave resonant cavity can be: the internal effective aperture of each band resonant cavity is 5mm, the outer diameter is 20mm, and the SMB or MMCX type quick connector is used to achieve convenient band replacement. The Q value of each band resonant cavity can be about 50 to 500, and the required Q value is determined according to specific experiments.

[0067] In this embodiment, the parameters of the coil-type ultra-uniform superconducting magnet may be: magnetic field uniformity 10 ppm@40 mm DSV, maximum field strength 1.8 T, and air gap 100 mm.

[0068] 2) Dilution refrigerator system (Since this part is the main improvement point of the embodiment of the present disclosure, it is listed separately for description, and its corresponding Figure 1 Refrigerator in

[0069] In this embodiment, the parameters of the refrigerator may be: a dilution refrigerator without liquid helium consumption, a minimum temperature of 10 mK, a cooling power of 400 uW at 100 mK, and a cooling power of 1 W at 4 K.

[0070] In this embodiment, the preferred parameters of the refrigerator chamber 201 can be: including a 50K cold plate 2055, a 3K cold plate 2054, a 1K cold plate 2053, a 100mK cold plate 2052 and a 10mK cold plate 2051. Among them, the 50K cold plate 2055, the 3K cold plate 2054 and the 1K cold plate 2053 all need to be equipped with a thermal radiation shielding cover (not shown in the figure). The outer diameter of the rear end of the refrigerator is 95mm, and the effective inner diameter of the rear sample space is 40mm.

[0071] The refrigeration system is inserted from above into the magnet air gap of the electron paramagnetic resonance system.

[0072] 3) Special system connectors

[0073] It mainly includes a sample insertion rod 207 and a microwave transmission line 208 .

[0074] In this embodiment, the resonant cavity 203 is mounted on a sample plug 207 made of a heat-conducting metal material, and the other end of the sample plug 207 is fixed on a 10mK minimum temperature cold plate 2051, and there is no connection between other cold plates (2052, 2053, 2054 and 2055). In this embodiment, the parameters of the microwave transmission line can be: a semi-rigid coaxial transmission line, the outer diameter of the line can be 3.5mm; the outer shell and inner core of the line can be made of materials that are not easy to conduct heat but easy to conduct electricity, such as silver-plated stainless steel and superconducting materials.

[0075] To further improve the cooling effect, a plurality of heat sinks 206 are arranged on the microwave transmission line 208 .

[0076] 4) Electric guide rail 204

[0077] In this embodiment, the parameters of the electric guide rail 204 can be: load capacity greater than 3 tons, working stroke 1.5 meters, positioning accuracy 0.1mm. The size of the guide rail working panel is 550mm*550mm.

[0078] The magnet 202 in this embodiment can have a pad height of 230mm on both sides, and a pad distance of 600mm on both sides. The guide rail is equipped with a jack with a height stroke of 20mm, which is used to support or lower the magnet after positioning. After the guide rail jack is raised, the total height of the working panel from the ground is 240mm. At this time, the guide rail working panel directly supports the magnet 202 and transports and positions it. After the guide rail jack falls, the magnet 202 is separated from the guide rail surface and directly supported on the ground.

[0079] In the figure, the tail end of the refrigerator is cylindrical, the outer diameter of which is compatible with the magnet gap, and the inner diameter of the tail end of the refrigerator is compatible with the resonant cavity.

[0080] In this embodiment, in order to optimize the system cooling process and measure the temperature performance of the actual system, a thermometer can be used to measure the actual working temperature of the system and the sample by means of auxiliary spin polarization calibration.

[0081] When the system installed the S-band microwave resonant cavity, a calibrated RuO2 resistance thermometer was installed in the resonant cavity. As the temperature decreased, the resistance value gradually increased. The results showed that the lowest temperature of the resonant cavity was below 10mK without an actual test sample.

[0082] Furthermore, in this embodiment, the spin polarization level of rare earth ions can be used to accurately determine the actual working temperature of the sample. The system is equipped with an X-band ENDOR resonant cavity, which is loaded with 20ppm concentration 143 Nd isotope-doped YSO crystals also contain about 1ppm of even-numbered isotopes (including 142 Nd, 164 Nd, 148 Nd). The external test magnetic field is parallel to the D1 axis of the crystal. Figure 3 The test results of the electron spin echo at 6.5K are given, which include 16 items. 143 The spectral line of Nd and two spectral lines of Nd isotopes with even mass numbers.

[0083] Figure 4A The spin echo signals obtained by changing the cold plate temperature under the 4581G magnetic field are given. The magnetic resonance signals obtained under this test magnetic field come from Nd isotopes with even mass numbers. The spin evolution time selected in the experiment is 2us, which is much lower than the electron spin coherence lifetime (20us~200us) at all test temperatures.

[0084] The electron spin of Nd isotopes with even mass numbers is 1 / 2, the nuclear spin is zero, and it is a simple two-level system under a magnetic field. The relative size of its spin echo is proportional to the population difference of the target transition. According to the Boltzmann distribution, the population difference of the two-level at different temperatures can be strictly calculated:

[0085]

[0086] Where h is Planck's constant, v = 9.56 GHz is the microwave frequency, h*v is the energy of the resonant microwave photon, k is the Boltzmann constant, and T is the sample temperature. When T approaches absolute zero 0K, the spin echo reaches a relative maximum value of 1.

[0087] Figure 4BIt can be seen that as the temperature of the cold plate decreases, the sample echo signal gradually increases. The signal-to-noise ratio of the device at an operating temperature of 0.1K can be improved by more than 20 times compared to commercial instruments at an operating temperature of 4.5K. The experimental results are completely consistent with the spin polarization level predicted by the Boltzmann distribution, thus strictly proving that the sample operating temperature reaches 0.1K.

[0088] In the embodiment of the present disclosure, an original pulsed electron paramagnetic resonance spectrometer was developed, and the thermometer showed that the no-load temperature of the sample chamber reached below 10mK. Based on this device, the Nd 3+ The ultra-low temperature spin echo test of ions can calibrate the actual working temperature of the sample to 0.1K based on the size of the spin echo signal. This is the lowest temperature three-dimensional resonant cavity pulsed electron paramagnetic resonance spectrometer reported in the world. All its components are universal electrical devices. The device is stable and fully functional, and has broad application prospects.

[0089] Those skilled in the art can clearly understand that for the convenience and simplicity of description, only the division of the above-mentioned functional modules is used as an example. In actual applications, the above-mentioned functions can be assigned to different functional modules as needed, that is, the internal structure of the device can be divided into different functional modules to complete all or part of the functions described above.

[0090] The specific embodiments described above further illustrate the purpose, technical solutions and beneficial effects of the present disclosure. It should be understood that the above description is only a specific embodiment of the present disclosure and is not intended to limit the present disclosure. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present disclosure should be included in the protection scope of the present disclosure.

Claims

1. A pulsed electron paramagnetic resonance spectrometer, characterized in that include: a microwave excitation generating unit for generating at least one microwave pulse; A microwave conduction unit, comprising a sample insertion rod, a resonant cavity and a microwave transmission line for transmitting microwaves, wherein the microwave transmission line is connected between the microwave excitation generating unit and the resonant cavity, the resonant cavity is configured to place a sample, and the resonant cavity is installed at one end of the sample insertion rod; A refrigerator and magnet unit, comprising a refrigerator and an electric guide rail for realizing ultra-low temperature cooling of a microwave resonant cavity at the order of 0.1 Kelvin, wherein the refrigerator comprises a multi-layer cold plate arranged along the direction in which the microwave transmission line passes through, so as to cool the microwave transmission line step by step, the other end of the sample insertion rod is fixed on the cold plate with the lowest temperature, and has no connection with other cold plates, the microwave transmission line is arranged to pass through the cold plate layer by layer, and a heat sink and an adapter are installed at each cold plate of the microwave transmission line to fully cool the outer shell and inner core of the microwave transmission line cable, the resonant cavity is arranged in the refrigerator, and the microwave transmission line is arranged to penetrate into the refrigerator and be connected to the resonant cavity; the refrigerator and magnet unit also comprises a magnet for providing a magnetic field for reaching the sample magnetic resonance test, the resonant cavity is arranged in the room temperature gap of the magnet, and the electric guide rail is used to carry and position the magnet; Wherein, the microwave resonant cavity is a microwave resonant cavity including multiple working bands of L, S, and X and double resonance of electrons and nuclei.

2. The pulsed electron paramagnetic resonance spectrometer according to claim 1, characterized in that: The conductive medium of the microwave transmission line is silver-plated stainless steel, silver-plated CuNi and NbTi superconductor.

3. The pulsed electron paramagnetic resonance spectrometer according to claim 1, characterized in that: The refrigerator tail end is cylindrical, the outer diameter of which is compatible with the magnet gap, and the inner diameter of which is compatible with the resonant cavity.

4. The pulsed electron paramagnetic resonance spectrometer according to claim 1, characterized in that: The sample insert comprises a thermally conductive metal material.

5. The pulsed electron paramagnetic resonance spectrometer according to claim 1, characterized in that: Each level of the cold plate is provided with a heat radiation shielding cover.

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