Method for diagnosing ion temperature of supercold strongly coupled plasma

Abstract

The application provides a method for diagnosing ion temperature of an ultracold strongly coupled plasma, comprising the following steps: heating an atomic source to form a diffused neutral hot atomic gas; constructing a magneto-optical trap by combining a laser field with a gradient magnetic field; trapping and confining the neutral hot atomic gas by the magneto-optical trap to form a cold atomic group with a certain density; introducing a laser with a suitable wavelength to near-threshold photoionize the cold atomic group after focusing to form an ultracold plasma; using an ion lens electric field to lead out and accelerate ions in the ultracold plasma, and using a two-dimensional position-sensitive detector to record the spatial distribution of the ions; combining an inverse Abelian transform numerical inversion method to reconstruct a three-dimensional velocity distribution of the ions; using a Maxwell-Boltzmann velocity distribution law to fit the velocity distribution of the ions to extract ion temperature in the ultracold plasma. The method applies ion velocity imaging technology to the diagnosis of ion dynamics of the ultracold plasma, and can be applied to the ion dynamics research of the ultracold plasma.

Description

Technical Field

[0001] This invention relates to the technical field of plasma physics detection, and in particular to a diagnostic method for the ion temperature of ultracold strongly coupled plasma. Background Technology

[0002] Ultracold plasma is an extreme form of plasma where the initial temperature of electrons ranges from 1 to 1000 K, while the initial temperature of ions can be as low as mK, even at densities as low as 10⁻⁶ K. 8 cm -3 Under these conditions, ultracold plasmas all possess the characteristics of strongly coupled plasmas, i.e., the Coulomb coupling parameter. Greater than 1, where a is the Wigner-Seitz radius and k B is Boltzmann's constant, and T is the temperature of the plasma.

[0003] The strong coupling characteristic of plasma means that the Coulomb potential energy between particles dominates plasma evolution, replacing thermal kinetic energy. This is crucial in plasmas under extreme conditions such as those found in white dwarfs. Compared to high-temperature, high-density plasmas, atomic processes in ultracold plasmas are relatively simple, facilitating numerical simulations and enabling "desktop" experimental platforms. Therefore, experimental and theoretical research on ultracold plasmas will contribute to our understanding of the properties of high-energy-density plasmas generated in processes such as nuclear explosions and inertial confinement fusion, as well as the properties of warm, dense matter.

[0004] Threshold photoionization magneto-optical traps are a common technique for forming ultracold plasmas, where ion temperatures evolve from mK to K. Accurate measurement of ion temperature is crucial for studying the strong coupling properties of ultracold plasmas. Currently, ion temperature diagnosis primarily employs spectroscopic methods, measuring the fluorescence or absorption spectra of ions in the plasma and utilizing the Doppler effect to obtain the ion temperature. However, these spectroscopic methods are limited to the study of alkaline earth metal atomic systems.

[0005] TCKillian et al. used absorption imaging to study ion dynamics in strontium ultracold plasma (PRL. 2004, 92: 143001). By using Doppler broadening of the ion absorption spectrum, they obtained the relationship between ion temperature and time, showing that the ion temperature rises to 1.4 K within the first 250 ns, with a Coulomb coupling parameter Γ = 2. SDBergeson et al. measured the spatial distribution of calcium ion fluorescence in calcium ultracold plasma (PRL. 2005, 95: 235001), obtaining an ion equilibrium temperature of approximately 0.5 K through ion diffusion velocity, corresponding to a Coulomb coupling parameter Γ = 4. Lyon et al., through Ca... +Reionization further improved the Coulomb coupling parameter of the ultracold plasma. Experiments and simulations showed that secondary ionization could increase Γ = 2 to Γ = 6.8 (PRE.2015 91:033101). Langin et al. further cooled strontium ions by using lasers to re-cool them, increasing the Coulomb coupling parameter of the ultracold plasma to around Γ = 11 (Science 2019 363:61–64).

[0006] The above research shows that the optical diagnostic method for ion temperature has achieved great success, but it also has significant limitations: (1) Because it requires laser of a suitable wavelength for excitation, the optical diagnostic method is only applicable to ultracold plasmas formed by extranuclear two-electron or multi-electron atoms, and not to alkali metal atomic systems; (2) The initial density of common ultracold plasmas is around 10 8 ~10 10 cm -3 However, in the later stages of plasma diffusion, the density decreases significantly, making it difficult for optical diagnostic methods to effectively remove noise interference in order to meet the requirements of spectral detection accuracy.

[0007] Therefore, a universal and direct detection method is still lacking for the ion dynamics and temperature diagnosis of ultracold strongly coupled plasmas. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a diagnostic method for the ion temperature of ultracold strongly coupled plasmas. This method applies ion velocity imaging technology to the diagnosis of ion dynamics in ultracold plasmas. This diagnostic method is universally applicable to the study of ion dynamics in ultracold plasmas and can overcome the dependence on and stringent requirements of optical detection methods on the system.

[0009] To achieve the above objectives, the present invention provides the following technical solution:

[0010] A diagnostic method for the ion temperature of ultracold strongly coupled plasma includes the following steps:

[0011] The atomic source is heated to form a diffused neutral thermal atomic gas within the vacuum chamber;

[0012] A magneto-optical trap is constructed by using a laser field formed by three beams and six paths of continuous lasers, combined with a gradient magnetic field generated by an anti-Helmholtz coil. The magneto-optical trap is a classic atomic three-dimensional laser cooling and trapping device.

[0013] Neutral hot atomic gas diffused within a vacuum chamber is captured and imprisoned using a magneto-optical trap, forming cold atomic clusters of a certain density.

[0014] A laser of a suitable wavelength is introduced, focused, and applied to cold atomic clusters to ionize them, forming ultracold plasma;

[0015] After the formation of ultracold plasma, charged particles are accelerated by the electric field of the ion lens in ion velocity imaging and fly toward the two-dimensional position sensitive detector, which records the spatial distribution of ions.

[0016] Based on the two-dimensional spatial distribution data of ions recorded by the detector, and combined with numerical inversion algorithms, the three-dimensional velocity distribution of ions is reconstructed.

[0017] The velocity distribution of ions was obtained by fitting the Maxwell-Boltzmann velocity distribution law, and the ion temperature in the ultracold plasma was extracted.

[0018] Furthermore, the formation of cold atomic clusters of a certain density includes the following steps:

[0019] Three continuous laser beams enter through the observation window of the vacuum chamber and are reflected by a mirror placed opposite, forming three pairs of opposing and orthogonal light paths, serving as three-dimensional cooling lasers for atoms.

[0020] A pair of coils are placed symmetrically outside the vacuum chamber, and currents of equal magnitude but opposite direction are input, forming an anti-Helmholtz coil structure, which generates a gradient magnetic field with a horizontal and vertical magnetic field strength ratio of 1:2.

[0021] An optical path system constructed using a three-dimensional cooling laser, combined with a gradient magnetic field, captures neutral hot atomic gas within a vacuum chamber, forming cold atomic clusters of a certain density.

[0022] Furthermore, the continuous laser is generated by a semiconductor laser or a Ti:sapphire laser, and the laser linewidth of the continuous laser is ≤1MHz.

[0023] Furthermore, the formation of ultracold plasma includes the following steps:

[0024] Atoms are excited from their ground state to their first excited state using a cooling laser, followed by cyclic cooling.

[0025] A laser of a suitable wavelength is introduced as an ionizing laser, which is then focused and applied to excited-state cold atoms to ionize them, forming ultracold plasma.

[0026] Furthermore, the ionizing laser is generated by a pulsed dye laser with continuously tunable wavelength, the wavelength of which is near the ionization threshold.

[0027] Furthermore, the electric field of the ion lens for ion velocity imaging is obtained by applying different voltages to a series of electrodes to achieve an electric field distribution; the equipotential line distribution of the ion lens electric field is like that of an optical lens, which can achieve the focusing effect of ions.

[0028] Furthermore, the two-dimensional position sensitive detector includes two microchannel plates (MCPs), a fluorescent screen, and a CCD camera, and is used to record the two-dimensional spatial distribution of ions.

[0029] Furthermore, the two-dimensional spatial distribution of the ions is converted into a two-dimensional velocity distribution of the ions after system calibration.

[0030] Furthermore, the numerical inversion algorithm is an inverse Abelian transform numerical inversion method, including the MEVIR or MEVELER algorithm; the numerical inversion algorithm is used to reconstruct the three-dimensional velocity distribution of ions.

[0031] Furthermore, the Maxwell-Boltzmann velocity distribution law is as follows:

[0032]

[0033] Where T is the ion temperature, kJ / kJ B is the Boltzmann constant.

[0034] Based on the above technical solution, compared with existing optical diagnostic methods, the technical effects achieved by the present invention are as follows:

[0035] (1) The diagnostic method for ultracold strongly coupled plasma ion temperature provided by this invention has broader applicability. In ultracold plasmas formed by alkali metal atomic systems, ions have stable full-shell structures. Developing deep ultraviolet lasers for exciting and probing their inner shells remains a significant challenge, and spectroscopic detection methods are not suitable for such alkali metal atomic systems. The velocity imaging technology used in the diagnostic method of this invention is applicable to all ion types and is not limited by optical transitions, overcoming the limitations of spectroscopic detection methods and expanding the detection range of ultracold plasmas.

[0036] (2) The diagnostic method for ultracold strongly coupled plasma ion temperature provided by this invention has a higher signal-to-noise ratio. Density is an extremely important physical parameter for observing and analyzing ultracold plasma. As the evolution process progresses, the plasma density gradually decreases. Thus, in the later stages of evolution when the density is low, the spectroscopic detection method will introduce significant noise, affecting the accuracy of the experimental results. The velocity imaging technology used in the diagnostic method of this invention can maintain a high signal-to-noise ratio even for low-density ion clusters during the measurement process, and has good detection accuracy. Attached Figure Description

[0037] Figure 1 This is a flowchart of the diagnostic method for ultracold strongly coupled plasma ion temperature according to Embodiment 1 of the present invention.

[0038] Figure 2This is a schematic diagram illustrating the design principle of the lens electric field in Embodiment 1 of the present invention.

[0039] Figure 3 This is a spatial distribution diagram of ions corresponding to the ultracold plasma evolution of 600 ns in Example 4 of the present invention.

[0040] Figure 4 This is a graph showing the evolution of ion temperature over time within 1200 ns in Example 4 of the present invention. Detailed Implementation

[0041] To facilitate understanding of the present invention, a more comprehensive description will be given below in conjunction with the accompanying drawings and specific embodiments. The drawings illustrate preferred embodiments of the invention. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.

[0042] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0043] Example 1

[0044] A diagnostic method for the ion temperature of ultracold strongly coupled plasma is disclosed. This method directly measures the ion temperature by introducing the electric field of a velocity imaging ion lens as the extraction electric field of the ions.

[0045] Figure 1 A flowchart of the diagnostic method for ultracold strongly coupled plasma ion temperature in this embodiment is provided, as follows: Figure 1 As shown, the diagnostic method includes the following steps:

[0046] S1. The atomic source is heated to form a diffused neutral thermal atomic gas in the vacuum chamber;

[0047] S2. A magneto-optical trap is constructed by using a laser field formed by three beams and six paths of continuous lasers, combined with a gradient magnetic field generated by an anti-Helmholtz coil. This magneto-optical trap is a classic atomic three-dimensional laser cooling and trapping device.

[0048] S3. Use a magneto-optical trap to capture and imprison the neutral hot atomic gas diffused in the vacuum chamber, forming cold atomic clusters of a certain density;

[0049] S4. Introduce a laser of a suitable wavelength, focus it, and apply it to the cold atom cluster to ionize it and form an ultracold plasma;

[0050] S5. After the formation of ultracold plasma, charged particles are accelerated by the electric field of the ion lens in ion velocity imaging and fly towards the two-dimensional position sensitive detector, which records the spatial distribution of ions.

[0051] S6. Based on the two-dimensional spatial distribution data of ions recorded by the detector, and combined with the numerical inversion algorithm, the three-dimensional velocity distribution of ions is reconstructed;

[0052] S7. The velocity distribution of ions is obtained by fitting the Maxwell-Boltzmann velocity distribution law, and the ion temperature in the ultracold plasma is extracted.

[0053] As a further description of the technical solution in this embodiment, in steps S2 and S3, forming cold atom clusters of a certain density specifically includes the following steps:

[0054] S31. A continuous laser generated by a semiconductor laser enters through the observation window of a vacuum chamber and is reflected by a mirror placed opposite it, forming three pairs of opposing and orthogonal light paths, which serve as a three-dimensional cooling laser for atoms.

[0055] S32. Place a pair of coils symmetrically outside the vacuum chamber, input currents of equal magnitude but opposite direction, forming an anti-Helmholtz coil structure, and generate a gradient magnetic field with a horizontal and vertical magnetic field strength ratio of 1:2.

[0056] S33. Using the optical path system of a three-dimensional cooling laser component, combined with a gradient magnetic field, neutral hot atomic gas is captured in a vacuum chamber to form cold atomic clusters of a certain density.

[0057] The "three beams and six paths" in this embodiment describes a laser optical path structure. The laser field formed by the continuous laser beams in this "three beams and six paths" configuration is formed by three pairs of laser beams propagating in opposite directions and with orthogonal directions. After the continuous laser beams are incident, a reflector is placed in each dimension directly opposite the direction of the incident laser beams, ensuring that the optical path returns strictly along its original path. This results in a six-path laser field structure of "three incident beams and three reflected beams".

[0058] In some embodiments, continuous laser light can also be generated by a Ti:sapphire laser. The linewidth of the continuous laser light is ≤1 MHz.

[0059] As a further description of the technical solution in this embodiment, in step S4, the cold atom clusters are ionized to form an ultracold plasma of a certain density, specifically including the following steps:

[0060] S41. Atoms are excited from the ground state to the first excited state by resonant excitation and then cooled cyclically using a cooling laser;

[0061] S42. Introduce a laser of a suitable wavelength as an ionizing laser, which, after being focused, acts on the excited-state cold atoms to ionize them and form ultracold plasma.

[0062] In some embodiments, in step S42, the ionizing laser is typically generated by a pulsed dye laser with a continuously tunable wavelength, the wavelength of which is near the ionization threshold.

[0063] The appropriate wavelength laser referred to in this embodiment, on the one hand, when forming cold atom clusters of a certain density, selects a cooling laser of a corresponding appropriate wavelength according to the different types of target atoms. Through the formation of a "three-beam six-path" optical path, combined with the gradient magnetic field generated by the anti-Helmholtz coil, the atomic gas generated from the atomic source is captured in the magneto-optical trap to form cold atom clusters of a certain density.

[0064] On the other hand, when generating charged particles, an ionizing laser of appropriate wavelength is selected according to the transition energy level of the selected target cold atom, and then focused onto the cold atom cluster to generate charged particles.

[0065] In the diagnostic method of this embodiment, the process of generating plasma is similar to that of traditional optical diagnostic methods, both requiring the introduction of an ionizing laser of appropriate wavelength to ionize cold atomic clusters and form (generate) ultracold plasma. The appropriate wavelength laser mentioned in this embodiment refers to the fact that different atoms have different energy levels and ionization thresholds, therefore the selected laser wavelength also varies. The appropriate wavelength laser needs to be selected based on the type of atoms in the ionized cold atomic cluster.

[0066] It should be noted that traditional optical diagnostic methods require the introduction of a probe light to excite the ions in the plasma in order to obtain the ion temperature. In this case, for ultracold plasmas, since the energy levels of ions produced by different atoms are different, the wavelength of the probe light used to excite the ions is also different, so it is necessary to select an appropriate wavelength, such as common alkaline earth metal calcium ions and strontium ions. The diagnostic method proposed in this embodiment is based on charged particle detection, which is completely different from optical diagnostic methods. It is applicable to all atomic systems and does not require the introduction of additional probe light to excite the ions. In ultracold plasmas formed by alkali metal atomic systems, since the ions are in a full shell, introducing probe light for optical diagnosis is not suitable. The reason is that an ultraviolet laser with an extremely short wavelength (e.g., less than 100 nm) is required to excite the alkali metal ions, but this is a huge challenge for current laser development.

[0067] As a further description of the technical solution in this embodiment, in step S5, the electric field of the ion lens for ion velocity imaging is obtained by adding different voltages to a series of electrodes to obtain the electric field distribution; the equipotential line distribution of the ion lens electric field is like that of an optical lens, which can achieve the focusing effect of ions.

[0068] Figure 2The design principle diagram of the lens electric field in this embodiment is given, as follows: Figure 2 As shown, in the lens electric field, three ion clusters are set with an initial position spacing of 3 mm, an initial velocity of 200 m / s, and directions divided into 8 groups at 45° intervals.

[0069] Under the influence of the electric field, the ions arriving at the detector can be divided into 5 groups, each corresponding to ions with different velocity directions. These 5 groups of ions have velocity directions of 0-180°, 450°-135°, 90°, 225°-315°, and 270°, respectively. Ions with the same velocity direction but different initial positions are focused on the detector, with a maximum focal spot size of 30 μm, which is smaller than the detector pixel size (1 pixel to 72 μm), thus meeting the requirements for velocity imaging.

[0070] Additionally, (e) shows Rb + The three rings on the detector have velocities of 200 m / s, 300 m / s, and 400 m / s, respectively.

[0071] In the simulation, the target atom used was a rubidium atom. Figure 2 Simulation results show that the focusing lens electric field has excellent focusing ability and high resolution, which meets the expected requirements.

[0072] In some embodiments, the two-dimensional position-sensitive detector includes two microchannel plates (MCPs), a fluorescent screen, and a CCD camera, which is used to record the two-dimensional spatial distribution of ions.

[0073] As a further description of the technical solution in this embodiment, in step S7, the Maxwell-Boltzmann velocity distribution law is:

[0074]

[0075] Where T is the ion temperature, kJ / kJ B is the Boltzmann constant.

[0076] Example 2

[0077] The diagnostic method for ultracold strongly coupled plasma ion temperature in Example 1 above has the following specific detection principle:

[0078] Depending on the type of target atom, a cooling laser of appropriate wavelength is introduced. The resulting "three beams and six paths" optical path, combined with the gradient magnetic field generated by the anti-Helmholtz coil, captures atomic gas generated from the atomic source in the magneto-optical trap, forming a cold atom cluster of a certain density.

[0079] Based on the selected target cold atom's transition energy level, an ionizing laser of appropriate wavelength is introduced, focused, and applied to the cold atom cluster to generate charged particles.

[0080] Photoionization follows the laws of conservation of momentum and energy. Due to the significant mass difference between electrons and ions, electrons acquire energy exceeding the ionization limit of photons. To ensure that the electron temperature in ultracold plasma does not become too high, near-threshold ionization is typically employed. After photoionization, ions remain almost stationary, while electrons, with higher energy, begin to diffuse outward, causing a local charge imbalance. Excess ions form Coulomb potential wells through internal interactions. Initially, these Coulomb potential wells are not deep enough, allowing high-energy electrons to still escape their confinement.

[0081] As the number of photoionized atoms increases and high-energy electrons continue to escape, the depth of the Coulomb potential well deepens. When the depth of the potential well becomes comparable to the energy of the electrons, it gradually traps subsequently generated electrons. After being trapped, the electrons redistribute their energy through collisions, and some electrons with energies higher than the potential well will continue to escape, causing the potential well depth to deepen further. As the evaporation and cooling process continues, the potential well traps almost all subsequently generated electrons, thus forming an ultracold plasma.

[0082] After the formation of ultracold plasma, its charged particles, such as ions, are accelerated towards a two-dimensional position-sensitive detector under the influence of the electric field of the ion lens. By recording the position distribution of ions on the detector, the initial three-dimensional velocity distribution of the ions is reconstructed using the inverse Abelian transform. Finally, the temperature of the ions is extracted based on the Maxwell-Boltzmann velocity distribution law.

[0083] Example 3

[0084] In the diagnostic method for ultracold strongly coupled plasma ion temperature in Example 1, a numerical inversion algorithm is used to reconstruct the two-dimensional spatial distribution data of ions to obtain the three-dimensional velocity distribution of ions. The numerical inversion algorithm used is the inverse Abelian transform numerical inversion method, including algorithms such as MEVIR or MEVELER. That is, after obtaining the two-dimensional spatial distribution data from a two-dimensional position-sensitive detector, the three-dimensional velocity distribution of ions can be reconstructed using inverse Abelian transform numerical inversion methods such as the MEVIR or MEVELER algorithm.

[0085] Both the MEVIR and MEVELER methods are based on the concept of maximum entropy, and the inversion results have a smooth baseline with less baseline fluctuation across the entire range. Therefore, the MEVIR or MEVELER algorithm will be used to process two-dimensional spatially distributed data in future studies.

[0086] Example 4

[0087] This embodiment uses rubidium atoms in an alkali metal atom system as an example to illustrate a method for diagnosing the ion temperature of ultracold strongly coupled plasma. The method for diagnosing the ion temperature of ultracold strongly coupled plasma in this embodiment specifically includes the following steps:

[0088] S1. Place the rubidium bulb inside the metal valve, which is connected to the vacuum chamber. Wrap a heating belt around the metal valve and heat it to approximately 45°C. 87 Rb evaporates, forming a diffuse gas of neutral hot atoms.

[0089] S2. An ECDL semiconductor laser outputs a continuous laser with a wavelength of 780nm. After being split by an optical fiber, it forms a "three-beam, six-path" cooling optical path. Combined with the gradient magnetic field generated by the anti-Helmholtz coil, a classic three-dimensional laser cooling and trapping device for atoms—the magneto-optical trap—is constructed to capture and imprison neutral hot atomic gas diffused in a vacuum chamber. The gradient magnetic field has a longitudinal range of 10G / cm and a transverse range of 5G / cm.

[0090] S3. Introduce a cooling laser with a wavelength of 780nm, a linewidth of <1MHz, and a power of 6-7mW, and excite 5 through resonance. 2 S 1 / 2 (F=2)→5 2 P 3 / 2 (F'=3) Achieves cyclic cooling, trapping up to 10 atoms in the magneto-optical trap. 7 The diameter and temperature of the cold atom clusters are 1.4 mm and 500 μK, respectively.

[0091] S4. A 355nm pulsed laser is generated by frequency doubling of an Nd:YAG laser to pump the dye laser, producing pulsed lasers with a wavelength of 460-490nm, where the pulse width is 5ns and the linewidth is 0.02cm. -1 A 480nm wavelength laser was selected as the ionizing laser and focused onto 5P-state atoms to form ultracold plasma through threshold photoionization.

[0092] S5. After the ultracold plasma is formed, it is accelerated under the action of the electric field of the ion lens and flies towards the two-dimensional position sensitive detector. Taking ions as an example, the two-dimensional position distribution of ions is recorded by CCD.

[0093] To ensure the quasi-neutral state of the plasma, this embodiment uses a pulsed high-voltage generator PVX-4130 to generate a pulsed electric field, and the timing and duration of the electric field are controlled by a DG645. Based on this, the ion dynamics at different evolution moments are detected. Figure 3 This is a spatial distribution diagram of ions corresponding to the ultracold plasma evolution of 600 ns in this embodiment, as shown below. Figure 3 As shown, a two-dimensional position-sensitive detector recorded the spatial distribution of the ultracold plasma evolution over 600 ns.

[0094] S6. Based on the spatial distribution of ions recorded in S3, the position space is converted to the velocity space through system calibration. Finally, the three-dimensional initial velocity distribution of ions is reconstructed using the inverse Abelian transform.

[0095] S7. Based on the obtained ion velocity distribution information, the Maxwell-Boltzmann velocity distribution law is used for fitting to finally obtain the ion temperature in the ultracold plasma.

[0096] Figure 4 The evolution of ion temperature over time from generation to 1200 ns in the ultracold plasma of this embodiment is presented. According to previous reports [PRL.2004,93:265003 and PRL.2004,92:143001(2004)], ions undergo disorder-induced heating within an evolution time of 1 μs, causing the ion temperature to rise to about 2 K.

[0097] like Figure 4 As shown, in the measurement results of this embodiment, the ions heated to 2K at approximately 900 ns. This result is consistent with the conclusions reported in the literature, which fully demonstrates the feasibility of the diagnostic method of this embodiment and the reliability of the test results, laying the foundation for its widespread application in the future.

[0098] The above description is merely an example and illustration of the structure of this invention, and while the description is specific and detailed, it should not be construed as limiting the scope of this invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this invention, and these obvious substitutions all fall within the protection scope of this invention.

Claims

1. A method for diagnosing the ion temperature of ultracold strongly coupled plasma, characterized in that, Includes the following steps: The atomic source is heated to form a diffused neutral thermal atomic gas within the vacuum chamber; A magneto-optical trap is constructed by using a laser field formed by three beams and six paths of continuous lasers, combined with a gradient magnetic field generated by an anti-Helmholtz coil. The magneto-optical trap is a classic atomic three-dimensional laser cooling and trapping device. Neutral hot atomic gas diffused within a vacuum chamber is captured and imprisoned using a magneto-optical trap, forming cold atomic clusters of a certain density. A laser of a suitable wavelength is introduced, focused, and applied to cold atomic clusters to ionize them, forming ultracold plasma; After the formation of ultracold plasma, charged particles are accelerated by the electric field of the ion lens in ion velocity imaging and fly toward the two-dimensional position sensitive detector, which records the spatial distribution of ions. Based on the two-dimensional spatial distribution data of ions recorded by the detector, and combined with numerical inversion algorithms, the three-dimensional velocity distribution of ions is reconstructed. The velocity distribution of ions was obtained by fitting the Maxwell-Boltzmann velocity distribution law, and the ion temperature in the ultracold plasma was extracted.

2. The diagnostic method according to claim 1, characterized in that, The formation of cold atomic clusters of a certain density includes the following steps: Three continuous laser beams enter through the observation window of the vacuum chamber and are reflected by a mirror placed opposite, forming three pairs of opposing and orthogonal light paths, serving as three-dimensional cooling lasers for atoms. A pair of coils are placed symmetrically outside the vacuum chamber, and currents of equal magnitude but opposite direction are input, forming an anti-Helmholtz coil structure, which generates a gradient magnetic field with a horizontal and vertical magnetic field strength ratio of 1:

2. An optical path system constructed using a three-dimensional cooling laser, combined with a gradient magnetic field, captures neutral hot atomic gas within a vacuum chamber, forming cold atomic clusters of a certain density.

3. The diagnostic method according to claim 2, characterized in that, The continuous laser is generated by a semiconductor laser or a Ti:sapphire laser, and the laser linewidth of the continuous laser is ≤1MHz.

4. The diagnostic method according to claim 1, characterized in that, The formation of ultracold plasma includes the following steps: using a cooling laser to excite atoms from the ground state to a first excited state, followed by cyclic cooling; A laser of a suitable wavelength is introduced as an ionizing laser, which is then focused and applied to excited-state cold atoms to ionize them, forming ultracold plasma.

5. The diagnostic method according to claim 4, characterized in that, The ionizing laser is generated by a pulsed dye laser with a continuously tunable wavelength, the wavelength of which is near the ionization threshold.

6. The diagnostic method according to claim 1, characterized in that, The electric field of the ion lens in the ion velocity imaging is obtained by applying different voltages to a series of electrodes to obtain the electric field distribution; the equipotential lines of the electric field of the ion lens are like those of an optical lens.

7. The diagnostic method according to claim 1, characterized in that, The two-dimensional position sensitive detector includes two microchannel plates, a fluorescent screen and a CCD camera, and is used to record the two-dimensional spatial distribution of ions.

8. The diagnostic method according to claim 7, characterized in that, The two-dimensional spatial distribution of the ions is converted into a two-dimensional velocity distribution of the ions after system calibration.

9. The diagnostic method according to claim 1, characterized in that, The numerical inversion algorithm is an inverse Abelian transform numerical inversion method, including the MEVIR or MEVELER algorithm; the numerical inversion algorithm is used to reconstruct the three-dimensional velocity distribution of ions.

10. The diagnostic method according to claim 1, characterized in that, The Maxwell-Boltzmann velocity distribution law is as follows: Where T is the ion temperature, kJ / kJ B is the Boltzmann constant.

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