Thomson scattering diagnostic system for the XuanLong-50 experiment

Li, H. Y.; Li, S. J.; Xie, Q. F.; Liu, J. H.; Bai, Ruixin; Tao, Ran; Lun, Xulei; Li, N.; Bo, X. K.; Liu, C. Q.; Han, Lei; Deng, B. H.

doi:10.1063/5.0088785

Cited by 9 publications

(5 citation statements)

References 18 publications

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Section: Sample Plasma As Analysis Targetsupporting

confidence: 88%

“…Averaged bulk electron and ion temperatures estimated from the four fluid model[8] are 200 eV and 35 eV, respectively. These estimations are consistent with a Thomson scattering measurement to a similar plasma[9] and indicate that the pressure of the bulk components is ≈20 Pa.Solid square points in figure1(d) show signals of 39 flux loops surrounding the plasma depicted in figure 1(b). Note that contributions from the external coil currents are subtracted and these signal values are solely from the plasma current.…”

supporting

confidence: 86%

“…These plasmas are characterized by the presence of copious energetic electrons (EEs) that carry the plasma current as revealed by the equilibrium analysis using the four fluids model [8]. X-ray measurements suggest that this EE component is in the particle energy range from several tens of keV up to several hundreds of keV [7] while Thomson scattering measurement shows that bulk electron temperature is ≈100 eV [9]. The EE component accounts for a quite large percentage of plasma pressure, being more than 95% of the total plasma pressure, while it accounts for only a small fraction in density.…”

Section: Introductionmentioning

confidence: 99%

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Particle orbit description of cyclotron-driven current-carrying energetic electrons in the EXL-50 spherical torus

Maekawa

Peng

Liu³

2023

Nucl. Fusion

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In EXL-50 plasma currents over hundred kA are non-inductively generated and maintained solely by ECH power with an efficiency of $\sim$1A/W. These currents are carried by energetic electrons (EE) in the energy range from several tens keV up to several hundreds keV which also account for almost all pressure in plasma. This EE component can be viewed as a large number collection of various periodic orbits of energetic particles. Based on this picture we have developed a method for particle orbit description of the EE component in a typical plasma at Ip=121 kA as analysis target. We use a fluid description as a bridge to describe successfully the EE component as a collection of various passing and trapped orbits in the approximation of monochromatic particle energy with good matching to the flux loop signals.The description has revealed characteristics of passing and trapped particles. Passing particles carry almost all toroidal current, while they account for only 20 $\%$ of total particle number of the EE component. While net current carried by trapped particles is a very small fraction, they account for a major fraction in number and carry a large positive current outside the last closed flux surface (LCFS) and a large negative current inside. As a result, trapped particles redistribute the current from inside of LCFS to outside both radially and vertically, generating a large vertically elongated cross section in current as well as number density profiles. There is a ridge like structure along LCFS in the current density profile, while no such structure in the number density profile. The results suggest that forward passing particles are more advantageous in confinement than backward passing particles. This advantage increases with particle energy and contribute to current generation observed in EXL-50 experiments.

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Section: Sample Plasma As Analysis Targetsupporting

confidence: 88%

supporting

confidence: 86%

Section: Introductionmentioning

confidence: 99%

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Particle orbit description of cyclotron-driven current-carrying energetic electrons in the EXL-50 spherical torus

Maekawa

Peng

Liu³

2023

Nucl. Fusion

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“…The equilibrium of an ECW plasma without a central solenoid has been widely demonstrated [21][22][23][24][25][26], and the existence of plasma equilibrium provides a fundamental platform for the study of turbulence transport. Low-frequency density fluctuations and the corresponding particle pump-out effect were clearly observed with Thomson scattering diagnostics [27] and microwave interferometer [28] in EXL-50 ECW plasma. The experimental results show that the intensity of density fluctuations increases with the increase in the heating power under similar fueling.…”

Section: Introductionmentioning

confidence: 83%

Particle pump-out induced by trapped electron mode turbulence in electron cyclotron heated plasmas on XuanLong-50 spherical torus

Wang,

Li,

Bai

et al. 2023

Nucl. Fusion

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The particle pump-out effects induced by low frequency (<200 kHz) density fluctuations were observed in electron cyclotron wave (ECW) heated solely plasmas on spherical torus XuanLong-50 (EXL-50) without a central solenoid. The intensity of the relative density fluctuations increased with increase of ECW power and decayed when ECW was turned off while plasma current was sustained. The electron densities maintained relatively high and steady when the density fluctuations were completely absent, indicating that the outward transport of electrons was dominated by particle pump-out effect of ECW. The density fluctuations were modulated by supersonic molecular beam injection (SMBI) pulse and the modulation amplitude decreases with increase of electron density at same ECW injection power and decrease of ECW power at same electron density, respectively. Analysis found that there was a critical value of electron temperature gradient for triggering the density fluctuations, and the intensity of the relative density fluctuations was positively correlated with electron temperature gradient and approximately inversely proportional to effective collision frequency. With plasma parameters similar to those of EXL-50 experiments, the HD7 code simulations show that trapped electron mode (TEM) turbulence can be excited by electron temperature gradient higher than the critical value observed in the experiment. In addition, the dependences of the mode growth rate (supposed to be proportional to saturation level of fluctuations in quasi-linear theory) and the measured intensity of the density fluctuation are comparable. The simulated outward particle flux integrated over poloidal wave number spectrum is significant and proportional to electron temperature gradient. These observations demonstrate that the density fluctuation is TEM turbulence, which is driven by electron temperature gradient and induces particle pump-out when electron density/effective electron collision frequency is low. The potential relevance of the work with controls of plasma profile, impurities, helium ash, and heat transport in future reactors of similar low effective collision frequency is discussed.

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“…Figure 1 illustrates a typical discharge in the EXL-50 system, showcasing various plasma parameters. The subfigures, arranged from top to bottom, depict the plasma current and B V (z ~ 0 m, R ~ 0.3 m), integral density, hard Xray intensity [37], loop voltage and electron temperature and density profiles. The bottom two sets of profiles are electron temperature and density profiles obtained through Thomson scattering diagnostic (TS) measurements during the 2-3 s interval [38].…”

Section: Exl-50 and Energetic Electron Currentmentioning

confidence: 99%

Experimental confirmation of the linear relation between plasma current and external vertical magnetic field in EXL-50 spherical torus energetic electron plasmas

DONG 董,

WANG 王,

LIU 刘

et al. 2024

Plasma Sci. Technol.

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A three-fluid equilibrium plasma with bulk plasma and energetic electrons has been observed on the Xuanlong-50 (EXL-50) spherical torus, where the energetic electrons play a crucial role in sustaining the plasma current and pressure. In this study, the equilibrium of a multi-fluid plasma was investigated by analyzing the relationship between the external vertical magnetic field (B<sub>V</sub >), plasma current (Ip), the poloidal ratio (βp) and the Shafranov formula. Remarkably, our research demonstrates some validity of the Shafranov formula in the presence of multi-fluid plasma in EXL-50 spherical torus. This finding holds significant importance for future reactors as it allows for differentiation between alpha particles and background plasma. The study of multi-fluid plasma provides a significant reference value for the equilibrium reconstruction of burning plasma involving alpha particles.

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Thomson scattering diagnostic system for the XuanLong-50 experiment

Cited by 9 publications

References 18 publications

Particle orbit description of cyclotron-driven current-carrying energetic electrons in the EXL-50 spherical torus

Particle orbit description of cyclotron-driven current-carrying energetic electrons in the EXL-50 spherical torus

Particle pump-out induced by trapped electron mode turbulence in electron cyclotron heated plasmas on XuanLong-50 spherical torus

Experimental confirmation of the linear relation between plasma current and external vertical magnetic field in EXL-50 spherical torus energetic electron plasmas

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