A quasi-optical microwave interferometer for the XuanLong-50 experiment

Li, S.J.; Bai, Ruixin; Tao, Ran; Li, N.; Lun, Xulei; Liu, L.C.; Liu, Y.; Liu, M.S.; Deng, B. H.

doi:10.1088/1748-0221/16/08/t08011

Cited by 9 publications

(5 citation statements)

References 7 publications

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“…When the electric current of a 12-turn TF coils per turn was set to about 100 kA, the fundamental and higher ECR layers (up to five resonances) coexist within the EXL-50 vacuum region (as shown in figure 1(a)). The electron density is measured using a single-chord tangential microwave interferometer [27]. Two CdTe detectors with energy resolution are applied to observe the forward and backward bremsstrahlung hard x-ray (HX) emission [28].…”

Section: Methodsmentioning

confidence: 99%

Solenoid-free current drive via ECRH in EXL-50 spherical torus plasmas

Shi

Liu²,

Song³

et al. 2022

Nucl. Fusion

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As a new spherical tokamak (ST) designed to simplify engineering requirements of a possible future fusion power source, the EXL-50 experiment features a low aspect ratio (A) vacuum vessel (VV), encircling a central post assembly containing the toroidal field coil conductors without a central solenoid. Multiple electron cyclotron resonance heating (ECRH) resonances are located within the VV to improve current drive effectiveness. Copious energetic electrons are produced and measured with hard X-ray detectors, carry the bulk of the plasma current ranging from 50kA to 150kA, which is maintained for more than 1s duration. It is observed that over one Ampere current can be maintained per Watt of ECRH power issued from the 28-GHz gyrotrons. The plasma current reaches Ip>80kA for high density (>51018m-2) discharge with 150kW ECHR heating. An analysis was carried out combining reconstructed multi-fluid equilibrium, guiding-center orbits of energetic electrons, and resonant heating mechanisms. It is verified that in EXL-50 a broadly distributed current of energetic electrons creates smaller closed magnetic-flux surfaces of low aspect ratio that in turn confine the thermal plasma electrons and ions and participate in maintaining the equilibrium force-balance. effectiveness. Copious energetic electrons are observed via hard X-ray detectors, carry the bulk of the plasma current ranging from 50kA to 150kA, which is maintained for more than 1s duration. It is observed that over one Ampere current can be maintained per Watt of ECRH power issued from the 28-GHz gyrotrons. The plasma current with high line-density (approaching 〖10〗^19 m^(-2)) has been achieved for plasma currents as high as 76kA. An analysis was carried out combining reconstructed multi-fluid equilibrium, guiding-center orbits, and resonant heating mechanisms. It is verified that in EXL-50 a broadly distributed current of energetic electrons creates smaller closed magnetic-flux surfaces of low aspect ratio that in turn confine the thermal plasma electrons and ions and participate in maintaining the equilibrium force-balance.

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Section: Methodsmentioning

confidence: 99%

Solenoid-free current drive via ECRH in EXL-50 spherical torus plasmas

Shi

Liu²,

Song³

et al. 2022

Nucl. Fusion

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“…The plasma density is diagnosed using an interferometer (Li et al. 2021). Energetic electron energy is diagnosed by the HX bremsstrahlung radiation from the plasma (figure 1 a ).…”

Section: Resultsmentioning

confidence: 99%

Generation of energetic electrons by an electron cyclotron wave through stochastic heating in a spherical tokamak

Wang,

Cheng,

Liu

et al. 2023

J. Plasma Phys.

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This study presents novel findings on stochastic electron heating via a random electron cyclotron wave (ECW) in a spherical tokamak. Hard x ray measurements demonstrate the time evolution of hard x ray counts at different energy bands, consistent with predictions from the stochastic heating model. The ECW heating rate shows a positive correlation with applied power, confirming the effectiveness of stochastic heating. Remarkably, the ECW-driven plasma current remains insensitive to ECW incidence angle, consistent with model predictions. The observed stochastic heating of electrons offers potential for exploring innovative non-inductive current drive modes in spherical tokamaks. This research contributes to the understanding of plasma behaviour and motivates the development of new models for non-inductive current drive in fusion devices.

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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: 82%

“…Figure 1 shows the typical density and temperature profiles measured by TS (averaged over 10 laser pulses), where the black and blue lines correspond to ECW input powers of 310 kW and 170 kW, respectively. The plasma density fluctuations and line-integrated density are measured using a microwave interferometer [28]. According to the forward scattering theory, the interferometer measures the maximum fluctuation wave number k ∼ 5 cm −1 [48], and TEM-induced density fluctuations can be observed.…”

Section: Spherical Torus Exl-50 and Hd7 Codementioning

confidence: 99%

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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A quasi-optical microwave interferometer for the XuanLong-50 experiment

Cited by 9 publications

References 7 publications

Solenoid-free current drive via ECRH in EXL-50 spherical torus plasmas

Solenoid-free current drive via ECRH in EXL-50 spherical torus plasmas

Generation of energetic electrons by an electron cyclotron wave through stochastic heating in a spherical tokamak

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

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