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

A significant number of confined energetic electrons have been observed outside the Last Closed Flux Surface (LCFS) of the solenoid-free, ECRH sustained plasmas in the EXL-50 spherical torus. Several diagnostics have been applied, for the first time, to investigate the key characters of energetic electrons. Experiments reveal the existence of high-temperature low density electrons, which can carry relatively a large amount of the stored energy. The boundary between the thermal plasma and the energetic electron fluid appears to be clearly separated and the distance between the two boundaries can reach tens of centimeters (around the size of the minor radius of the thermal plasma). This implies that the Grad-Shafranov equilibrium is not suitable to describe the equilibrium of the EXL-50 plasma and a multi-fluid model is required. Particle dynamics simulations of full orbits show that energetic electrons can be well confined outside the LCFS. This is consistent with the experimental observations.

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Experimental study of non-inductive current start-up using electron cyclotron wave on EXL-50 spherical torus

Wang¹,

Guo²,

Shi³

et al. 2022

Plasma Phys. Control. Fusion

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Although experiments have demonstrated the feasibility of the electron-cyclotron-wave (ECW) non-inductive current start-up, the physical mechanism of the current start-up remains unclear, particularly the role of the preferential confinement of collisionless tail electron currents ( jTPC)and vertical charge-separation currents (jVTF). Therefore, jTPC and jVTF were observed using limiter probes during the ECW non-inductive current start-up on an EXL-50 spherical Torus to understand the significance of these values. It was found that jTPC increased and jVTF decreased during the start-up, indicating the dominant role played by jTPC in this process. Furthermore, it was found that the product of the gas pressure and vertical magnetic field has a limit for the ECW non-inductive current start-up. Lastly, we found that the ECW non-inductive current start-up can be realized only for sufficiently low vertical fields and gas pressures in EXL-50.

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

Cited by 5 publications

References 30 publications

Assessments of the performance of neutral beam injection on the spherical tokamak EXL-50

Assessments of the performance of neutral beam injection on the spherical tokamak EXL-50

Experimental study of the characteristics of energetic electrons outside LCFS in EXL-50 spherical torus

Experimental study of non-inductive current start-up using electron cyclotron wave on EXL-50 spherical torus

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