Speaker
Description
In the DEMO reactor, the enormous heat flux released from the core to the divertor plasma reaches several times that of ITER. Therefore, research is being conducted on advanced divertors aimed at reducing heat flux by increasing the plasma wetted area under divergent magnetic field and generating detached plasma. It is extremely important to investigate the effect of plasma flow acceleration due to magnetic field gradients on the formation of detached plasma using advanced divertors with divergent magnetic field (magnetic nozzles). The present study elucidates the formation process of attached plasma and detached plasma when the magnetic field gradient near the end-target is varied. Our research group, previously, developed a linear divertor simulator (TPDsheet-ICR) that applies ion cyclotron resonance heating (ICRH) to a high-density sheet plasma (approximately 10¹⁹ m⁻³) to increase the ion temperature. Utilizing this divertor simulator, we have successfully observed the process of transitioning from attached to detached plasma in experimental conditions [1,2]. In this experiment, a high-speed camera with an Arbba-prism was used to measure the two-dimensional emission intensity distribution in the Balmer series (Hα, Hγ) and the Fulcher-band wavelength range (600–640 nm) emitted from the plasma in the divergent magnetic field region. The plasma electron density and temperature were measured using a Langmuir probe. The experimental results revealed that, in the configuration of the divergent magnetic field, an increase in the magnetic field gradient resulted in an increase in electron temperature and caused the transition from attached plasma to detached plasma to occur at higher gas pressures. Furthermore, an increase in the ICR power resulted in an elevated electron temperature, thereby inducing the transition from a detached to an attached plasma. The results of the two-dimensional emission intensity distribution of the Balmer series and the Fulcher-band, along with the electron temperature, clarified the effect of the magnetic field gradient on detached plasma formation.
[1] A.Tonegawa,et al,Fusion Eng. & Des,203(2024)114441.
[2] A.Tonegawa,et al,Nucl.Materials & Energy,41(2024)101802.