Asymmetrical Distribution of Plasma Parameters Nearby Divertor Plates of Small-Sized Tokamaks

Recently, the onset density and temperature asymmetries between the low-field side and high-field side during the rise of central plasma have been observed for small-sized divertor tokamaks in the edge transport barrier mode. Using the B2SOLPS5.0 2D code, the density asymmetrical profiles were simulated and analyzed. The simulation results showed that the onset of the detachment at the outer divertor plate is linked to the density asymmetries.

As a result, the main reason for this density asymmetry between the divertor plates is the drifts, which in turn cause a variance in the temperatures of electrons and ions. Additionally, the poloidal E × B drift, which is responsible for carbon screening and higher power losses, can significantly impact these asymmetries. Further, the poloidal part of E_r × B can increase the radial electric field, hence their combined actions can provide a noticeable in-out asymmetry.

Both the attached and detached inner/outer divertor plates exhibited insignificant pressure and electron temperature asymmetries over the inner/outer midplanes, according to the study. And last, the simulation outputs revealed that outer plate detaching bifurcation occurs based on four circumstances: E × B drift, carbon impurity, the normal direction of the toroidal magnetic field, and relatively low radially anomalous transport coefficients.