Subsonic and supersonic divertor solutions

It is necessary to operate a divertor with a sufficiently high plasma density at the symmetry point n s , i.e. adjacent to the main plasma, to satisfy the Lawson criterion and, at the same time, a low enough value of the plasma temperature at the target plate T t to minimize sputtering. The possibilities for realizing these two objectives simultaneously are examined. It is found that the combination of high n s and low T t can require that the plasma flow be supersonic before reaching the divertor sheath. It is not known if such plasma conditions are stable.