It is necessary to operate a divertor with a sufficiently high plasma density at the symmetry point ns, 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 Tt, to minimize sputtering. The possibilities for realizing these two objectives simultaneously are examined. It is found that the combination of high ns and low Tt can require that the plasma flow be supersonic before reaching the divertor sheath. It is not known if such plasma conditions are stable.