Electrostatic drift modes in a closed field line configuration

The stability of electrostatic drift waves in a closed field line configuration in collisionality regimes ranging from collisional to collisionless is compared. The maximum sustainable pressure gradient is found to be dependent on the ratio of the temperature and density gradients (η≡d ln T/d ln n). The eigenmodes are seen to be flute-like. The stability boundary was found to be similar when both ions and electrons are collisional, when they are collisionless, and for collisional electrons and collisionless ions. The largest stable pressure gradients are obtained for η⩾2/3. As the collisionality is reduced one observes some reduction of the region of stability.