The flute instability of a plasma confined in a gas-dynamic trap where the mean free path of the particles λ is small compared with the trap length L is examined. In analysing the instability the influence on the oscillations both of the energy and particle injection which maintains the system in steady state and also of the damping of perturbations which results from plasma flowing out through the mirrors is included. An expression is obtained for the growth rate of the flute instability which is used in formulating the necessary and sufficient criterion of stability. It is found that in certain conditions, even when the flute instability has been suppressed, an instability with a characteristic growth rate of the order of the reciprocal of the plasma life-time can still develop in the trap. The effects examined in the paper are also of interest for open traps with λ > L.
粒子の平均自由行程λがトラップ長Lに比べて小さいガス動的トラップに閉じ込められたプラズマのフルート不安定性を調べた。不安定性の解析において、系を定常状態に維持するエネルギーおよび粒子入射の振動への影響と、ミラーを通してプラズマが流出することによる摂動の減衰の両方が含められる。フルート不安定性の成長率の式が得られ、これは安定性の必要十分条件を定式化するために用いられる。特定の条件下では、フルート不安定性が抑制された場合でも、プラズマ寿命の逆数のオーダーの特性成長率を持つ不安定性がトラップ内で発生し得ることが見出された。本論文で調べた効果は、λ > L の開放トラップにとっても興味深い。