Negative Ion Plasmas

负离子等离子体在等离子体物理及其应用中具有新的特点，需要从理论和实验两方面进行研究。这里介绍了我们最近在负离子等离子体上的实验，包括对以前实验的简要回顾。在我们的实验中，通过在单端q机等离子体中引入少量的SF6气体来产生负离子等离子体。负离子（sf6 ^-）与正离子（K^+）的密度比（n_-/n_+）连续控制在0.9999范围内。我们的主要兴趣是负离子的存在对典型等离子体波特性和不稳定性的影响，即电子等离子体波、离子波、静电离子回旋波不稳定性和负离子等离子体中的漂移波不稳定性。观测到的它们的性质与理论预测一致。结果还表明，其中一些波和不稳定性在确定n_-/n_+比值时非常有用，特别是在(n_+-n_-/n_+<< 1的情况下。

Negative ion plasmas have new features in plasma physics and its applications, which are to be investigated from both theoretical and experimental points of view. Here our recent experiments on negative ion plasmas are presented, including a brief review of the previous experiments. In our experiments, negative ion plasmas are produced by introducing a small amount of SF6 gas into a single-ended Q-machine plasma. The density ratio of negative (SF_6^-) to positive (K^+) ions, n_-/n_+, is controlled continuously in the range up to 0.9999. Our main interests are in effects of an existence of negative ions on characteristics of typical plasma waves and instabilities, i.e., electron plasma waves, ion waves, electrostatic ion cyclotron wave instability, and drift wave instability in negative ion plasmas. Their properties observed are consistent with theoretical predictions. It is also shown that some of these waves and instabilities are quite useful in determining the ratio n_-/n_+, especially in case of (n_+-n_-/n_+<< 1.