Characteristics and scaling properties of the geodesic acoustic mode (GAM), a coherent, radially-sheared high frequency (∼15 kHz) zonal flow oscillation, are studied systematically using time-delay-estimation techniques applied to localized, multi-point density fluctuation measurements obtained by beam emission spectroscopy on DIII-D. The GAM amplitude is shown to increase strongly with increasing safety factor, q95, and to likewise become undetectably small for q95 < 4.2, qualitatively consistent with theoretical predictions based on collisional damping as well as simulations. The radial structure of the GAM exhibits peak amplitude in the radial range 0.88 < r/a < 0.95 with a rapid amplitude reduction inside and outside this region. The measured frequency is close to the predicted frequency, though some deviation to higher frequency is observed at lower q. The GAM amplitude is also shown to increase with plasma elongation, κ, while its frequency decreases.
地磁声模（GAM）——一种相干、径向剪切的约15 kHz高频带状流振荡——的特性与标度律，通过将时间延迟估计技术应用于DIII-D上束发射光谱法获得的局域多点密度涨落测量，进行了系统研究。结果表明，GAM振幅随安全因子q95的增大而显著增强，并在q95 < 4.2时变得不可检测地小，这与基于碰撞阻尼的理论预测及模拟结果定性一致。GAM的径向结构在0.88 < r/a < 0.95范围内呈现峰值振幅，且在该区域内外振幅迅速减小。实测频率接近预测值，但在较低q值下观测到向更高频率的偏移。此外，GAM振幅随等离子体拉长比κ增大而增加，而其频率则随之降低。