HF heating experiment, with linear power ramp from 50 to 92 dBW, was conducted to determine the HF threshold power levels for the onset of detectable plasma waves and the onset of artificial ionization inferred from HF-enhanced plasma lines (HFPLs). The threshold free-space electric field at 200-km altitude, where HFPLs were detected, is about 53 mV/m. However, the HF electric field near the reflection height is enhanced by a swelling factor ~ 3.76 and also conversion to a linear dipole pump mode ( $\surd 2$ ); the actual threshold field is about 281 mV/m that is consistent with theory. Artificial ionization in the lower region was detectable via UHF radar. Short wavelength upper-hybrid waves, which were excited parametrically by the HF heating wave at higher threshold, implement Doppler shifted harmonic-cyclotron resonance interaction, via finite Larmour radius effect, to effectively accelerate electrons. Monitoring the spectral power of the parametric decay instability (PDI) line in the HFPLs by radar was shown to determine the artificial ionization onset time more precisely than that by observing the start of a sharp downward trend in the altitude of the HFPLs; at this time, the HF free-space electric field slightly below 200-km altitude is about 550 mV/m. Langmuir cascade lines in the HFPLs are separated by intervals about double the ion-acoustic frequency (about 4–5 kHz) generated by the PDI. These lines, observed at lower power facilities, were not observed. The upper-hybrid OTSI and PDI excited at HighPower Active Auroral Research Program (HAARP) and the mode competition nonlinear-damping mechanism are suggested as the processes, suppressing cascade enhanced HFPLs.

中文翻译：

---

在低 F 区电离层中 HF 增强等离子体线和人工电离开始的阈值功率的实验确定

HF 加热实验，从 50 到 92 dBW 的线性功率斜坡，用于确定可检测等离子体波的开始和从 HF 增强等离子体线 (HFPL) 推断的人工电离开始的 HF 阈值功率水平。检测到 HFPL 的 200 公里高度的阈值自由空间电场约为 53 mV/m。然而，反射高度附近的 HF 电场增强了~3.76 的膨胀因子，并且还转换为线性偶极泵模式（$\surd 2$）；实际阈值场约为 281 mV/m，与理论一致。通过 UHF 雷达可以检测到较低区域的人工电离。短波长上混合波，由高频加热波在较高阈值参数激发，实现​​多普勒频移谐波回旋共振相互作用，通过有限的拉莫尔半径效应，有效地加速电子。研究表明，通过雷达监测 HFPL 中参数衰减不稳定性 (PDI) 线的频谱功率，可以比观察 HFPL 高度急剧下降趋势的开始更精确地确定人工电离开始时间；此时，稍低于200公里高度的HF自由空间电场约为550 mV/m。HFPL 中的朗缪尔级联线以大约两倍于 PDI 产生的离子声频率（约 4-5 kHz）的间隔分隔。在低功率设施中观察到的这些线没有被观察到。在高功率主动极光研究计划 (HAARP) 中激发的上混合 OTSI 和 PDI 以及模式竞争非线性阻尼机制被建议作为抑制级联增强 HFPL 的过程。