We discuss the experimental conditions responsible for a drastic decrease in the power threshold of parametric decay instabilities under auxiliary electron cyclotron resonance heating (ECRH) in toroidal magnetic fusion devices when the upper hybrid (UH) resonance for the pump wave is absent. We show that for a finite-width pump in the presence of a non-monotonic (hollow) density profile occurring due to plasma equilibrium in the magnetic islands or anomalous particle fluxes from the ECR layer, 3D localization of one or both daughter waves is possible. This localization leads to the full suppression of daughter wave energy losses from the decay layer and a substantial increase in the nonlinear pumping efficiency. This decreases the power threshold of nonlinear excitation, which can be easily overcome in current ECRH experiments utilizing 1 MW microwave beams. Different scenarios of extraordinary and ordinary wave decays are investigated. The secondary decays of primary daughter wave...

中文翻译：

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环形聚变装置中强大微波束的低功率阈值参数衰减不稳定性

我们讨论了在环形磁聚变装置中辅助电子回旋共振加热（ECRH）下不存在泵浦波的上混合（UH）共振时，参数衰减不稳定性的功率阈值急剧降低的实验条件。我们表明，对于有限宽的泵，如果存在非单调（空心）密度分布，这是由于磁岛中的等离子体平衡或来自ECR层的异常粒子通量引起的，则一个或两个子波的3D定位是可能的。这种局部化导致完全抑制了来自衰减层的子波能量损失，并大大提高了非线性泵浦效率。这降低了非线性激励的功率阈值，在当前使用1 MW微波束的ECRH实验中可以轻松克服这一点。研究了异常波和普通波衰减的不同情况。主子波的二次衰变...