We hereby report a study on confinement and electron loss dynamics in the magnetic trap of an electron cyclotron resonance ion source using a special multi-diagnostic setup that has allowed the simultaneous collection of plasma radio-self-emission and x-ray images in the range 500 eV–20 keV. Argon plasmas were generated in single- and two-close-frequency heating (SFH and TCFH) modes. Evidence of turbulent regimes has been found: for stable and unstable configurations quantitative characterizations of the plasma radio self-emission have been carried out, then compared with local measurements of plasma energy content evaluated by x-ray imaging. This imaging method is the only one able to clearly separate x-ray radiation coming from the plasma from that coming from the plasma chamber walls. X-ray imaging has also been supported and benchmarked by volumetric spectroscopy performed via silicon drift and high-purity germanium detectors. The obtained results in terms of x-ray intensity signal coming from the plasma core and from the plasma chamber walls permit the estimation of the average ratio: plasma vs. walls (i.e. plasma losses) as a function of input RF power and pumping wave frequency, showing an evident increase (above the experimental errors) of the intensity in the 2–20 keV energy range due to the plasma losses in the case of unstable plasma. This ratio was well correlated with the strength of the instabilities, in SFH operation mode; in TCFH mode, under specific power balance conditions and frequency combinations, it was possible to damp the instabilities, and thus the plasma losses were observed to decrease and a general reconfiguration of the spatial plasma structure occurred (the x-ray emission was more concentrated in the center of the plasma chamber). Finally, a simplified model was used to simulate electron heating under different pumping frequencies, prompting discussion of the impact of velocity anisotropy vs the onset of the instability, and the mechanism of particle diffusion in the velocity space in stable and unstable regimes.
我在此报告一项研究，该研究利用一套特殊的多诊断装置，对电子回旋共振离子源磁阱中的约束和电子损失动力学进行了研究，该装置能够同时采集能量范围在500 eV–20 keV的等离子体自发射无线电波图像和X射线图像。研究在单频加热（SFH）和双频邻近加热（TCFH）两种模式下产生了氩等离子体。实验发现了湍流态存在的证据：针对稳定和不稳定构型，对等离子体自发射无线电波进行了定量表征，并将其与通过X射线成像评估的局部等离子体能量含量进行了比较。这种成像方法是唯一能够清晰区分来自等离子体本身和来自等离子体室壁的X射线辐射的手段。X射线成像还通过硅漂移探测器和高纯锗探测器进行的体积光谱测量得到了验证和交叉校准。所获得的关于来自等离子体芯部和室壁的X射线强度信号的结果，使得能够估算平均比值：即等离子体损失与输入射频功率和泵浦频率的函数关系，结果显示在不稳定等离子体情况下，2–20 keV能量范围内的强度显著增加（超出实验误差范围）。该比值与不稳定性强度在SFH模式下表现出良好的相关性；而在TCFH模式下，在特定的功率平衡和频率组合条件下，不稳定性可以被抑制，从而观察到等离子体损失减少，并且等离子体空间结构发生重构（X射线发射更集中于等离子体室中心）。最后，利用一个简化模型对不同泵浦频率下的电子加热进行了模拟，引发了对速度各向异性与不稳定性触发之间关系的讨论，以及稳定和非稳定状态下速度空间中粒子扩散机制的探讨。