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首页> 外文期刊>Plasma physics and controlled fusion >Modelling radio-frequency plasma cleaning of fusion optics
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Modelling radio-frequency plasma cleaning of fusion optics

机译：融合光学造型射频等离子清洗

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Metallic mirrors are to be used extensively within ITER for diagnostics and real time control. Erosion of the first wall within ITER will cause particles to be redeposited around the machine, including on these first mirrors, which will cause a reduction in reflectivity and a degradation in quality of signal received by the detectors. Powering these mirrors to form capacitively-coupled plasmas (CCPs) with an induced self bias, and using the ions within the plasmas to bombard and remove the deposits, has shown some experimental success in recovering mirror reflectivity. In this work the ion energy distribution functions (IEDFs) from an Ar CCP formed on a 5 cm radius metallic mirror are modelled and investigated using the hybrid plasma equipment model. Initially a geometry variation is done showing that a simple increase in reactor volume can significantly impact the spatial distribution of the ion flux to the mirror surface leading to non-uniform etch rates across the surface, even after the maximum bias has been achieved. The ion energies need to be sufficient to remove depositions (focussing on the first wall material of Be which forms a surface oxide BeO) but not subsequently damage the underlying mirror. In order to achieve this both the voltage (50-1000 V) and the frequency (13.56-60 MHz) have been varied within the model showing trends that may lead towards IEDF optimisation. The increase in voltage increases the self bias linearly and the plasma density super-linearly, whereas increasing the frequency barely effects the self bias while increasing the plasma density sub-linearly. Both increases cause an increase in ion flux for these reasons but both also decrease the homogeneity of the ion flux across the mirror surface which will be required should the energies be above the threshold for the mirror. These results are also unique to the geometry being investigated and thus the conclusion is that it would be prudent to model individual mirror geometries to find optimal parameters. This becomes especially clear with the introduction of a perpendicular magnetic field into the simulation that significantly reduces electron transport within the plasma.
机译：金属镜将广泛用于ITER以进行诊断和实时控制。第一墙内的第一墙的侵蚀将导致粒子在机器周围重新沉积，包括这些第一镜子，这将导致探测器接收的信号质量的反射率和降低。向这些镜子供电以形成具有诱导的自偏压的电容耦合的等离子体（CCP），并使用等离子体内的离子轰击并移除沉积物，在回收镜反射率时已经示出了一些实验成功。在这项工作中，使用混合等离子体设备模型建模和研究了来自形成在5cm半径金属镜上的AR CCP的离子能量分布功能（IEDFS）。最初进行了几何变化，表明反应器体积的简单增加可以显着地影响离子通量的离子通量的空间分布，即使在实现最大偏差之后，即使在达到最大偏差之后，也能够显着地影响镜面。离子能量需要足以去除沉积（聚焦在形成表面氧化物Beo的第一壁材料上），但随后不会损坏下面的镜子。为了实现这一点，电压（50-1000 V）和频率（13.56-60 MHz）在模型中已经变化，示出了可能导致IEDF优化的趋势。电压的增加增加了自偏置线性和等离子体密度超短线性，而增加频率几乎没有偏置自偏置，同时增加等离子体密度的子线性。由于这些原因，这两种增加都会导致离子通量增加，但这两者也降低了镜面上的离子通量的均匀性，如果能量高于镜子的阈值，则应需要。这些结果对所研究的几何也是独一无二的，因此结论是模拟各个镜像几何形状以找到最佳参数将是谨慎的。随着将垂直磁场引入模拟中，这尤其清楚地变得显着降低了等离子体内的电子传输。

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