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The implications of high-Z first-wall materials on noble gas wall recycling

机译：高Z第一壁材料对稀有气体壁回收的影响

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Recent experiments in ASDEX Upgrade (AUG) have experienced surprisingly high He plasma impurity concentrations. Such high He concentrations have not been observed with C walls, they were only observed since the increase in the W first-wall coverage of ASDEX Upgrade to 85%. The high He plasma concentration appears to be linked to the fraction of W surfaces open to plasma contact that are not covered by boronization layers and to the number of He glow discharges performed for wall conditioning prior to normal plasma operation. This points to the different retention and release properties of W and C for He. To elucidate these differences dedicated laboratory experiments have been performed. To study the retention, different types of W and C targets, including those used in ASDEX Upgrade, were implanted with ~3He at 200 and 600eV and the amount of retained He was determined through thermal effusion spectroscopy (TES) and ion beam analysis methods. These experiments showed that W can retain up to 10 times more He than C depending on the energy of the implanted ~3He. The TES measurement showed that both W and C start to out gas He at ≈400 K which is not reached at the first-wall in AUG. Therefore the differences in the release of He from W and C surfaces due to particle bombardment was investigated. ~3He implanted W and C substrates were exposed to ~4He or H_2 plasmas and the loss of ~3He was measured. For an H_2 plasma and 100eV bias, three times more He is released from W than from C. For ~4He and 100eV bias between 2 and 10 times more ~3He was released from W than from C depending on the type of W and C. The release rate of He from W and C through particle induced release was found to be equal. Therefore the stronger release of He from W can be explained by the higher retention of He in W.
机译：最近在ASDEX升级（AUGEX）中进行的实验经历了令人惊讶的高He血浆杂质浓度。在C壁上未观察到如此高的He浓度，仅在ASDEX升级版的W第一壁覆盖率增加至85％时才观察到。高的He等离子体浓度似乎与W接触等离子体但未被硼化层覆盖的W表面分数以及在正常等离子操作之前进行壁调节的He辉光放电次数有关。这表明了W和C对He的保留和释放特性不同。为了阐明这些差异，已经进行了专门的实验室实验。为了研究保留率，向不同类型的W和C目标（包括在ASDEX升级中使用的W和C目标）注入了200和600eV的〜3He，并通过热渗流光谱（TES）和离子束分析方法确定了保留的He量。这些实验表明，取决于注入的〜3He的能量，W最多可以比C保留10倍以上的He。 TES测试显示，W和C都在≈400K时开始释放出He，这在AUG的第一壁没有达到。因此，研究了由于粒子轰击而从W和C表面释放He的差异。将〜3He注入的W和C衬底暴露于〜4He或H_2等离子体，并测量〜3He的损失。对于H_2等离子体和100eV偏压，从W释放的He量比从C中释放的He多三倍。对于W和C的类型，从W释放的〜4He和100eV偏压〜3He的量比从C中释放的He的2至10倍。发现He从W和C通过颗粒诱导释放的释放速率是相等的。因此，He从W中的较高保留可以解释He从W中释放的更强。

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