First results from protective ECRH diagnostics for Wendelstein 7-X
First results from protective ECRH diagnostics for Wendelstein 7-X
复制标题
Wendelstein 7-X 保护性 ECRH 诊断的第一个结果
DOI：
10.1088/1741-4326/aa6ab2
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发表时间：
2017
期刊：
影响因子：
3.3
通讯作者：
T. Stange
中科院分区：
文献类型：
--
作者：
S. Marsen;Y. Corre;H. Laqua;V. Moncada;D. Moseev;H. Niemann;M. Preynas;T. Stange
温德尔斯坦7-X（W 7-X）是一种具有稳态能力的优化仿星器。主要的加热系统是电子回旋共振加热（ECRH），工作频率为140 GHz，提供高达9 MW的微波功率。动力由X或O模式的前转向准光学发射器发射到机器中。而在X模式下，第一次通过吸收为99%，其仅为40%。70%在O模式。在X2截止密度为1.2 <$1020 m−3以上的高密度操作中，可以预见到O2模式加热。已经开发了一套诊断程序，以保护机器免受容易损坏容器组件的非吸收ECRH功率的影响。撞击内壁的非吸收功率由嵌入第一壁中的波导测量（ECA诊断）。为了防止内壁过热或产生电弧，采用了动态范围为450 °的近红外敏感视频诊断。1200 °C集成在ECRH发射器中。碳瓦的热计算预测，在50 ms的时间尺度上，等离子体启动失败或吸收不良的情况下，温度升高超过检测阈值。然而，在击穿失败的实验中，即在长达50 ms的时间内没有ECRH吸收，通过红外相机测量的温度升高仅为ΔT ≤ 70 ℃。在具有1.5%透射率的放电中，测得的温度升高是相当的。机器内部的杂散辐射水平通过所谓的嗅探器探头测量，嗅探器探头类似于微波二极管探测器，其被设计为收集所有接近探测表面的辐射，而与入射角和偏振无关。五个嗅探器探头安装在不同的环形位置。它们被集成到ECRH联锁系统中。在W7-X的第一个运行阶段，这是唯一可用的血浆联锁系统。信号质量被证明是足够高的一个可靠的终止在吸收不良的情况下。在10 ms的击穿阶段之后，嗅探器探测信号下降超过一个数量级。特别是在运行的最初几天，大多数放电由于杂质流入而死于辐射崩溃。在这种情况下，由于杂散辐射水平的增加，加热功率被可靠地切断。此外，ECRH测辐射热计与较慢的响应时间在发射器端口和空的诊断端口被用来估计在端口的杂散辐射水平。在发射器端口中，可以表明，杂散辐射可能导致长时间放电时波纹管过热。讨论了可能的应对措施。
Wendelstein 7-X (W7-X) is a steady state capable optimised stellarator. The main heating system is electron cyclotron resonance heating (ECRH) operating at 140 GHz providing up to 9 MW microwave power. The power is launched into the machine by front steerable quasi-optical launchers in X- or O-mode. While in X-mode the first pass absorption is 99%, it is only 40... 70% in O-mode. O2-mode heating is forseen for high density operation above the X2 cutoff density of 1.2⋅1020 m−3. A set of diagnostics has been developed to protect the machine from non absorbed ECRH power which can easily damage in vessel components. The non absorbed power hitting the inner wall is measured by waveguides embedded in the first wall (ECA diagnostic). In order to prevent the inner wall from overheating or arcing, a near-infra red sensitive video diagnostic with a dynamic range of 450...1200 °C was integrated in the ECRH launchers. Thermal calculations for the carbon tiles predict a temperature increase above the detection threshold for scenarios of plasma start-up failure or poor absorption on a time scale of 50 ms. However, the temperature increase measured by an IR camera in experiments with failed break down, i.e. no ECRH absorption for up to 50 ms, was only ΔT≈70 ∘ C. In discharges with ≈ 5% transmission the measured temperature increase was comparable. The stray radiation level inside the machine is measured by so called sniffer probes resembling microwave diode detectors which were designed to collect all radiation approaching the probing surface independent of incident angle and polarization. Five sniffer probes are installed at different toroidal positions. They were integrated in the ECRH interlock system. During the first operational phase of W7-X this was the only available plasma interlock system. The signal quality proofed to be high enough for a reliable termination in case of poor absorption. After a breakdown phase of 10 ms, the sniffer probe signals dropped by more than an order of magnitude. Especially in the very first days of operation, most discharges died by a radiative collapse due to impurity influx. In this case the heating power was reliably switched off due to the increased level of stray radiation. Moreover, ECRH bolometers with a slower response time in the launcher ports and an empty diagnostic port were used to estimate the stray radiation level in the ports. In the launcher ports it could be shown that the stray radiation could lead to an overheating of the bellows in long discharges. Possible counter measures are discussed.