Ochoukov R, Dreval M, Bobkov V, Faugel H, Herrmann A, Kammerloher L, Leitenstern P
Max Planck Institute for Plasma Physics, Boltzmannstr. 2, 85748 Garching, Germany.
Institute of Plasma Physics, National Science Center Kharkov Institute of Physics and Technology, Kharkov 61108, Ukraine.
Rev Sci Instrum. 2020 Jun 1;91(6):063506. doi: 10.1063/5.0010788.
This manuscript presents a new method of interpreting the ion temperature (T) measurement with a retarding field analyzer (RFA) that accounts for the intermittent/turbulent nature of the scrape off layer (SOL) plasmas in tokamaks. Fast measurements and statistical methods are desirable for an adequate description of random fluctuations caused by such intermittent events as edge localized modes (ELMs) and blobs. We use a RFA that can sweep its current-voltage (I-V) characteristics with up to 10 kHz. The RFA uses an electronics compensation stage to subtract the capacitive pickup due to the finite connecting cable capacitance, which greatly improves the signal-to-noise ratio. In the 10 kHz case, a single I-V characteristic is obtained in time, which is an order of magnitude faster than the ELM cycle. The fast sweeping frequency allows us to reconstruct the T probability density function (PDF), which we use as the T representation. The boundary conditions that we place on the I-V characteristics when calculating the T values impact the resulting T PDF. If the boundaries are insensitive to the plasma fluctuations, then the most probable T value of the PDF (20 eV-25 eV) is similar to the T value obtained via the classical conditional averaging method (20 eV-27 eV). However, if the boundary conditions follow the fluctuations, then the PDF-based method gives a substantially higher most probable T value (35 eV-60 eV). Overall, we show that a fast sweeping RFA diagnostic should be used in intermittent SOL plasmas to reconstruct the PDF for accurate T measurements.
本手稿提出了一种用减速场分析仪（RFA）解释离子温度（T）测量结果的新方法，该方法考虑了托卡马克装置中刮削层（SOL）等离子体的间歇性/湍流性质。对于充分描述由诸如边缘局域模（ELM）和团块等间歇性事件引起的随机波动而言，快速测量和统计方法是很有必要的。我们使用了一种能够以高达10 kHz的频率扫描其电流-电压（I-V）特性的RFA。该RFA使用一个电子补偿级来减去由于有限的连接电缆电容而产生的电容性拾取信号，这大大提高了信噪比。在10 kHz的情况下，能在短时间内获得一条I-V特性曲线，这比ELM周期快一个数量级。快速扫描频率使我们能够重建T概率密度函数（PDF），我们将其用作T的表示形式。在计算T值时，我们对I-V特性施加的边界条件会影响最终得到的T PDF。如果边界对等离子体波动不敏感，那么PDF的最可能T值（20 eV - 25 eV）与通过经典条件平均法获得的T值（20 eV - 27 eV）相似。然而，如果边界条件跟随波动，那么基于PDF的方法会给出一个高得多的最可能T值（35 eV - 60 eV）。总体而言，我们表明在间歇性SOL等离子体中应使用快速扫描RFA诊断方法来重建PDF，以进行准确的T测量。
