Dunai D, Zoletnik S, Sárközi J, Field A R
KFKI Research Institute for Particle and Nuclear Physics, EURATOM Association, P.O. Box 49, H-1525 Budapest, Hungary.
Rev Sci Instrum. 2010 Oct;81(10):103503. doi: 10.1063/1.3488458.
An avalanche photodiode based (APD) detector for the visible wavelength range was developed for low light level, high frequency beam emission spectroscopy (BES) experiments in fusion plasmas. This solid state detector has higher quantum efficiency than photomultiplier tubes, and unlike normal photodiodes, it has internal gain. This paper describes the developed detector as well as the noise model of the electronic circuit. By understanding the noise sources and the amplification process, the optimal amplifier and APD reverse voltage setting can be determined, where the signal-to-noise ratio is the highest for a given photon flux. The calculations are compared to the absolute calibration results of the implemented circuit. It was found that for a certain photon flux range, relevant for BES measurements (≈10(8)-10(10) photons/s), the new detector is superior to both photomultipliers and photodiodes, although it does not require cryogenic cooling of any component. The position of this photon flux window sensitively depends on the parameters of the actual experimental implementation (desired bandwidth, detector size, etc.) Several detector units based on these developments have been built and installed in various tokamaks. Some illustrative results are presented from the 8-channel trial BES system installed at Mega-Ampere Spherical Tokamak (MAST) and the 16-channel BES system installed at the Torus Experiment for Technology Oriented Research (TEXTOR).
为了在聚变等离子体中进行低光水平、高频束发射光谱（BES）实验，开发了一种基于雪崩光电二极管（APD）的可见波长范围探测器。这种固态探测器比光电倍增管具有更高的量子效率，并且与普通光电二极管不同，它具有内部增益。本文描述了所开发的探测器以及电子电路的噪声模型。通过了解噪声源和放大过程，可以确定最佳放大器和APD反向电压设置，在给定光子通量下信噪比最高。将计算结果与所实现电路的绝对校准结果进行比较。结果发现，对于与BES测量相关的特定光子通量范围（≈10⁸ - 10¹⁰ 光子/秒），新探测器优于光电倍增管和光电二极管，尽管它不需要对任何组件进行低温冷却。这个光子通量窗口的位置敏感地取决于实际实验实施的参数（所需带宽、探测器尺寸等）。基于这些进展已经制造了几个探测器单元，并安装在各种托卡马克装置中。给出了安装在兆安球形托卡马克（MAST）上的8通道试验BES系统和安装在面向技术研究的环形实验（TEXTOR）上的16通道BES系统的一些说明性结果。
