Impact of GEM foil hole geometry on GEM detector gain A. Karadzhinova, A. Nolvi, R. Veenhof et al.-GEM detectors for WEST and potential application for heavy impurity transport studies D. Mazon, A. Jardin, C. Coston et al.

The measurement system based on gas electron multiplier detector is developed for soft X-ray diagnostics of tokamak plasmas. The multi-channel setup is designed for estimation of the energy and the position distribution of an X-ray source. The focal measuring issue is the charge cluster identification by its value and position estimation. The fast and accurate mode of the serial data acquisition is applied for the dynamic plasma diagnostics. The charge clusters are counted in the space determined by 2D position, charge value, and time intervals. Radiation source characteristics are presented by histograms for a selected range of position, time intervals, and cluster charge values corresponding to the energy spectra.

This paper presents the data acquisition system for GEM-detector (Sauli in Nucl Instrum Methods Phys Res Sect A Accel Spectrom Detect Assoc Equip 386(2–3): 531–534, 1997. https://doi.org/10.1016/S0168-9002(96)01172-2) based cameras and spectrometers (Chernyshova et al. in Fusion Eng Des, 2017. https://doi.org/10.1016/j.fusengdes.2017.03.107). The system is modular (Czarski et al. in Rev Sci Instrum 87(11): 11E336, 2016. https://doi.org/10.1063/1.4961559) and supports 1D and 2D GEM arrays with software-defined readout modes. Channel count can vary from 8 up to hundreds. The readout electronics consists of two units—radiation tolerant Analog Front End and rack-mount data processing unit. Data processing is split into two parts—real-time hardware, based on FPGA and software, based on embedded multicore CPUs and hardware accelerators. The FPGA subsystem together with PCIe interface and multi-core Xeon processors forms low latency, high-performance processing chain suitable for applications requiring feedback. The detectors in tokamaks operate in the high magnetic field, so the system was equipped with multipoint magnetic field measurement synchronized with detector readout. The system also includes custom HV supply, developed for triple GEM detectors operating in the high-rate mode. Dedicated protection and diagnostic subsystems were developed as well to ensure safe and reliable operation of the detector in harsh conditions. To support the operation of the detector in the high-temperature surrounding, the liquid cooling subsystem was developed (Wojenski et al. in J Instrum 11(11): C11035, 2016).