Conceptual design and development of GEM based detecting system for tomographic tungsten focused transport monitoring

Abstract

Implementing tungsten as a plasma facing material in ITER and future fusion reactors will require effective monitoring of not just its level in the plasma but also its distribution. That can be successfully achieved using detectors based on Gas Electron Multiplier (GEM) technology. This work presents the conceptual design of the detecting unit for poloidal tomography to be tested at the WEST project tokamak. The current stage of the development is discussed covering aspects which include detector's spatial dimensions, gas mixtures, window materials and arrangements inside and outside the tokamak ports, details of detector's structure itself and details of the detecting module electronics. It is expected that the detecting unit under development, when implemented, will add to the safe operation of tokamak bringing the creation of sustainable nuclear fusion reactors a step closer.

Parallel computing in soft X‐rays plasma diagnostic systems for thermal fusion reactors—feasibility studies for GPUs

“…The objective of the plasma impurities diagnostic is to convert photons originating from plasma metallic content into a sampled electric signal and to digitally process it to obtain information on the time, energy, and location of the radiation. In a dedicated signal converter and amplifier called the gaseous electron multiplier (GEM), photons are converted as electron clouds , observed as a collection of electric impulses . The occurrences of the impulses , called events , are aggregated as valid data for further processing.…”

“…It is dedicated to low‐latency measurements of soft X‐rays to investigate impurities in plasma. The device provides output signals allowing tomographic reconstruction of spatial radiation distribution . It acquires data at high rates and reduces their throughput at runtime.…”

“…Among them, there is a measurement of soft X‐rays in the spectral range corresponding to the metallic impurities emission. Controlling the impurities is extremely important to increase a reaction efficiency and to provide a safe mode of operation . Without such control, metallic particles can accumulate and cause disruptions damaging the reactor …”

“…A heterogeneous field‐programmable gate array (FPGA) and server‐based architecture was proposed for impurities diagnostic . Positive results were achieved with Intel Xeon CPUs and Intel Xeon Phi coprocessors in handling intensive computations .…”

Tomographic capabilities of the new GEM based SXR diagnostic of WEST

“…The WEST SXR diagnostic will be equipped with two new Gas Electron Multiplier (GEM) based poloidal cameras with a total of ~ 200 pixels, including 50 µm thick Beryllium windows that cut off SXR spectrum below 1 -2 keV. They will work in "photon-counting mode" [7,8] in contrast with former silicon barrier diodes working in "current mode". Thus the system will perform 2D tomographic reconstructions with spectral resolution in tunable energy bands.…”