Beam modelling and hardware design of an imaging heavy ion beam probe for ASDEX Upgrade

The imaging heavy ion beam probe (i-HIBP) developed at the ASDEX Upgrade tokamak is a new diagnostic concept for investigations at the edge of high temperature plasmas. By means of a heavy alkali beam injector, a neutral primary beam of an energy of 70 keV is injected into the fusion plasma, where it is ionized generating a fan of secondary beams. These are deflected by the magnetic field of the tokamak and intersect a scintillator plate in the limiter shadow of the tokamak. The light pattern on the scintillator detected with a high speed camera contains radial information on the density, electrostatic potential and the magnetic field in the edge region of the plasma. For the design of the i-HIBP, a detailed beam model including the 3D tokamak magnetic field and beam attenuation effects for cesium and rubidium atoms is developed in order to find the optimum injection scheme within the limited space of the tokamak environment for maximum signal intensities. Based on the optimized injection, the arrangement of the injector outside the vacuum-vessel and the detailed design of the optical in-vessel system is determined.Helmholtz Association grant no. VH-NG-135

Characterization of scintillator screens under irradiation of low energy 133Cs ions

An imaging heavy ion beam probe (i-HIBP) diagnostic, for the simultaneous measurement of plasma density, magnetic field and electrostatic potential in the plasma edge, has been installed at ASDEX Upgrade. Unlike standard heavy ion beam probes, in the i-HIBP the probing (heavy) ions are collected by a scintillator detector, creating a light pattern or strike-line, which is then imaged by a camera. Therefore, a good characterization of the scintillator response is needed. Previous works focused on the scintillator behaviour against irradiation with light ions such as hydrogen and alpha particles. In this work we present the characterization of several scintillator screens — TG-Green (SrGa2S4:Eu2+), YAG-Ce (Y3Al5O12:Ce3+) and P11 (ZnS:Ag) — against irradiation with 133Cs+ ions, in an energy range between 5 and 70 keV and ion currents between 105 and 107ions/(s·cm2). Three main properties of the scintillators have been studied: the ionolumenescence efficiency or yield, the linearity and the degradation as a function of the fluence. The highest yield was delivered by the TG-Green scintillator screen with > 8·103 photons/ion at 50 keV. All the samples showed a linear response with increasing incident ion flux. The degradation was quantified in terms of the fluence F1/2, which leads to a reduction of the emissivity by a factor of 2. TG-Green showed the lowest degradation with F1/2= 5.4·1014ions/cm2. After the irradiation the samples were analyzed by Scanning Electron Microscopy (SEM), Rutherford Backscattering Spectrometry (RBS) and Particle Induced X-ray Emission (PIXE). No trace of Cs was found in the irradiated regions. These results indicate that, among the tested materials, TG-Green is the best candidate for the i-HIBP detector.European Union’s Horizon 2020 (grant agreement No. 805162)Helmholtz Association VHNG-1350Spanish Ministry of Science and Innovation FJC2019-041092-I

Characterization of scintillator screens under irradiation of low energy 133Cs ions

An imaging heavy ion beam probe (i-HIBP) diagnostic, for the simultaneous measurement of plasma density, magnetic field and electrostatic potential in the plasma edge, has been installed at ASDEX Upgrade. Unlike standard heavy ion beam probes, in the i-HIBP the probing (heavy) ions are collected by a scintillator detector, creating a light pattern or strike-line, which is then imaged by a camera. Therefore, a good characterization of the scintillator response is needed. Previous works focused on the scintillator behaviour against irradiation with light ions such as hydrogen and alpha particles. In this work we present the characterization of several scintillator screens - TG-Green (SrGa2S4:Eu2+), YAG-Ce (Y3Al5O12:Ce3+) and P11 (ZnS:Ag) - against irradiation with 133Cs+ ions, in an energy range between 5 and 70 keV and ion currents between 105 and 107 ions/(s·cm2). Three main properties of the scintillators have been studied: the ionolumenescence efficiency or yield, the linearity and the degradation as a function of the fluence. The highest yield was delivered by the TG-Green scintillator screen with > 8·103 photons/ion at 50 keV. All the samples showed a linear response with increasing incident ion flux. The degradation was quantified in terms of the fluence F1/2, which leads to a reduction of the emissivity by a factor of 2. TG-Green showed the lowest degradation with F1/2= 5.4·1014 ions/cm2. After the irradiation the samples were analyzed by Scanning Electron Microscopy (SEM), Rutherford Backscattering Spectrometry (RBS) and Particle Induced X-ray Emission (PIXE). No trace of Cs was found in the irradiated regions. These results indicate that, among the tested materials, TG-Green is the best candidate for the i-HIBP detector.This work received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 805162). G. Birkenmeier acknowledges funding from the Helmholtz Association under grant no. VHNG-1350. J. Galdon-Quiroga acknowledges funding from the Spanish Ministry of Science and Innovation under grant no. FJC2019-041092-I