High-efficiency fast scintillators for "optical" soft x-ray arrays for laboratory plasma diagnostics

Area of Science:

• Plasma physics
• Fusion energy research
• X-ray detection technology

Background:

• Conventional silicon (Si)-based diode arrays are used in magnetically confined fusion plasma research.
• These arrays are employed for imaging, tomographic reconstruction, magnetohydrodynamics, transport, and turbulence studies.
• There is a need for improved detector technology to enhance plasma diagnostics.

Purpose of the Study:

• To investigate scintillator-based optical soft x-ray (OSXR) arrays as a replacement for Si-based diode arrays.
• To evaluate different scintillator materials and substrates for soft x-ray detection.
• To develop and test a prototype OSXR array for fusion plasma diagnostics.

Main Methods:

• Experimental survey of scintillator candidates measuring soft x-ray to visible light conversion efficiencies.
• Investigation of glass and fiber-optic face-plates (FOPs) as substrates.
• Use of a thin aluminum foil for visible light reflection.
• Design, construction, and testing of a prototype eight-channel OSXR array using CsI:Tl.

Main Results:

• Columnar thallium-doped cesium iodide (CsI:Tl) on an FOP identified as the best scintillator candidate.
• CsI:Tl exhibits a luminescence decay time suitable for required time resolutions (1-10 microseconds).
• The prototype OSXR array showed lower induced noise compared to Si-based arrays during operation on the National Spherical Torus Experiment, particularly during neutral beam injection.

Conclusions:

• Scintillator-based OSXR arrays, specifically using CsI:Tl, are a viable and advantageous alternative to Si-based diode arrays for fusion plasma diagnostics.
• The OSXR technology offers improved performance with lower noise levels.
• The OSXR concept is applicable to both harsh fusion environments and less demanding laboratory plasma spectroscopy.