Scintillator-based optical soft x-ray (OSXR) arrays may in the near future, replace the conventional diode arrays used for plasma imaging, tomographic reconstruction, magnetohydrodynamics, transport and turbulence studies in magnetically confined fusion plasma research. We have performed an experimental survey among eight scintillator candidates, measuring relative and absolute soft x-ray to visible light conversion efficiencies (CE). Further investigations, took into account glass and fiberoptic plates (FOP) as substrates, and a thin aluminum foil (150 nm) needed to reflect back to the optical detector the visible light emitted by the scintillator. We have concluded that columnar (crystal growth) thallium doped cesium iodine (CsI:Tl) deposited on a FOP, is the best candidate for the above mentioned plasma diagnostics. Its luminescence decay time (of the order of 2-8 ?s) measured at the Current Drive Experiment Upgrade (CDX-U) and the National Spherical Torus Experiment (NSTX) at the Princeton Plasma Physics Laboratory (PPPL), was also found to be suitable for our needs and the development of OSXR arrays. A first eight channel OSXR array based on using CsI:Tl was designed, built and compared to its diode counterpart; its operation on NSTX showed a lower level of neutron-induced noise during neutral beam heated plasma discharges.
Citation: Nuclear Instruments & Methods
Pub Type: Journals
detector arrays, plasma diagnostics, scintillators, soft x-rays