Phosphor screens are used in many applications to convert incident radiation to visible wavelengths that can be readily measured by modern detectors. For many such systems it is necessary to tailor the phosphor screen thickness to the wavelength range of interest in order to maximize the efficiency. Here, we describe the experiments made to determine the luminescent efficiency of thin Y3Al5O12:Ce (P-46) phosphor screens (1–22 mg cm−2) in the vacuum ultraviolet and x-ray ranges. We use current and previous measurements to obtain fitting parameters for a granular unidimensional radiation transfer model developed. In the model, we take into account the effects of scattering and absorption of the luminescent light emitted and we discuss the effects of grain size and shape on the model. Finally, we find that a screen thickness of ∼1.7 mg cm−2 is optimum for incident radiation between 1.2 and 124 nm but this thickness becomes wavelength dependent at shorter wavelengths (0.025–1.2 nm).

We outline designs for several rare-earth-based phosphor powder detector systems for monitoring the broadband VUV plasma radiation in the TJ-II torsatron device. These include a global radiation detector, a detector with temporal and spectral resolution, and a third with radial scanning capabilities. We describe the selection of a phosphor powder for this application having good response from the soft x ray to the VUV, a fast response time, and the capability of operation at high temperatures. In addition, we give details of a method developed in-house for depositing thin uniform layers of powder on glass substrates for use as phosphor screens. Finally, we present some detector test results obtained in the plasma of the TJ-I U torsatron.

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