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The spatial distributions of the density, temperature and effective charge of the particles in a fusion plasma are important parameters. One of the main diagnostics for such investigations are pinhole cameras with semiconductor diodes looking at the radiation in the soft X-ray spectral range. The spectral efficiency of the detectors should be well known. The efficiency can be calculated by means of the absorption cross-sections of the semiconductor, in this case silicon, and the metallic dead layers of the diodes. Previously, the sensitive thickness of diodes which are not fully depleted, because the electric field does not extend over the whole thickness, was calculated with Poisson's equation. Investigations showed that also at low bias voltages the physical thickness seems to be the active thickness. This may be explained by charge diffusion.
This report presents experimental investigations of the efficiency of three different types of silicon diodes, namely a surface barrier diode which is used in the Wendelstein 7-AS experiment, an ion-implanted diode which is used in ASDEX Upgrade and an ion-implanted diode which is used for Thomson scattering experiments. The source of radiation is a filtered X-ray tube, the energy ranging from 1.5 keV to about 20 keV. Additional investigations of the sensitivity for visible light are made for five different types of diodes.

Additional information

Authors: FUCHS C, Max-Planck-Institut für Plasmaphysik, Garching bei München (DE)
Bibliographic Reference: Report: IPP 1/292 DE (1995) 91pp.
Availability: Available from Max-Planck-Institut für Plasmaphysik, 85748 Garching bei München (DE)
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