Measurements and characteristics of $\hbox {Al}_{2}\hbox {O}_{3}{:}\hbox {Cr}^{3+}$ coating for the proton beam imaging system

Abstract

Introduction

To set up an online proton beam diagnostic system near the neutron production target of China Spallation Neutron Source (CSNS), a luminescence coating sprayed on the target window and a corresponding optic system were fabricated. In the work, the fabrication of $\hbox {Al}_{2}\hbox {O}_{3}{:}\hbox {Cr}^{3+}$ coating was explored. Measurements on the sprayed samples were performed to analyze the characteristics of the $\hbox {Al}_{2}\hbox {O}_{3}{:}\hbox {Cr}^{3+}$ coating.

Fabrication and tests of coating samples

Three kinds of powders with different Cr concentrations were used to fabricate the luminescence coating samples. The flame spraying, plasma spraying and D-gun spraying processes were explored. Photoluminescence (PL), X-ray diffraction (XRD), scanned electron mirror (SEM) and radioluminescence experiment by 300 MeV deuterium beam were carried out to analyze and characterize the samples.

Results

The emission spectrum excited by 532-nm laser has two obvious peaks at 692.9 nm and 694.3 nm. The samples by flame spraying process with the powders obtained from melting method show higher luminescence intensity than the samples by plasma spraying process. It is observed that the luminescence intensity has some relationships with the alpha phase in the samples, which is deduced from the XRD and photoluminescence tests results. A lower temperature during the flame spraying process will help to keep more alpha phase in the material. The selected four samples show successful fluoresced results in the radioluminescence experiment.

Conclusions

The luminescence intensity of the coating is improved greatly by the studies on the fabrication process and the characteristics of the samples. The luminescence coating used in beam diagnostics will be fabricated by the confirmed technical process. More works will be continued to improve the characteristics of the luminescence light by controlling Cr concentration and annealing in $1200\sim 2000\,{^\circ {\hbox {C}}}$ environment in the future.