Research on Rotatable Radiation Conversion Target Used in High-energy Microfocus Industrial CT

The radiation conversion target with high conversion efficiency and excellent heat dissipation performance is the key component of highenergy microfocus industrial CT. In order to produce highflux, microfocus Xrays via bremsstrahlung, very high beam power will be deposited in a small area on this conversion target. For the static conversion target used in the common industrial CT, there is a great chance that this target will be melted under the hitting of high energy and high average current beams. Therefore, an advanced rotatable radiation conversion target suitable for highenergy (6 MeV) microfocus (with diameter of 100 μm) industrial CT was designed to settle this bottleneck problem in this paper. By simulating and analyzing the Xray conversion efficiency and residual electron beam energy, the optimal thickness of the conversion target was determined, which is 3 mm. Further thermal analysis shows that, under the operation condition of electron beams (with electron beam energy of 6 MeV, macro pulse length of 5 ms, macro pulse current of 1.5 mA and focal spot diameter of 100 μm), static target will be melted after few macro pulses. Using a rotatable radiation conversion target with 2 000 r/min, the transient temperature rise is only 137° for one macro pulse, and the steady state temperature is 197°, which is much lower than the melting point of tungsten material. Based on these simulation results, a rotatable radiation conversion target was designed and fabricated. In addition, a special design of insitu ultrasmall beam size measurement system was realized in this conversion target system, which is mainly composed of a retractable ultrathin YAG screen and a 45° reflecting mirror. Finally, the rotatable radiation conversion target was successfully installed and applied to the highenergy microfocus industry CT verification device of the Institute of Applied Electronics, China Academy of Engineering Physics. In beam experiment, the rotating target can indeed withstand the bombardment of the electron beam under operation condition of electron beams, thus verifying the effectiveness and reliability of the rotating radiation conversion target. In comparison, the static conversion target without rotating milts within ten minutes. The actual performance of the rotating radiation conversion is further proved by the proofofprinciple experiment of highenergy microfocus Xray CT, where a 5 lp/mm linepair is clearly distinguished. These results demonstrate the feasibilities of the rotating radiation conversion target.