For the mitigation of the electron cloud effect (ECE), which will be a serious problem in high-intensity positron/proton ring, we used a commercial method called “thermal spraying,” (by which copper powder is melted and sprayed onto an aluminum substrate) to create a rough surface with a low secondary electron yield (SEY) on the inner wall of the beam pipes, and investigated its suitability for accelerators.
First, to the copper thermal spray (T.S.)-coated small samples, we measured the following key properties of T.S. coating: SEY profile, roughness parameters, surface composition, outgassing rate, adhesive strength, impedance, and dust generation rate.
Next, an aluminum beam pipe with an optimized T.S. coating was produced and installed in the positron ring (LER) of SuperKEKB. We measured the electron density in the beam pipe, and tried to interpret the behavior of this electron density data via simulations.
The lowest δmax (the maximum SEY within the scanning range) of the T.S. coating reached ～0.7 after conditioning. The measured electron densities of the T.S.-coated beam pipe were comparable with those of the TiN-coated beam pipe. Thus, the T.S. coating can be considered a candidate technology for reducing ECE, though room for improvement remains, such as relatively high levels of dust and impedance.