Experimental Studies on Grooved Surfaces to Suppress Secondary Electron Emission

Grooved surfaces are effective to suppress the secondary electron emission, and can be a promising technique to mitigate the electron cloud effect in positron/proton storage rings. Aiming for the application in a dipole-type magnetic field, various shapes of triangular grooved surfaces have been studied at KEK. The grooves tested here have vertex angles of 20−30°, depths of 2.5−5.0 mm, and vertex roundness of 0.05−0.2 mm. In a laboratory, the secondary electron yields (SEY) of small test pieces were measured using an electron beam in a magnetic-free condition. The grooved surfaces clearly had low SEY compared to flat surfaces of the same materials. The grooves with sharper vertexes had smaller SEY. A test chamber installed in a wiggler magnet of the KEKB positron ring was used to investigate the efficacy of the grooved surface in a strong magnetic field. In the chamber, a remarkable reduction in the electron density around the beam orbit was observed compared to the case of a flat surface with TiN coating.