We have applied a scanning Auger electron microscope to measure secondary electron coefficients (δ) of the niobium plate used for the superconducting RF cavities in TRISTAN Main Ring. The secondary electron emission from the superconducting RF cavities plays a crucial role in determining the maximum accelerating fields.
Surface morphology, exposure to the air, and surface treatments influence greatly on the electron emission from the niobium surfaces. In particular, ultrasonic rinsing in H₂O₂ after electropolishing and surface smoothing of the niobium plate to eliminate scratches has been shown to be very effective in suppressing the electron emission from the niobium surfaces.