Ionisation Efficiency in Conical Hot Cavities

Surface ionisation in a new type of hot cavity characterised by the shape of a truncated cone is considered in the paper. Influence of the hot cavity shape and its temperature on the ionisation efficiency of stable and long-lived nuclides is under investigation and the supremacy of elongated conical cavities is proven. The role of the extraction opening size is studied and its optimal diameter ( ≈ 1 mm) is found for the considered cavity shapes. It is shown that the extraction voltages of 1-2 kV are large enough to obtain high efficiencies and saturation of the current-voltage curves is observed above these values. Changes of ionisation effciency with the ioniser temperature are investigated - increase of ion yield with T is observed. It was proven that cold spots inside the ioniser cavity (near the extraction opening - in the considered case) can degrade ion source performance by several tens percent.