U3DS, a Compact Mass-Analyzer for Large High Current-Density Ribbon Ion Beams

摘要

A very compact analyzer, named U3DS, with a resolving power of around 30 is described, for delivering mass-analyzed ribbon ion beams from the ion source through a resolving slit to a substrate. The distance from ion source to substrate may be less than the breadth of the beam and of the substrate, for example about 1 meter, for a ribbon beam with a breadth of 2.2m or more. The simple apparatus comprises a long yoke spanning the ion beam breadth, i.e. the large dimension, with a U-shaped cross section. There is no component of magnetic field along the beam breadth dimension, which as a result may be extremely large without increasing the number of ampere turns required. The trajectories of the ions in this field have the form of 3-dimensional S-shapes. The benefits can be summarized: Increasing the breadth of the beam requires the same number of ampere-turns, but the apparatus gets larger only in linear proportion to the beam breadth. Net deflection is linearly proportional to 1/mass. Focal length is short, so the equipment is compact. High fields up to ~ 1 Tesla can be used in spite of the large beam dimensions, and this carries subtle benefits for high beam current densities - the current which can be stably transmitted is far higher. In contrast, the power and the weight of a conventional magnet increase with the square of the beam breadth, or even worse, while the deflection is only proportional to the square root of 1/mass. All scaling effects of the new analyzer are highly favorable for very large beams.