Effects of vertical misalignment of superconducting coils in cyclotrons

A vertical beam loss on the extraction elements of the K500 cyclotron has been observed during commissioning of the Coupled Cyclotron Project. The cause was found to be the misalignment of coils, and the coil shift vertically about 1 mm made a correction. The vertical displacement of a 9.5 MeV/u Ar beam prior to the correction was roughly 4 mm at a magnetic focusing bar. The effect of coil misalignment seems to be pronounced during beam extraction because the gradient of coil field is high in the extraction region and the magnetic elements employed for radial focusing are misaligned with the coil field. The observed off-center of the Ar beam could also be partly explained by a coherent beam oscillation prior to the extraction if assuming the coil was tilted as the vertical focusing tune approaches one. Balancing of the electromagnetic forces on the coil support links is a usual method of alignment for superconducting coils. In reality a fine adjustment of the coil position may be needed with a beam because readings of the forces on the links could be imprecise indication of the coil position as the coil is supported by the matrix of support links. The coil alignment issue is discussed also for a superconducting separated-sector cyclotron.