ION-MATRIX SHEATH IN A CYLINDRICAL BORE

The potential structure, electric field, and sheath width for the ion- matrix sheath in a cylindrical bore are calculated. The appropriate sc aling length for this problem is found to be square-root 2 times large r than the planar ion matrix sheath width. If the radius of the bore i s less than this scaling length, then the sheaths from ''opposite'' si des of the bore overlap, and the potential drop from the axis to the s idewalls decreases with the square of the bore radius. This limits the maximum energy of ions impacting the target. For bores larger than th is scaling length, the asymptotic planar solutions are rapidly approac hed.