Crossing geometry for Main Ring on Doubler collisions

A discussion is given of the two basic methods for bringing about Main Ring on Doubler collisions: the transposed and kissing geometries. There are many variations in each case depending on parameters such as the amount of ''prebending'' given each beam by tilting nearby bend magnets. The 50-m length of the straight section is a severe limitation in both methods. In general, the transposed geometry has more flexibility and is better suited for experiments. For example, essentially the full 50 meters can be left free for experiments; this case has no common magnets and could be used with anti p's in the Doubler and protons in the Main Ring, if for some reason the two beams could not be stored in the same ring. Or, the luminosity can be increased by ''squeezing'' the beams to a smaller, even zero, crossing angle with a remaining free space of approximately 8 meters. The transposed case also has the advantage that the interaction point remains fixed, while in the kissing geometry it moves up and down as dictated by the ratio of beam momenta