One type of tapered plant that is easy to treat theoretically, which has minimum interstage flow for a specified separation, and which is approximated by all isotope separation plants designed for minimum cost, is the so-called ideal cascade. An ideal cascade is one in which

1. The heads separation factor (1 is constant.

2. The heads stream and tails stream fed to each stage have the same composition:

хі+і=Уі-=2і (і = 2, 3, …,л —1)

The theory of such cascades was developed by P. A. M. Dirac and R. Peierls in England and by

K. Cohen and I. Kaplan in the United States and is described in The Theory of Isotope Separation by Cohen [C3]. The most important results are summarized in Secs. 8 through 12 of this chapter, with some changes in terminology and notation.