Kerst, D.W.; Cole, F.T.; Crane, H.R.; Jones, L.W.; Laslett, L.J.; Ohkawa, T.; Sessler, A.M.; Symon, K.R.; Terwilliger, K.M.; Nilsen, N.V.; Attainment of Very High Energy by Means of Intersecting Beams of Particles
Phys. Rev. 102 (1956) 590;
Reprinted in The Physical Review - the First Hundred Years, AIP Press (1995) CD-ROM.
In planning accelerators of higher and higher energy, it is well appreciated that the energy which will be available for interactions in the center-of-mass coordinate system will increase only as the square root of the energy of the accelerator. The possibility of producing interactions in stationary coordinates by directing beams against each other has often been considered, but the intensities of beams so far available have made the idea impractical. Fixed-field alternating-gradient accelerators
offer the possibility of obtaining sufficiently intense beams so that it may now be reasonable to reconsider directing two beams of approximately equal energy at each other. In this circumstance, two 21.6 BeV accelerators are equivalent to one machine of 1000 BeV. (Extracted from introductory part of the paper.).
Related references See also K. R. Simon, Phys. Rev. 98 (1955) 1152A1;
D. W. Kerst et al., Phys. Rev. 98 (1955) 1153A3;
K. M. Terwilliger et al., Phys. Rev. 98 (1955) 1153A2;
L. W. Jones et al., Phys. Rev. 98 (1955) 1153A1;
First realistic proposal for probing high energies by colliding beams of particles.