This monograph is concerned with the study of nuclear and nucleon structure through the scattering of high energy electrons. The history of this field is well summarized in the proceedings of the Conference on 35 Years of Electron Scattering held at the University of Illinois in 1986 to commemorate the 1951 experiment of Lyman, Hanson, and Scott; this experiment provided the first observation of the finite size of the nucleus by electron scattering [Ly51, Il87]. Hofstadter and his colleagues, working in the High Energy Physics Laboratory (HEPL) at Stanford University in the late 1950's, beautifully and systematically exhibited the shape of the charge distributions of nuclei and nucleons through experiments at higher momentum transfer [Ho56, Ho63]. Subsequent experimental work at HEPL, the Bates Laboratory at M.I.T., Saclay in France, NIKHEF in Holland, and both Darmstadt and Mainz in Germany (as well as other laboratories), utilizing parallel theoretical analysis [Gu34, Sc54, Al56, de66, Ub71], clearly exhibited more detailed aspects of nuclear structure. Experiments at higher electron energies and momentum transfers at the Stanford Linear Accelerator Center (SLAC) by Friedman, Kendall, and Taylor, together with theoretical developments by Bjorken, for the first time demonstrated the pointlike quark–parton substructure of nucleons and nuclei [Bj69, Fr72]. This work played a key role in the development of modern theories of the strong interaction. Major efforts today at CEBAF, the Continuous Electron Beam Accelerator Facility (now known as TJNAF, the Thomas Jefferson National Accelerator Facility) in the U.S., Bates, Mainz, SLAC, DESY in Germany, and CERN in Geneva (using muons) contribute to the development of our understanding of nuclei and nucleons.

Quite dramatic progress has been made in the production and utilization of polarized e± beams at CERN's LEP, at HERA at DESY and at the Stanford linear collider SLC. The motivation for trying to overcome the tremendous technical problems involved derives from two sources:

1. (i) the realization that longitudinally polarized electrons permit extremely accurate measurement of the fundamental parameters of the Standard Model of electroweak interactions;

2. (ii) the discovery in 1987, by the European Muon Collaboration (Ashman et al., 1988), that only a very small fraction of the proton's spin appeared to be carried by its quarks, leading to what was characterized as a ‘crisis in the parton model’ (Leader and Anselmino, 1988). This made it important to carry out further studies of deep inelastic lepton–hadron scattering using longitudinally polarized leptons colliding with a longitudinally polarized proton target.

Though not a primary impetus, it turns out also that polarized e± permit an exceedingly accurate calibration of the beam energy at LEP and HERA.

The problems involved in having stable polarized beams are quite different in circular storage rings and in linear accelerators. Hence we shall discuss the two cases separately.

The natural polarization of electrons circulating in a perfect storage ring

As mentioned in the introduction to Chapter 6, in principle a circulating electron beam gradually acquires a natural polarization in which its magnetic moment μe becomes aligned parallel to the guide field B.