Spontaneous polarisation of beams

1
Spontaneous polarisation of beams
Compton back-scatter laser beam off circulating
e or e-. Get asymmetry which measures
polarisation. Why should beams be
polarised? Sokolov-Ternov effect (Doklady
8(1964) 1203 one of many fundamental
Russian contributions to accelerator theory).
Electron energy is less if mag. moment aligned
with B. Synchrotron radiation allows slow
transition to lower state. Ideal machine would
build up to 100 polarisation. Actual machine
has lots of perturbing B-fields (e.g. focussing
quadrupoles) not parallel to bending field. If
incoherent, limit peak polarisation. If
coherent, can resonate turn-after -turn with
precession of spins around main B direction.
Depolarises beam.