Depolarisation in large electron storage rings

It is shown from elementary considerations that polarised beams of electrons or positrons are unlikely to be obtained in storage rings much above about 30 GeV in top energy. Normal design criteria in such machines result in large energy spreads which straddle depolarising resonances. The requirement that such resonances be weak enough as not to cause substantial depolarisation, imposes control of vertical closed-orbit errors and beam size beyond that which is currently believed to be feasible. (11 refs).