 This can cause instabilities along a bunch train and even instabilities within a single bunch, which are known as head-tail instabilities.A few remedies have been proposed to deal with this, such as putting ridges in the accelerator tube, adding antechambers to the tube, coating the tube to reduce the yield of electrons from the surface, or creating an electric field to pull in stray electrons.At the PEP-II accelerator at SLAC National Accelerator Laboratory, the vacuum pipe which contains the positron ring has a wire coiled around its entire length.