 This may be accomplished using either dipole electrostatic or dipole magnetic fields, but because most storage rings store relativistic charged particles it turns out that it is most practical to utilise magnetic fields produced by dipole magnets.However, electrostatic accelerators have been built to store very low energy particles, and quadrupole fields may be used to store (uncharged) neutrons; these are comparatively rare, however.Dipole magnets alone only provide what is called weak focusing, and a storage ring composed of only these sorts of magnetic elements results in the particles having a relatively large beam size.