Local Dispersion Insert: A Novel Focusing Element for Accelerators

The Local Dispersion Insert is a novel three-quadrupole cell which produces local dispersion and beta waves while leaving all other beam parameters (in particular, the tunes) unchanged. The obtained local dispersion wave can be effectively used to control the transition energy and the so-called ${\gamma }_T$ jump of an accelerator. Since the desired ${\gamma }_T$ jump can be obtained by locally decreasing the dispersion, the well-known problems which accompany the conventional ${\gamma }_T$ jump schemes, in particular large maximal dispersion, are absent. As an example we show how the Local Dispersion Insert changes the transition energy in the Main Injector at Fermi National Accelerator Laboratory.