Algorithms to get a circulating beam

Abstract

Two algorithms based of trajectory fitting have been used to obtain rapidly a circulating beam in LEP with strong focusing lattices.A new algorithm called "orbit closure" uses the beam positions measured at the first and the second turn. From their difference, it computes two corrector strengths per plane such that the second turn passes at the same place as the first turn at about ten BPM locations. This produces a closed orbit amplitude with an r.m.s. value close to that of the first turn trajectory.A new 'first turn threader' has been tried. It detects places where an oscillation with an r.m.s. amplitude larger than a specified value starts, and computes two corrector strengths to cancel it. By iterating this process, it should be possible to correct by steps the first turn trajectory so that its r.m.s. amplitude is below a specified value.The orbit closure has been applied with success to a very low emittance lattice (135 in the horizontal plane) in LEP.

Low emittance lattice for LEP

“…value was between 3 and 2mm. Then the orbit closure algorithm [5] was applied and a circulating beam was obtained after having applied it iteratively and having made a systematic horizontal tune-shift of about +0.2 in order to compensate for the anharmonic effects. Another experiment devoted to accumulate more current had various troubles and only 59A were stored with the damping wigglers on.…”