Upgraded electron ring design for the electron - nucleus collider ( ELISe ) *

The conceptual design of the Electron-Ion Collider (EAR) is described in [1]. In order to fulfil the demanding requirements, especially for fission experiments at ELISe, the interaction zone (IZ) at the intersection of the EAR with the bypass section of the NESR has to be optimized. Nevertheless the already defined base parameters should remain unchanged: the working point νx = 4.2, νy = 3.2; the beta-functions at the IZ; βx*= 100 cm, βy*= 15 cm; and the emittances εx,z= 4⋅10 cm⋅rad. A variety of other lattice options is in principle available, due to the flexible arcs optics. The maximum for the β-functions is increased up to 45 m, in order to restore problems with nonlinear dynamics and dynamic aperture (DA). A chromaticity correction of the betatron tunes and other investigations addressing chromatic aspects, together with a simple DA estimation were discussed previously [2]. This work concentrates on working out a routine procedure for chromaticity compensation with simultaneous DA optimization. The idea of the DA enlargement, chromaticity compensation through sextupole lenses is the following [3], [4]: (i) the initial vector of natural chromaticity (ξx, ξy) is divided into small portions. (ii) Each portion is compensated with a single pair out of the sextupole families (SXi, SYj) that gives the largest DA for this step. (iii) Finally the chromaticity is compensated with a DA being optimized simultaneously. Let's call this procedure "best pairs method". The DA was estimated through track calculations using the SAD code [5]. With 10 "independent" chromatic sextupoles available, one can find 45 different combinations. For each pair at each step of the chromaticity compensation the DA is calculated. The number of chromaticity compensation steps should be at least close to the number of possible combinations [3]. As far as the DA is affected not only by sextupole fields but also by the fringe fields of the quads, the latter were switched on during DA optimization. That helps, for example, to suppress the tune-amplitude dependence, generated by fringes.