A comprehensive study is under way to define the best configuration for a next generation, world class neutron source, ISIS II. The design is being lead by users, in consultation with target and neutronic experts as well as accelerator physicists. Accelerator studies include the possibility of using novel FFA (fixed field alternating gradient) accelerator technology, as well as more conventional RCS (rapid cycling synchrotron) and AR (accumulator ring) designs [1]. The present baseline specification is to supply 1.25 MW proton beam at 1.2 GeV, split between 1 MW, 40 Hz target and 0.25 MW, 10 Hz target.

The synchrotron group is leading the work on the latter, conventional designs [2]. Whilst the RCS and AR rings are conventional, the demands for the design stretch key parameters beyond current state of the art. In addition, desire to reduce costs and optimise beam properties, is driving studies to achieve lower loss and thus improve understanding of high intensity beams.

The project requires designs of a number of machine options, to allow detailed comparison and identification of the best choice. This includes design of an RCS and AR that is constrained to fit in the existing ISIS Hall (thus reducing cost), and also a relatively unconstrained “green field” design.

The main parameters, lattice and layout of the present working design for the RCS that fits in the ISIS hall are shown in Table 1 and Figure 1. Further details may be found in [1, 2 refs].

Figure 1: Schematic Layout of ISIS II RCS (left) and sector lattice (right)

Main areas of work required for the designs are: lattice optimisation, longitudinal dynamics, transverse dynamics studies, 3D dynamics simulation and optimisation, injection straight design, foil optimisation, collimation design, extraction and assessment of dominant losses due to instabilities and space charge. Further details on the R&D that underpins much of this work are outlined in the Accelerator Physics R&D section.

[1] J B Lagrange et al, Progress on Design Studies for the ISIS II Upgrade, http://jacow.org/ipac2019/papers/tupts068.pdf

[2] C M Warsop et al, Studies for Major ISIS Upgrades via Conventional RCS and Accumulators Ring Designs http://jacow.org/ipac2018/papers/tupal058.pdf