Double-double bend achromat cell upgrade at the Diamond Light Source: From design to commissioning

Diamond has recently successfully commissioned a major change in the lattice consisting of the substitution of a standard double-bend achromat (DBA) cell with a modified four-bend achromat (4BA) cell called ``double-double bend achromat'' (DDBA). This work stems from the original studies initiated in 2012 towards a Diamond upgrade and provides the benefit of an additional straight section in the ring available for insertion devices. This paper reviews the DDBA design and layout, the implications for technical subsystems, the associated engineering challenges and the main results of the commissioning completed in April 2017.