Simulation of difference between beam sizes in the present-day ALS vs. the much smaller one in ALS-U, together with representations of their storage-ring magnet lattices.

The electron beam’s horizontal size will be smaller in the ALS-U (top right) compared to the ALS (top left) as a result of replacing the present three-bend achromat sector (bottom left) with a nine-bend achromat (bottom right). The bend magnets are the blue objects.

As we collectively explored possibilities for upgrading the ALS to support forefront user science for decades, achieving the desired reduction in electron-beam emittance while fitting the machine into the existing, limited space was challenging. This challenge called for a collaborative effort, where we brought our unique skills and perspectives to the table, adapting novel ideas, applying accelerator physics modeling and theory skills, and pushing the limits of today’s accelerator technologies.

While most of the multi-bend achromat designs used in the latest generation of light sources employ up to seven bends per sector, we adopted a non-conventional, highly nonlinear design. We fine-tuned this design by deploying advanced numerical optimization methods, which our group was among the first to apply to lattice design.

Diagrams show differences in accelerator layout between ALS and ALS-U

Among many other changes, the ALS-U Project will replace the storage ring and add an accumulator/damping ring (mounted on the shielding wall).

Considerable effort has gone into ensuring that the collective effects—some enhanced mainly by the new machine and beam characteristics—could be controlled. We built a detailed beam impedance model for both the ALS-U rings, characterized the potential instabilities, helped to develop a new design for the higher-harmonic rf cavity (HHCs) system (leveraging the R&D carried out by the Berkeley Accelerator Controls and Instrumentation Program). These efforts advanced the existing theory of beam dynamics in the presence of HHCs (described in two recent papers).

With the physics design recently completed, work is now gearing up in preparation for commissioning.