Dear ALS community,
Within the portfolio of U.S. light sources, the Advanced Light Source (ALS) is optimized to serve the soft x-ray community with high-brightness photon beams. In addition to this core mission, the ALS serves a broad and diverse user community spanning infrared to hard x-rays.
The ALS Upgrade (ALS-U) Project will dramatically increase the soft x-ray brightness and coherent flux of the ALS. This will be accomplished through a combination of replacing the existing storage ring with a high-brightness multibend achromat storage ring, adding an accumulator ring, and adding a few new insertion devices and upgraded insertion-device beamlines.
One of the important decisions the ALS-U Project has been weighing is which technology to implement to have the best chance of preserving the ALS’s highly valuable and productive tender and hard x-ray programs. Taking into account both user needs as well as the project’s technical risk, schedule, and cost, we have decided to move forward with permanent magnet (3.2 T) source points.
At the start of the project, we established a high-level project goal to include high-field bend magnets to accommodate users of tender x-rays and beyond. The new storage ring will employ relatively low-field (0.87 T) bending magnets to minimize the beam emittance, and the flux curve of these magnets peaks in the soft x-ray region. Thus, high-field bend magnets are necessary to preserve capabilities at higher energies. However, any solution to preserve these capabilities must be compatible with the other ALS-U Project parameters. Specifically, it must have acceptably small performance impact on the soft x-ray capabilities, maintain the project schedule, and have an acceptable risk and cost impact.
To fulfill the high-level goal as well as these other boundary conditions, the project team evaluated two technologies: permanent magnets (3.2 T source points) and superconducting magnets (4.6 T source points). As compared with the 0.87 T bends alone, the flux and brightness of both high-field magnet solutions are up to an order of magnitude higher in the tender regime and two to three orders of magnitude higher at hard x-ray energies. The difference in flux and brightness between the two high-field options is small for tender x-rays and is up to a factor of about two for typical x-ray energies used at hard x-ray beamlines at the ALS.
The project team evaluated both options thoroughly and found significant differences between the technology and project schedule risks of the two options. The superconducting magnet could have promised a higher hard x-ray flux, but would have presented technical, cost, and schedule risks that we judged too high to allow for successful execution of the project. The permanent magnet solution has a high likelihood of being successful and is fully compatible with the project schedule.
Our decision to implement the permanent magnet solution preserves users’ access to competitive tender and hard x-ray capabilities at the ALS and enables the high-field bend beamline programs to make use of the increased brightness that will be available at the upgraded ALS.
Dave Robin, ALS-U Project Director
Steve Kevan, ALS Director