About MAX 4U

MAX 4^U brings back our fourth-generation storage ring to the forefront: the best medium-energy (i.e., below 4 GeV) lightsource in Europe and the world.
MAX 4^U fulfills our ambitions to strengthen our beamline capabilities on our 3 GeV fourth-generation lightsource to secure the excellence, leadership, resilience and relevance of Swedish research and innovation with X-rays for the next decades.

MAX 4^U is MAX IV Laboratory’s proposal to upgrade its 3 GeV storage ring (R3), the world’s first fourth-generation storage ring, inaugurated in 2016.
The name captures the idea of taking MAX IV to the next level — for the user community and for science.
The vision driving MAX 4U is to ensure the excellence, relevance, and leadership of Swedish academic and industrial research with X-rays for the next decades.

The MAX 4^U project has two components:

1. An X-ray science and instrumentation component to strengthen our capabilities across our beamline portfolio on this storage ring. This comprehensive beamline readiness programme spans most of our existing undulator beamlines to ensure they can optimally benefit from the superior performance of the source and will add one (1) new beamline.
2. A source enhancement with an accelerator upgrade to reduce the electron beam emittance

When MAX IV opened in 2016, it set the global benchmark for fourth-generation lightsources, with performance 3 to 20 times better than that of any other synchrotron at the time. Since then, four comparable facilities — ESRF-EBS in France, Sirius in Brazil, SLS2.0 in Switzerland, and APS-U in the USA — have been upgraded to fourth-generation status, and many more are planned globally over the next decade.
The broader accelerator community has also made rapid advances in Multi-Bend Achromat (MBA) lattice design, the technology underpinning fourth-generation performance. This has also led to advances in optimized beamline design and instrumentation to fully exploit such sources.

Without action, MAX IV risks losing the competitive edge that has made it the X-ray lightsource of choice for researchers in Sweden, across Europe, and beyond. MAX 4^U is our strategic response: it returns MAX IV to the forefront of X-ray science, securing Swedish and European research leadership for the coming decades. As Sweden’s national synchrotron facility, maintaining this leadership is critical.

MAX 4^U will be the first upgrade of a fourth-generation lightsource. Conventional third-to-fourth-generation upgrades essentially strip away and rebuild the entire storage ring, often requiring beamline relocations and significant recommissioning, major civil engineering, and extended shutdowns.

MAX 4^U is different in several important ways:

• It is a more “surgical” intervention on the accelerator that achieves a major performance boost through minimal changes to existing hardware, reducing cost and disruption to our User Science programme.
• It does not involve relocating or realigning beamlines.
• It capitalizes on ten years of unique operational experience on a fourth-generation source.

No.
MAX 4^U will be the first upgrade of a fourth-generation lightsource.
It will bring back MAX IV to the forefront of fourth-generation medium-energy (i.e., below 4 GeV) synchrotron facilities.
This is an important distinction from what is happening at other facilities across the world, which are either transitioning from third- to fourth-generation or being built as fourth-generation synchrotron sources.
MAX IV is the only facility already operating at fourth-generation level since 2016 that is now planning to go further.

No.
MAX 4^U has not yet received formal approval or funding.
MAX 4^U is currently in the proposal development phase.
A conceptual design study on the accelerator was completed in 2025. MAX IV is currently developing the MAX 4^U Science Case in dialogue with the user community, the technical design of the upgraded fourth-generation accelerator lattice, and the beamline readiness programme. The latter will strengthen the capabilities of our existing beamlines and add a new beamline.

MAX 4^U is at the proposal stage with an emittance goal below 75 pm·rad. The MAX 4^U Science Case is being developed and is expected to be completed by the end of 2026.
Preliminary cost and schedule estimates indicate a total project cost of 1000 MSEK, a completion by the autumn of 2032, a downtime of up to 14 months, assuming a possible positive funding decision in the 2028 research bill.
A conceptual design of the accelerator was completed in 2025 and is available on the MAX 4^U webpage. The detailed technical design started in January 2026.
A detailed study of the potential performance benefits to the beamlines started in 2025. Throughout 2026, it is being further developed with the most up-to-date accelerator design parameters. A detailed beamline readiness programme will be developed.

The estimated total cost of MAX 4^U is 1 BSEK.

The upgrade has two components that share the cost nearly equally:

1. An X-ray science component to strengthen our capabilities across our beamline portfolio on this storage ring. It includes the addition of one (1) new beamline and upgrades to many of our existing undulator beamlines.
2. An accelerator upgrade to further reduce the electron beam emittance

No.
The existing beamlines and their developments are funded by our regular operation funds. MAX 4^U is expected to be funded separately.

Preliminary schedule estimates indicate a completion by the autumn of 2032, a downtime of up to 14 months, assuming a possible positive funding decision in the 2028 research bill.
More detailed scheduling information will be shared as plans mature.

MAX 4^U is progressing through well-defined conceptual and technical design phases. Implementation timelines will be confirmed following completion of the technical design phase and a positive funding decision. More detailed scheduling information will be shared as plans mature.

The upgrade leverages years of experience with Multi-Bend Achromat (MBA) lattices. The conceptual design phase has selected lattice options through risk analysis and initial simulations. The technical design phase will refine these choices with engineering validation, will further identify risks and propose mitigations. A comparable process will be used for the beamline readiness programme.

We will follow an existing process, referred to as Expression of Interest, the details and timeline of which are not available yet. This process will involve gathering beamline proposals from the user community through consultation. Proposals will be reviewed and prioritized with involvement of multiple review committees, leading to a recommendation to the MAX IV board. We expect the process to start during 2026.

MAX IV has multiple sources. Users of beamlines located on our 1.5 GeV storage ring and the Short Pulse Facility are unaffected by MAX 4^U.
Those beamlines are expected to remain operational and support our User Science programme during the installation of the modifications to the 3 GeV storage ring.