The Advanced Photon Source
a U.S. Department of Energy Office of Science User Facility

FAQs about the APS Upgrade

Argonne’s Advanced Photon Source (APS) is undergoing a comprehensive upgrade that will keep the light source facility at the forefront of global X-ray science for the next quarter century and beyond. During the installation and commissioning period of the new electron storage ring, all operations, including scientific experiments, have paused.

Below is a series of Frequently Asked Questions (FAQ) about the APS Upgrade and the future of the facility, as recorded during Q&A sessions with the APS User community. The latest information about the APS Upgrade is available at the project website.


Why is the upgrade necessary? (May 2021)

As research becomes more diverse and competitive, scientists need the best tools. The X-rays generated at the upgraded APS will be up to 500 times brighter than current capabilities. The resulting images will be sharper with higher resolution and generated at a fraction of the speed, revealing discoveries and data we have not even considered.

When will the installation period for the APS upgrade be complete? (May 2024)

The upgraded APS began commissioning the new storage ring in April 2024. Beamlines will be brought back into operation over the course of the next year. Getting back online as fast and as safely as possible is a priority not just for the project, but for the photon science community as a whole.

When will the beamline I use shut down/come back online?(May 2024)

This varies by beamline. Most of the beamlines will be commissioned starting when the storage ring reaches 25mA. This could mean beamlines will be available within a month or two of the upgraded APS returning to operations. However, for feature beamlines and major enhancements, we will need to stagger the work. All beamlines will return to operation over the course of a year.

What is the best way to stay informed about the progress of the upgrade? (May 2024)

This varies by beamline. Most of the beamlines will be commissioned starting when the storage ring reaches 25mA. This could mean beamlines will be available within a month or two of the upgraded APS returning to operations. However, for feature beamlines and major enhancements, we will need to stagger the work. All beamlines will return to operation over the course of a year.

What is the best way to stay informed about the progress of the upgrade? (May 2024)

The APS Upgrade website will contain the latest information. We also send out a monthly Upgrade Update to the user community.

How much does the upgrade cost?(May 2024)

The upgrade cost $815 million and re-uses more than $1.5 billion in existing infrastructure.

Are there any new updates to the beamline construction schedule? (Nov. 2021)

Of the 68 previous beamlines at the APS, 41 required construction related to the upgrade. Beamlines not particularly affected by the upgrade should come back quickly; feature beamlines, if they are brand new, will likely take at least six months for commissioning before we transition to the full user program.

The most current information about the APS Upgrade can be found here.

Does the beamline schedule include the completion of shielded transports and other major projects? (May 2024)

All elements of the beamline installations are taken into account when determining if a beamline is ready to return to operation. We continually look for opportunities to move beamlines up in the schedule.

How long will it take the upgraded beam to ramp up to full strength? (May 2024)

We are planning for the first run period beginning summer 2024 with 50 mA operation. We anticipate to be at 100 milliamps within six months if there are no significant hardware failures. We estimate the upgraded APS will be at 200 milliamps roughly 16 months after the installation period ends. Note that brilliance limited experiments will see significant performance improvements over the previous APS even at the lower currents . Users should check with beamline scientists about what the future X-ray properties will be at each beamline.


Why will the upgraded APS use a horizontal injection scheme instead of vertical one, and does this have an impact on operating modes (e.g., 48-bunch mode vs. 324-bunch mode)? (May 2021)

The decision to implement a horizontal injection scheme was not based on the impact on operating modes. The decision to go from vertical to horizontal was made due to lingering concerns about the technical systems associated with the septum magnets, as well as the vacuum quality in the stored beam channel. We did not have the same concerns about the horizontal injection scheme so we chose the more reliable, less risky implementation.

Will the upgrade reduce beam loss? (Nov. 2021)

We expect more beam loss initially as we learn how to operate the new machinery and keep the equipment protected. The radiofrequency (RF) system in place at the APS is not being replaced as part of the upgrade, and we will continue using it for the next seven to eight years until the current klystrons are replaced with solid state amplifiers. However, new systems, power supplies, and magnets should result in a decline in beam loss associated with aging or obsolescent equipment. The APS is highly reliable, but we are always working to decrease beam loss and maximize availability of user operations.

What is the frequency of re-injection and what effect will that have on the beam in both 48-bunch and 324-bunch mode? (Nov. 2021)

The APS Upgrade will have two modes of operation: 324-bunches (low charge per bunch) and 48-bunches (high charge per bunch). To maintain 1% average current constancy, there will need to be different intervals between injection periods, depending on what mode you’re in. For example, for 324-bunch, injections will occur once every few seconds (less than 10 seconds) depending on lifetime to maintain constancy. For 48-bunch, the period between injections is longer (more like 30 seconds).

The APS-U swap-out injection scheme extracts a stored bunch and injects a new bunch on the central beam orbit. This is quite different than the previous top-off injection scheme, in which we add charge to existing bunches with off-axis injection. In the swap-out scheme, the injected bunch will have a larger emittance than the equilibrium emittance of the other stored bunches and thus have a minor impact on the total brightness for the few milliseconds after injection. We have estimated the impact to be < 2% during this period. The impact could be higher if we are not able to produce the necessary charge in the injector for each injection cycle. We are working to upgrade the injectors to make sure that we are able to provide the necessary charge for each injection. We are also planning to provide the appropriate timing signals to each beam line when each injection occurs.


What will be the duration of a single X-ray bunch after the APS Upgrade (in 324-bunch and in 48-bunch)? (Nov. 2021)

In 48-bunch mode, the bunch duration (rms) will be 104 picoseconds, with bunch spacing at 76.7 nanoseconds. In 324-bunch mode, the bunch duration (rms) will be 88 picoseconds with bunch spacing at 11.4 nanoseconds.

Is there a plan for how time will be divided between the 324-bunch and 48-bunch modes after the upgrade, both for the period immediately after the beamline is turned back on as well as the long-term vision?(Nov. 2021)

The APS-U will be commissioned in the “brightness” 324-bunch mode. Although we will be able to deliver “timing” 48-bunch mode following APS-U commissioning in a lower total average current, we will be continuing studies and adding hardware upgrades towards achieving 200 mA in the “timing” mode. The time scale for this development will be discussed following the storage ring commissioning. The long-term split is an operational choice and has not yet been determined.

Is hybrid single mode totally out of the question? Is there any way to implement it? (Nov. 2021)

We have no plans to pursue hybrid single mode because of the requirement for symmetric beam fill patterns. We are introducing a bunch-lengthening system with a higher harmonic RF system that stretches the bunch to make it longer than it would normally be. This reduces the charge density, which increases the Touschek lifetime (the dominant effect). To work properly, a symmetric fill pattern is required. Once the APS-U is commissioned, we may study the possibility of symmetric hybrid patterns, which are possible in principle.


How will the upgrade benefit my research? (May 2021)

There is no single answer to this question because so many different types of measurements happen on the APS and will continue to happen on the APS after the upgrade. However, we know there will be immediate large benefits for experiments reliant on sub-micron X-ray beams, imaging (phase contrast), and coherence exploitation. We anticipate higher resolution lensless imaging and faster dynamics, and we know there will be a significant benefit for high-energy experiments. Superconducting undulators provide higher flux and will extend coherence techniques to higher energies.

What areas of science might not benefit from the upgrade? What will you be doing for those proposals? (May 2021)

All areas will benefit from the upgrade in some capacity and all proposals will continue to be judged on their scientific merit.

For those who use softer X-rays for our research, how will this upgrade help us? (May 2021)

The APS is optimized to produce higher energy X-rays, but all beamlines will benefit from the increased current and better machine performance. Experiments such as X-ray absorption spectroscopy that use larger beam sizes on bending magnets will gain by a factor of two from the higher current. As the APS has aged, critical systems have experienced challenges expected with aging technologies. The upgraded APS will replace these systems, thus providing improvements in beam stability and reliability.

How are you going to keep up with all the data collected after the upgrade? (May 2021)

The APS team is working with our colleagues in Argonne’s computing divisions to develop data pipelines and analysis now, with the goal of having them ready for implementation when the upgraded APS comes online. Data volume is the biggest issue on the feature beamlines, since they will have newer faster, larger detectors. Other beamlines should work just as well as they did before, but strategies for their data analysis will also continue to evolve.

Will the coherence of the beam make data analysis more difficult, if I am interested in averaging? (May 2021)

It should not be difficult to get time/special averaged measurements that do not exploit the beam coherence. However, you will have to work hard to preserve coherence.


How can I access the APS on site as a user? (May 2021)

The APS is open to on-site users. Site access can only be granted to users identified as onsite users on approved Experiment Safety Assessment Forms (ESAFs), or if a Gate Pass is requested and processed by the User Program Office. Visit the My APS Portal to request a Gate Pass or email

Will user institutions need new user agreements? (May 2021)

No. Existing user agreements will stay in place and Argonne will not need to renegotiate with every institution.

Are you planning an early scientific commissioning period? (May 2024)

This varies by beamline. Most of the beamlines will = come back shortly after the installation period ends. We have put out calls for proposals on the APS feature beamlines and opened the general user program call to schedule beam time on untouched beamlines or those beamlines with modest upgrades (meaning ones that only need roughly one month of commissioning).

How will access be determined to upgraded beamlines? Regular general user proposals? Will there be early science partnerships or access during commissioning time? How will we apply for this time? (May 2024)

Special review committees including current review committees plus subject matter experts are evaluating proposals for first experiments on the feature beamlines and two to three groups per feature beamline will be involved in scientific commissioning. After technical commissioning, scientific experiments could begin.

On the non-feature beamlines, committees will look for experiments that will produce high impact science early but also make particularly effective use of new capabilities of the source. These will follow the precedent of our traditional general user program.

Will partner user proposals be considered or encouraged on upgraded beamlines to help develop new capabilities? (May 2022)

Not at the beginning. Until we know the APS is working and ready for general user proposals, the emphasis will be to get the upgraded APS up and running with its new capabilities. After that, we can start considering partner/user proposals.

When will future calls for proposals to use the upgraded APS go out? (May 2024)

The APS User Office will provide a calendar of general user dates of interest for the post-upgrade runs when that information is known.

With ESRF and MAX IV running, are there any changes of expectations to beams or experiment performance, post upgrade, to learn from their operations? May 2024

We have monitored the commissioning of both light sources in real time and both were impressive. There are opportunities to learn from their experiences, and we hope to do more of it.

Can I borrow equipment for experiments at other light sources? (May 2021)

No. This would be very difficult to do logistically, and the risk of equipment breakage is too high.

When the upgraded APS begins operating in 2024, will its improved brightness and data collection speed result in an increase in the number of successful proposals? (May 2021)

Typically, the number of proposals that can run is not limited by brightness or flux, but by staffing levels. We are always exploring ways to gain efficiencies and accommodate more users and measurements. The upgraded APS will generate larger, more complex data sets, but will not necessarily lead to a greater number of successful proposals.

Will remote access to beamlines still be available once the upgraded APS is back up and running? (May 2021)

Yes, the upgraded APS will still allow for remote access on beamlines capable of supporting remote access. When the COVID-19 pandemic started, the APS worked hard to implement and enhance remote data-taking capabilities, and we will continue to do so when the upgraded APS is online. However, onsite user presence remains critical in order for users to optimally use the upgraded APS’ capabilities and beam time. This is particularly true for complex in situ/operando conditions/reaction studies. The feedback loop between users and beamline scientists in extracting the maximum potential from the measurements is difficult to realize with fully remote users.

Will requesting remote access hurt or help my chances of securing beam time? (May 2021)

Requesting remote access will neither hurt nor help users’ chances of securing beam time. However, due to variations in expertise and/or bandwidth, there are limits as to what the beamline staff can do for users. Scope and scale of measurements could be affected.

Will the beamline I use move to somewhere else in the upgraded APS? (May 2021)

Minimizing the number of relocations was a key part of the beamline construction plan. Due to the construction of the Long Beamline Building and other factors, some relocations were necessary. Other programs will close or evolve, like the soft X-ray XCMD program at 4-ID-C and the structural biology program currently at 19-ID. The current map of beamlines can be found here.


What if I have more questions not answered here?

Users with questions regarding access, registration, legal agreements, and proposals should contact the APS Users Office at Other questions can be submitted via Please check this FAQ page for updates.