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

FAQs about the APS Upgrade

After 25 years of leading scientific discoveries, Argonne’s Advanced Photon Source (APS) will undergo a massive 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 period of the new electron storage ring, all operations, including scientific experiments, will pause. Below is a series of Frequently Asked Questions (FAQ) about the APS upgrade and the future of the facility.

Additional FAQs from the APS-U Q&A session on November 10, 2021

In an ongoing effort to keep the scientific community informed about progress and developments related to the APS Upgrade, Argonne hosted a second Q&A session on November 10, 2021. Questions and answers appear below. Our next Q&A session is currently scheduled for May 2022.

What progress was made in 2021?

The APS Upgrade project showed remarkable progress on many fronts in 2021. Roughly 98% of the overall design of the project is complete; more than 70 front-end-table assemblies are complete; superconducting undulator research and development is complete; the X-ray optical components with longer production times have been ordered, and construction of the Long Beamline Building is on schedule and within budget.  

Additionally, the U.S. Department of Energy (DOE) conducted an Independent Project Status Review of the APS Upgrade October 26-29, and 22 reviewers drawn from across the DOE national laboratory complex provided feedback on all aspects of the project. They praised the APS-U staff for impressive progress during the pandemic; they also provided several recommendations.

Are there any new updates to the beamline construction schedule?

Of the 67 existing beamlines at the APS, 41 will need construction related to the upgrade. That means we must spread out the work, including the building of shielded enclosures on the APS floor. Every shielded enclosure and all shielded transport on APS beamlines will need shielding verification.  Detailed planning for this work has started and meetings will be held with every beamline to develop schedules.

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 Coherent High-Energy X-ray (CHEX) and Instrumentation Development, Evaluation and Analysis (IDEA) beamline is in the scientific commissioning phase now at 28-ID. The Advanced Spectroscopy and LERIX (ASL) beamlines at 25-ID will replace work done at 20-ID, as well as time-resolved work done at 7-ID and 11-ID-D. Vendors have completed the enclosures at 25-ID and utilities installation is complete. Mirror and monochromator installation should be possible in early 2022.

Construction of the High Energy X-ray Microscopy (HEXM) beamline enclosure in the Long Beamline Building at 20-ID is planned to begin in May 2022. Then work will start in earnest on other beamlines, beginning with the Coherent Surface Scattering Imaging (CSSI) beamline at 9-ID followed by the X-ray Photoelectron Correlation Spectroscopy (XPCS) program at 8-ID (currently scheduled for September 2022).

We will confirm announcements about beamline access approximately one year prior by email and in townhall sessions for each user community.

How can the APS help me find other facilities where I can conduct experiments during the APS’ year-long shutdown?

Use of other DOE facilities requires submission of a proposal to the appropriate light source user facility. Other DOE facilities will not set aside time for displaced APS users. We are developing a matrix of beamlines detailing and comparing APS capabilities with capabilities elsewhere in the DOE complex. Although beamlines at various facilities are not exactly the same, the matrix should help you identify roughly equivalent capabilities at other facilities.

Will the upgrade reduce beam loss?

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 expected time to ramp up to 100 milliamps after the upgrade? 200 milliamps? 

When the one-year shutdown ends, we conservatively expect to be at 25 milliamps. We will then increase that current in stages to 100, 150, and ultimately 200 milliamps. We will take into account the possibility of issues with vacuum conditioning, feedback systems, beamlines and the storage ring itself.  

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

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.

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

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 will extract a stored bunch and inject a new bunch on the central beam orbit. This will be quite different that the current topoff injection scheme where 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. 

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?

The upgrade will support both modes, but the long-term split has not yet been determined.

Is hybrid single mode totally out of the question? Is there any way to implement it during APS-U?

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.

Where can I find more info?

Visit APS Upgrade or read APS User News for useful information about the upgrade and answers to frequently asked questions. Users with questions regarding access, registration, legal agreements, and proposals should contact the APS Users Office at Other questions can be submitted via


Frequently Asked Questions from the May 11, 2021 APS-U Q&A


Why is the upgrade necessary?

As research becomes more diverse and competitive, scientists need the best tools, including the ultimate 3D X-ray microscope. 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 begin?

The installation period will begin April 17, 2023, 10 months later than originally announced.

Why was the installation period delayed?

The COVID-19 pandemic caused Argonne National Laboratory and other Department of Energy (DOE) national laboratories to suspend or limit operations for most of 2020 and much of 2021. Vendors worldwide, who deliver critical components for the upgrade, also experienced production delays, operations interruptions and logistical challenges. A 10-month delay not only addresses the impacts of COVID-19, but also allows all three run cycles planned for 2022 to occur.

When will the installation period for the APS upgrade be complete?

The installation period will take 12 months, so the upgraded APS will begin initial operations in April 2024.

Is there any risk the installation period will last longer than one year?

There are always risks, but the project team is working to mitigate them. Because of the intentional 10-month delay, we expect all equipment for the storage ring will be onsite and tested before the installation period starts. This includes all the large sub-assemblies that make up the new storage ring – some of them weighing up to 30 tons.  By doing the prep work and practicing on those pieces before the installation period starts, we have high confidence we can meet the 12-month installation schedule. To meet the schedule, the APS will run two installation shifts per day. Finally, we are keeping the removal period separate from the installation period to promote a degree of overlap and internal float.

What if there is another delay?

While there is a very small risk of additional delay, we believe the new completion date for the installation period is achievable based on events to date and projections into the future. Minimizing disruption to the user community has been a core deliverable of the APS Upgrade from day one. If another delay proves necessary, we will notify users. The APS Upgrade web page will include regular updates and schedules to keep all stakeholders regularly informed.

Will the APS continue operating in 2022 and 2023 before the new shutdown date?

The APS will continue operating for all three user runs scheduled for 2022. There will be an operations run in the early months (January to April) of 2023, with exact scheduled dates to be determined.

When will the beamline I use shut down/come back online?

This varies by beamline. Most of the beamlines will continue to operate up until the storage installation period begins, and resume shortly after the installation period ends. This could mean within a month of the shutdown’s conclusion.  However, for feature beamlines and major enhancements, we cannot accomplish all work during the shutdown, so we will need to stagger the work. Several beamlines will shut down early. We are re-drafting the schedule due to the 10-month delay and we are committed to giving users of every beamline one year’s notice if the beamline will shut down prior to the installation period.  

How much does the upgrade cost?

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


How will the upgrade benefit my research?

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?

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?

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?

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.

What is the actual beam size at the sample without focusing?

Without focusing, the X-ray beam will be roughly 0.5 x 0.5 mm at 30 meters from the undulator source.  This is similar to the current beam size in the vertical direction and about a factor of two smaller in the horizontal.

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)?

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. 

If a decision on the split between the 48-bunch versus the 324-bunch mode has not been made yet, can a hybrid mode be accommodated?

We are not currently planning for a hybrid mode with a single asymmetric isolated bunch, but the APS will continue to explore options for different filling patterns. We have plans for symmetric fill patterns of 48 and 324 bunches.

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

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 long will it take the upgraded beam to ramp up to full strength?

We are planning for the first run period in April 2024 to provide nominally 50% of beam for user operations. Modeling our expectations on the European Synchrotron Radiation Facility (ESRF), we believe we can ramp up quickly to stable operations. If there are no significant hardware failures, we expect to be at 100 milliamps within six months. We estimate the upgraded APS will be at 200 milliamps roughly 12 months after the installation period ends.  Note that the conversion from electron beam current to X-ray beam properties will be different in the upgraded APS era as compared to now. Users should check with beamline scientists about what the future X-ray properties will be at each beamline.


When can I get back onsite?

Although the APS and ANL currently remain in limited operations due to the COVID-19 pandemic, a limited number of external users are being allowed (capped at maximum of 2 per experiment).   These requirements continue to evolve can these changes will be communicated via email.  However, check APS website and My APS portal for latest guidance. 

Will Argonne require COVID-19 vaccinations to go onsite?

Yes, users are required to provide proof of vaccination or proof of participation in a testing program to get access to the ANL site.  Please check APS website and My APS portal for details on process for doing so.  

Will users be able to return to in-person work at the beamlines before the installation period begins?

Yes, Argonne currently allowing a limited number of users for on-site experimental work (capped at two per experiment).   Information will be shared with users via email as requirements change.  Latest guidance is provided on  APS website and My APS portal.

Will user institutions need new user agreements?

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

When is the last call for APS proposals before the installation period?

The call for proposals for the 2023-1 cycle (the last run period using the APS) will be October 2022.

Are you planning an early scientific commissioning period?

This varies by beamline. Most of the beamlines will shut down when the installation period starts and come back shortly after that period ends. We will use the normal 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).  On the APS feature beamlines, we are developing a separate review process to identify key high-impact first experiments that will be scheduled during an early scientific commissioning period before the beamline fully opens to general users.

When is the first call for proposals to use the upgraded APS?

All general user (and other) proposals will expire when the installation period begins. We anticipate that there will be a new proposal call for general user operations during the shutdown. The APS User Office will provide a calendar of general user dates of interest for the post-upgrade runs when that information is known.

Where can I find another beamline for my research during the installation period?

There is no time specifically set aside at the other DOE light sources for APS general users in search of beam time. APS staff is working on developing resources for users looking for a beamline with similar capabilities to one at the APS. The installation period will be complete and the upgraded facility will be operational before the Advanced Light Source (ALS) at Lawrence Berkeley National Laboratory is scheduled to shut down for its own upgrade, which is scheduled for 2025. 

Can your staff help me with experiments at other light sources?

Most staff will be extremely busy with the upgrade, so their ability to help on other experiments will be very limited. We will consider requests on an individual basis, but our likelihood of supporting these requests is small.

Can I borrow equipment for experiments at other light sources?

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?

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?

Yes, the upgraded APS will still allow for remote access on beamlines capable of supporting remote access. During the COVID-19 pandemic, we have 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?

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?

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 are necessary. The beamlines for 20-ID, 33-ID, USAXS, and Bionanoprobe will move. 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.

Will chilled water, compressed air, experimental hutches, etc. still be available during the installation?

For the most part, yes. We have already completed several upgrades with a focus on attaining a higher order of cleanliness, including the addition of redundant cooling towers. Upgrades to air compressors, the liquid nitrogen distribution system, and a Module C liquid nitrogen storage tank for Sectors 18-27 replacement are also complete, so we do not anticipate a major shutdown of utilities.

Will there be constraints regarding accessing the experiment hall floor during the shutdown, and how do we coordinate that with the CAT Beamlines?

Some isolation will need to happen during the installation and commissioning period. We are currently working out the plan for controlling access during this period and will communicate and coordinate that with users in the future.

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.