Optimizing Magnet Design with Melike Abliz of Argonne National Laboratory

Challenge

Argonne National Laboratory (ANL) conducts advanced research using powerful X-rays generated by ANL’s Advanced Photon Source (APS), a U.S. Department of Energy (DOE) Office of Science user facility. The APS is undergoing a comprehensive upgrade that will increase the brightness of the X-ray beams by up to 500 times. The APS Upgrade (APS-U) team wanted to know whether narrowing the pole width of their hybrid permanent magnet (HPPM) undulators would give them the magnetic field they needed. A lot of investigation was required to determine whether they were doing the right thing. From a physics point of view, narrowing the pole must increase the field.

Also, magnetic crosstalk is challenging to measure during the equipment design phase and is often assessed by testing the physical product, but the APS-U team needed to know in advance how much magnetic crosstalk would occur between their storage ring magnets.

Solution

SIMULIA Opera, a finite element analysis software suite, provided the answer. Opera allows users to simulate electromagnetic and electromechanical systems in 2D and 3D. Its ability to provide accurate low-frequency simulations makes it ideal for designing magnets, electric motors, and electrical machines.

Benefits

SIMULIA Opera provided precise simulation results based on Melike Abliz’s experiments. It provided an effective way to validate the results expected from narrowing the pole width of the HPPM undulators. This allowed the APS-U Team to incorporate these technical developments into their design.

Optimizing Magnet Design with Melike Abliz

Argonne National Laboratory (ANL) is a U.S. Department of Energy science and engineering research center in Illinois. It’s where scientists from many disciplines strive to answer some of humanity’s biggest questions. Some are exploring ways to design better materials for energy, electronics, or medicine. Others are improving our understanding of biological molecules and cells or mapping the brain to understand more about neurological diseases. These diverse projects all have something in common: they use powerful X-rays generated by ANL’s Advanced Photon Source (APS) facility.

Advanced research of this kind needs bright beams of X-ray light and that’s what the APS generates. It uses a series of particle accelerators to push electrons up to high speeds, then injects them into a storage ring that measures 1.1 kilometers in circumference.

“When you inject an electron beam into a storage ring and accelerate it using magnets, it produces photon X-rays, which can be used in many different areas of scientific research,” explained Melike Abliz, a physicist at ANL. “Research using photons enables important developments in areas like material science, geophysical behavior, and medicine. For example, accelerator machines produce photons used to treat cancer.”

Making Better, Brighter X-ray Beams

After more than 25 years of service, the APS is being upgraded. The APS Upgrade project (APS-U) is a mammoth task that will see the current electron storage ring replaced with a state-of-the-art multi-bend achromat (MBA) lattice – a special arrangement of magnets that can produce low emittance, high brightness beams of radiation. Existing beamlines (pathways for the particles) will be enhanced as part of the project and new feature beamlines will be added – some housed in a new building – to make use of the increased brightness and coherence of the APS X-ray beams.

“In Europe, an MBA lattice storage ring has already been introduced and tested, enabling people to reduce beam size and increase the brightness of X-rays from the accelerator machine,” Abliz said. “In the APS-U project here in the U.S., we are targeting higher brightness than other facilities around the world. We will see X-rays up to 500 times brighter than current machines can deliver, yielding more advanced research results for our users.”

A Matter of Magnets

In simple terms, the APS uses magnets to deflect a particle beam. Insertion devices, such as undulators and wigglers, deflect the beam trajectory multiple times along its path, increasing the brightness and spectrum of the X-rays.

“Every time a particle beam is deflected by the magnetic field, it releases photons,” Abliz said. “We have a bending magnet beamline source (known as a sector insertion device front end), and we enhance the photon intensity using an insertion device – a permanent type of magnet that makes the particle beam wiggle as it passes. Every time the beam changes direction, it releases a photon, giving users a very bright X-ray for their research.”

Replacing the original electron storage ring with an MBA lattice structure will increase the brightness, coherence, and stability of the X-ray beams. But to enhance the resolution and contrast even further, the APS-U team also wanted to squeeze the photon beam to a smaller size by reducing the operation gap – the minimum distance between the jaws of the insertion device, which can be moved to tune the energy and intensity of the X-ray.

“On the front end, we will operate the insertion device with a smaller gap than the current APS uses,” Abliz said. “This will allow us to provide a very bright X-ray to our users, making a big difference for research in fields like medicine and geophysical materials. Brighter X-rays enable people to see the biological structures of their samples in more detail, for example.”

Cutting the Crosstalk

Between the storage ring magnets, there is also magnetic interference. Also known as crosstalk, its effects can include scattering the photons, which could muddy research results and make them unusable.

Magnetic crosstalk is difficult to measure during the equipment design phase and is often assessed by testing the physical product, but the APS-U team needed to know in advance exactly how their upgrade would affect x-ray performance.

Using Opera, the APS-U team simulated magnetic crosstalk between adjacent ring magnets of different types (the Q2 quadrupole and M1 longitudinal gradient magnets). Once they had built those magnets, the team measured their crosstalk and compared it against the simulation results. They found a precise match between the two.

Simulation Gets Sound Results

Minimizing the magnetic force between top and bottom jaws of the HPPM undulators was a major design challenge for the APS upgrade team. They needed to reduce the operation gap from its current 10.5mm to 8.5mm. The problem was that shaving off that 2mm would increase the magnetic force exponentially for the APS undulators.

 “If the magnetic force is too much for the undulators, they cannot function properly when users open and close the gap and there’s the potential for failure or inconsistency,” Abliz said. “As a result, we needed to decrease the magnetic force between the top and bottom jaw of the undulators.”

By narrowing the pole by 30%, the team would be able to manage the magnetic force and operate it with an 8.5mm gap to enhance photon brightness from the undulators. Special design skills would be needed to achieve that without increasing field roll-off.

“Some of our technical developments have never been done before anywhere in the world,” Abliz said. “We didn’t know whether narrowing the pole width would give us the magnetic field we wanted, so a lot of investigation was needed to determine whether we were doing the right thing. In principle, from a physics point of view, narrowing the pole width must increase the field. But we needed a way to verify that.”

SIMULIA Opera, a finite element analysis software suite, provided the answer. Opera allows users to simulate electromagnetic and electromechanical systems in 2D and 3D. Its ability to provide accurate low-frequency simulations makes it ideal for designing magnets, electric motors, and electrical machines.

“Opera can provide precise simulation results based on my design experiments,” Abliz said. “It provided an effective way to validate the results we expected from narrowing that pole width.”

In addition, the team ran various simulations based on advanced designs for the undulators, which produce the X-rays by passing an electron beam through a periodic array of magnets. Once again, after they built the undulators, the physical testing results confirmed Opera’s simulation results.

As part of the APS-U project research and development phase, the team also introduced a novel design concept for canceling the leakage field of the septum magnet, used to separate or deflect beams of charged particles. On building a prototype and measuring its leakage field, they again confirmed a close match with the Opera simulation.

“Our work with simulation impacted the final design parameters of the upgraded APS,” Abliz said. “We advanced the design by narrowing the pole, minimizing field roll-off, and increasing the field without increasing magnetic force of our HPPM undulators. After we narrowed the pole, we took care of all the other field qualities by incorporating those technical developments into our design.”

Ready for Future Challenges

As the APS-U project nears completion, Abliz credits Opera with helping to smooth the path.

“Opera can provide the fields we expect from our designs,” Abliz said. “For example, with other simulation tools, you cannot reduce the mesh size if you need to make changes, which means you can’t get precise field results. But if I set all the parameters for a new magnet design in Opera and meshed them, it gives me a very close indication of how that magnet will behave.”

Thanks in part to those accurate simulation results, APS users can look forward to more advanced research results from much brighter X-rays when the new storage ring is installed.

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