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Fermilab magnet team helps bring brighter beams to APS Upgrade Project at Argonne

Argonne National Laboratory was attracted to the expertise of this Fermilab magnet team. The team recently developed a pre-prototype magnet for Argonne's APS Upgrade Project. Photo: Doug Howard, TD

A magnet two meters long sits in the Experiment Assembly Area of the Advanced Photon Source at Argonne National Laboratory. The magnet, built by Fermilab's Technical Division, is fire engine red and has on its back a copper coil that doesn't quite reach from one end to the other. An opening on one end of the magnet's steel casing gives it the appearance of a rectangular alligator with its mouth slightly ajar.

"It's a very pretty magnet," said Argonne's Glenn Decker, associate project manager for the accelerator. "It's simple and it's easy to understand conceptually. It's been a very big first step in the APS Upgrade."

The APS is a synchrotron light source that accelerates electrons nearly to the speed of light and then uses magnets to steer them around a circular storage ring the size of a major-league baseball stadium. As the electrons bend, they release energy in the form of synchrotron radiation — light that spans the energy range from visible to X-rays. This radiation can be used for a number of applications, such as microscopy and spectroscopy.

In 2013, the federal Basic Energy Sciences Advisory Committee, which advises the Director of the Department of Energy's Office of Science, recommended a more ambitious approach to upgrades of U.S. light sources. The APS Upgrade will create a world-leading facility by using new state-of-the-art magnets to tighten the focus of the APS electron beam and dramatically increase the brightness of its X-rays, expanding its experimental capabilities by orders of magnitude.

Instead of the APS' present magnet configuration, which uses two bending magnets in each of 40 identical sectors, the upgraded ring will deploy seven bending magnets per sector to produce a brighter, highly focused beam.

Because the APS Upgrade requires hundreds of magnets — many of them quite unusual — Argonne called on experts at Fermilab and Brookhaven National Laboratory for assistance in magnet design and development.

Fermilab took on the task of designing, building and testing a pre-prototype for a groundbreaking M1 magnet — the first in the string of bending magnets that makes up the new APS arrangement.

"At Fermilab we have the whole cycle," said Fermilab's Vladimir Kashikhin, who is in charge of magnet designs and simulations. "Because of our experience in magnet technology and the people who can simulate and fabricate magnets and make magnetic measurements, we are capable of making any type of accelerator magnet."

The M1's magnetic field is strong at one end and tapers off at the other end, reducing the impact of processes that increase the beam size, producing a brighter beam. Because of this change in field, this magnet is different from anything Fermilab had ever built. But by May, Fermilab's team had completed and tested the magnet and shipped it to Argonne, where it charged triumphantly through a series of tests.

"The magnetic field shape they were asking for was a little bit challenging," said Dave Harding, the principal investigator leading the project at Fermilab. "Getting the shape of the steel to produce that distribution and magnetic field required some tinkering. But we did it."

Although this pre-prototype magnet is unlikely to be installed in the complete storage ring, scientists working in this collaboration view the M1 development as an opportunity to learn about technical difficulties, validate their designs and strengthen their skills.

"Getting our hands on some real hardware injected a dose of reality into our process," Decker said. "We're going to take the lessons we learned from this M1 magnet and fold them into the next iteration of the magnet. We're looking forward to a continuing collaboration with Fermilab's Technical Division on magnetic measurements and refinement of our magnet designs, working toward the next world-leading hard X-ray synchrotron light source."

Ali Sundermier

Photos of the Day

Egret goes fishing

An egret in front of Wilson Hall spots a fish ... Photo: Bridget Scerini, TD
... and nabs it. Photo: Bridget Scerini, TD
In the News

Weyl fermions are spotted at long last

From Physics World, July 23, 2015

Evidence for the existence of particles called Weyl fermions in two very different solid materials has been found by two independent groups of physicists. First predicted in 1929, Weyl fermions also have unique properties that could make them useful for creating high-speed electronic circuits and quantum computers.

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Frontier Science Result: DES

Cosmic shear cosmology with the Dark Energy Survey

The constraints we deduce from DES SV lensing data (in purple) on the amount of matter in the universe, Ωm, and the amplitude of fluctuations in that matter, σ8. We also show measurements from data from a previous lensing experiment, CFHTLenS (in orange), and the Planck satellite that measures the cosmic microwave background from the early universe (in red), that disagreed with each other. For each data set we show contours that contain 68 percent and 95 percent of the probability, and have marginalized over other cosmological nuisance parameters.

As light from galaxies billions of light-years away travels to us, it is subtly deflected by the gravitational influence of massive structures along its path. This effect, called weak gravitational lensing, encodes important information about the way the universe expanded and how structure within it grew in the past. This information is key to unlocking the biggest mystery in cosmology, the nature of the accelerated expansion of the universe, an effect called dark energy. The Dark Energy Survey, or DES, seeks answers to this mystery by mapping an eighth of the night sky.

DES measures weak gravitational lensing signals by correlating the shapes of hundreds of millions of galaxies. The subtle weak lensing deflections by large-scale structure shear the shapes of the galaxies. This effect is tiny — a very small "stretch" to galaxy images that already come in a wide variety of shapes and sizes — and it is only by comparing and correlating these large numbers of galaxies that we can beat down the noise. Even worse, the Earth's atmosphere and the telescope optics distort the images even more than the signal we are looking for, and these distortions must be carefully removed to uncover the weak lensing signals.

But if we can beat these challenges, then the coherent pattern of galaxy stretching will provide a map and a history of gravity and the growth of structure in the universe that tells the story of the last 8 billion years of the cosmos.

Precise shape measurements are not the only requirement for learning about dark energy from DES. The survey must also estimate the distances to all its galaxies, which is done by measuring their redshifts, the fractional stretching of their light due to the expansion of the universe. Because DES takes images in broad color filters, it can see only a very coarse spectrum of the light from each galaxy and so can get only very approximate distances to each galaxy. These photometric redshifts, as they're called, have their own complexities that must be carefully controlled so that distance errors don't ruin the constraints on dark energy from DES data.

This month DES released a collection of papers making these high-precision galaxy shape measurements, understanding the redshifts of the galaxies and using this information to constrain cosmology. This early data set is sensitive mainly to two numbers: the amount of matter in the universe and how much that matter has pulled together gravitationally into the structures that form the skeleton of galaxies and galaxy clusters. Two of the most powerful existing cosmology surveys, the Planck Satellite and Canada-France-Hawaii Telescope Lensing Survey, seem to disagree about these quantities, and the DES measurements sit squarely half way between them.

Despite containing millions of galaxies, the data that went into this analysis is only a tiny fraction of the full survey, just a few percent. The final DES data set will be more than 30 times bigger, requiring even more accurate galaxy shape and redshift measurements than what was achieved for this first analysis. When completed and analyzed, DES data will provide powerful new information about the history, contents and likely future of the universe.

Matthew R. Becker, Stanford University, and Joe Zuntz, University of Manchester for the Dark Energy Survey

Learn more about the results in these four arXiv papers.

In Brief

'Rock the LHC' video contest: The votes are in!

Thirteen-year-old Russell Farnsworth explains how doing research at the LHC is like solving a puzzle.

Russell Farnsworth, 13, is the first-place winner of the 2015 "Rock the LHC" contest for his video "Why the LHC totally rocks!" Russell will receive a free, two-day trip to tour Fermilab and meet U.S. scientists who work on the Large Hadron Collider. View Russell's winning video.

In the News

Game of quarks: a guide for the perplexed

From NPR's 13.7, July 22, 2015

Nature is the ultimate puzzle player, as scientists at the European Center for Nuclear Research (CERN) found out last week.

In the late 1950s, particle physics was in crisis. Being the branch of physics that studies the structure of matter, particle physicists search for the smallest bits of stuff that make up everything that exists — the elementary particles. To get the designation of "elementary," a particle can't be made of smaller bits: an elementary particle is a fundamental brick of matter, a concept that goes back to the Greek philosophers Leucippus and Democritus, who, around 400 BCE, proposed that matter was made of indivisible chunks called atoms (from the Greek "a-tomos" — that which can't be cut).

The problem physicists faced at that time was that as energies in experiments with colliding particles grew, so did the number of "elementary" particles. Called hadrons, their numbers mounted to hundreds. Hardly "elementary" by any measure.

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