Magnetics Business & Technology - July/August 2024 - 13

FEATURE ARTICLE
roughly 50% more than the strength of the niobium-titanium focusing
magnets currently in the Large Hadron Collider.
Scientists had never used Nb3Sn in a large-scale accelerator
project because it is extremely difficult to work with.
" It's brittle like glass, " said Giorgio Apollinari, the head of the
HL-LHC accelerator upgrade project at the U.S. Department of
Energy's Fermi National Accelerator Laboratory. " When properly
handled, glass can last for centuries, like in a cathedral window,
but then one day you knock it, and it breaks. We spent a lot of
time figuring out how to treat and handle this material and address
its brittleness.
the CERN-US collaboration: the delivery of final cryo-assemblies
ready for the installation in the LHC. "
Overcoming challenges with the prototypes
" The contribution of our US colleagues has been instrumental in
developing the design and procedures for these magnets, and
the regular cross-checks of manufacturing and test data have
helped the teams on both sides of the Atlantic to overcome many
challenges, " said Ezio Todesco, who is in charge of the HL-LHC
interaction region magnets for CERN, as he explained in early
December.
The CERN Technology department is developing a series of ten
magnets (eight, plus two spare), each 7.2 metres in length. This
work builds on the HL-LHC Accelerator Upgrade Project (AUP),
based in the USA, which is currently manufacturing 20 (16, plus
four spares) quadrupole magnets, each 4.2 metres long. Recent
tests at Fermilab showed that these magnets operate at target
current at both 1.9 kelvin (-71.25 °C) and 4.5 kelvin (-268.65 °C),
thus meeting the project requirements. The CERN team is relying
on the same design and similar manufacturing procedures as AUP
but scaling them up to 7.2-m-long magnets.
This 13-meter-long assembly for the HL-LHC upgrade comprises two
superconducting magnets. It was shipped from Fermilab to CERN.
" Designing, building and successfully testing these advanced
Nb3Sn magnets with accelerator-quality features is a first for
humanity and represents a major progress in accelerator technology, "
said Apollinari. " But this initial success is only part of the
story. "
Shipping magnets and their components among the U.S. laboratories
has been a backbone of the upgrade project. But according
to Apollinari, safely sending a 25-ton cryo-assembly around
the world is a challenge. " You can't just go to the store and buy
Styrofoam or bubble wrap to package it for shipment, " he said.
The magnet needed to arrive at CERN in mint-condition and incur
no damage during the transit. So the magnet team started as any
good scientific team would: with a dummy-magnet made from 25
tons of concrete and iron, and loaded with sensors.
" We drove a block of concrete around the U.S. and then sent it by
ship to CERN, " Apollinari said. " The sensors were so good that
we could tell when the truck was going over railroad tracks. " From
this data, they were able to design shipping equipment - their
special version of " bubble wrap " - and a shipment plan that took
into account how much force and acceleration the magnet could
tolerate from the turbulence the magnet might experience during
its journey.
After one month on land and at sea, the real magnet finally arrived
at CERN in November 2023, where it is currently being evaluated.
Eventually, CERN personnel will install this magnet - along with
7 more from the United States and 8 from CERN - 100 meters
underground in the LHC tunnel to focus the particle beams approaching
the collision points of the two largest LHC experiments:
ATLAS and CMS. The HL-LHC installation will start in 2025, with
the plan to start colliding protons with the upgraded machine in
2029.
Said CERN HL-LHC project leader Oliver Bruening, " The arrival
of this first cold-mass assembly marks the start of a new phase of
www.MagneticsMag.com
July/August 2024 * Magnetics Business & Technology 13
The successful test at CERN, which ran from August to October,
achieved the target current of 16.53 kA at both 1.9 K and 4.5 K.
The target current corresponds to the 7 TeV LHC operation, plus
a 300 A margin. Although operation is planned at 1.9 K, the ability
to reach target current at 4.5 K confirms design robustness and a
comfortable operation margin for the HL-LHC and beyond.
This is the third fulllength
magnet to be
tested as part of a
recovery plan decided
on after performance
limitations were observed
on the first two
prototypes. The other
magnets showed no
signs of degradation
when tested, but were
always limited to below
target current when
operated at 4.5 K. The
team at CERN paused
production to investigate
this limitation. By
improving the design of
the outer shell, reducHarriet
Kung, deputy director for science
programs in the DOE's Office of Science,
signs the first U.S. magnet assembly for
the high-luminosity upgrade to the Large
Hadron Collider in October.
ing peak stress on the magnet during coil assembly and changing
the parameters of the coil manufacturing process, they eliminated
the limitations and the third magnet has outshone its predecessors.
" Thank
you to all the contributors for the excellent results and efficient
teamwork and for deriving practical and robust engineering
solutions to bring niobium-tin technology to the maturity level required
for accelerator magnet applications, " says Arnaud Devred,
the TE-MSC group leader. " This is a fantastic result for the project, "
says Oliver Brüning, HL-LHC project leader. " It means that
niobium-tin is viable for 7-m-long accelerator magnets and is an
enabling technology for HL-LHC. "
For more info, see www.energy.gov/science, www.home.cern.
http://www.energy.gov/science http://www.home.cern http://www.MagneticsMag.com
Magnetics Business & Technology - July/August 2024

Table of Contents for the Digital Edition of Magnetics Business & Technology - July/August 2024
