HQ02a
is a superconducting quadrupole magnet made from high performance
niobium tin that will play a key role in developing a new beam focusing
system for CERN’s Large Hadron Collider.
The U.S. LHC Accelerator Program (LARP) has successfully tested a
powerful superconducting quadrupole magnet that will play a key role in
developing a new beam focusing system for CERN’s Large Hadron Collider
(LHC). This advanced system, together with other major upgrades to be
implemented over the next decade, will allow the LHC to produce 10 times
more high-energy collisions than it was originally designed for.
Dubbed HQ02a, the latest in LARP’s series of High-Field Quadrupole
magnets is wound with cables of the brittle but high-performance
superconductor niobium tin (Nb
3Sn). Compared to the
final-focus quadrupoles presently in place at the LHC, which are made
with niobium titanium, HQ02a has a larger aperture and superconducting
coils designed to operate at a higher magnetic field. In a recent test
at the Fermi National Accelerator Laboratory (Fermilab), HQ02a achieved
all its challenging objectives.
LARP is a collaboration among the U.S Department of Energy’s
Brookhaven National Laboratory (Brookhaven), Fermilab, Lawrence Berkeley
National Laboratory (Berkeley Lab), and the SLAC National Accelerator
Laboratory (SLAC), working in close partnership with CERN. LARP has
also supported research at the University of Texas at Austin and Old
Dominion University.
“Congratulation to all the LARP team for this brilliant result,” said
Lucio Rossi, leader of the High Luminosity LHC project at CERN. “The
steady progress by LARP and the other DOE supported programs clearly
shows the benefits of long-term investments to make serious advances in
accelerator technology.”
“In the context of the LARP magnet program, this marks the end of the
R&D phase and the beginning of the focused development of the
magnets that will be installed for the LHC luminosity upgrade”, said
Eric Prebys of Fermilab who has served as director of LARP for the last
five years. “However, the implications go well beyond that, in that it
establishes high performance niobium tin as a powerful superconductor
for use in accelerator magnets. This success is a tribute to the skill,
hard work, and collaborative spirit of all of the people involved.”
Toward future physics at the LHC
Wound
with high performance superconducting niobium tin, the new HQ02a
quadrupole has a larger aperture and superconducting coils designed to
operate at a higher magnetic field than previous final focusing magnets.
Last year’s discovery of the Higgs boson fulfilled one of the major
goals of the LHC, arguably the most powerful and complex scientific
instrument ever built. Yet precision measurements of the Higgs are still
to be made, as well as explorations of new physics including
supersymmetry, dark matter, extra dimensions, and other wonders. The
LHC’s present complement of Interaction Region Quadrupole magnets, which
focus the beams toward the collision points inside the experiments,
will reach performance limits well below what’s required for this
ambitious physics program. One of the primary goals of LARP is to
support CERN’s plan to replace these focusing magnets in about 10 years
as part of the High Luminosity LHC project.
The number of useful physics events generated by a collider can be
calculated from a parameter called integrated luminosity. For the past
decade, CERN has anticipated a series of upgrades that will increase the
LHC’s integrated luminosity 10-fold – the goal of the High Luminosity
LHC project, consistently recognized as a top priority for the worldwide
particle physics program. This goal presents extraordinary challenges,
requiring a global effort to push the state of the art in a number of
critical technologies.
The most specific need is for more powerful magnets to focus the
proton beams at the interaction points. Not only must the magnets
produce a stronger field, they will also require a larger temperature
margin and have to cope with the intense radiation, which comes hand in
hand with the planned increase in the rate of energetic collisions.
These requirements go beyond the capabilities of niobium titanium, the
material on which all previous accelerator superconducting magnets have
been based.
Niobium tin is an advanced superconducting material that can operate
at a higher magnetic field and with a wider temperature margin than
niobium titanium. Unfortunately, niobium tin is brittle and sensitive to
strain – critical factors where intense electrical currents and strong
magnetic fields create enormous forces as the magnets are energized.
Large forces can damage the fragile conductor or cause sudden
displacements of the superconducting coils, releasing energy as heat and
possibly resulting in a loss of the magnets’ superconducting state,
called a “quench.” When combined temperature, field, and current density
cross a critical boundary into ordinary conductivity, the enormous
flood of electrons that previously rushed unimpeded through the
superconductor slams into a wall of electrical resistance.
Accelerator magnets are designed to withstand these disruptive and
potentially damaging events. Nevertheless, the ability to reach the
operating level with few or no quenches is an essential performance
requirement.
At
Fermilab’s Vertical Magnet Test Facility, the new HQ02a quadrupole
achieved all its challenging objectives. (Photo by Guram Chlachidze,
Fermilab)
In order to address these challenges, LARP adopted a mechanical
support structure based on a thick aluminum shell, pre-tensioned at room
temperature using water-pressurized bladders and interference keys.
This design concept, developed at Berkeley Lab under the DOE General
Accelerator Development program, was compared to the traditional
collar-based clamping system originally used in Fermilab’s Tevatron and
all subsequent high energy accelerators, and scaled-up to 4 m length in
the LARP Long Racetrack and Long Quadrupoles. The HQ models further
refined this mechanical design approach, in particular by incorporating
full coil alignment.
LARP’s HQ02a is designed like all LHC magnets to operate in
superfluid helium at temperatures close to absolute zero. However, it
has a larger beam aperture than the present focusing magnets – 120
millimeters in diameter compared to 70 millimeters – and the magnetic
field in the superconducting coils that surround the magnet reaches 12
tesla, 50 percent higher than the present 8 tesla. The corresponding
field gradient, the rate of increase of field strength over the
aperture, is 170 tesla per meter.
Another key objective of the HQ02a design is to minimize any
deviations from the precise magnetic field patterns required to focus
the beams at the interaction point, and to maintain this high field
quality during ramping up to full magnetic field strength. To address
these requirements, the LARP High-Field Quadrupole program incorporated a
newly designed cable to minimize induced currents, plus precise
alignment at all phases of coil fabrication, assembly and magnetic
excitation.
“The desired performance characteristics were clearly demonstrated by
the test recently completed at Fermilab,” says Berkeley Lab’s GianLuca
Sabbi, who directed the HQ02 development. “The magnet quickly achieved
its design field gradient with low sensitivity to ramp-rate effects.
This result was made possible by the expertise and dedication of many
scientists, engineers, and technicians at all the collaborating
laboratories.”
As the last step in a decade-long progression of niobium-tin
technology advancements by LARP, the sterling performance of HQ02a has
reaffirmed the key design elements for focusing magnets that will meet
the needs of CERN’s High Luminosity upgrade.
“This is a major step forward in reaching our ultimate goals,” said
Bruce Strauss, LARP program manager at DOE’s Office of Science. “It
should not be regarded as a single accomplishment but rather the
realization of a significant number of individual goals in the design,
construction, and testing of Nb
3Sn beam-line magnets.”
# # #
Additional Media Contacts:
Kurt Riesselmann, Fermilab,
media@fnal.gov, (630) 840-3351
Justin Eure, Brookhaven Lab,
jeure@bnl.gov, (631) 344-2347
The development of HQ02a was a major collaborative undertaking
involving the LARP laboratories and their industrial partners. The
superconducting niobium-tin wire was manufactured by Oxford
Superconducting Technology of New Jersey, cabled at Berkeley Lab, and
insulated with a fiberglass sleeve by New England Electric Wire. The
coils were wound at Berkeley Lab with parts designed and procured by
Fermilab, then sent to Brookhaven Lab for high-temperature reaction and
impregnation with epoxy resin. Magnet assembly was performed at Berkeley
Lab and the test was performed at Fermilab. Additional tests at
Fermilab and CERN are expected in the next months.
Among the key contributors are Dan Dietderich, Arup Ghosh and Arno
Godeke for the development, fabrication and characterization of the new
cable; Mike Anerella, Franck Borgnolutti, Rodger Bossert, Dan Cheng,
Helene Felice, Abdi Salehi, Jesse Schmaltzle, and Miao Yu for the HQ02
magnet design, fabrication, and assembly; Maxim Martchevsky and Prabir
Roy for the improved electrical instrumentation and high voltage
testing; Guram Chlachidze for planning and execution of the test,
together with Joe DiMarco, Darryl Orris, Tiina Salmi, and Xiaorong Wang;
Giorgio Ambrosio for contributions to the coil analysis and revision
process as the leader of the Long High-Field Quadrupole program; and
Ezio Todesco for his support and advice as the magnet work package
coordinator in the High Luminosity LHC project.
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