Slide 1
Novel Tunable Permanent Magnet Quadrupoles for the CLIC Drive
BeamBen Shepherd, Jim Clarke, Norbert Collomb, Graham StokesSTFC
Daresbury Laboratory, UK
Antonio Bartalesi, Michele Modena, and Mike StruikCERN, Geneva,
Switzerland
CLIC Workshop 2014CERN, 3-7 February 2014
Artwork: S. Kimball1The CLIC Drive BeamThe drive beam
decelerates from 2.4 GeV to 0.24 GeV transferring energy to the
main beamAs the electrons decelerate, quadrupoles are needed every
1m to keep the beam focusedThe quadrupole strengths scale with the
beam energyThe CLIC accelerator length is ~42km so there are
~42,000 quadrupoles needed
Quadrupole TunabilityThe nominal maximum integrated gradient is
12.2T and the minimum is 1.22TFor operational flexibility each
individual quadrupole must operate over a wide tuning range70% to
120% at high energy (2.4 GeV)7% to 40% at low energy (0.24 GeV)
12.2 T1.22 TQuadrupole SpecificationParameterHigh-energy
endLow-energy endUnitsNumber of
quadrupoles41400Strength12.21.22TStability5x10-4Integrated gradient
quality0.1%Good field region11.5mmMinimum bore radius13mmMaximum
width391mmMaximum height391mmMaximum length270mmPermanent Magnet
OptionThe integrated magnet strength requirement is very
challenging (given the space constraints) for a conventional
electromagnetThe nominal power consumption for the EM version will
be ~8MW in nominal mode and up to ~17 MW in tune-up modeTotal Power
Load limit to air within the tunnel is only 150 W/m (all
components)A PM quad would potentially have many advantagesVastly
reduced electrical powerVery low operating costsNo cooling water
needsVery low power to airWe have been investigating the PM option
for the drive beam5Permanent Magnet ChallengesThere are many
existing PM quadrupole examplesThe combination of high strength,
large tunability, high field quality, and restricted volume meant
that a new design was requiredAdditional challenges for PM include
possible radiation damage, field variation with temperature, PM
strength variation from block to block (material and engineering
tolerances)The complete tuning range (120% to 7%) could not be met
by a single designWe have broken the problem down into two magnet
designs one high energy and one low energyQuadrupole TypesHigh
energy quad Gradient very highLow energy quad Very large dynamic
rangeErik Adli & Daniel Siemaszko
Low Energy QuadHigh Energy Quad7NdFeB magnets with Br = 1.37 T
(VACODYM 764 TP)4 permanent magnet blocks each 18 x 100 x 230
mmMounted at optimum angle of 40Max gradient = 60.4 T/m (stroke = 0
mm)Min gradient = 15.0 T/m (stroke = 64 mm)Pole gap = 27.2 mmField
quality = 0.1% over 23 mm
Stroke = 64 mm
Poles are permanently fixed in placeHigh Energy Quad Design
Stroke = 0 mm
High Energy Quad Animation
Engineering of High Energy QuadSingle axis motion with one motor
and two ballscrewsTwo linear encoders to check position on both
sides with 1mm accuracyMaximum force is 16.4 kN per side, reduces
by x10 when stroke = 64 mmPM blocks bonded to steel bridge piece
and protective steel plate also bondedSteel straps added as extra
security
Very tight space constraintsPM Quads in CLICNorbert
Collomb11Assembled Prototype
Measured GradientMeasured Integrated GradientMeasured Field
Quality
Magnet Centre Movement
The magnet centre moves upwards by ~100 m as the permanent
magnets are moved away3D modelling suggests this is due to the
rails being ferromagnetic (r ~ 100, measured) and not mounted
symmetrically about the midplane should be easy to fixMotor/gearbox
assembly may also be a contributing factorLow Energy Quad
DesignLower strength easier but requires much larger tunability
range (x10)Outer shell short circuits magnetic flux to reduce quad
strength rapidlyNdFeB magnets with Br = 1.37 T (VACODYM 764 TP)2
permanent magnet blocks are 37.2 x 70 x 190 mmMax gradient = 43.4
T/m (stroke = 0 mm)Min gradient = 3.5 T/m (stroke = 75 mm)Pole gap
= 27.6 mmField quality = 0.1% over 23 mm
Stroke = 0 mmStroke = 75 mm
Poles and outer shell are permanently fixed in place.
Low Energy Quad AnimationEngineering of Low Energy
QuadSimplified single axis motion with one motor and one
ballscrewTwo linear encoders to check position on both sides with
1mm accuracyMaximum force is only 0.7 kN per sidePM blocks bonded
within aluminium support frame
Assembly at Daresbury
Assembly of poles
Outer shell added
PM block in frame
Poles
Outer shell
Lowering into measurement rig
Insertion of PMs
PMs inserted
Motor added
Low Energy Quad assembledNext: PM dipolesSTFC-CERN work package
from April 2014: investigate PM dipoles for:Drive Beam Turn Around
Loop (DB TAL)Main Beam Ring to Main Linac (MB RTML)Total power
consumed by both types: 15 MWReduced-length DB TAL prototype to be
constructed by Dec 2015TypeQuantityLength (m)Strength (T)Pole Gap
(mm)Good Field Region (mm)Field Quality Range (%)MB
RTML6662.00.53020 x 201 x 10-4 10 DB TAL5761.51.653 40 x 401 x
10-410100 SummaryThe CLIC Drive Beam quadrupoles are rather
challenging magnets because of their high strength and tight space
constraintsPM driven quads have many advantages in terms of
operating costs, infrastructure requirements, and power load in the
tunnelWe have shown that only two PM designs are required to cover
the entire range of gradients requiredThe high energy quad has been
prototyped and measured and found to successfully generate the
expected integrated gradientThe magnetic centre moves vertically as
the gradient is adjusted and modelling suggests this is due to
non-symmetric ferromagnetic railsFurther tests will be made to
confirm thisThe low energy quad has been designed and assembly of
the prototype is almost complete at DaresburyIt will undergo a
similar set of magnetic tests at Daresbury and then CERN
AcknowledgmentsDaresbury Laboratory teamMagnet design: Ben
Shepherd, Jim Clarke, Neil MarksMechanical design: Norbert Collomb,
James Richmond, Graham StokesCERN teamProject lead: Michele
ModenaMagnet measurements: Antonio Bartalesi, Mike Struik, Marco
Buzio, Samira KasaeiSupporting cast: Alexandre Samochkine, Dmitry
Gudkov, Evgeny Solodko, Alexander Aloev, Alexey Vorozhtsov, Guido
Sterbini
Thanks for your attention!Artwork: J. Flesher