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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