Development of Adjustable Permanent Magnet Quadrupoles
Ben Shepherd
ASTeC, STFC Daresbury Laboratory, UK
ALERT 2019 workshop: Advanced Low Emittance Rings Technology
Ioannina, Greece
10-12 July 2019
www.astec.stfc.ac.uk@astecstfc
Overview
• Motivation
• Use of PMs in accelerators
• The ZEPTO project
• Outlook and conclusions
Ben Shepherd ∙ ALERT 2019 ∙ Ioannina, Greece ∙ 10-12 July 2019 2
Permanent MagnetsMotivation and use in accelerators
Ben Shepherd ∙ ALERT 2019 ∙ Ioannina, Greece ∙ 10-12 July 2019 3
Motivation – electricity consumption• Particle accelerators are big energy users
• Magnets can account for 10-20% of the energy use of accelerators
LHC (CERN)
•77 MW average
•37 MWmagnets and cryogenics
Diamond Synchrotron (UK)
•6-7 MW
•0.75 MWmagnets
Spallation Neutron Source (USA)
•28 MW (summer)
•2.5 MWmagnets
CLIC design (CERN)
•582 MW
•124 MWmagnets
CERN, Electricity Flyer 2015DLS, tweetSNS, tweet
IOP, Physics World June 2019
Ben Shepherd ∙ ALERT 2019 ∙ Ioannina, Greece ∙ 10-12 July 2019 4
Green issues are in the news!
Motivation – electricity cost• Cost of electricity is going up and will probably continue to do so
UK average electricity prices (p/kWh)
DECC Quarterly Energy Prices, March 2015 / Ovo Energy
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UK Office of National Statistics SN04153 (2016)
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EU-28 electricity prices (c/kWh)
Eurostat “Electricity price statistics”, 2017
Ben Shepherd ∙ ALERT 2019 ∙ Ioannina, Greece ∙ 10-12 July 2019 5
Permanent MagnetsEnergy density (BH) in PM
• Permanent magnets already widely used in accelerators: mostly for undulators and wigglers in light sources
• Best materials today:• Nd2Fe14B for
highest strength (Br)• Sm2Co17 for
highest stability (Hcj)• Pr2Fe14B at low
temperature (77 K)
Br > 1.45 T
BH in second quadrant for today’s materials
Ben Shepherd ∙ ALERT 2019 ∙ Ioannina, Greece ∙ 10-12 July 2019 6
Vacuumschmelze, Rare Earth PMs
PMs in accelerators
Advantages
• No power, so no heat
• No water, so no vibration
• Compact
Disadvantages
• Tuning difficult – and slow
• PMs variable
• Temperature dependent
• Radiation damage
Ben Shepherd ∙ ALERT 2019 ∙ Ioannina, Greece ∙ 10-12 July 2019 7
PM Temperature Variation
• Permanent magnets have high temperature coefficients• NdFeB: -0.1%/°C
• SmCo: 0.03%/°C
• Possible to compensate using FeNi shunt• Alloy with low
Curie temperature (55°C)
• Reduce dB/B to 10-5/°Caround room temperature
PM
FeNi shunt
YokePoles
Bertsche et al, PAC95 FAP21Foster et al, EPAC98 TUX02ABenabderrahmane, IPAC2017 THYB1
Ben Shepherd ∙ ALERT 2019 ∙ Ioannina, Greece ∙ 10-12 July 2019 8
External energy source
Release of energy
Decrease of ordering of magnetic moments
Decrease of magnetic
anisotropy
Nucleation of an inverse domain
Expansion of domain wall
Demagnetisation
PM Radiation Damage• Exposure to radiation leads to PM demagnetisation
• Two mechanisms:• Energy release in wide region caused by low-energy particles (γ, e-, n0)
Similar to demagnetisation caused by heating
• Local hot spot caused by high-energy neutronDemagnetisation correlates with star density (hadronic inelastic/elastic collisions)
• Amount of demagnetisation depends on dose and energy
Bizen et al, NIM A 574 (2007) p401-406Bizen, ERL2011 WG5005Maréchal, EPAC2006 THPCH135
Ben Shepherd ∙ ALERT 2019 ∙ Ioannina, Greece ∙ 10-12 July 2019 9
Radiation Damage Prevention
• Choose magnets with higher coercivity Hcj• NdFeB OK to 1015 neutrons/cm2
• SmCo OK to 1019 neutrons/cm2
• Design magnetic circuit with higher permeance• Changes internal magnetic field, reduce nucleation of inverse domains
• Change shape or working point of magnet permeance
• Reduce the temperature (increases coercivity)• NdFeB at room temperature: 27% demagnetisation for 1.5x1014 electrons at 2.5 GeV• At 140 K, 1% demagnetisation with same dose of e-
• Bake the magnets• Unbaked NdFeB: 2% demagnetisation for 5x1014 electrons at 2 GeV• Bake to 415 K for 24h (gives 0.7% demag): 0.2% demagnetisation with same dose
• Partial substitution of Dy for Nd in NdFeB (increases coercivity)
• Move magnets away from beam! Bizen et al, EPAC2004 WEPLT103Bizen et al, NIM A A 515 (2003) 850–852
Shepherd, CERN-ACC-2018-0029Ben Shepherd ∙ ALERT 2019 ∙ Ioannina, Greece ∙ 10-12 July 2019 10
Permanent Magnet Quadrupoles
Ben Shepherd ∙ ALERT 2019 ∙ Ioannina, Greece ∙ 10-12 July 2019 11
Permanent Magnet Quadrupoles
• Halbach array
• Typically small aperture
• Fixed (and quite high) gradient
• For ri = 10 mm, re = 20 mm, Br = 1.38 T, M = 16 G = 130 T/m
• Widely used
• Also dipoles, sextupoles…
Halbach, NIM 169, p. 1-10 (1980)Benabderrahmane, IPAC2017 THYB1
𝐺 = 2𝐵𝑟𝐾1
𝑟𝑖−1
𝑟𝑒Number of segments M 4 8 12 16 20 24
Efficiency factor K 0.32 0.77 0.89 0.94 0.96 0.97
ri
re
SABR Enterprises LLC
Ben Shepherd ∙ ALERT 2019 ∙ Ioannina, Greece ∙ 10-12 July 2019 12
CBETA PM Combined Function Magnets
• Combined function magnets using custom Halbach array
• Field error correction using thin steel rods
Ben Shepherd ∙ ALERT 2019 ∙ Ioannina, Greece ∙ 10-12 July 2019 13
Brooks, IPAC2019 THPTS088Brooks, JAI 2019
ESRF PM Quadrupole
• Designed for light sourceswith a port for X-ray light
• Medium fixed gradient
• PM block tolerances not critical for good field quality
• Prototype built:• 85 T/m gradient
• 226 mm length
• 12 mm bore radius
• Field quality (with shimming): 1x10-3 within ±7 mm (H), ±5 mm (V) N’gotta et al, Phys. Rev. Accel. Beams 19, 122401 (2016)
Ben Shepherd ∙ ALERT 2019 ∙ Ioannina, Greece ∙ 10-12 July 2019 14
ILC adjustable PM quadrupole• Designed for ILC final focus
• Based on Gluckstern “5-ring” design
• Total length 270 mm, bore radius 25 mm
• Adjustable by rotating rings• Maximum integrated gradient 6.8 T (average 26 T/m)• Minimum 0.02 T (0.006 T/m)
• Axis shift 50 µm (H), 100 µm (V) in 40-100% range
• Also studied:• Double nested ring PMQ: 10 mm bore radius, 230 mm length
16.5-115 T/m (6.7 T/m steps)• Fast-cycling PM sextupole (25 Hz)• PM octupole
Mihara et al, IEEE Trans. Appl. Supercon. 16, 2 (2006), p224-227Iwashita et al, IEEE Trans. Appl. Supercon. 22, 3 (2012), 4000905-4000905Iwashita, LCWS2014 Ben Shepherd ∙ ALERT 2019 ∙ Ioannina, Greece ∙ 10-12 July 2019 15
SOLEIL Adjustable Quadrupole: QUAPEVA
Marteau et al, APL (2017)
• Iron-cobalt poles
• Rotating PM cylinders for adjustment
• Prototype parameters:• 12 mm gap
• 100 mm length
• 110-210 T/m gradient (factor of 2 adjustment range)
• Centre movement: 20 µm
• Triplet of quadrupoles installed on COXINEL laser-plasma beamline
Ben Shepherd ∙ ALERT 2019 ∙ Ioannina, Greece ∙ 10-12 July 2019 16
More tunable quadrupoles
• NLC prototype
• Four independent PMs with linear motion
• 6.5 mm bore radius
• 420 mm length
• 17-163 T/m
• CLIC QD0 prototype
• High-gradient, narrow aperture
• Coils for adjustment
• 4.13 mm bore radius
• 100 mm length
• 150-514 T/m gradient
Gottschalk, PAC05 MPPT029
Modena, Low Consumption Magnet Workshop 2014
Ben Shepherd ∙ ALERT 2019 ∙ Ioannina, Greece ∙ 10-12 July 2019 17
• Developed for CLIC by STFC in collaboration with CERN
• NdFeB magnets with Br = 1.37 T (VACODYM 764 TP)
• 4 permanent magnet blocks each 18 x 100 x 230 mm
ZEPTO Quadrupoles: High Strength
Stroke = 0 mm
Stroke = 64 mm• Gradient 15-60 T/m
• Pole gap 27.2 mm
• Field quality ±0.1% over 23 mm
• Length 230 mm
Poles are permanently fixed
in place
Ben Shepherd ∙ ALERT 2019 ∙ Ioannina, Greece ∙ 10-12 July 2019 18
ZEPTO Q1 Prototype
• Prototype built at STFC Daresbury Laboratory and measured at CERN
• Single motor drives movement through gearboxes and LH/RH ballscrew
• Maximum force: 16.4 kN per side
• Confirmed gradient, field quality, tuning range
• Magnetic centre movement 100 µm due to ferromagnetic rails
Shepherd et al, IEEE Transactions on Applied Superconductivity, vol. 22, no. 3, pp. 4004204-4004204, June 2012Shepherd et al, IPAC2013 THPME043 “Prototype Adjustable Permanent Magnet Quadrupoles For CLIC”
Ben Shepherd ∙ ALERT 2019 ∙ Ioannina, Greece ∙ 10-12 July 2019 19
ZEPTO Quadrupoles: Low Strength• Outer shell short-circuits magnetic flux
to reduce quad strength rapidly
• NdFeB magnets with Br = 1.37 T (VACODYM 764 TP)
• 2 PM blocks are 37.2 x 70 x 190 mm
• Gradient range 3.5-43 T/m
• Pole gap 27.6 mm
• Field quality ±0.1% over 23 mm
• Length 190 mm
Stroke = 0 mm Stroke = 75 mm
Poles and outer shell are
permanently fixed in place
Shepherd et al, IPAC2014 TUPRO113“Design and Measurement of a Low-Energy Tunable Permanent Magnet Quadrupole Prototype”
Ben Shepherd ∙ ALERT 2019 ∙ Ioannina, Greece ∙ 10-12 July 2019 20
ZEPTO Q2 Prototype
• Prototype built at STFC Daresbury Laboratory and measured at CERN
• Confirmed gradient, field quality, tuning range
• Magnetic centre movement 80 µm
• Patented design of both quadrupoles
• Ongoing collaboration with CERN to develop PM-based concepts for CLIC design study
Shepherd et al 2014 JINST 9 T11006Clarke et al, IEEE Transactions on Applied Superconductivity, vol. 24, no. 3, pp. 1-5, June 2014Clarke et al, patents WO2012046036, US8829462
Ben Shepherd ∙ ALERT 2019 ∙ Ioannina, Greece ∙ 10-12 July 2019 21
ZEPTO-DLS Project• STFC are designing and building a ZEPTO tunable PM
quadrupole for Diamond's BTS transfer line• Replacement for an existing electromagnetic quadrupole• Funded by STFC’s Proof of Concept fund (PoCF),
£120k for materials and STFC staff costs • Further step towards commercialisation of our innovative
magnets• ‘Live’ demonstration of PM quadrupole technology on a
working accelerator
• Project plan and milestones• Stage 1: magnetic and mechanical design
Final design review July 2019• Stage 2: procurement and build
Assembly complete March 2020• Stage 3: testing and verification
Testing complete May 2020• Stage 4: delivery and installation
Installation complete July 2020• Stage 5: operation on DLS
Report after first year September 2021
• Quadrupole specifications• Max integrated gradient 7.6 T• Min integrated gradient 0.2 T• Aperture diameter 32 mm• Field quality ΔG/G0 < 5x10-3 at r ≤ 10 mm• Splittable to allow installation around
vacuum chamber
CAD model of the design
Survey targets
Magnet frame and
poles
PM carriage (x2)
Drive system
Adjustable feet (x4)
PM blocksSm2Co17, Br 1.03 T72x94x268 mm90 mm movement
Ben Shepherd ∙ ALERT 2019 ∙ Ioannina, Greece ∙ 10-12 July 2019 22
Small-aperture tunable quadrupoles• Specifications
• Gradient: 85 T/m
• Aperture diameter: 25 mm
• Tuning range: ±10% using coils
• Wedge-shaped PMs• NdFeB, Br 1.30 T
• 44 mm long, 28 mm at wide end
Ben Shepherd ∙ ALERT 2019 ∙ Ioannina, Greece ∙ 10-12 July 2019 23
Current density [A/mm²] 7.0 0.0 -7.0
Gradient [T/m] 81.7 71.7 61.5
Integrated gradient [T] 9.596 8.494 7.342
Relative to nominal +12.9% -13.6%
Magnetic length [mm] 117.4 118.4 119.4
2D profile
3D model
-0.012
-0.01
-0.008
-0.006
-0.004
-0.002
0
0.002
0 2 4 6 8 10 12
Fiel
d q
ual
ity,
GL
/ G
L₀
x [mm]
7.00
0.00
-7.00
Permanent Magnet Dipoles
Ben Shepherd ∙ ALERT 2019 ∙ Ioannina, Greece ∙ 10-12 July 2019 24
• Upgrade of Sirius design from 3BA to 5BA• Circumference: 480 m 518 m• Emittance: 1.7 nm rad 250 pm rad
• PM-based “Superbend”: 20 magnets• 105x55x30 mm NdFeB blocks, Br 1.36 T• 3.2 T in magnet centre• 0.5 T + 9.5 T/m on flanks• Minimum gap 11 mm
• Adjustments• Low field pole shift, ±5 mm: B ±4% • Floating pole angle, ±3°: G ±4% • “Control gap”, -3.2mm: 3% in B and G
Sirius “Superbend” Dipole
Citadini, MT-25 (2017) Tue-Af-Po2.02-07; private communication
Ben Shepherd ∙ ALERT 2019 ∙ Ioannina, Greece ∙ 10-12 July 2019 25
floating poles
• ESRF-EBS upgrade: DBA 7BA• 3.8 nm rad 134 pm rad
• Sm2Co17 PMs combined with steel poles and yokes
• Length 1.7 m in 5 modules; gap 25.5-30.5 mm
• Field:• DL1 0.17-0.67 T
• DL2 0.17-0.54 T
• Total of 128 magnets needed for ESRF upgrade
ESRF Longitudinal Gradient Dipoles
Benabderrahmane, IPAC2017 THYB1
Ben Shepherd ∙ ALERT 2019 ∙ Ioannina, Greece ∙ 10-12 July 2019 26
SPring-8 Adjustable PM Dipole• SPring-8-II upgrade: 5BA lattice at 6 GeV• Emittance reduced to 100-150 pm rad• Dipoles:
• One normal bend (NB):0.95 T, 420 mm length, 25 mm gap
• Four longitudinal gradient bends (LGBs):0.79 T, 1750 mm length, 25 mm gap
• Adjustable PM prototypes• Move top and bottom steel plates to adjust field• NB prototype built (100 mm length), now being tested
• 0.007-0.118 T using 40 mm stroke (factor 14 adjustment range)• Temperature compensation using FeNi alloy, 10-4/°C
• LGB protype in manufacture• PM-based DC septum
• Fixed PM dipole magnet installed in booster to storage ring transport line• 1.1 T, 2 m length
Watanabe et al, Phys. Rev. Accel. Beams 20, 072401 (2017)
Courtesy of T. Watanabe
Ben Shepherd ∙ ALERT 2019 ∙ Ioannina, Greece ∙ 10-12 July 2019 27
ZEPTO Dipole Design• Prototype based on specifications for CLIC DB turnaround loops
• PM block: 500x400x200 mm, NdFeB VACODYM 745, Br 1.38 T
• 0.46-1.1 T tuning range (355 mm stroke), gap 44 mm
• Built and tested at Daresbury Laboratory
A.R. Bainbridge et al, IPAC2017 THPIK105 “The ZEPTO Dipole”
Ben Shepherd ∙ ALERT 2019 ∙ Ioannina, Greece ∙ 10-12 July 2019 28
Tuning range
ZEPTO Dipole Measurements
Ben Shepherd ∙ ALERT 2019 ∙ Ioannina, Greece ∙ 10-12 July 2019 29
Dipole on the measurement bench
Pole gap issue:0.25 mm difference end-end
Flu
x d
ensi
ty /
T
Position / mm
0.475
0.477
0.479
-250 -150 -50 50 150 250
0.475
0.477
0.479
-250 -150 -50 50 150 250
Fixed
Field in midplane
Bainbridge et al, IMMW21 (2019)
Danfysik Green Magnetshttp://www.danfysik.com/en/products/magnets/permanent/
Bødker et al, IPAC2014 TUPRO080
• PM dipole with coils for adjustment
• 30° dipole for ASTRID2 injector, Aarhus
• 1 T, 30 mm gap, 1000 mm length
• Adjustment range: ±3%
• Temperature compensating material used to reduce temperature variation to < 30ppm/°C
Ben Shepherd ∙ ALERT 2019 ∙ Ioannina, Greece ∙ 10-12 July 2019 30
0
1000
2000
3000
4000
5000
6000
7000
Halbach, r=6mm ILC fixed ESRF Gottschalk ZEPTO-Q1 ZEPTO-Q2 ILC nested rings ILC 5-ring QUAPEVA CLIC QD0
equ
ival
ent
Am
per
e-t
urn
s p
er p
ole
[A
]
Summary of PM projects
fixed linear motion rotation coils
0
5
10
15
20
25
30
35
40
SPring-8 ZEPTO-D1 Danfysik/ASTRID2
equ
ival
ent
Am
per
e-t
urn
s [k
A]
linear motion coils
𝑁𝐼 =𝐺𝑟2
2𝜇0
To calculate “equivalent Ampere-turns”:
Quadrupoles Dipoles
𝑁𝐼 =𝐵𝑔
𝜇0
To calculate “equivalent Ampere-turns”:
Ben Shepherd ∙ ALERT 2019 ∙ Ioannina, Greece ∙ 10-12 July 2019 31
(Ad
just
able
in s
tep
s)
Conclusions
• Many accelerators are now using PM dipole and quadrupoles
• Several advantages to using PMs:• Compact• Low power• No vibration
• Disadvantages can be mitigated• Tuning• Temperature variation• Radiation effects
• Variety of different tuning methods
Ben Shepherd ∙ ALERT 2019 ∙ Ioannina, Greece ∙ 10-12 July 2019 32
