magnets for a new low emitance storage ring at...
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Magnets for a new low emitance storage ring at ESRF
J. Chavanne ,G. Le Bec, P. N’Gotta, J.F. Bouteille
J. Chavanne
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Outline
New magnet lattice • Why? • Magnet requirement
Magnet design • Specifications • Constraints
Magnetic measurements • Integral • local
Summary
J. Chavanne
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Electron Beam Parameters
Parameter Existing lattice New lattice Energy [Gev] 6.03 6.03
Circumference [m] 844 844
Beam Current [mA] 200 200
Horizontal emittance [nm] 4 0.16
Vertical emittance [pm] 5 3
Energy Spread [%] 0.1 0.1
Beta at ID center , H x V [m] 37.6 x 3 (high Beta) 0.37 x 3 (low Beta)
3.35 x 2.79
Beam Size at ID center H x V [µm] 400 x 3.9 50 x 3.9
23.5 x 3.7
Beam Divergence at ID H x V [µrad] 10 x 1.3 107 x 1.3
6.9 x 1.3
Reduction of horizontal emittance by a factor of 25
J. Chavanne
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1015
1016
1017
1018
1019
1020
1021
1022
1023
Bril
lianc
e [P
h/s/
0.1%
bw/m
m2 /m
r2 ]
3 4 5 6 7 8 91 keV
2 3 4 5 6 7 8 910 keV
2 3 4 5 6 7 8 9100 keV
Photon Energy
1.6 m W150
4 m Helical U88
3.2 m U42
4.8 m U35
4 m CPMU18
Present lattice (plain) New lattice (dashed )
0.85 T bending magnet
4 m CPMU14
Electron beam: 6 GeV I=0.2 A
Higher brilliance
H emittance V emittance Energy spread [%]
Present 4 nm 5 pm 0.1
New lattice 0.16 nm 3 pm 0.1
J. Chavanne
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ESRF magnet lattice today: DBA (2BA)
New Lattice 7BA
Constraint: • same energy • fit new magnet lattice in existing ring (844 m) • Keep existing BM sources
Emittance reduction
! x ! E2 / N 3
Electron energy
Number of identical dipoles
J. Chavanne
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ESRF S10 Lattice
Quadrupole 55 to 80 Tm-1
Dipoles with longitudinal gradient
0.6 -> 0.15 T 0.4 -> 0.15 T
Sextupoles ~1500Tm-2
Octupoles ( ~ 50 000 Tm-3)
High gradient quadrupoles 100 Tm-1
Combined dipole quadrupoles 0.85 T / 45 Tm-1
and 0.3 T / 50 Tm-1
J. Chavanne
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Magnet type Quantity Total magnetic length[m] share
Dipole 7 11.38 65% Quadrupole 16 4.17 24% Sextupole 6 1.68 10% Octupole 4 0.4 2%
All magnets 33 17.6 100%
Total length of a cell: 26.376 m Length of ID straight section: 5.8 m
~ 3 m of drift space distributed between magnets ~ 8 m presently
Limited longitudinal space is a specificity of the new ESRF lattice
ESRF Accelerator upgrade: 1056 magnets to build
Compact magnet lattice
J. Chavanne
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Aperture and good field region
S10 All Horizontal [mm] Vertical [mm] Vacuum chamber aperture (radius) 15.1 10.1 Good field region (radius) 8.3 5.5
S10 Centre (high gradient) Horizontal [mm] Vertical [mm] Vacuum chamber aperture (radius) 8.3 5.5 Good Field Region (radius) 7 5
0 5 10 15 20 250
5
10
15
[m]
s [m]
x= 75.580 p/p=0.000
z= 27.620 32 periods, C= 844.405
0
0.05
0.1
0.15
disper
sion [m
]
x
z
x
S10 centre
Initial parameters for preliminary study
J. Chavanne
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J. Chavanne
Road map
• Project not yet funded (decision early 2015)
• Go ahead with prototype development and magnetic measurements
• 2013-2015
• Magnetic design • Mechanical design • First prototypes
• Improvement/development of magnetic measurement systems
• stretched wire/vibrating wire benches • Local field mapping • Other …
• …… 2019 all magnet installed
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• 3D magnetic modeling using RADIA
Native field integral calculation Electron beam tracking in magnet Efficient parameterization for various optimization
§ Pole shape § Geometrical errors budget § Electrical power § ….
J. Chavanne
• Achievable Magnet performance/ field quality in defined aperture
• Impact on vacuum chamber technology
• Impedance issue,….., etc
• Energy efficiency
Magnet design approach
P.M dipole
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J. Chavanne
Insertion Device Photon Beam Electron Beam
• Small bore radius = tight mechanical tolerances
• Mechanical length (limited space) à short coils
• Photon beam path specific to SR sources (open magnets)
• … etc
Geometrical design constraints
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Building Block
Sm2Co17 Magnet Min. gap 90 mm
Iron yoke
Pole Vertical field along beam path
(3D simulations)
PM weight ~ 25kg Total weight 400 ~500 kg Magnetic length: 2.07 m
Dipole with longitudinal gradient
J. Chavanne
Field tuning Dedicated movable shims : ± 3 % Coil: ± 100 A.turns ± 1.5 % of total Deflection angle
ESRF has a long experience with Permanent magnet systems (Insertion Devices)
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Pole shape optimization
∆B/B0
∆B/B,<10-4 (-15 mm <x<15 mm)
x
x
-200
-100
0
100
x10-6
-15 -10 -5 0 5 10 15
60 mm
Max field 0.6 T
J. Chavanne
20 mm
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35
30
25
20
15
10
5
0
-5
mm
2.01.81.61.41.21.00.80.60.40.20.0
Longitudinal position [m]
420
-2
mm
Electron trajectory
Best line fit
Fit ResidualsTranslated magnet modules
Magnet modules arrangement
Whole magnet oriented along mean beam path Modules translated horizontally by few millimeters Residual offsets vs local magnetic axis ±2.5 mm
All magnets with longitudinal gradient= 640 modules with similar shape and different amount of magnet blocks
~ 3.2 tons ( 380 dm3) of Sm2Co17 permanent magnets needed for all 128 magnets
J. Chavanne
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J. Chavanne
Combined dipole/quadrupoles Purpose : restore exiting BM source points for the new lattice
0.85 T 0.4 T soft end
6mrad @ 0.4 T 6mrad @ 0.85 T
0.334 T / 50 Tm-1
0.85 T / 45 Tm-1
6mrad @ 0.85 T
6mrad @ 0.334 T
Magnetic design under study Possibly based on Permanent Magnets as other dipoles Field tunability …..
Existing lattice
New lattice
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High gradient quadrupoles
No laminations • Storage ringà Constant field • Stringent mechanical tolerances • Demanding alignment
Field quality • Asymmetric GFR (∆G/G<10-3) • Optimization of the pole profile
Optimization criteria • Field quality in GFR • Power consumption • Compactness
J. Chavanne
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High gradient quadrupole design
Design parameters • Spec: 100 T/m x 335 mm • Bore radius: 11 mm
Magnet length • Mechanical length: 360 mm (iron
+coils) • 1 kW
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High gradient quadrupole design
Gradient vs. current Variation of multipole content (reference: 130 A)
Magnet close to saturation
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Integrated sextupole : 420 T/m nominal
2D sextupole: 1500 T/m2
Bore radius 19 mm
500
400
300
200
100
0
Inte
grat
ed se
xtup
ole
[T/m
]
1.51.00.50.0Average current density [A/mm2]
1200
1000
800
600
400
200
0
Power [W
]
correctors
Sextupole magnet
Mechanical length < 300 mm
Sextupole homogeneity < 1% in GFR
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Laminate yoke
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Octupoles
Needed for this lattice
Horizontal homogeneity of integrated octupole < 10 % in GFR
10
5 5 10x [mm]
[%]
2
1
1
Integrated octupole> 5000 T/m2
Mechanical length ≤ 100 mm
J. Chavanne
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Magnetic measurements
Stretched wire: • Integrated multipoles analysis • magnetic center • Other variants (vibrating wire) Adequate for
• Quadrupoles • Sextupoles • Octupoles • Dipole modules
• Curved magnets will need dedicated curved coils
ESRF stretched wire bench
Integral measurements
J. Chavanne
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Local field measurements
Rely on existing experience with Insertion Device Hall Mapping
Several units in operation • Modern mutli-axis control • High positioning accuracy • Appropriate for open magnets • Search coil vs hall sensors
Used for • Curved magnets (dipole) • Combined dipole/quadrupole
To be probably adapted for dipoles & combined function magnets
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J. Chavanne
Usual alignment based on fiducialisation not sufficient In situ alignment on girder with stretched wire/ vibrating wire seems better option RMS alignment error of 20 µm looks feasible ( wire length ~ 3m) (see Stretched wire measurements of magnet girders, G. Le Bec on Wednesday)
Difficult and essential part
Appropriate for straight magnet assembly (eg. quadrupoles sextupoles, etc) Magnet girder with combined dipole/quadrupole need other approach
Magnet alignment
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Summary
Very challenging magnets in focus @ ESRF
• Field performance close to magnetic saturation for quadrupoles, sextupoles
• High stability permanent magnet materials must enter in the process
• Preliminary magnetic design to be completed (combined function magnets)
• Magnetic measurements
• Stretched/vibrating wire is a good option
• Local field mapping to be refined
More to come at next IMMWs …..
J. Chavanne