CLIC FFD
Final Focusing Magnet Assessment
And
Proposal for a short term R&D effort
Global requirements
magnets can be constructed, supported, and monitored so as to meet alignment tolerances
5 May. 2009
CLIC main parameters
value
Center-of-mass energy
3 TeV
Peak Luminosity
7·1034 cm-2 s-1
Repetition rate
50 Hz
Beam pulse length
200 ns
Average current in pulse
1A
Hor./vert. IP beam size bef. pinch
53 / ~1 nm
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Final Focusing
final
doublet
(FD)
f1
f1
f2
IP
f2
f2 (=L*)
Use telescope optics to demagnify beam by factor M = f1/f2 typically f2=
L*
The final doublet FD requires magnets with very high quadrupole
gradient in the range of ~250 Tesla/m  superconducting or
permanent magnet technology.
5 May. 2009
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CLIC FF doublet parameters
QF1 QD0
L*
3.5
m
Gradient
200 - 575
T/m
Length
3.26 - 2.73
m
Aperture (radius)
4.69 - 3.83
mm
Outer radius
< 35 - < 43
mm
Octupolar error
106
T/m3
Dodec. error
1016
T/m5
Peak field
0.94 - 2.20
T
Field stability
10^-4
Energy spread
±1
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%
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Example
Parameter
Design Value
Unit
Gradient G
500
T/m
Magnet Aperture 2*R
mm
Beam height h
2 (PM)
20 (SC)
1
Focal length L*
3.5
m
De-amplification y
50
-
crossing angle Φ
20
mrad
nm
IP*z = G * R^2/(2 * µº) = (500*1*10^-6)/(2*4*π*10^-7)=6.25*10^2/ π=198 [A]
– Ampere-turns/pole [Br (@ pole tip) = 500 mT]
Inner cryostat for SC magnet Rsc = 10 mm
IP*z = G * R^2/(2 * µº) = (500*100*10^-6)/(2*4*π*10^-7)=6.25*10^4/ π=19800 [A]
– Ampere-turns/pole [Br (@ Rsc) = 5 T]
5 May. 2009
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Max G
SC type
Temp [K ]
Bcr [T]
J [A/m2]
G [T/m]
Nb-Ti
1.9
5
6*10^9
300
Nb3Sn
1.9
5
1*10^10
500
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Design issues for permanent magnets
(1)
•
•
•
•
•
•
PM quadrupoles might appear as an attractive option for the FFD. A variety of
materials are available which can be selected for a specific application.
Flux density gradients in the order of magnitude required for CLIC have been
achieved with short samples [4].
Machining to the necessary dimensional tolerances is not a fundamental problem
and the cross-sectional dimensions are basically rather modest. Intrinsic
drawbacks are however given by the environment through the exposure to
external magnetic field, temperature variation and ionizing radiation.
The design of the magnet must in addition take the magnetization spread of +- 10
% between individual PM material bricks into account. Longitudinal variation of
several % have to be expected. For anisotropic materials the orientation direction
can normally be held within 3° of the nominal with no special precautions.
In practice this requires an iterative adjustment of geometrical dimensions,
selection of components and shimming.
For quadrupoles a precise balancing between opposite poles is one of the difficult
requirements. Since this tuning is exposed to environmental and operational
changes, a recalibration, if necessary, would imply a full reconstruction and
recommissioning of the magnet.
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Design issues for permanent magnets
(2)
• Orientation direction (and tolerance of orientation direction is critical)
• Anisotropic magnets must be magnetized parallel to the direction of
orientation to achieve optimum magnetic properties.
• Supply of components (bricks) magnetized or magnetization of assembled
magnet
• Coating requirements (Nd Fe B)
• Acceptance tests or performance requirements
• Not advisable to use any permanent magnet material as a structural
component of an assembly.
• Square holes (even with large radii), and very small holes are difficult to
machine.
• Magnets are machined by grinding, which may considerably affect the
magnet cost.
• Magnets may be ground to virtually any specified tolerance.
5 May. 2009
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PM materials
•
•
•
•
•
Strontium Ferrite may be considered for the following features:
Cost, ease of fabrication, radiation hardness and stability over temperature and
time. Drawback is certainly the reversible temperature coefficient of the residual
field Br of -0.19%/°C. However, adding compensation shims allows to minimize
the effect. This method requires a number of modify, measure, correct cycles.
Samarium cobalt is roughly 30 times more expensive and has suspect radiation
resistance [4].
Alnico is approximately 10 times more expensive and due to lower coercivity, an
Alnico design will result in a tall, bulky magnet.
Barium Ferrite is a largely obsolete material with no advantages over Strontium
Ferrite and should not be seriously considered.
Br Gauss
Hci Oersteds
BH(max) MGO
Temp variation %
Cost $/ cc
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Sr Ferrite
3850
3050
3.5
0.18
0.04
Nd-Iron
12300
12000
35.0
0.11
7.75*
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SM-Cobalt
10500
11000
26.0
0.045
3.66
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PM Materials & Features
Material
samarium cobalt (Sm2Co17)
neodymium iron boron (NdFeB)
SmxErl-xCo
Strontium Ferrite (SrFe )
Barium Ferrite (BaFe )
Alnico
Pros
No pwr cables
No cryo
No vibration
High coercivity
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Characteristics
Brittle
corrosion resistant, no coating required
Ductile
susceptible to corrosion, requires coating
can lose strength under irradiation
ultrahigh coercivity grades show very small
remanence losses, <0.4%±0.1%, for absorbed
doses up to 3 Mgy from 17 MeV electrons
irradiation by 200 MeV protons does reduce the
remanence considerably
Curie T ~ 300 degC
Stability ~ 10-6/hr
dT = -0.19%/°C
obsolete
Lower performance
Cons
Adjust. Range limitation
Demagnetization, requires shielding
Temperature gradient, requires temperature
stabilization
Radiation tolerance
Net force in Solenoid (μ > 1)
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Permanent Quad Concepts
•A new style of permanent magnet multipole has been described.
•achieve linear strength and centerline tuning at the micron level
by radially retracting the appropriate magnet(s).
• Magnet position accuracies are modest and should be easily
achievable with standard linear encoders
Rotatable PM (Nd-Fe-B) Block
to Adjust Field (+/- 10%)
PM (Strontium
Ferrite) Section
Steel Pole Pieces
(Flux Return Steel
Not Shown)
P
M
Steel
PM
5 May. 2009
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Double Ring Structure –Adjustable PMQ-
•High gradient  heat load during adjustment
The double ring structure
PMQ is split into inner ring and outer ring. Only the outer ring is rotated 90 around
the beam axis to vary the focal strength.
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The first prototype of
“superstrong” Permanent Magnet Quad.
Cut plane view
Soft iron
PM
Axial view
PHOTO
Integrated strength GL=28.5T (29.7T by calc.)
magnet size. f10cm
Bore
f1.4cm
Field gradient is about 300T/m
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dB
GL  
dz
dr
13
Magnetic Center Shift
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Design issues for SC magnet
•
•
•
•
•
•
Design and construction of SC low-B quadrupoles for particle accelerators can rely on
widespread and large experience. The demanding tolerances for CLIC however are several
magnitudes above already achieved performances. Whereas the field quality (multipole,
homogeneity) might be manageable [9], stability issues (electrical, vibrations, temperature)
are major issues.
Contrary to PM magnets tuning for different beam energies and compensation of external
magnetic fields is possible but might require correction coils and consequently increase the
complexity and cross-section.
The required high field strength would however be rather demanding for the mechanical
design and will also have an impact on the cross-section of the magnet.
In addition the magnet aperture is determined by the space requirements for the inner bore
of the cryostat and therefore obviously larger than in the case of a PM design.
In the framework of the GDE (global design effort) SC magnet concepts have been proposed
and prototype work is in progress [7].
By applying a serpentine winding technique the diameter for the cryostat of a prototype
quadrupole could be reduced to the order of magnitude necessary for an equivalent PM [8].
5 May. 2009
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SC Magnet Features
Pros
Cons
Ramping, adjust setting
Services; i.e. cables, cryo lines)
Low sensitivity to external fields
Quench, Training, thermal movements, deformations
Temperature stability
Vibrations
Knowledge base, state of the art
Cryostat Cross-section, inner bore radius
Iron free magnet, no external force
High gradient
multipole, geometrical tolerances
SC back leg coil
Coil dominated
5 May. 2009
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IP Magnet Development
• ILC – Americas WS
(14- 16 Oct. 2004 @ SLAC)
– For Energy and Optics Tuning  adjustable magnet is
desirable.
– SC Quadrupole concept similar to HERA II meets basic
requirements.
– Not enough knowledge about stabilization on nm
level.
– Realistic Prototype required BUT cooling concept
needs to be defined; i.e.
(4.5 degK sub-cooled, 2 degK superfluid, conduction cooled,
…)
5 May. 2009
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5 May. 2009
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Test & Measurement Program
•
•
•
•
•
•
•
Center Stability
Strength
Multipolar contents (good field region)
Repeatability in Tuning
Radiation Hardness
Vibration
Geometry
5 May. 2009
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FDD R&D Project
• FF Quad magnet technology
– High gradient ( N x 100 T/m) requires permanent/SC
technology
– Combination of both types?
– Need to define strategy, resources, timescale.
Task
Magnets Conception
Modeling (FEM), Simulation
Optics, beam performance
Design
Models, Prototypes, Test assemblies
El. Magnetic measurements
Survey, Expertise
5 May. 2009
Qualification
El. Eng. / Physicist
Mech. Eng.
Beam optics specialist
Draftsman
Technician, Mech. Eng.
El. Eng.
Survey Eng.
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Conclusions
• It is obvious, that substantial studies and prototyping will be
necessary for both technologies in order to be able to make a firm
statement about feasibility and cost.
• Considerable work on SC magnets can be – and has been –done on
existing magnets for evaluating vibration, repeatability and related
issues.
• PM magnets of large size which could be used for similar studies are
not known.
• A possible strategy could therefore consist in continuing work on
existing SC magnets for early detection of major problems.
• In parallel would be interesting of following and/or joining ongoing
or starting development projects for SC and PM quadrupole
magnets (e.g. in the field of FELs etc).
5 May. 2009
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