clic ffd

CLIC FFD

Final Focusing Magnet AssessmentAnd

Proposal for a short term R&D effort

Global requirementsmagnets can be constructed, supported, and monitored so as to meet alignment tolerances

5 May. 2009 2Detlef Swoboda @ CTC

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 1 A

Hor./vert. IP beam size bef. pinch 53 / ~1 nm

f1 f2 f2

IP

final doublet

(FD)

5 May. 2009 3

Final Focusing

Use telescope optics to demagnify beam by factor M = f1/f2 typically f2= L*

f1 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.

Detlef Swoboda @ CTC

CLIC FF doublet parameters

5 May. 2009 Detlef Swoboda @ CTC 4

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 %

Example


Parameter Design Value Unit

Gradient G 500 T/m

Magnet Aperture 2*R 2 (PM)20 (SC)

mm

Beam height h 1 nm

Focal length L* 3.5 m

De-amplification y 50 -

crossing angle Φ 20 mrad

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]

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]

Inner cryostat for SC magnet Rsc = 10 mm

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

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.


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.


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.


Sr Ferrite Nd-Iron SM-CobaltBr Gauss 3850 12300 10500

Hci Oersteds 3050 12000 11000BH(max) MGO 3.5 35.0 26.0

Temp variation % 0.18 0.11 0.045Cost $/ cc 0.04 7.75* 3.66

PM Materials & Features


Material Characteristicssamarium cobalt (Sm2Co17) Brittle

corrosion resistant, no coating requiredneodymium iron boron (NdFeB) Ductile

susceptible to corrosion, requires coatingcan lose strength under irradiationultrahigh coercivity grades show very small remanence losses, <0.4%±0.1%, for absorbed doses up to 3 Mgy from 17 MeV electronsirradiation by 200 MeV protons does reduce the remanence considerablyCurie T ~ 300 degC

SmxErl-xCo Stability ~ 10-6/hrStrontium Ferrite (SrFe ) dT = -0.19%/°CBarium Ferrite (BaFe ) obsoleteAlnico Lower performance

Pros ConsNo pwr cables Adjust. Range limitationNo cryo Demagnetization, requires shieldingNo vibration Temperature gradient, requires temperature

stabilizationHigh coercivity Radiation tolerance

Net force in Solenoid (μ > 1)

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

Steel

PM

PM

Steel Pole Pieces (Flux Return Steel Not Shown)

Rotatable PM (Nd-Fe-B) Blockto Adjust Field (+/- 10%)

PM (Strontium Ferrite) Section


Double Ring Structure –Adjustable PMQ-

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.


• High gradient heat load during adjustment

The first prototype of “superstrong” Permanent Magnet Quad.

Integrated strength GL=28.5T (29.7T by calc.) 　　　　　　　　　　　　 magnet size. f10cmBore f1.4cmField gradient is about 300T/m

PHOTO

Cut plane view

Axial view

PM

Soft iron

dzdrdB

GL


Magnetic Center Shift


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].


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 coilCoil dominated

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, …)

Test & Measurement Program

• Center Stability• Strength• Multipolar contents (good field region)• Repeatability in Tuning • Radiation Hardness• Vibration• Geometry


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 Qualification Magnets Conception El. Eng. / Physicist Modeling (FEM), Simulation Mech. Eng. Optics, beam performance Beam optics specialist Design Draftsman Models, Prototypes, Test assemblies Technician, Mech. Eng. El. Magnetic measurements El. Eng. Survey, Expertise Survey Eng.


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).


clic ffd

Documents

detlef swoboda

permanent magnets

direction of orientation

criticalanisotropic

sc magnet rsc

magnet assessmentandproposal

permanent magnet technology

pm quadrupoles