CLIC FFD

1. CLIC FFD Final Focusing Magnet Assessment And Proposal for a short term R&D effort

2. Global requirements magnets can be constructed, supported, and monitored so as to meet alignment tolerances Detlef Swoboda @ CTC

3. Final Focusing f1 f2 (=L*) Use telescope optics to demagnify beam by factorM = 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. Detlef Swoboda @ CTC

4. CLIC FF doublet parameters Detlef Swoboda @ CTC

5. Example 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 magnetRsc = 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] DetlefSwoboda @ CTC

6. Max G Detlef Swoboda @ CTC

7. 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. Detlef Swoboda @ CTC

8. 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. Detlef Swoboda @ CTC

9. 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. Detlef Swoboda @ CTC

10. PM Materials & Features Detlef Swoboda @ CTC

11. 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) Detlef Swoboda @ CTC

12. 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. Detlef Swoboda @ CTC

13. 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 Detlef Swoboda @ CTC

14. Magnetic Center Shift Detlef Swoboda @ CTC

15. 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]. Detlef Swoboda @ CTC

16. SC back leg coil SC Magnet Features Coil dominated Detlef Swoboda @ CTC

17. 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 degKsuperfluid, conduction cooled, …) Detlef Swoboda @ CTC

18. Detlef Swoboda @ CTC

19. Test & Measurement Program • Center Stability • Strength • Multipolar contents (good field region) • Repeatability in Tuning • Radiation Hardness • Vibration • Geometry Detlef Swoboda @ CTC

20. 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. Detlef Swoboda @ CTC

21. 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). Detlef Swoboda @ CTC