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 5 May. 20092Detlef Swoboda @ CTC CLIC main parametersvalue Center-of-mass energy3 TeV Peak Luminosity7·1034 cm-2 s-1 Repetition rate50 Hz Beam pulse length200 ns Average current in pulse1 A Hor./vert. IP beam size bef. pinch53 / ~1 nm

3. 5 May. 20093 Final Focusing Use telescope optics to demagnify beam by factor M = f 1 /f 2 typically f 2 = L * f1f1 f 2 (=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 5 May. 2009Detlef Swoboda @ CTC4 QF1 QD0 L*3.5m Gradient200 - 575T/m Length3.26 - 2.73m Aperture (radius)4.69 - 3.83mm Outer radius< 35 - < 43mm Octupolar error106T/m3 Dodec. error1016T/m5 Peak field0.94 - 2.20T Field stability10^-4 Energy spread± 1%

5. Example 5 May. 2009Detlef Swoboda @ CTC5 ParameterDesign ValueUnit Gradient G500T/m Magnet Aperture 2*R 2 (PM) 20 (SC) mm Beam height h1nm Focal length L*3.5m De-amplification y50- crossing angle Φ20mrad I P *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] I P *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

6. Max G 5 May. 2009Detlef Swoboda @ CTC6 SC typeTemp [K ]Bcr [T]J [A/m2]G [T/m] Nb-Ti1.956*10^9300 Nb3Sn1.951*10^10500

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. 5 May. 2009Detlef Swoboda @ CTC7

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. 5 May. 2009Detlef Swoboda @ CTC8

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. 5 May. 2009Detlef Swoboda @ CTC9

10. PM Materials & Features 5 May. 2009Detlef Swoboda @ CTC10 MaterialCharacteristics samarium cobalt (Sm2Co17) Brittle corrosion resistant, no coating required neodymium iron boron (NdFeB) 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 Sm x Er l-x CoStability ~ 10 -6 /hr Strontium Ferrite (SrFe )dT = -0.19%/°C Barium Ferrite (BaFe )obsolete AlnicoLower performance ProsCons No pwr cablesAdjust. Range limitation No cryoDemagnetization, requires shielding No vibration Temperature gradient, requires temperature stabilization High coercivityRadiation tolerance Net force in Solenoid (μ > 1)

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 Steel Pole Pieces (Flux Return Steel Not Shown) Rotatable PM (Nd-Fe-B) Block to Adjust Field (+/  10%) PM (Strontium Ferrite) Section 5 May. 200911Detlef Swoboda @ CTC

12. 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. 5 May. 200912Detlef Swoboda @ CTC High gradient  heat load during adjustment

13. The first prototype of “superstrong” Permanent Magnet Quad. Integrated strength GL=28.5T (29.7T by calc.) magnet size.  10cm Bore  1.4cm Field gradient is about 300T/m PHOTO Cut plane view Axial view PM Soft iron 5 May. 200913Detlef Swoboda @ CTC

14. Magnetic Center Shift 5 May. 2009Detlef Swoboda @ CTC14

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]. 5 May. 2009Detlef Swoboda @ CTC15

16. SC Magnet Features 5 May. 2009Detlef Swoboda @ CTC16 Pros Cons Ramping, adjust settingServices; i.e. cables, cryo lines) Low sensitivity to external fieldsQuench, Training, thermal movements, deformations Temperature stabilityVibrations Knowledge base, state of the artCryostat Cross-section, inner bore radius Iron free magnet, no external forceHigh gradient multipole, geometrical tolerances SC back leg coil Coil dominated

17. IP Magnet Development 5 May. 2009Detlef Swoboda @ CTC17 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, …)

18. 5 May. 2009Detlef Swoboda @ CTC18

19. Test & Measurement Program Center Stability Strength Multipolar contents (good field region) Repeatability in Tuning Radiation Hardness Vibration Geometry 5 May. 2009Detlef Swoboda @ CTC19

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. 5 May. 200920Detlef 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). 5 May. 2009Detlef Swoboda @ CTC21

22. FFD Support & Tuning The FFD is subject to several severe constraints. One being the high beta function values required to satisfy the beam height of 1 nm specified at the CLIC interaction point. The resulting high gradient of the beta function makes it extremely difficult to obtain mechanical and magnetic tolerances over the length of more than 3 m for the quadrupole magnet. If permanent magnets are used a possible concept is the subdivision into a number of short sections which can independently be aligned and tuned. A stabilization study [5] used piezo electric elements to achieve an active alignment control in the nanometer range. This technology can be applied to an arrangement as shown. It is suggested to insert piezo elements in the upper and lower support. This will allow to obtain vertical alignment as well as rotation around the magnet axis for each magnet element separately. The decreasing values of the beta function close to the IP lead also to a relaxation of the alignment tolerances for the magnet sections close to the IP. Another possibility would be a tuning by moving sections axially with respect to the IP. 5 May. 2009Detlef Swoboda @ CTC22

23. FF doublet (NLC ZDR) 5 May. 200923Detlef Swoboda @ CTC

24. 24 CLIC Linear Collider (~2019): Final doublets in cantilever 2m50 Detector Vertical beam size at the interaction point: 1nm Tolerance of vertical relative positioning between the two beams to ensure the collision with only 2% of luminosity loss: 1/10nm Interaction point Scope of FFS Below 5Hz: Beam position control with deflector magnets efficient Above 5Hz: Need to control relative motion between final doublets 5 May. 2009Detlef Swoboda @ CTC