Magnet design at the ESRF G. Le Bec, J. Chavanne, J.-F. Bouteille, P. N’gotta Low Emittance Rings workshop 2013, Oxford, UK Overview Context • New ESRF lattice • Design constraints Magnetic design • • • • • Simulation tools Dipoles Quadrupoles Tolerances Crosstalk Summary and conclusion G. Le Bec et al. -- Low Emittance Rings workshop, Oxford, 2013 I - Context G. Le Bec et al. -- Low Emittance Rings workshop, Oxford, 2013 S10 Lattice Quadrupole 55 to 80 Tm-1 High gradient quadrupoles 100 Tm-1 Octupoles Dipoles with longitudinal gradient 0.16 0.6 T Combined dipole quadrupoles 0.85 T / 45 Tm-1 and 0.3 T / 50 Tm-1 Sextupoles 2000 to 3000 Tm-2 G. Le Bec et al. -- Low Emittance Rings workshop, Oxford, 2013 S10 Lattice Zone 1 Zone 2 Magnet Tolerance in GFR 2-poles DB/B < 10-4 4-poles DG/G < 10-3 6-poles DH/H < 10-2 Zone 1 Zone 1 Horizontal [mm] Vertical [mm] Vacuum chamber aperture (radius) 15 10 Good field region (radius) 13 9 Zone 2 (high gradient) Horizontal [mm] Vertical [mm] Vacuum chamber aperture (radius) 8.3 5.5 Good field region (radius) 7 5 G. Le Bec et al. -- Low Emittance Rings workshop, Oxford, 2013 S10 Lattice G. Le Bec et al. -- Low Emittance Rings workshop, Oxford, 2013 S10 Lattice Apertures needed for X-ray ports G. Le Bec et al. -- Low Emittance Rings workshop, Oxford, 2013 S10 Lattice Limited longitudinal space between magnets (3 m/cell) G. Le Bec et al. -- Low Emittance Rings workshop, Oxford, 2013 Magnet designs Field quality Integrated strength Bore radius Horizontal aperture Power consumption Magnet length G. Le Bec et al. -- Low Emittance Rings workshop, Oxford, 2013 Magnet designs Dipoles • Longitudinal field gradient • Good field quality Combined dipole-quadrupoles • High gradient / high field • Good field quality Quadrupoles • High gradient • Good field quality • Tuning Sextupoles are more conventionnal G. Le Bec et al. -- Low Emittance Rings workshop, Oxford, 2013 Permanent vs. resistive magnets PM Resistive Scale factor k B1 Bk Magnet size at constant aperture Smaller Bigger Tuning range 5 to 10 % Up to 100 % Resistance to radiation damage Good for Sm2Co17 Good Field quality Good if iron dominated Good Experience in storage rings Insertion devices Steerers Multipole magnets Other aspects… • No knob with PM magnets • PM price vs. running cost • Environmental aspects? G. Le Bec et al. -- Low Emittance Rings workshop, Oxford, 2013 Permanent vs. resistive magnets Under study To be studied Dipole with long. gradient PM+coils Resistive Dipole-quadrupole Resistive PM+coils Quadrupole Resistive Resistive+PM Sextupole Resistive Octupole Resistive G. Le Bec et al. -- Low Emittance Rings workshop, Oxford, 2013 II – Magnet design G. Le Bec et al. -- Low Emittance Rings workshop, Oxford, 2013 3D Simulation tools RADIA software • Volume integral method • Fully parameterized 3D models • Field integrated computation Field analysis tools • 2D field and integrated field multipoles • Circular and elliptic multipoles • 3D multipole expansion (a) Optimization tools • Pole shape optimization • Sensitivity analysis • Fast computations (b) (a) Simulation of the magnetic interaction between quadrupole and dipole magnets. (b) Tangential field map at r = 7 mm. G. Le Bec et al. -- Low Emittance Rings workshop, Oxford, 2013 Dipole with longitudinal gradient Iron yoke Sm2Co17 Magnet Pole Magnetic design view Vertical field along beam path e- Arrangement of PM dipole modules (top view) G. Le Bec et al. -- Low Emittance Rings workshop, Oxford, 2013 Dipole with longitudinal gradient Sm2Co17 permanent magnets • Resistance to radiation damage • Temperature stability • PM mass/dipole: 25 kg Iron blocs Tuning coil • +/- 2.5 % at 150 A turns Local field tuning • Iron shims • +/- 5 % accessible Local shimming G. Le Bec et al. -- Low Emittance Rings workshop, Oxford, 2013 High gradient quadrupole Design parameters • Spec: 100 T/m x 335 mm Iteration #1 • • • • Bore radius: 11 mm Iron length: 300 mm Power: 1 kW Vertical gap between poles: 8 mm Electrical power vs. magnet length Iteration #2 • • • • Bore radius: 12.5 mm Iron length: 335 mm Power: 1.4 kW Vertical gap between poles: 10 mm Magnetic design view G. Le Bec et al. -- Low Emittance Rings workshop, Oxford, 2013 Field quality optimization 40 10-4 Before optimization 10 10-4 Standard pole profile: truncated hyperbola After optimization • Computation time <1h with a 3D model Optimized pole profile Gradient error plots (1000 Dg/g). Top: Dg/g < 0.4%, before optimization. Bottom: Dg/g < 0.1%, after optimization. The field was specified within the green ellipse. G. Le Bec et al. -- Low Emittance Rings workshop, Oxford, 2013 Mechanical tolerances Random errors on pole profiles Field errors at 7 mm (HG quadrupole) Gradient errors at 7 mm (HG quadrupole) On axis field error (dipole) Two questions: • Achievable tolerances for 500 mm long magnets ? • Which field quality is really necessary for beam dynamics ? G. Le Bec et al. -- Low Emittance Rings workshop, Oxford, 2013 Mechanical tolerances Repeatability of magnet assembly Magnet opening Vacuum chamber installation Horizontal misalignment and quadrupole roll angle Vertical offset and octupolar gradient error at 7 mm G. Le Bec et al. -- Low Emittance Rings workshop, Oxford, 2013 Mechanical tolerances Mechanical measurements • Typical CMM accuracy: a bL • Example: 4ft FARO arm, 500 mm long magnet [μm] 5 0.008 L[mm] 9 μm • Arbitrary surfaces are not easy to measure Magnetic measurements • Stretched wire measurements • Small bore radius: higher sensitivity to position errors • Accuracy of a few 10-4 b2 at r =12 mm Sensitivity of stretched wire harmonic measurements to linear stage errors, at r =12mm G. Le Bec et al. -- Low Emittance Rings workshop, Oxford, 2013 Magnetic crosstalk Compact lattice • Short space between magnets • Magnetic interaction between neighboring magnets ? 3D multipole expansion B r , , z Im n kmn z ei n r n 2 m1 n 1 m0 Br r , , z Re n 2m kmn z ei n r n 2 m1 n1 m0 High gradient quadrupole and PM dipole. Distance between yokes is d. • The kmn functions are obtained from the 2D FFT of the field B r0 , , z • The m=0 terms contribute to the integrated field • The m>0 terms are induced by the fringe field and lead to aberrations G. Le Bec et al. -- Low Emittance Rings workshop, Oxford, 2013 Magnetic crosstalk 3D multipoles 2D field map B (r, , z) at r = 7 mm Main field harmonics with non-zero integral. k01: dipole (r0ei) k02: quadrupole (r1ei2) Fringe field induced harmonics. k11: sextupole like (r2ei) k12: octupole like (r3ei2) G. Le Bec et al. -- Low Emittance Rings workshop, Oxford, 2013 Magnetic crosstalk Integrated field errors Quadrupole magnet • Bore radius 12.5 mm • Length: 335 mm, gradient: 100 T/m Dipole magnet • Vertical aperture 22 mm • Length: 400 mm, Max field: 0.65 T Impact @ d=100 mm • Quad. centre displacement: 4 µm • Quadrupole decreases by 0.05 % • Parasitic sextupole: DB/B=10-3, DG/G =2 10-3 Impact @ d=55 mm • Quad. centre displacement: 20 µm • Quadrupole decreases by 0.2 % • Parasitic sextupole: DB/B=2 10-3, DG/G =4 10-3 Integrated field errors due to the crosstalk between a dipole and a quadrupole. Normalization by the quadrupole integrated field at r = 7 mm. G. Le Bec et al. -- Low Emittance Rings workshop, Oxford, 2013 Magnetic crosstalk Local field errors Crosstalk dipolequadrupole • Parasitic dipole and sextupole are correlated • Impact on the whole quad length at large d • Additionnal extremity effect at smaller d G. Le Bec et al. -- Low Emittance Rings workshop, Oxford, 2013 III – Summary and conclusion G. Le Bec et al. -- Low Emittance Rings workshop, Oxford, 2013 Challenges Magnetic design • • • • Strong gradients Short space between magnets Some exotic devices Reasonable power consumption Manufacturing • Tight tolerances • Machining cost and delays Magnetic measurements • Small aperture • Alignment of high gradient magnets Short planning • More than 1000 magnets • Installation completed in 2019 G. Le Bec et al. -- Low Emittance Rings workshop, Oxford, 2013 Prototype magnet designs Status of prototype magnets Magnet Technology Magnetic design Mechanical design Dipole with long. gradient PM Well advanced Well advanced High gradient quadrupole Resistive Well advanced In progress Combined dipole-quad Resistive Started Sextupole Resistive Well advanced Octupole Resistive Well advanced Well advanced G. Le Bec et al. -- Low Emittance Rings workshop, Oxford, 2013 To do Design • Combined dipole-quadrupole • Resistive dipoles and hybrid quadrupoles for comparison • Correctors Prototypes • Manufacturing • Magnetic measurements TDS • June 2014 Serial magnets • Design • Manufacturing and tests Installation G. Le Bec et al. -- Low Emittance Rings workshop, Oxford, 2013
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