Comparison of CEPC IR Sextupole Magnet Excitation Current

Schemes comparison for CEPC IR sextupole magnet about the excitation current Yingshun Zhu Institute of High Energy Physics, Chinese Academy of Sciences Aug. 30, 2021 CEPC working day

Outline Introduction Excitation current of sextupole magnet in 2018 CDR parameter Excitation current of sextupole magnet in updated CDR parameter Summary

Introduction Conceptual design of CEPC Interaction Region sextupole magnets was performed in 2018, using Superconducting magnet technology; the excitation current is more than 1KA. Recently, the requirement for IR sextupole magnets is updated; the magnet bore and pole field is reduced. Conceptual design and field calculation is performed. The result shows that, conventional sextupole magnet technology can be used to meet the updated requirement. The updated excitation current is small than 200A.

Excitation current of sextupole magnet in 2018 CDR parameter Superconducting magnet technology for IR sextupoles. The field in coil is around 2.7T at Higgs. Maximum current 1470A at Higgs. For tt bar, current will be 50% higher. Parameters of sextupole magnets at Higgs operation

Reduction of the pole tip field by physics optimization (Y.Wang) ????? ???=1 2??(? + )2 2 = 2*(vacuum chamber width + gap for installation) 10mm Inner aperture ? of the vacuum chamber Determined by the resistive wall impedance as it s larger than the beam stay clear region Reduced from 56mm to 33mm (factor larger than and about 0.42 ) Just reserve additional 2mm for beam stay clear region The growth of the resistive wall impedance is acceptable as short total length of sextupoles. (by Y. D. Liu) Gradient ??of the sextupole 33% margin for tuning has been removed (factor 0.67) Half length of the CDR value while keeping the integrated strength (factor 2.0 ) To get enough dynamic aperture just fulfill the requirement with currently considered effects more and more effects will be considered when the design of the machine go forward

Excitation current of sextupole magnet in updated CDR parameter Recently, the requirement for IR sextupole magnets is updated. (Y.Wang) The magnet aperture and pole field is reduced. If using conventional sextupole magnet technology, the magnet bore aperture is around 42 mm. Pole tip field is around 0.8T; Feasible .

2D field simulations are performed; different layouts.

If using DT4 pole, the magnet saturates around 3700 T/m2. Using FeCoV for pole, the field strength 3886T/m2can be achieved. DT4 is used for the yoke.

2D By along x 2D field harmonics (unit, 1 10-4) n Bn/B3@R=15.4mm HSIRU 10000 0.10 -0.07 -0.04 Bn/B3@R=14.9mm HSIRD 10000 0.08 -0.05 -0.01 3 9 15 21

Design parameters for the four types sextupole magnets at tt bar: VSIRD HSIRD VSIRU HSIRU Field strength (T/m2) 3179 3658 3037 3886 Magnet bore (mm) 42 42 42 42 Magnetic length (mm) 300 400 300 300 Copper, 7 7, 4.5 Conductor size (mm) Turns per pole 39 105 119 99 127 Excitation current (A Coil resistance ( ) 0.14 0.16 0.14 0.14 Voltage drop (V) 14.7 19.0 13.9 17.8 Joule loss (KW) 1.5 2.3 1.4 2.3 Number of water circuits 3 3 3 3 Temperature rise of coil (deg) 5.5 9.5 5.0 8.0 Core section (mm) 510 501.7 The current at H,W and Z model will decrease.

Summary With the updated requirement for CEPC IR sextupole magnets (CDR), conceptual design of sextupole magnets is performed. The bore aperture and pole tip field have been reduced, so conventional sextupole magnet technology can be used to meet the updated requirement (FeCoV pole used). In the conceptual design, the calculated field strength and multipole field content meet the requirement. In the updated design, the excitation currents of sextupole magnets are all small than 200A.

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