Design study of CEPC Alternating Magnetic Field Booster

Design study of CEPC Alternating Magnetic Field Booster Tianjian Bian Jie Gao Michael Koratzinos （CERN） Dou Wang CEPC BD Meeting, Sept 25, 2015

Wiggling Bend Scheme Ø The inject energy is 6 Ge. V. Ø If all the dipoles have same sign, 33 Gs@6 Ge. V may cause problem. Ø In wiggling bend scheme, adjoining dipoles have different sign. Ø This scheme will avoid the low field problem. Ø Shorten the Damping times greatly.

Off-Axis-Quads@6 Ge. V n Defocusing Quad with Off-Axis Beam Ø Off-axis-quads have dipole compnent. Ø Every defocusing quad turn the beam by 0. 000872 rad. Ø 1952 off-axis-quads turn the beam by 0. 851072 rad, which lower dipoles field.

Linear Optics

Parameters n Contrast with the old disign Main Parameter Old@6 Ge. V New@6 Ge. V @120 Ge. V U 0 [Me. V/turn] 0. 019 0. 71 3013 Damping times(x/y) [s] 115. 6/115. 6 2. 4/3. 1 14. 43 E-3/14. 43 E-3 Emittances(x) [pi nm] 0. 0157 0. 15 6. 29 Strength of dipole [Gs] 33 -170/+227 657 Length of dipole [m] 19. 6*1 4. 9*4 Length of FODO [m] 47. 2

Parameters n Linac parameters Parameter Symbol Unit Value E- beam energy Ee- Ge. V 6 E+ beam energy Ee+ Ge. V 6 Repetition rate frep Hz 50 E- bunch population Ne- 2× 1010 E+ bunch population Ne+ 2× 1010 Energy spread (E+/E-) σE <1× 10 -3 Emitance (E-) 0. 1 mm mrad Emitance (E+) 0. 1 mm mrad

Dynamic Aperture n 1000 turns(182 ms) 9 sigma@injected emit 14 sigma@injected emit 365 sigma@equilibrium emit

Conclusion n The low field problem is solved by the wiggling bend scheme. Strength of dipole increase from 33 Gs to -170/+227 Gs. n Shorter damping times are obtained. 2. 4 s in x direction and 3. 1 s in x direction. It is also good news for DA. n Energy Spread of the Linac beam is 0. 1%. In this design(normalized by injected emit, 1000 turns): DA(x)=19 sigma@1%, DA(y)=18 sigma@1% DA(x)=14 sigma@2%, DA(y)=9 sigma@2% In the old design, about 6 sigma in the horizontal and 3 sigma in the vertical(80000 turns @0. 5%). But I don't think it solve the DA problem.

What to Do Next n Strength of dipole increase from -170 Gs to 657 Gs, it will cross 0 opint. So the way of ramping need carefully design. And also the effect of dipole with 0 strength must take into consideration. n 60° FODO cells will produce octupole terms. So more families of sextupole is need for nonlinear optics optimization. n Scan DA Carefully. At least 15000 turns(2. 7 s) is needed. 0. 5% energy spread may be OK.

Thanks for your attention!