CEPC Booster Design Progress (Low field) T.J. Bian, X.H. Cui, Y.Y. Wei, C. Zhang CEPC-SPPC Symposium April 8-9, 2016

CEPC Booster Design Progress (Low field) Introduction Lattices of different cell length Dynamic aperture issues Background field in BEPC tunnel Pre-booster consideration Summary

One collider RF station: One booster RF station: 1. Introduction ½ RF ½ RF One collider RF station: 650 MHz five-cell SRF cavities; 4 cavities/module 12 modules, 8 m each RF length 120 m P.S. RF IP1 RF (4 IPs, 1132.8 m each) BTCe+ BTCe- 8 arcs 5852.8 m each D = 17.428 km RF IP4 IP2 RF C = 54. 752 km One booster RF station: 1.3 GHz 9-cell SRF cavities; 8 cavities/module 4 modules, 12 m each RF length 48 m 4 arc straights 849.6 m each RF LTB IP3 P.S. RF P.S. Linac ½ RF ½ RF

Comments on the CEPC-Booster PCDR (February 14-16, 2015, IHEP) Consider using combined function magnets (dipole with quadrupole/ sextupole terms) in the booster to reduce the number of components, increase the effective bending radius, reduce RF power and voltage, and reduce the construction costs. Determine the full tolerances on all known injection errors from the booster into the CEPC ring including short term (seconds) variations and long term (24 hours). Investigate whether longer pulse kickers can be made with sufficient tolerances to allow more than one bunch transfer per pulse into CEPC from the booster. ( Responced) ( Discuss with Magnet group)

Evaluate whether adding magnetic shielding (mu-metal) of the earth’s field mounted over the vacuum system between magnets will help the low energy operation of the booster. Develop a scheme to mask detector event triggering near the time of the injected top-up bunches by both the booster and detector design teams. Investigate whether the RF system for the booster could have the same frequency as that of the CEPC collider, thus, being less expensive to develop and have reduced long range maintenance costs. Check for issues in field quality, cycling, and ramping control of magnets arising from the low magnetic fields at the booster injection energy of 6 GeV. Consider an equal cell length to the collider ring to simplify the installation, etc. ( Discuss with RF Group) ( Responced)

CEPC design study towards CDR Optimization of lattice: Lcell=47.2m vs. Lcell=70.8 m. (ZC, CXH) Linear optics Chromaticity correction and dynamic aperture Machine errors and correction Sawtooth effect and their correction; Low field at injection and its tolerance: test, simulation and mitigation; (BTJ) Consideration of a pre-booster; (ZC) Instability: further simulation study. (BTJ) Injection: physical design. (ZC) Ejection: work together with collider injection. (CXH) Design of transfer line from linac to booster. (ZC) Design of transfer line from booster to collider. (CXH) Provide a full parameter list of reference design including field, aperture, RF, kicker pulse length, vacuum, diagnostics, and tolerances. (All) Cooperation with hardware systems in R & D. (ZC) (CXH WYY)

Lcell=47.2m vs. Lcell=70.8 m: Lattice function 1. Lattices of different cell length FODO cell Lcell=47.2m vs. Lcell=70.8 m: Lattice function SUP

Lcell=47.2m vs. Lcell=70.8 m: Lattice function BYPASS RING

Lcell=47.2m vs. Lcell=70.8 m: Parameters (E = 120 GeV, C = 54375 m)

Lcell=47.2m vs. Lcell=94.4 m: Lattice function FODO Cell RING SUP

3. Dynamic Aperture Issues Due to the weak damping at Low Energy, electrons in the booster should be stable at least during the time ramping to 120 GeV, 2s(12000Turns). The beam size at low energy is determined by the injection. In the booster, on center injection is adopted, and the Linac emittance is 0.3mm.mrad. At the DA tracking point, sx=5-6mm, sy=3-4mm. For injection, 3-5 Sigma dynamic aperture is needed. Energy Spread of the Linac beam is 0.1%, so maybe a 0.5% energy acceptance is enough? We should consider tune footprint in the dynamic aperture

Lcell=47.2m : Different tracking turns Dp/p = +2% Dp/p = +1% Dp/p = 0 Dp/p = -1% Dp/p = -2% Nturns =240 Nturns =5000 r = ey/ex = 0.01 nsixt=2 Lcell=47.2 m , nx=191.8, ny=191.7 tracking turns =12000 Dp/p = +2% Dp/p = +1% Dp/p = 0 Dp/p = -1% Dp/p = -2% Nturns =12000 Nturns =24000 r = ey/ex = 0.01 nsixt=2 Lcell=70.8 m , nx=128.2, ny=128.3 tracking turns =12000

Lcell=70.8m : Different tracking turns Dp/p = +2% Dp/p = +1% Dp/p = 0 Dp/p = -1% Dp/p = -2% Nturns =240 Nturns =5000 r = ey/ex = 0.01 nsixt=2 Lcell=47.2 m , nx=191.8, ny=191.7 tracking turns =12000 Dp/p = +2% Dp/p = +1% Dp/p = 0 Dp/p = -1% Dp/p = -2% Nturns =12000 Nturns =24000 r = ey/ex = 0.01 nsixt=2 Lcell=70.8 m , nx=128.2, ny=128.3 tracking turns =12000

Lcell=47.2m vs. Lcell=70.8 m: Dynamic aperture Dp/p = +2% Dp/p = +1% Dp/p = 0 Dp/p = -1% Dp/p = -2% r = ey/ex = 0.01 nsixt=2 Lcell=47.2 m , nx=191.8, ny=191.7 tracking turns =24000 Dp/p = +2% Dp/p = +1% Dp/p = 0 Dp/p = -1% Dp/p = -2% r = ey/ex = 0.01 nsixt=2 Lcell=70.8 m , nx=128.2, ny=128.3 tracking turns =24000

Remarks For the very long damping time of the CEPC booster at 6 GeV, the tracking turns for DA should be large enough. The DA’s of 12000 turns and 24000 turns look similar; Lcell=47.2m and Lcell=70.8 m are comparable in view point of DA, which needs to be improved to meet the linac parameters of ex,y=0.3 mm·mrad and sE=110-3. DA simulation with machine errors is being carried on.

FMA result

Dynamic aperture optimization Different ideas have been tried to enlarge the dynamic aperture. The one with Non-interleaved sextupoles is the best at present. p

FMA result for on-momentum particles

4. Background field in BEPC tunnel 【实验目的】 测量加速器设备产生的杂散磁场的大小， 作为CEPC设计的参考。 【实验时间】 2015年11月13日上午8:30-10:00 【测量仪器】LakeShore410 高斯计 【实验步骤】 （1）在BEPCII隧道外将高斯计清零。 （2）在以下地点测量磁场Bx，By和Bz分量的分布 十字通道，注入点，弧区B铁和Q铁之间，直线段，对撞区，励磁电缆 （3）对可能的场源进行屏蔽后进行测量

Magnetic field measurement in BEPCII tunnel 1.6 ~ 2 Gauss magnetic field is found at all places far from accelerator magnets in the BEPCII tunnel； This indicates that power cabling is one of major sources of the background field; Careful design of cabling system is proposed.

5. Pre-booster consideration Boosting: EBooster, inj =10-15-20 GeV  Bbooster, inj = 51.2-76.8-102.4 Gs, x,y,booster, inj = 26.9 - 8.0 - 3.4 s Accumulating: t x,y, inj ~ 0.5-1 s   (5-10) in APB Damping: x0(15 GeV) ~ 0.1 mmmrad   (1-5) in Booster

Bending radius E=15GeV  = 90 m B=0.56 T U0=49.8 MeV sE=1.3510-3

Injection Energy E=15GeV  = 90 m R= 180 m

Emittance E=15 GeV

Layout of APB Eee=15GeV, Epp=60GeV e- inj. e- inj. e- ej. e- inj. RF NB=144, NS=6 C =1382.4 m e0=0.10 mmmr NB=144, NS=4 C =1228.8 m e0=0.10 mmmr NB=144, NS=4 C =1152.0 m e0=0.10 mmmr e+ ej. e+ ej. (e+ ej.) RF RF e- ej. e- ej. (e- ej.) e+ inj. e+ ej. e+ inj. e+ inj. e- inj. e- inj. e- ej. e- inj. RF NB=96, NS=4 C =1108.8 m e0=0.29mmmr NB=96, NS=6 C =1411 m e0=0.29 mmmr NB=96, NS=4 C =1209.6 m e0=0.29 mmmr e+ ej. e+ ej. (e+ ej.) RF RF e- ej. e- ej. (e- ej.) e+ inj. e+ inj. e+ ej. e+ inj.

Layout of APB (Ns=6, NB=144) APB e- inj. e+ inj. & Accu. (1-5) e- ej. 120 GeV APB Linac Booster (e- ej.) RF 15 GeV 1382.4 m (e+ ej.) x=8s, B=76.8 Gs @15GeV 2-2.5 GeV e+ inj. & Accu. (5-10) e+ ej. e- inj. 60ns half-sine wave e+ B cycle Kicker B cycle frep=50 Hz e- B cycle

Lattice functions of APB FODO cell ARC Super-Period Ring

Main parameters of APB (Ns=6, NB=144)

Summary Design study on booster towards CDR has been carried on as planned. Update the booster design to meet the design progress of the collider (circumference, configuration, emittance, injection, etc.); Work together with hardware groups.

Backup slides

Lcell=47.2m vs. Lcell=70.8 m: Dynamic aperture Dp/p = +2% Dp/p = +1% Dp/p = 0 Dp/p = -1% Dp/p = -2% r = ey/ex = 0.01 nsixt=2 Lcell=47.2 m , nx=191.8, ny=191.7 tracking turns =240 Dp/p = +2% Dp/p = +1% Dp/p = 0 Dp/p = -1% Dp/p = -2% r = ey/ex = 0.01 nsixt=2 Lcell=70.8 m , nx=128.2, ny=128.3 tracking turns =240

Lcell=47.2m vs. Lcell=70.8 m: Dynamic aperture Dp/p = +2% Dp/p = +1% Dp/p = 0 Dp/p = -1% Dp/p = -2% r = ey/ex = 0.01 nsixt=2 Lcell=47.2 m , nx=191.8, ny=191.7 tracking turns =5000 Dp/p = +2% Dp/p = +1% Dp/p = 0 Dp/p = -1% Dp/p = -2% r = ey/ex = 0.01 nsixt=2 Lcell=70.8 m , nx=128.2, ny=128.3 tracking turns =5000

Lcell=47.2m vs. Lcell=70.8 m: Dynamic aperture Dp/p = +2% Dp/p = +1% Dp/p = 0 Dp/p = -1% Dp/p = -2% r = ey/ex = 0.01 nsixt=2 Lcell=47.2 m , nx=191.8, ny=191.7 tracking turns =12000 Dp/p = +2% Dp/p = +1% Dp/p = 0 Dp/p = -1% Dp/p = -2% r = ey/ex = 0.01 nsixt=2 Lcell=70.8 m , nx=128.2, ny=128.3 tracking turns =12000