CEPC/SppC Status -Report from Accelerator Group J. Gao On behalf of CEPC/SppC Group IHEP The 4 th CEPC Meeting Shanghai Jiaotong University, Sept. 13, 2014 Future High Energy Particle Colliders in China

Talks and discussions in accelerator session TalkCEPC/SppC StatusJie Gao 1High field magnetsQingjin Xu 2 Design of collision areaYiwei Wang 3 Beam collective effectsNa Wang 4 Design of injection systemXiaohao Cui 6DiscussionChairperson: Jie Gao  Participants: Yifang Wang, Weiren Chou, Jie Gao, Qingjin Xu, Jiyuan Zhai, Yiwei Wang, Na Wang, Xiaohao Cui, et al participated

Writing assigned for Pre-CDR 4CEPC - accelerator physics 4.1Main parameters Guo Yuanyuan, Geng Huiping, Wang Dou, Xiao Ming, Gao Jie 4.2Lattice Geng Huiping, Wang Dou, Guo Yuanyuan, Wang Na, Wang Yiwei, Xiao Ming, Peng Yuemei, Bai Sha, Su Feng, Xu Gang, Duan Zhe, Gao Jie 4.3IR and MDI Wang Dou, Geng Huiping, Wang Yiwei, Bai Sha,, Gao Jie 4.4Beam instabilityWang Na, Wang Yiwei 4.5Beam-beam effects Zhang Yuan, Guo Yuanyuan, Wang Dou, Xiao Ming, Gao Jie 4.6Synchrotron radiationMa Zhongjian, Geng Huiping 4.7Injection and beam dumpCui Xiaohao, Su Feng, Xu Gang 4.8BackgroundYue Teng 4.9PolarizationDuan Zhe  Visitors from other labs in the world participate the Pre-CDR joint works

International participation (April, 2014) Visitors name PeriodTopics Dick TalmanApril 13th –May 15thParameters and other topics Armen ApyanApril 1st –April 30thGuineaPig and CAIN Yoshihiro FunakoshiApril 1st-April 15thParameter, injection and others Dmitry ShatilovApril 1st- April 16thBeam-beam simulation Kazuhito OhmiApril 16th-April 30thBeam-beam simulation Yunhai CaiApril 16th –April 30thLattice and FFS Yuhong ZhangApril 16th-April 30thElectron proton collider

Pre-CDS status Finished the draft Writing Preparing

CEPC Layout LTB : Linac to Booster BTC : Booster to Collider Ring BTC IP1 IP2 e+e- e+ e- Linac (240m) LTB CEPC Collider Ring(50Km) Booster(50Km) BTC Is the machine parameter choice consistent and reasonable? Why CEPC takes one ring design?

Luminosity from colliding beams For equally intense Gaussian beams Expressing luminosity in terms of beam-beam limitation Geometrical factor: - crossing angle - hourglass effect Particles in a bunch Transverse size (RMS) Collision frequency 7 The expression for in storage ring colliders is of primary importance, since is not a constant, but a machine parameter dependent value, including N Ip

Beam-beam tune shift limit analytical calculations For lepton collider: For hadron collider: where SppC (actual parameter list) FCC (pp) (theory and design) Formulae from private note of J. Gao r_e is electron radius γ= is normalized energy R is the dipole bending radius N_IP is number of interaction points r_p is proton radius J. Gao, Nuclear Instruments and Methods in Physics Research A 533 (2004) 270–274 J. Gao, Nuclear Instruments and Methods in Physics Research A 463 (2001) 50–61

ParameterUnitValueParameterUnitValue Beam energy [E]GeV120Circumference [C]km53.6 Number of IP[N IP ] 2SR loss/turn [U 0 ]GeV3 Bunch number/beam[n B ] 50Bunch population [Ne] 3.71E+11 SR power/beam [P]MW50Beam current [I]mA16.6 Bending radius [  ] m6094 momentum compaction factor [  p ] 4.15E-05 Revolution period [T 0 ]s1.79E-04Revolution frequency [f 0 ]Hz emittance (x/y)nm 6.79/  IP (x/y) mm800/1.2 Transverse size (x/y) mm 73.7/0.16  x,y /IP 0.1/0.074 Beam length SR [  s.SR ] mm2.35 Beam length total [  s.tot ] mm2.66 Lifetime due to Beamstrahlung min80 lifetime due to radiative Bhabha scattering [  L ] min56 RF voltage [V rf ]GV6.87RF frequency [f rf ]MHz650 Harmonic number [h] Synchrotron oscillation tune [ s ] Energy acceptance RF [h]%5.56 Damping partition number [J  ] 2 Energy spread SR [  .SR ] %0.13 Energy spread BS [  .BS ] %0.07 Energy spread total [  .tot ] %0.15nn 0.22 Transverse damping time [n x ] turns81 Longitudinal damping time [n  ] turns40 Hourglass factorFh0.679Luminosity /IP[L]cm -2 s E+34 Main parameters for CEPC

CEPC Beam-beam simulations The current main parameters has been checked with beam- beam simulation, proved the reasonability. （ Ohmi, Zhang Yuan, Demitry Shatilov)

CEPC lattice layout IP1 IP2 RF Critical parameters for CEPC: Circumference: 50 km SR power: 50 MW/beam 16*arcs 2*IPs 8 RF cavity sections (distributed) 6 straights (for injection and dump) Filling factor of the ring: ~80%

Lattice of arc sections  Length of FODO cell: 48m  Phase advance of FODO cells: 60/60 degrees  Dispersion suppressor on each side of every arc  Length: 96m

Lattice of straight sections  Length straight: 144m  Phase advance of FODO cells: 60/60 degrees  FFS is temporarily replaced by FODO cells  Length of each IP section: 576m  Used for workpoint adjustment

14 Dynamic aperture of the MR  2 families of sextupoles are used for chromaticity correction  Working point of the ring (.08,.22)  Achieved dynamic aperture ： ~100  x /1500  y

 Use 2 pairs of electrostatic separators  Beam separated at horizontal plane with orbit offset of 5  x  Maximum bunch number: 96 Pretzel scheme

CEPC lattice with FFS In current design: Circumference: 52.1 km 16*arcs: 2.64 km (60 FODO) 12*short straight: 352m (8 FODO) 4*long straight: ~700 m Bending radius: 5.7 km U0: 3.77GeV Nature emittance: 7.67 nm Nature energy spread: 0.19% Nature bunch length : 2.82mm Momentum compaction: 3.3E-5 (FFS)

Half Quad of dispersion suppressor IP FFS entrance condition: DX=DPX=0  x=  y=0 betax=75.6m betaY=25.6m FFS optics betaX*=0.8m betaY*=0.0012m L*=2.5m We use the same method as Yunhai’s example to make a new design of CEPC FFS. 17 Total length: 170 m

Lattice of the whole ring  Dynamic aperture: 16  x/ 30  y for on momentum particles

Dynamic Aperture (L*=2.5m) 5x5x 4y4y DA for 2%,-2% is 0 By Dou Wang and Demin Chou

The tune dependence on the energy deviation

Momentum bandwidth In MADX, the tunes suddenly drop to zero beyond 1%.

Tune diagram Dp=0 Dp=-2% Dp=1% Tune cross the second, third and fourth order, the beam is unstable, may cause the drop of the tune ?

Phase space after 1000 turns On momentum (dp=0) Tracking in x-pxTracking in y-py  Taking into account of the length of the sextupoles (0.3m) in FFS, without optimization of the FFS.  Far from the desired performance.

Phase space after 1000 turns On momentum (dp=1%) Tracking in x-pxTracking in y-py  the horizontal Dynamic aperture phase space seems not zero, but the vertical one drops to zero.

Phase space after 1000 turns Off momentum 2% Tracking in x-pxTracking in y-py  Dynamic aperture could be almost zero.

Primary IR optics with L*=1.5m betx*=0.8m, bety*=1.2mm, L*=1.5m IPFTCCYCCXMT FT: final telescopic transformer CCY: chromatic correction section y CCX: chromatic correction section x MT: matching telescopic transformer Yiwei Wang, 3 Sep 2014

Optics of whole ring IR+ARC

Dynamic Aperture On momentum Off momentum:  2%,  1%

Final Doublet Beam stay-clear region (L*=2.5m) – Rx=5 σx_inj, Ry=5 σy_inj –  x_inj=21.8nm,  y_inj=2.2nm (assume 10% coupling for injection beam) – Inner radius of vacuum chamber at Q1 and Q2: 1.8cm IP [m] Q1Q2 Rx Ry vacuum chamber L*=2.5m Q1: L=0.56m, R=1.8cm, G=-516T/m D2=1.14m Q2: L=0.58m, R=1.8cm, G=364T/m

CEPC Magnets’ specifications

CEPC SRF System Layout 8 RF sections In each ~ 150m section Main ring: - 12 x 8m cryomodules MHz 5-cell SRF cavity - 4 cavities / cryomodule Booster: - 4 x 12m cryomodules GHz 9-cell SRF cavity - 8 cavities / cryomodule 31 Superconducting RF Cavity ~ 20 x CW gradient less disruption to beam 100s times more efficient LLRF benefits compared to normal conducting

CEPC SRF System Parameters ParametersCEPC-ColliderCEPC-BoosterLEP2 Cavity Type 650 MHz 5-cell Nb N-doped 1.3 GHz 9-cell Nb N-doped 352 MHz 4-cell Nb/Cu sputtered Cavity number V cav / V RF 18 MV / 6.87 GeV20 MV / 5.04 GeV12 MV / 3.46 GeV E acc (MV/m) peak6 ~ 7.5 Q0Q0 4.2K Cryo AC power (MW)202.5 (15% DF)6.1 Cryomodule number96 (4 cav)32 (8 cav)72 (4 cav) RF input power / cav (kW)26020 peak125 RF source number384 (300 kW kly)256 (25 kW SSA)36 (1.2 MW/8 cav) RF AC power (MW)200 (260 installed)2.4 (15% DF)85 HOM damper power (W)26 k (ferrite+hook)5 (hook) (15% DF)300 (hook)

Coupler Power Handling Capability Impact on Main Ring Cost and Risk Coupler Power (kW) E acc (MV/m) Cavity # Module Cost (Billion CNY) M CNY / cavity (including coupler, tuner, LLRF, cryomodule, etc) Balance and optimize: coupler high power yield and operation risk, module and power distribution cost reduction, cavity operation margin risk, cryogenic installation and operation cost (due to Q-drop, field emission, gradient change), ring impedance …

650 MHz 5-cell Cavity internal Left end half cell Right end half cell Riris(mm) Alpha(deg) A(mm) B(mm) a(mm) b(mm) L(mm) D(mm)206.6 flatness2.17% coupling3.04% Ep/Eacc2.43 Hp/Eacc [mT/(MV/m)] Need further shape optimization, especially for the HOM properties

650 MHz 5-cell Cavity Parameters ParameterSymbolUnitValue RF frequency f RF MHz650 RF voltage V RF GV6.87 Cavity gradient E acc MV/m15.6 Effective length (five cells) L eff m1.147 Cavity voltage VcVc MV18 Number of cavities 384 Cavities in one cryomodule 4 Cryomodule length m8 Number of cryomodules 96 R/Q Ω514 Geometry factor GΩ268 Iris diameter mm156 Quality factor Q0Q0 2~3×10 10 External Q of input coupler Q ext 2.4×10 6 RF power per cavity P in kW260 Cavity longitudinal loss factor ※ k∥k∥ V/pC1.87 Cavity transverse loss factor ※ k⊥k⊥ V/pC m10 ※ σ z = 2.66 mm 3~4×10 10 for Vertical Test 18 MV/m for vertical test

650 MHz 5-cell Cavity HOMs Monopole Modef (GHz)R/Q (Ω) * Q L Limit TM E+5 TM E+5 Dipole Modef (GHz)R/Q (Ω/m) ** Q L Limit TE E+4 TM E+4 TE E+4 TM E+4 36 * k ∥ mode = 2πf · (R/Q) / 4 [V/pC] ** k ⊥ mode = 2πf · (R/Q) / 4 [V/(pC · m)]

1.3 GHz 9-cell Cavity Parameters ParameterSymbolUnitValue RF frequency f RF GHz1.3 RF voltage V RF GV5.04 Cavity gradient E acc MV/m20 Effective length (nine cells) L eff m1.038 Cavity voltage VcVc MV20 Number of cavities 256 Cavities in one cryomodule 8 Cryomodule length m12 Number of cryomodules 32 R/Q Ω1036 Geometry factor GΩ270 Iris diameter mm70 Quality factor Q0Q0 2×10 10 External Q of input coupler Q ext 1×10 7 RF power per cavity P in kW20 Lorentz force detuning factor kLkL Hz/(MV/m) 2 1 Cavity longitudinal loss factor ※ k∥k∥ V/pC5.8 Cavity transverse loss factor ※ k⊥k⊥ V/pC m25 ※ σ z = 3.89 mm Over-coupled for larger BW

1.3 GHz 9-cell Cavity HOMs Monopole Mode f (GHz)R/Q (Ω) * Q L measured TM TM Dipole Modef (GHz)R/Q (Ω/m) ** Q TE TM TM TE * k ∥ mode = 2πf · (R/Q) / 4 [V/pC] ** k ⊥ mode = 2πf · (R/Q) / 4 [V/(pC · m)]

HOM Power of the Collider CEPC Collider LEP2 Loss factor (HOM) V/pC below cut-off above cut-off HOM power per cavity 6.51 kW Operation 66nC 2*4 bunches 300W100 W200 W Design 100nC 2*36 bunches 6.6kW 2.2 kW (LHC 1 kW) 4.4 kW 1 ~ 2 kW extracted by the HOM coupler technically possible (LEP and LHC) KEKB16 kW SuperKEKB40 kW Add the broad band loss, 4 cavity module will generate ~ 40 kW HOM power A small fraction of power extracted by HOM coupler, most HOM power propagates in the cavities and finally go outside of the module.

5cell module of BNL 704MHz

41 Impedance budget Resistive wall impedance is calculated with analytical formulas Impedance of the RF cavities is calculated with ABCI ObjectContributions R [k  ] L [nH]k loss [V/pC] |Z // /n| eff [  ] Resistive wall (Al) RF cavities (N=378) Total

42 Single-bunch effects ParameterSymbol, unitValue Beam energyE, GeV120 CircumferenceC, km53.6 Beam currentI 0, mA16.6 Bunch numbernbnb 50 Natural bunch length  l0, mm 2.66 Emittance (horz./vert.)  x /  y, nm 6.79/0.02 RF frequencyf rf, GHz0.65 Harmonic numberh Natural energy spread e0e0 1.5E  3 Momentum compaction factor pp 4.15E  5 Betatron tune x / y / Synchrotron tune s Damping time (H/V/s)  x /  y /  z, ms 14/14/7 (paramter_lattice )

43 Bunch lengthening –Steady-state bunch shape is obtained by Haissinski equation –Bunch is shortened due to the capacitive impedance of the RF cavity( only resistive wall and RF cavity considered ) Pseudo-Green function wake (  z =0.5mm) Steady-state bunch shape Longitudinal microwave instability –Keil-Schnell criterion: –The threshold of the longitudinal impedance is |Z // /n| < .

44 Bunch lengthening with SuperKEKB’s geometry wake –LER wake+RW+RF (bunch is lengthened by 9.0%) –HER wake+RW+RF (bunch is lengthened by 18.5%)

45 Space charge tune shift Coherent synchrotron radiation –  z  1/2 /h 3/2 =9.2 (=> CSR shielded) –The threshold of bunch population for CSR is given by –The CSR threshold in BAPS is N b,Th = 5.0  >> N b = 3.7  –CSR is not supposed to be a problem in BAPS.  y =  1.7e  4,  x =  5.0e  6 (K. Bane, Y. Cai, G. Stupakov, PRST-AB, 2010)

46 Transverse mode coupling instability (TMCI) –The threshold of transverse impedance is |Z  | < 28.3 M  /m. –The equivalent longitudinal impedance is 2.66 , which is much larger than that of the longitudinal instability. Eigen mode analysis Considering only resistive wall impedance Beam current threshold: I b th =11.6mA (I 0 th =578mA)

47 Multi-bunch effects Transverse resistive wall instability with  pn = 2  f rev  (pn b + n + x,y )  The growth rate for the most dangerous instability mode is 1.1 Hz (  =0.9 s) in the vertical plane with mode number of  = 20.  The growth time is much higher than the transverse radiation damping time.  The resistive wall instability is not supposed to happen in the main ring! Growth rate vs. mode number in the vertical plane

Instability growth rate vs. vertical tuneInstability growth rate vs. chromaticity  Smaller decimal tune are preferred to alleviate the transverse resistive wall instability.  The growth rate is not quite sensitive to the chromaticity.

49 Electron cloud instability KEKBSuperKEKBSuperBCEPC Beam energy E, GeV Circumference L, m Number of e + /bunch, Emittance H/V  x /  y, nm 18/ / / /0.02 Bunch length  z, mm Bunch space Lsp, ns Single bunch effect Electron freq.  e /2 , GHz Phase angle  e  z /c Threshold density  e,th, m Multi-bunch effect p-e per meter n , p/(m)5.0E81.5E93.6E91.1E10 Characteristic frequency  G, MHz Phase angle  G L sp /c Threshold density for the single bunch effect is considerable high. The phase angle for the multi-bunch effect is about two orders higher, so the electrons are not supposed to accumulate and the multipacting effects is low.

50 Beam ion instability Ion trapping – With uniform filling pattern, the ions with a relative molecular mass larger than A x,y will be trapped. Fast beam ion instability – With uniform filling, the growth time considering ion oscillation frequency spread is 6.9ms, which is lower than the damping time. – Fast beam ion instability could occur with uniform filling. –The ions will not be trapped by the beam.

Booster bypass design Collider Booster: Outer of Collider CEPC

Booster lattice

FODO Lattice functions: booster vs. collider Version 1 Version 2

A SUP Lattice functions: booster vs. collider Version 1 Version 2

Dynamic aperture

Main Parameters Main Collider Booster Energy (GeV)12010~120 Circumference (Km)50 Bunch Number50 Emittance x/y (nm)6.8/0.0224/ Life time (min)30 Beam Current (mA)

Injection Options Geometrical Arrangement Booster Main Collider 2 m

Injection linac 6GeV Conventional Linac (option I)

Injection linac Challenge 1.N bunch e+ =2  nC/bunch e + 2.Polarization Main parameters ParameterSymbolUnitValue E - beam energyE e- GeV6 E + beam energyE e+ GeV6 Pulse widthΔtns0.7 Repetition ratef rep Hz100 E - bunch populationN e- 2×10 10 E + bunch populationN e+ 2×10 10 Energy spread (E + /E - )σEσE <1×10 -3

Injection linac Linac Frequency: 2856MHz Normal conducting Conventional Positron Source and a 0.2GeV Positron Beam Transport Line

Electron source Unpolarized Electron Source (Baseline) Polarized Electron Source (R&D) Electron Gun Gun typeThermionic Triode Gun CathodeY824 (Eimac) Dispenser Beam Current (max.) A10 High Voltage of Anode kV Bias Voltage of Grid V0 ~ -200 Pulse duration ns0.7 Repetition Rate Hz50~100 1.R&D on a superlattice GaAs/GaAsP photocathode 2.R&D on a (100kV-150kV) DC gun

Positron source Unpolarized Positron Source Conventional Positron Source + 0.2Gev e + transport line Positron source E - beam energy on the targetGeV4 E - bunch charge on the targetnC10 Target material W-Re Target thickness mm14 E + Yield Focus deviceFlux Concentrator5Tesla E+ Energy pre-accelerate MeV200

SppC Layout Medium Energy Booster(4.5Km) Low Energy Booster(0.4Km) IP4 IP3 SppC Collider Ring(50Km) Proton Linac (100m) High Energy Booster(7.2Km)

ParameterValueUnit Circumference52km Beam energy35TeV Dipole field20T Injection energy2.1TeV Number of IPs2 (4) Peak luminosity per IP1.2E+35cm -2 s -1 Beta function at collision0.75m Circulating beam current1.0A Max beam-beam tune shift per IP0.006 Bunch separation25ns Bunch population2.0E+11 SR heat dipole (per aperture)56W/m SppC main parameters

Beam-beam tune shift limit analytical calculations For lepton collider: For hadron collider: where SppC (actual parameter list) FCC (pp) (theory and design) Formulae from private note of J. Gao r_e is electron radius γ= is normalized energy R is the dipole bending radius N_IP is number of interaction points r_p is proton radius J. Gao, Nuclear Instruments and Methods in Physics Research A 533 (2004) 270–274 J. Gao, Nuclear Instruments and Methods in Physics Research A 463 (2001) 50–61

p-Linac: proton superconducting linac p-RCS: proton rapid cycling synchrotron MSS: Medium-Stage Synchrotron SS: Super Synchrotron Injector chain (for proton beam) Ion beams have dedicated linac (I-Linac) and RCS (I-RCS)

Main features on accelerator physics Very high luminosity: 1.2  cm -2 s -1 – Supported by powerful injector chain and strong focusing at IPs – Integrated luminosity enhancement by exploring emittance damping (synchrotron radiation) Very high synchrotron radiation power: 56 – High circulation current: 1 A (similar to HL-LHC) Machine protection by sophisticated collimation system (6.3 GJ per beam; inefficiency: ) Instability issues – Electron cloud, resistive wall (beam screen) etc. Challenges in lattice design – Insertion lattice (IP, injection, extraction, collimation) – Compatible with the existing CEPC rings

Technical challenges and R&D plan High field magnets: both dipoles (20 T) and quadrupoles (pole tip field: T) are technically challenging, key technology to be solved in the coming two decades by a strong R&D program (see the next slide) Beam screen and vacuum: the key issue to solve the problem with very high synchrotron radiation power inside the cold vacuum. Need to develop an effective structure and working temperature to guide out the high heat load when minimizing Second-Electron-Yield, heat leakage to cold mass, impedance in the fast ramping field, vacuum instability etc. Both design and R&D efforts in the coming decade are needed to solve this critical problem. Collimation system: requiring unprecedentedly high efficiency, may need some collimators in cold sections. Perhaps need new method and structure. R&D efforts are needed.

R&D plan of the 20 T accelerator magnets : Development of a 12 T operational field Nb 3 Sn twin-aperture dipole with common coil configuration and field quality; Fabrication and test of 2~3 T HTS (Bi-2212 or YBCO) coils in a 12 T background field and basic research on tape superconductors for accelerator magnets (field quality, fabrication method, quench protection) : Development of a 15 T Nb 3 Sn twin-aperture dipole and quadrupole with field uniformity; Fabrication and test of 4~5 T HTS (Bi-2212 or YBCO) coils in a 15 T background field : 15 T Nb 3 Sn coils + HTS coils (or all-HTS) to realize the 20 T dipole and quadrupole with field uniformity; Development of the prototype SppC dipoles and quadrupoles and infrastructure build-up. (Very Preliminary) 69

CEPC+SppC Layout LTB : Linac to Booster BTC : Booster to Collider Ring BTC IP1 IP2 e+e- e+ e- Linac (240m) LTB CEPC Collider Ring(50Km ) Booster(50Km ) BTC Medium Energy Booster(4.5Km) Low Energy Booster(0.4Km) IP4 IP3 SppC Collider Ring(50Km) Proton Linac (100m) High Energy Booster(7.2Km)

The critical path for CEPC and SppC CEPC: 1) Final Focus System included in the ring with adequate dynamic aperture 2) Prezel scheme evaluation for operation 3) HOM power absorption technology … SppC: 1)Lattice design with FFS 2)High field mgnets …

Summary Pre-CDR work for accelerators goes well in general The machine parameter choice are consistent and reasonable (could be more optimized later depending on FFS design progress) The key technology choice has been made such as rf frequences The urgent progress needed for Pre-CDR for CEPC) is to have a working design of collider lattice (including FFS), Prezel scheme’s impact on machine performance, rf system design (HOM)… Collaborations between FCC and other institutions and Universities in the world should be strengthened

Thank you for your attention Thanks go to the speakers who provide me their presentations and all participants during discussion Acknowledgements