Circular Electron Positron Collider CEPC Linac design FCCWEEK

环形正负电子对撞机 Circular Electron Positron Collider CEPC Linac design FCCWEEK 2018 11 April, 2018 Cai Meng, Guoxi Pei, Jingru Zhang, Xiaoping Li, Dou Wang, Jie Gao, Shilun Pei, Yunlong Chi Institute of High Energy Physics, CAS, Beijing FCCWEEK 2018

Outline • Introduction • Main parameters • Linac layout • Positron source design • Linac design • Electron linac • Positron linac • Summary FCC Week 2018, 9 13 April 2018, Amsterdam, Netherlands. CPEC Linac design 2

Outline • Introduction • Main parameters • Linac layout • Positron source design • Linac design • Electron linac • Positron linac • Summary FCC Week 2018, 9 13 April 2018, Amsterdam, Netherlands. CPEC Linac design 3

Introduction Main parameters • Linac design goal and principles • Simplicity Parameter • Layout • S band accelerating structure (2856. 75 MHz) • 2856. 75 MHz =3. 25 MHz× 879, Linac • 650 MHz =3. 25 MHz× 200, Booster • 1300 MHz =3. 25 MHz× 400, Collider • High Availability and Reliability • ~ 15% backups for Klystrons and accelerating structure • Always providing beams that can meet requirements of Booster FCC Week 2018, 9 13 April 2018, Amsterdam, Netherlands. e- Symbol Unit Value e- /e+ beam energy Ee /Ee+ Ge. V 10 Repetition rate frep Hz 100 /e+ bunch population Energy spread (e- /e+ ) Emittance (e- /e+ ) Ne-/Ne+ >9. 4× 109 n. C σE εr >1. 5 <2× 10 3 nm <120 e- beam energy on Target Ge. V 4 e- bunch charge on Target n. C 10 CPEC Linac design 4

Introduction Main parameters • Layout • Smaller emittance requirement possibility and high potential • Damping Ring for positron beam • Larger errors tolerance • Higher injection efficiency, easier injection design • Shorter damping time to damp the extraction beam of booster to collider • Bunch charge: 3 n. C • Enough redundancy and high bunch charge requirement possibility or potential • High electron beam energy ~4 Ge. V for positron production • One bunch per pulse • Only short-range Wakefield need to be considered üTwo bunch per pulse FCC Week 2018, 9 13 April 2018, Amsterdam, Netherlands. CPEC Linac design 5

Introduction Layout of Linac Positron Linac ESBS 50 Me. V • ESBS ( Electron Source and Bunching System) • 50 Me. V && 11 n. C for positron production • FAS (the First Accelerating Section) • Electron beam to 4 Ge. V && 10 n. C for positron production • PSPAS (Positron Source and Pre-Accelerating Section) • SAS (the Second Accelerating Section) • Positron beam to 4 Ge. V && 3 n. C • DR (Damping Ring) • Positron beam 1. 1 Ge. V/60 m • TAS (the Third Accelerating Section) • Positron beam to 10 Ge. V && 3 n. C • Positron beam larger than 200 Me. V && larger than 3 n. C FCC Week 2018, 9 13 April 2018, Amsterdam, Netherlands. CPEC Linac design 6

Introduction Layout of Linac Positron Linac ESBS FAS 50 Me. V 4 Ge. V • ESBS ( Electron Source and Bunching System) • 50 Me. V && 11 n. C for positron production • FAS (the First Accelerating Section) • Electron beam to 4 Ge. V && 10 n. C for positron production • PSPAS (Positron Source and Pre-Accelerating Section) • SAS (the Second Accelerating Section) • Positron beam to 4 Ge. V && 3 n. C • DR (Damping Ring) • Positron beam 1. 1 Ge. V/60 m • TAS (the Third Accelerating Section) • Positron beam to 10 Ge. V && 3 n. C • Positron beam larger than 200 Me. V && larger than 3 n. C FCC Week 2018, 9 13 April 2018, Amsterdam, Netherlands. CPEC Linac design 7

Introduction Layout of Linac Positron Linac ESBS PSPAS FAS 50 Me. V 4 Ge. V 200 Me. V • ESBS ( Electron Source and Bunching System) • 50 Me. V && 11 n. C for positron production • FAS (the First Accelerating Section) • Electron beam to 4 Ge. V && 10 n. C for positron production • PSPAS (Positron Source and Pre-Accelerating Section) • SAS (the Second Accelerating Section) • Positron beam to 4 Ge. V && 3 n. C • DR (Damping Ring) • Positron beam 1. 1 Ge. V/60 m • TAS (the Third Accelerating Section) • Positron beam to 10 Ge. V && 3 n. C • Positron beam larger than 200 Me. V && larger than 3 n. C FCC Week 2018, 9 13 April 2018, Amsterdam, Netherlands. CPEC Linac design 8

Introduction Layout of Linac Positron Linac ESBS FAS 50 Me. V DR PSPAS 4 Ge. V 200 Me. V • ESBS ( Electron Source and Bunching System) • 50 Me. V && 11 n. C for positron production • FAS (the First Accelerating Section) • Electron beam to 4 Ge. V && 10 n. C for positron production • PSPAS (Positron Source and Pre-Accelerating Section) SAS 1. 1 Ge. V 4 Ge. V • SAS (the Second Accelerating Section) • Positron beam to 4 Ge. V && 3 n. C • DR (Damping Ring) • Positron beam 1. 1 Ge. V/60 m • TAS (the Third Accelerating Section) • Positron beam to 10 Ge. V && 3 n. C • Positron beam larger than 200 Me. V && larger than 3 n. C FCC Week 2018, 9 13 April 2018, Amsterdam, Netherlands. CPEC Linac design 9

Introduction Layout of Linac Positron Linac ESBS FAS 50 Me. V DR PSPAS 4 Ge. V 200 Me. V • ESBS ( Electron Source and Bunching System) • 50 Me. V && 11 n. C for positron production • FAS (the First Accelerating Section) • Electron beam to 4 Ge. V && 10 n. C for positron production • PSPAS (Positron Source and Pre-Accelerating Section) SAS 1. 1 Ge. V TAS 4 Ge. V 10 Ge. V • SAS (the Second Accelerating Section) • Positron beam to 4 Ge. V && 3 n. C • DR (Damping Ring) • Positron beam 1. 1 Ge. V/60 m • TAS (the Third Accelerating Section) • Positron beam to 10 Ge. V && 3 n. C • Positron beam larger than 200 Me. V && larger than 3 n. C FCC Week 2018, 9 13 April 2018, Amsterdam, Netherlands. CPEC Linac design 10

Introduction Layout of Linac Electron Linac ESBS 50 Me. V • ESBS ( Electron Source and Bunching System) • EBTL (Electron Bypass Transport Line) • 50 Me. V && 3. 3 n. C • FAS (the First Accelerating Section) • Electron beam to 4 Ge. V && 3 n. C FCC Week 2018, 9 13 April 2018, Amsterdam, Netherlands. • Electron beam @ 4 Ge. V && 3 n. C • TAS (the Third Accelerating Section) • Electron beam to 10 Ge. V && 3 n. C CPEC Linac design 11

Introduction Layout of Linac Electron Linac ESBS FAS 50 Me. V 4 Ge. V • ESBS ( Electron Source and Bunching System) • EBTL (Electron Bypass Transport Line) • 50 Me. V && 3. 3 n. C • FAS (the First Accelerating Section) • Electron beam to 4 Ge. V && 3 n. C FCC Week 2018, 9 13 April 2018, Amsterdam, Netherlands. • Electron beam @ 4 Ge. V && 3 n. C • TAS (the Third Accelerating Section) • Electron beam to 10 Ge. V && 3 n. C CPEC Linac design 12

Introduction Layout of Linac Electron Linac EBTL ESBS FAS 50 Me. V 4 Ge. V • ESBS ( Electron Source and Bunching System) • EBTL (Electron Bypass Transport Line) • 50 Me. V && 3. 3 n. C • FAS (the First Accelerating Section) • Electron beam to 4 Ge. V && 3 n. C FCC Week 2018, 9 13 April 2018, Amsterdam, Netherlands. • Electron beam @ 4 Ge. V && 3 n. C • TAS (the Third Accelerating Section) • Electron beam to 10 Ge. V && 3 n. C CPEC Linac design 13

Introduction Layout of Linac Electron Linac EBTL ESBS TAS FAS 50 Me. V 4 Ge. V 10 Ge. V • ESBS ( Electron Source and Bunching System) • EBTL (Electron Bypass Transport Line) • 50 Me. V && 3. 3 n. C • FAS (the First Accelerating Section) • Electron beam to 4 Ge. V && 3 n. C FCC Week 2018, 9 13 April 2018, Amsterdam, Netherlands. • Electron beam @ 4 Ge. V && 3 n. C • TAS (the Third Accelerating Section) • Electron beam to 10 Ge. V && 3 n. C CPEC Linac design 14

Introduction Layout of Linac Accelerating structure Length m ~3 Frequency MHz S band/2856. 75 Aperture mm >19 MV/m 21 Acc. Gradient SLED Yes Mode 1 (Kly. ) >4 (Acc. tube) FCC Week 2018, 9 13 April 2018, Amsterdam, Netherlands. K. Yokoya and K. Bane, The longitudinal high–frequency impedance of a periodic accelerating structure, Proceedings of the 1999 PAC, New York, 1999. CPEC Linac design 15

Outline • Introduction • Main parameters • Linac layout • Positron source design • Linac design • Electron linac • Positron linac • Summary FCC Week 2018, 9 13 April 2018, Amsterdam, Netherlands. CPEC Linac design 16

Positron source Layout of PSPAS • Layout of positron source • Target (Conventional) • W@15 mm • Rms electron beam size: 0. 5 mm • AMD (Adiabatic Matching Device) • Length: 100 mm • Aperture: 8 mm 26 mm • Capture & Pre accelerating structure • Length: 2 m • Aperture: 25 mm • Gradient: 22 MV/m • Chicane • Wasted electron separation FCC Week 2018, 9 13 April 2018, Amsterdam, Netherlands. CPEC Linac design 17

Positron source Target design • Super. KEKB positron linac commissioning (3. 3 Ge. V) • 2014, N(e+)/N(e )~20% • 2015, N(e+)/N(e )~30% [designed 50%] • CEPC positron source • Positron bunch charge > 3 n. C • Electron beam: • 4 Ge. V • 10 n. C/bunch (maybe lower) • Electron beam: 4 k. W • Energy deposition • 0. 784 Ge. V/e @ FLUKA • 784 W water cooling • Target • tungsten • 15 mm • Beam size: 0. 5 mm FCC Week 2018, 9 13 April 2018, Amsterdam, Netherlands. CPEC Linac design 18

Positron source • Norm. RMS. Emittance Dynamic results of PSPAS D 1 A 1 • 2500 mm mrad • Energy: >200 Me. V • Positron yield Acceleration Deceleration Super. KEKB commissioning results • Ne+/Ne > 0. 55 @ [ 6°, 14°, 235 Me. V, 265 Me. V] FCC Week 2018, 9 13 April 2018, Amsterdam, Netherlands. CPEC Linac design 19

Positron source Incident e- beam energy e-/bunch [1010] Bunch/pulse Rep. rate Incident Beam power Beam size @ target Target thickness Target size Target Deposited power Capture system Magnetic field Aperture of 1 st cavity Gradient of 1 st cavity length of 1 st cavity Linac frequency e+ yield @ CS exit Parameters SLC LEP (LIL) KEKB/SUPER KEKB FCC-ee (conv. ) CEPC 33 Ge. V 3 5 1 120 Hz ~20 k. W 0. 6 0. 8 mm 6 X 0 70 mm Moving 4. 4 k. W AMD 6. 8 T >0. 5 T 18 mm 30 40 MV/m 1 m 2855. 98 MHz ~1. 6 e+/e 200 Me. V 0. 5 30 (20 ns pulse) 1 100 Hz 1 k. W (max) < 2 mm 2 X 0 5 mm Fixed 3. 3/3. 3 Ge. V 6. 25/6. 25 2/2 50 Hz/50 Hz 3. 3 k. W />0. 7 mm /4 X 0 14 mm Fixed/Fixed /0. 6 k. W /AMD /4. 5 T >0. 4 T /30 mm /10 MV/m 2 m 2855. 98 MHz /~0. 5 e+/e 4. 46 Ge. V 5. 53 2 200 Hz 15 k. W 0. 5 mm 4. 5 X 0 4 Ge. V 6. 25 1 100 Hz 4 k. W 0. 5 mm 4. 3 X 0 10 mm Fixed 0. 78 k. W AMD 6 T->0. 5 T 25 mm 22 MV/m 2 m 2856. 75 MHz ~0. 55 e+/e- λ/4 transformer 1 T >0. 3 T 25 mm/18 mm ~10 MV/m 3 m 2998. 55 MHz ~0. 003 e+/e (linac exit) 2. 7 k. W AMD 7. 5 T >0. 5 T 20 mm 30 MV/m 3 m 2855. 98 MHz ~0. 7 e+/e Tungsten radiation length X 0 is 0. 35 cm. FCC Week 2018, 9 13 April 2018, Amsterdam, Netherlands. CPEC Linac design 20

Outline • Introduction • Main parameters • Linac layout • Positron source design • Linac design • Electron linac • Positron linac • Summary FCC Week 2018, 9 13 April 2018, Amsterdam, Netherlands. CPEC Linac design 21

Linac design Electron linac • Focusing structure: Triplet • Long drift length for accelerating tubes • Beam size in Acc. tubes is small and easy control • Same beam envelopes at X/Y planes • 1 triplet+4 Acc. tubes 1 triplet+8 Acc. tubes • Operation mode : • High charge mode (positron production) • 4 Ge. V & 10 n. C • Low charge mode (electron injection) • 10 Ge. V & 3 n. C FCC Week 2018, 9 13 April 2018, Amsterdam, Netherlands. CPEC Linac design 22

Linac design Electron linac Positron production • High charge mode • 10 n. C @ 4 Ge. V • Energy spread (rms): 0. 5% • Emittance growth with errors FCC Week 2018, 9 13 April 2018, Amsterdam, Netherlands. CPEC Linac design 23

Linac design Electron linac Electron injection • High charge mode • 10 n. C @ 4 Ge. V • Energy spread (rms): 0. 5% • Emittance growth with errors • Low charge mode • 3 n. C @ 10 Ge. V • Energy spread (rms): 0. 15% • Emittance (rms): 5 nm FCC Week 2018, 9 13 April 2018, Amsterdam, Netherlands. CPEC Linac design 24

Linac design Positron linac • PSPAS SAS (DR) +TAS • SAS: 200 Me. V 4 Ge. V • Damping Ring @ 1. 1 Ge. V • TAS: 4 Ge. V 10 Ge. V • Transverse focusing structure • FODO, nesting on Acc. tubes • Triplet FCC Week 2018, 9 13 April 2018, Amsterdam, Netherlands. CPEC Linac design 25

Linac design Positron linac • Positron linac • 3 n. C && 10 Ge. V • Energy spread (rms): 0. 16% • Emittance with DR (rms): 40/24 nm • Emittance without DR (rms): 120/120 nm FCC Week 2018, 9 13 April 2018, Amsterdam, Netherlands. CPEC Linac design 26

Linac design Misalignment errors with correction • Positron linac • One to one correction scheme • Errors: Gaussian distribution, 3σ truncated • Beam orbit • RMS value< 0. 3 mm • Rms value< 0. 1 mm (high energy part) Error description Unit Value Translational error mm 0. 1 Rotation error mrad 0. 2 % 0. 1 mm 0. 1 Magnetic element field error BPM uncertainty FCC Week 2018, 9 13 April 2018, Amsterdam, Netherlands. CPEC Linac design 27

Linac design Field errors • Simulation condition • 5000 seeds • Accelerating tubes • phase errors and amp errors • 4 in 1 KLY, 4 accelerating tubes in one group • 3σ Gaussian FCC Week 2018, 9 13 April 2018, Amsterdam, Netherlands. • Energy spread < 0. 2% • Phase errors: 0. 5 degree (rms) • Grad. errors: 0. 5% (rms) • Energy jitter: 0. 2% CPEC Linac design 28

Linac design DR V 1. 0 Energy Circumference Repetition frequency Bending radius Dipole strength B 0 U 0 Damping time x/y/z 0 0 Nature z inj ext x/y inj / ext Energy acceptance by RF f. RF VRF Unit Ge. V M Hz M T ke. V ms % mm. mrad % % MHz MV Damping Ring Value 1. 1 58. 5 100 3. 62 1. 01 35. 8 12/12/6 0. 05 287. 4 7 (23 ps) 2500 704/471 0. 3/0. 06 1. 0 650 1. 8 FCC Week 2018, 9 13 April 2018, Amsterdam, Netherlands. @ D. Wang CPEC Linac design • Emittance not critical • One bunch in DR(200 ns) • 10 ms 20 ms • Two bunch: yes • IBS • Emittance growth • CSR (Coherent synchrotron radiation) • CSR Instability 29

Summary • The CEPC linac works with 100 Hz repetition, 10 Ge. V and one bunch per pulse; • The linac can provide positron beam and electron beam with 3 n. C bunch charge, which is larger than the requirements; • One preliminary damping ring is proposed; • By now seems it’s no problem in linac design and further works are on the way. FCC Week 2018, 9 13 April 2018, Amsterdam, Netherlands. CPEC Linac design 30

Linac design Short-Range Wakefield • k. Yokoya and K. bane’s Wakefield model • periodic linac structure FCC Week 9 13 Aprilhigh frequency 2018, Amsterdam, Netherlands. k. Yokoya and K. 2018, bane, “The longitudinal impedance of a periodic accelerating structure”, Proceedings of the. CPEC 1999 IEEE Particle Accelerator Conference Vol. 3 pag. 1725, New York, March 1999 Linac design 31

Injection Mode Higgs Injection Mode Top up Bunch number 242 Bunch Charge (n. C) 0. 72 1 0. 576 0. 87 0. 384 0. 55 Beam Current (m. A) 0. 5227 0. 726 2. 63 4 6. 91 10 Current threshold 1 m. A 4 m. A 10 m. A Number of Cycles 1 1 2 Current decay 3% Ramping Cycle (sec) (Up + Down） Filling time (sec) （e+，e-) 10 6. 6 3. 8 25. 84 45. 68 275. 2 Injection period (sec) 73. 1 131 438 600 s 900 s 2. 2 Hour (从230 m. A） 对撞 Full Injection time W Full Top up Z Full 1524 4. 17% FCC Week 2018, 9 13 April 2018, Amsterdam, Netherlands. 3% Top up Full 6000 4. 55% 3% 4. 3% CPEC Linac design 32

Error study Misalignment errors with correction • Electron linac • First orbit correction + multi particles simulation • Low charge • Beam orbit can be controlled well • High charge • Misalignments of Acc. Tubes • BPM noisy • Wakefield • In operation, the orbit and emittance growth can be controlled better; Correction is based on multi particles orbit • Meet the requirements for positron production FCC Week 2018, 9 13 April 2018, Amsterdam, Netherlands. CPEC Linac design 33