HKUST Jockey Club Institute for Advanced Study CEPC Linac Injector HEP218 22 Jan, 218 Cai Meng, Guoxi Pei, Jingru Zhang, Xiaoping Li, Dou Wang, Shilun Pei, Jie Gao, Yunlong Chi Institute of High Energy Physics, CAS, Beijing
Outline Introduction Main parameters Linac layout Positron source design Linac design Electron linac Positron linac Error study Summary
Outline Introduction Main parameters Linac layout Positron source design Linac design Electron linac Positron linac Error study Summary
Introduction Main parameters Linac design goal and principles Simplicity High Availability (necessary hot-standby backups,1%-2%) and Reliability Always providing beams that can meet requirements of Booster Parameter Symbol Unit Value e - /e + beam energy E e- /E e+ GeV 1 Repetition rate f rep Hz 1 e - /e + bunch population Ne-/Ne+ >9.4 1 9 nc >1.5 Energy spread (e - /e + ) σ E <2 1-3 Emittance (e - /e + ) ε r nm <12 e - beam energy on Target GeV 4 e - bunch charge on Target nc 1
Introduction Main parameters Layout Smaller emittance requirement possibility and high potential Damping Ring for positron linac Shorter damping time to damp the ejection beam of booster to the requirements Easy injection design and high efficiency Bunch charge Positron bunch charge decide the layout of linac and it s difficult to upgrade if not keep potential Enough allowance and high bunch charge requirement possibility or potential, designed 3 nc One-bunch-per-pulse Only short-range Wakefield need to be considered Frequency Collider: 65 MHz Booster: 13MHz Linac: 2856.75MHz (s-band) 2856.75MHz =3.25MHz 879 65 MHz =3.25MHz 2MHz 13 MHz =3.25MHz 4MHz
Introduction Layout of Linac Linac tunnel total length ~ 12m ESBS ( Electron Source and Bunching System): 5 MeV && 3.3 nc for electron injection/ 11nC for positron production FAS (the First Accelerating Section): Electron beam to 4 GeV && 3 nc for electron injection/ 1nC for positron production PSPAS (Positron Source and Pre-Accelerating Section) Positron beam larger than 2 MeV && larger than 3 nc SAS (the Second Accelerating Section) Positron beam to 4 GeV && 3 nc TAS (the Third Accelerating Section) Electron/Positron beam to 1 GeV && 3 nc EBTL ( Electron By-pass Transport Line) Transport line bypass scheme
Outline Introduction Main parameters Linac layout Positron source design Linac design Electron linac Positron linac Error study Summary
Positron source Layout of PSPAS Layout of positron source Target: W@15mm Rms electron beam size:.5mm AMD Length: 1mm Aperture: 8mm 26mm Capture & Pre-accelerating section Length:2 m Aperture: 25 mm Gradient: 22 MV/m Chicane Wasted electron separation Bunch length compression Magnetic field of the positron source and pre-accelerating section 5~6T.5T Bz (T) 7 6 5 4 3 2 Bz (T) 8 6 4 2 2 4 6 8 1 Position (mm) 1-2 2 4 6 8 1 12 14 Position (m)
Positron source Target design SuperKEKB positron linac commissioning (3.3 GeV) 214, N(e+)/N(e-)~2% 215, N(e+)/N(e-)~3% [designed 5%] CEPC positron 8 Positron bunch charge > 3 nc Energy=2 GeV 7 Energy=3.6 GeV Electron beam: Energy=4 GeV 4GeV 6 1nC/bunch (maybe lower) 5 Electron beam: 4 kw 4 Energy deposition 3.784 GeV/e- @ FLUKA 2 784 W water cooling 1 Target length (mm) Target tungsten 15 mm Beam size:.5 mm N e +/N e - @ target exit 5 1 15 2
Positron source Capture accelerating tubes Positron yield(@ capture accelerating tube exit) within some energy range with different capture accelerating tube phase (or different input phase for pre-accelerating section) and different accelerating gradient Deceleration mode (D1) Acceleration mode (A1) 22 MV/m (Considering energy and positron yield, lower accelerating gradient have acceptable positron yield decrease) 1.9.8 Gradient=1 MV/m Gradient=12 MV/m Gradient=14 MV/m Gradient=16 MV/m Gradient=18 MV/m D1 A1.7 Gradient=2 MV/m Gradient=22 MV/m.6 Gradient=24 MV/m N e +/N e -.5.4.3 Deceleration Acceleration.2.1 SuperKEKB -2-15 -1-5 5 1 15 2 Input phase (degree) Only energy cutoff EE < 15 MeV SuperKEKB commissioning results
Dynamic results of PSPAS Positron source Pre-accelerating section RF phase Norm. RMS. Emittance 25 mm-mrad Energy: >2 MeV Positron yield Ne+/Ne- ~=.55 [-6,14,235 MeV,265 MeV].3 X-Y X-Xp Norm.Rms.Emittance X&Y 4 1 4 1 1 X.2 2 Y 1.1 2 1-1 -2-4 -1 4 6 8 1 25 2 15 1-1 X(mm) 1-2 1 X(mm) Y-Yp.5 Phase-E 4.4 1 1 26 2-3.3.2 1-1 Phase 12 Z (cm) 2 Yp (mrad) 2 Beam power loss (W/cm) 1 15 Energy (MeV) -1-4 25 E (MeV) N,rm s 25 Xp (mrad) 3 Y(mm) (mm-mrad) 35-2 24.1 23-4 5 22 1 2 4 6 Z (cm) 8 1 12 24 26 28-1 1-1 -5 2 4 6 Z (cm) 8 1 12 14 Energy (MeV) Y(mm) Phase (deg) 1
Positron source Parameters SLC LEP (LIL) KEKB/SUPER KEKB FCC-ee (conv.)* CEPC Incident e- beam energy 33 GeV 2 MeV 3.3/3.3 GeV 4.46 GeV 4 GeV e-/bunch [1 1 ] 3-5.5-3 (2 ns pulse) 6.25/6.25 5.53 6.25 Bunch/pulse 1 1 2/2 2 1 Rep. rate 12 Hz 1 Hz 5 Hz/5 Hz 2 Hz 1Hz Incident Beam power ~2 kw 1 kw (max) 3.3 kw 15 kw 4 kw Beam size @ target.6 -.8 mm < 2 mm />.7 mm.5 mm.5 mm Target thickness 6X 2X /4X 4.5X 4.3X Target size 7 mm 5 mm 14 mm 1mm Target Moving Fixed Fixed/Fixed Moving/Fixed Deposited power 4.4 kw /.6 kw 2.7 kw.78kw Capture system AMD λ/4 transformer /AMD AMD AMD Magnetic field 6.8T->.5T 1 T->.3T /4.5T->.4T 7.5T->.5T 6T->.5T Aperture of 1st cavity 18 mm 25mm/18 mm /3 mm 2 mm 25 mm Gradient of 1st cavity 3-4 MV/m ~1 MV/m /1 MV/m 3 MV/m 22 MV/m length of 1st cavity 1m 3m 2m 3m 2m Linac frequency 2855.98 MHz 2998.55 MHz 2855.98 MHz 2855.98 MHz 2856.75 MHz e+ yield @ CS exit ~1.6 e+/e- ~.3 e+/e- (linac exit) /~.5 e+/e- ~.7 e+/e- ~.55 e+/e- Tungsten radiation length X is.35 cm.
Outline Introduction Main parameters Linac layout Positron source design Linac design Electron linac Positron linac Error study Summary
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) 4GeV & 1 nc Low charge mode (electron injection) 1 GeV & 3 nc
Linac design Electron linac Positron production 1.4 High charge mode 1 nc && 4 GeV Energy spread (rms):.5% Emittance growth with errors 1 4 1.2 1 Energy spread (%) 1 3 x, r m s y, r m s 4.1 4.5 (%).8.6 r m s (nm) 1 2 Energy (GeV) 4 3.95 3.9.4 1 2 3 1 1 1 2 3-5 5 s [m] Z (m) t (ps) 5 4 3 2 15 1 X r m s X m a x Y r m s Y m a x Energy (GeV) 2 1 Beam size (mm) 5 1 2 3 Z (m) 5 1 15 2 25 3 Z (m)
Linac design Low charge mode 3 nc && 1 GeV Energy spread (rms):.15% Emittance (rms): 5 nm Electron linac Electron injection 2 1 4 Energy spread (%) x, r m s 1.16 1.5 y, r m s 1.14 (%).5 1 r m s (nm) 1 2 Energy (GeV) 1.12 1.1 1.8 5 1 1 5 1 1.6-1 -5 5 1 s [m] Z (m) t (ps) 12 2 1 15 X r m s X m a x 8 Y r m s 1 Y m a x Energy (GeV) 6 4 2 Beam size (mm) 5 2 4 6 8 1 1 2 3 4 5 6 7 8 9 1 Z (m) Z (m)
Linac design Positron linac PSPAS SAS+TAS && Damping Ring SAS: 2 MeV 4 GeV Damping Ring: 1.1 GeV TAS: 4GeV 1 GeV Because of the larger emittance of positron beam, the lattice design of TAS is focused on positron beam, especially the transverse focusing structure.
Linac design Positron linac Transverse focusing structure FODO, nesting on Acc. tubes Triplet Positron linac Controlled β function Smaller beam size Need smaller β Longer period length Reduce quadrupole number Cause larger β (m) 5 4 3 2 KLY SLED KLY SLED KLY SLED KLY SLED KLY SLED x y 1-1 1 2 3 4 5 6 7 Z (m)
Linac design Positron linac Positron linac 3 nc && 1 GeV Energy spread (rms):.16% Emittance (rms): 4/24 nm 2.5 1 4 (%) 2 1.5 1.5 r m s (nm) 1 3 1 2 x, r m s y, r m s Energy (GeV) 1.15 1.1 1.5 1 9.95 9.9 2 4 6 1 1 2 4 6 9.85-1 -5 5 1 s [m] Z (m) t (ps) 12 2 1 15 X r m s X m a x 8 Y r m s 1 Y m a x Energy (GeV) 6 4 2 Beam size (mm) 5 2 4 6 1 2 3 4 5 6 7 Z (m) Z (m)
Linac design Damping Ring DR V1. Unit Value Energy GeV 1.1 Circumference M 58.5 Repetition frequency Hz 1 Bending radius M 3.6 Dipole strength B T 1.1 U kev 35.8 Damping time x/y/z Ms 12/12/6 δ %.49 ε mm.mrad 32 Nature σ z mm 7 (23ps) Extract σ z mm 7 (23ps) ε inj mm.mrad 25 ε ext x/y mm.mrad 716/471 δ inj /δ ext %.6/.7 Energy acceptance by % 1. RF f RF MHz 65 V RF MV 1.8
Error study Misalignment errors with correction Positron linac 5 seeds with correction 4 One-to-one correction scheme for each period Errors: Gaussian distribution, 3σ truncated Beam orbit RMS value<.3 mm Rms value<.1 mm (high energy part) Error description Unit Value Translational error mm.1 Rotation error mrad.2 Magnetic element field error %.1 BPM uncertainty mm.1 RMS beam orbit (mm) 6 X 5 Y 3 2 1 1 2 3 4 5 6 7 Z (m)
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
Linac design Energy jitter Simulation condition 5 seeds Accelerating tubes phase errors and amp errors 4 in 1 KLY, 4 accelerating tubes in one group 3σ--Gaussian 15 Energy spread <.2% Phase errors:.5 degree (rms) Amp errors:.5% (rms) Energy jitter:.2% 25 =.1 deg && V e r r =.1% e r r 2 =.3 deg && V e r r =.5 deg && V e r r =.3% e r r =.5% e r r 1 15 =1 deg && V e r r e = 1% r r Probability (%) 5 Probability (%) 1 5 -.6 -.4 -.2.2.4.6.1.15.2.25 (%) (%)
Linac design Status Parameter Symbol Unit Goal Status e - /e + beam energy E e- /E e+ GeV 1 1/1 Repetition rate f rep Hz 1 1 e - /e + bunch population Ne-/Ne+ >9.4 1 9 >1.875 1 1 Ne-/Ne+ nc >1.5 >3.* Energy spread (e - /e + ) σ E <2 1-3 e - :1.5 1-3 e + :1.6 1-3 Emittance@1GeV (e - /e + ) nm 12 e - : 5/ 5 e + : 4/24~12 e - beam energy on Target GeV 4 4 e - bunch charge on Target nc 1 1 * Enough allowance and high bunch charge requirement possibility or potential
Summary The physics design of CEPC Linac have been proposed and the simulated beam dynamics results can meet the requirements of Booster. The design of positron source have been proposed. Preliminary damping ring is proposed. There are no issue that defies solution for CEPC linac. Further optimization are undergoing.
Linac design Short-Range Wakefield k. Yokoya and K. bane s Wakefield model periodic linac structure k. Yokoya and K. bane, The longitudinal high-frequency impedance of a periodic accelerating structure, Proceedings of the 1999 IEEE Particle Accelerator Conference Vol. 3 pag. 1725, New York, March 1999