Transcript Future High Energy Physics Accelerators under Studies

Future High Energy Particle Colliders in China
CEPC/SppC Status
-Report from Accelerator Group
J. Gao
On behalf of CEPC/SppC Group
IHEP
The 4th CEPC Meeting
Shanghai Jiaotong University, Sept. 13, 2014
Talks and discussions in accelerator session
Talk
1
2
3
4
6
CEPC/SppC Status Jie Gao
High field magnets Qingjin Xu
Design of collision
area
Yiwei Wang
Beam collective
Na Wang
effects
Design of injection
system
Xiaohao Cui
Discussion
Chairperson: 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
4
CEPC - accelerator physics
4.1
Main parameters
4.2
Lattice
4.3
4.4
IR and MDI
Beam instability
4.5
4.6
4.7
4.8
4.9
Beam-beam effects
Synchrotron radiation
Injection and beam dump
Background
Polarization
Guo Yuanyuan, Geng Huiping, Wang Dou, Xiao Ming,
Gao Jie
Geng Huiping, Wang Dou, Guo Yuanyuan, Wang Na,
Wang
Yiwei, Xiao Ming, Peng Yuemei, Bai Sha, Su Feng, Xu
Gang
, Duan Zhe, Gao Jie
Wang Dou, Geng Huiping, Wang Yiwei, Bai Sha, , Gao
Jie
Wang Na, Wang Yiwei
Zhang Yuan, Guo Yuanyuan, Wang Dou, Xiao Ming, Gao
Jie
Ma Zhongjian, Geng Huiping
Cui Xiaohao, Su Feng, Xu Gang
Yue Teng
Duan Zhe
 Visitors from other labs in the world participate the Pre-CDR
joint works
International participation (April, 2014)
Visitors name
Period
Topics
Dick Talman
April 13th –May 15th
Parameters and other topics
Armen Apyan
April 1st –April 30th
GuineaPig and CAIN
Yoshihiro Funakoshi
April 1st-April 15th
Parameter, injection and others
Dmitry Shatilov
April 1st- April 16th
Beam-beam simulation
Kazuhito Ohmi
April 16th-April 30th
Beam-beam simulation
Yunhai Cai
April 16th –April 30th
Lattice and FFS
Yuhong Zhang
April 16th-April 30th
Electron proton collider
Pre-CDS status
Finished the draft
Writing
Preparing
CEPC Layout
e+
IP1
LTB
e+ e- Linac
(240m)
BTC
LTB : Linac to Booster
e-
BTC
IP2
BTC : Booster to Collider Ring
Is the machine parameter choice consistent and reasonable?
Why CEPC takes one ring design?
Luminosity from colliding beams
• For equally intense Gaussian beams
Collision frequency
2
Nb
L f
R
2
4
Particles in a bunch
Geometrical factor:
- crossing angle
- hourglass effect
Transverse size (RMS)
• Expressing luminosity in terms of beam-beam limitation
The expression for  y (max) in storage ring
colliders is of primary importance, since
 y (max) is not a constant, but a machine
parameter dependent value, including NIp
7
Beam-beam tune shift limit analytical calculations
For lepton collider:
 y,max 
J. Gao, Nuclear Instruments and Methods in Physics
Research A 533 (2004) 270–274
2845 
1
re
6RN IP
 0.072 (CEPC )
r_e is electron radius
γ= is normalized energy
R is the dipole bending radius
N_IP is number of interaction points
 x,max  2 y ,max  0.11(CEPC)
J. Gao, Nuclear Instruments and Methods in Physics
Research A 463 (2001) 50–61
For hadron collider:
 max
where
f(x )  1 
x
2

4f(x )
max N IP
2
2
x
 exp( 
0
4f 2(x )

2845
t2
2
2845

f  x
)dt
6R
rp N IP
Formulae from private note of J. Gao
rp
6 RN IP
r_p is proton radius
SppC (actual parameter list)
x  2.03656
f(x )  0.0417
 max  0.0064
FCC (pp) 0.005 (theory and design)
Main parameters for CEPC
Parameter
Unit
Beam energy [E]
GeV
Number of IP[NIP]
Bunch number/beam[nB]
SR power/beam [P]
MW
Bending radius [r]
m
Revolution period [T0]
s
emittance (x/y)
nm
Transverse size (x/y)
mm
mm
Beam length SR [s.SR]
Lifetime due to
Beamstrahlung
RF voltage [Vrf]
Parameter
Circumference [C]
SR loss/turn [U0]
Bunch population [Ne]
Beam current [I]
momentum compaction
6094
factor [ap]
1.79E-04 Revolution frequency [f0]
6.79/0.02
bIP(x/y)
1
73.7/0.16 x,y/IP
%
5.56
%
0.13
Beam length total [s.tot]
lifetime due to radiative
Bhabha scattering [tL]
RF frequency [frf]
Synchrotron oscillation tune
[ns]
Damping partition number
[Je]
Energy spread BS [d.BS]
%
0.15
n
turns
81
Fh
0.679
2.35
min
80
GV
6.87
Harmonic number [h]
Energy acceptance RF
[h]
Energy spread SR [d.SR]
Energy spread total
[d.tot]
Transverse damping
time [nx]
Hourglass factor
Value
120
2
50
50
116244
Longitudinal damping time
[ne]
Luminosity /IP[L]
Unit
km
GeV
mA
Value
53.6
3
3.71E+11
16.6
4.15E-05
Hz
5991.66
mm
800/1.2
0.1/0.074
mm
2.66
min
56
MHz
650
0.199
2
%
0.07
0.22
turns
40
cm-2s-1 1.8E+34
CEPC Beam-beam simulations
The current main
parameters has been
checked with beambeam simulation,
proved the
reasonability.
（Ohmi, Zhang Yuan,
Demitry Shatilov)
CEPC lattice layout
Critical parameters for CEPC:
RF
• Circumference: 50 km
IP1
RF
• SR power: 50 MW/beam
• 16*arcs
RF
RF
RF
RF
• 2*IPs
• 8 RF cavity sections (distributed)
• 6 straights (for injection and dump)
• Filling factor of the ring: ~80%
RF
RF
IP2
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
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
14
Pretzel scheme
 Use 2 pairs of electrostatic separators
 Beam separated at horizontal plane with orbit offset of 5x
 Maximum bunch number: 96
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)
(FFS)
FFS optics
betaX*=0.8m
betaY*=0.0012m
IP
Half Quad of
dispersion suppressor
L*=2.5m
FFS entrance condition:
DX=DPX=0
ax=ay=0
betax=75.6m
betaY=25.6m
Total length: 170 m
• We use the same method as Yunhai’s example to make a new design of CEPC FFS.
17
Lattice of the whole ring
 Dynamic aperture: 16x/ 30y for on momentum particles
Dynamic Aperture (L*=2.5m)
DA for 2%,-2% is 0
4y
By Dou Wang and
Demin Chou
5x
The tune dependence on the energy deviation
Momentum bandwidth
In MADX, the tunes suddenly drop to zero beyond 1%.
Tune diagram
1.0
0.8
Tune cross the second,
third and fourth order,
the beam is unstable,
may cause the drop of
the tune ?
0.6
0.4
Dp=1%
0.2
Dp=-2%
Dp=0
0.0
0.0
0.2
0.4
0.6
0.8
1.0
Phase space after 1000 turns
On momentum (dp=0)
Tracking in x-px
Tracking 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-px
Tracking 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-px
 Dynamic aperture could be almost zero.
Tracking in y-py
Primary IR optics with L*=1.5m
• betx*=0.8m, bety*=1.2mm, L*=1.5m
IP
FT
CCY
CCX
MT
Yiwei Wang,
3 Sep 2014
FT: final telescopic
transformer
CCY: chromatic
correction section y
CCX: chromatic
correction section x
MT: matching
telescopic
transformer
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
– ex_inj=21.8nm, ey_inj=2.2nm (assume 10% coupling for injection beam)
– Inner radius of vacuum chamber at Q1 and Q2: 1.8cm
IP
Q1
Q2
[m]
•
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
Ry
Rx
CEPC Magnets’ specifications
Dipole magnet
Quantity
Beam energy (GeV)
Bending angle (rad)
Bending radius (m)
Magnetic gap (mm)
Magnetic Length (m)
Maximum field strength (T)
Good field region, GFR (mm)
Field uniformity across GFR
Integral field deviation (magnet to magnet)
Quadrupole magnet
Quantity
Beam energy (GeV)
Aperture diameter(mm)
Magnetic Length (m)
Maximum field gradient (T/m)
Good field region, GFR radius (mm)
Harmonic field errors across GFR
Integral field deviation (magnet to magnet)
type A
type B
1984
120
3.17E-03
5683.74
100 (as LEP)
18
0.07
type A
type B
2304
120
125
2
10
Sextupole magnet
type A(SF)
type B(SD)
Quantity
Beam energy (GeV)
Aperture diameter(mm)
Magnetic Length (m)
Strength of sextupole field (T/m^2)
Good field region, GFR radius (mm)
Harmonic field errors across GFR
992
120
150 (as LEP)
0.4
180
992
120
150
0.7
180
CEPC SRF System Layout
8 RF sections
In each ~ 150m section
• Main ring:
- 12 x 8m cryomodules
- 650 MHz 5-cell SRF cavity
- 4 cavities / cryomodule
• Booster:
- 4 x 12m cryomodules
- 1.3 GHz 9-cell SRF cavity
- 8 cavities / cryomodule
Superconducting RF Cavity
• ~ 20 x CW gradient
• less disruption to beam
• 100s times more efficient
• LLRF benefits
compared to normal conducting
31
CEPC SRF System Parameters
Parameters
CEPC-Collider
CEPC-Booster
LEP2
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
384
256
288
Vcav / VRF
18 MV / 6.87 GeV
20 MV / 5.04 GeV
12 MV / 3.46 GeV
Eacc (MV/m)
15.5
20 peak
6 ~ 7.5
Q0
2(3)E10 @ 2K
2E10 @ 2K
3.2E+9 @ 4.2K
Cryo AC power (MW)
20
2.5 (15% DF)
6.1
Cryomodule number
96 (4 cav)
32 (8 cav)
72 (4 cav)
RF input power / cav (kW) 260
20 peak
125
RF source number
384 (300 kW kly)
256 (25 kW SSA)
36 (1.2 MW/8 cav)
RF AC power (MW)
200 (260 installed) 2.4 (15% DF)
HOM damper power (W)
26 k (ferrite+hook) 5 (hook) (15% DF) 300 (hook)
85
Coupler Power Handling Capability
Impact on Main Ring Cost and Risk
Coupler Power
(kW)
Eacc
(MV/m)
Cavity #
Module Cost
(Billion CNY)
156
9.3
640
2.6
260
15.5
386
1.5
330
19.7
302
1.2
4M 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 …
33
650 MHz 5-cell Cavity
Need further shape
optimization, especially
for the HOM properties
internal
Riris(mm)
Alpha(deg)
A(mm)
B(mm)
a(mm)
b(mm)
L(mm)
D(mm)
flatness
coupling
Ep/Eacc
Hp/Eacc [mT/(MV/m)]
77.96
2.24
94.4
94.4
20.03
22.09
115
206.6
Left end
half cell
84.46
16.727
92.1
92.1
13.76
21.14
114
206.6
2.17%
3.04%
2.43
4.23
Right end
half cell
84.46
16.39
91
91
13.71
20.29
113
206.6
34
650 MHz 5-cell Cavity Parameters
Parameter
RF frequency
RF voltage
Cavity gradient
Effective length (five cells)
Cavity voltage
Number of cavities
Cavities in one cryomodule
Cryomodule length
Number of cryomodules
R/Q
Geometry factor
Iris diameter
Quality factor
External Q of input coupler
RF power per cavity
Cavity longitudinal loss factor※
Cavity transverse loss factor※
Symbol
fRF
VRF
Eacc
Leff
Vc
Unit
MHz
GV
MV/m
m
MV
Value
650
6.87
15.6
1.147
18
384
Q0
Qext
Pin
kW
4
8
96
514
268
156
2~3×1010
2.4×106
260
k∥
k⊥
V/pC
V/pC m
1.87
10
m
R/Q
G
Ω
Ω
mm
18 MV/m for
vertical test
3~4×1010 for
Vertical Test
※
σz = 2.66 mm
650 MHz 5-cell Cavity HOMs
Monopole Mode
f (GHz)
R/Q (Ω) *
QL Limit
TM011
1.173
84.8
2.54E+5
TM020
1.427
54.15
3.28E+5
Dipole Mode
f (GHz)
R/Q (Ω/m)**
QL Limit
TE111
0.824
832.23
1.13E+4
TM110
0.930
681.15
1.39E+4
TE122
1.232
544.5
1.73E+4
TM112
1.440
101.53
9.3E+4
∥mode = 2πf ·(R/Q) / 4 [V/pC]
** k
⊥mode = 2πf ·(R/Q) / 4 [V/(pC·m)]
*k
36
1.3 GHz 9-cell Cavity Parameters
Parameter
RF frequency
RF voltage
Cavity gradient
Effective length (nine cells)
Cavity voltage
Number of cavities
Cavities in one cryomodule
Cryomodule length
Number of cryomodules
R/Q
Geometry factor
Iris diameter
Quality factor
External Q of input coupler
RF power per cavity
Lorentz force detuning factor
Cavity longitudinal loss factor※
Cavity transverse loss factor※
Symbol
fRF
VRF
Eacc
Leff
Vc
Unit
GHz
GV
MV/m
m
MV
m
R/Q
G
Q0
Qext
Pin
kL
k∥
k⊥
Ω
Ω
mm
kW
Hz/(MV/m)2
V/pC
V/pC m
Value
1.3
5.04
20
1.038
20
256
8
12
32
1036
270
70
2×1010
Over-coupled
1×107 for larger BW
20
1
5.8
※ σ = 3.89 mm
25
z
1.3 GHz 9-cell Cavity HOMs
Monopole
Mode
TM011
QL
f (GHz)
R/Q (Ω) *
2.450
156
58600
TM012
3.845
44
240000
Dipole Mode
f (GHz)
R/Q (Ω/m)**
Q
TE111
1.739
4283
3400
TM110
1.874
2293
50200
TM111
2.577
4336
50000
TE121
3.087
196
43700
*k
∥mode = 2πf ·(R/Q) / 4 [V/pC]
** k
⊥mode = 2πf ·(R/Q) / 4 [V/(pC·m)]
measured
38
HOM Power of the Collider
CEPC
Collider
Loss factor (HOM)
V/pC
HOM power
per cavity
3.29
LEP2
0.66
below
cut-off
above
cut-off
0.22
0.44
Operation 66nC
300W
100 W
2*4 bunches
6.51 kW
Design 100nC
2.2 kW
6.6kW
2*36 bunches
(LHC 1 kW)
1 ~ 2 kW extracted by the HOM coupler technically
possible (LEP and LHC)
200 W
4.4 kW
KEKB
16 kW
SuperKEKB
40 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
Impedance budget
• Resistive wall impedance is calculated with analytical formulas
• Impedance of the RF cavities is calculated with ABCI
Object
Contributions
R [k]
L [nH]
kloss [V/pC]
|Z///n|eff []
Resistive wall (Al)
6.6
87.1
210.9
0.0031
RF cavities (N=378)
29.3
--
931.2
---
Total
35.9
87.1
1142.1
0.0031
1500
Beam
RW
RF
Total
wake, V/pC
1000
500
0
-500
-1000
-1500
-10
-5
0
z, mm
5
10
W (s)  Rc (s)  Lc2(s)
41
Single-bunch effects
Parameter
Symbol, unit
Value
Beam energy
E, GeV
120
Circumference
C, km
53.6
Beam current
I0, mA
16.6
Bunch number
nb
50
Natural bunch length
l0, mm
2.66
Emittance (horz./vert.)
ex/ey, nm
6.79/0.02
RF frequency
frf, GHz
0.65
h
116245
Natural energy spread
e0
1.5E3
Momentum compaction factor
ap
4.15E5
n x /n y
179.08/179.22
ns
0.199
tx/ty/tz, ms
14/14/7
Harmonic number
Betatron tune
Synchrotron tune
Damping time (H/V/s)
(paramter_lattice20140416)
42
• Longitudinal microwave instability
– Keil-Schnell criterion:
I th 
– The threshold of the longitudinal
impedance is |Z///n| < 0.026 .
E
 e 0 2 l
e
Z
R | |eff
n
2 a p
• 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)
11
7000
wake, V/pC
3000
-1000
-5000
-9000
0
10
20
30
z, mm
40
Pseudo-Green function wake (z=0.5mm)
Beam line density (a.u.)
Beam
RW
RF
Total
2
x 10
without wake
with wake
1.5
1
0.5
0
-5 -4 -3 -2 -1
0 1
z/z
2
3
4
Steady-state bunch shape
5
43
• Bunch lengthening with SuperKEKB’s geometry wake
– LER wake+RW+RF (bunch is lengthened by 9.0%)
4
11
x 10
2
wake, V/pC
1
0
-1
Beam
RW
RF
SuperKEKB LER
LER+RW+RF
-2
-3
-4
0
10
20
30
z, mm
Beam line density (a.u.)
2
x 10
without wake
with wake
1.5
1
0.5
0
-5 -4 -3 -2 -1
40
0 1
z/z
2
3
4
5
– HER wake+RW+RF (bunch is lengthened by 18.5%)
4
11
x 10
2
2
wake, V/pC
1
0
-1
Beam
RW
RF
SuperKEKB HER
HER+RW+RF
-2
-3
-4
-5
0
10
20
30
z, mm
40
Beam line density (a.u.)
3
x 10
without wake
with wake
1.5
1
0.5
0
-5 -4 -3 -2 -1
0 1
z/z
2
3
4
5
44
• Coherent synchrotron radiation
(K. Bane, Y. Cai, G. Stupakov, PRST-AB,
2010)
– zr1/2/h3/2=9.2 (=> CSR shielded)
– The threshold of bunch population for CSR is given by
S
S  0.50  0.12
th
re Nb r 1/ 3
2n sd 
4/3
z
,

 z r 1/ 2
h3 / 2
– The CSR threshold in BAPS is Nb,Th = 5.01012 >> Nb = 3.71011.
– CSR is not supposed to be a problem in BAPS.
• Space charge tune shift
n x, y
b x , y ( s)
re Nb

ds
(2 )3 / 2  3 z   x, y (s)( x (s)   y (s))
ny = 1.7e4,
nx = 5.0e6
45
• Transverse mode coupling instability (TMCI)
Z 
4n s Eb
eI b R  b  
– 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.
2
• Eigen mode analysis
s
( - b )/ 
• Considering only resistive wall
impedance
• Beam current threshold:
Ibth=11.6mA (I0th=578mA)
1
0
-1
-2
-3
0
5
10
15
Ib, mA
46
Multi-bunch effects
• Transverse resistive wall instability
nb I b c

t
4 ( E / e)n x, y
1

e
( pn 0 / a p ) 2  t2
p  
Re Z  ( pn )
2
with pn = 2frev  (pnb + n + nx,y)
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!
(20, 1.1)
0
y
1/ t , Hz
 The growth rate for the most dangerous
instability mode is 1.1 Hz (t=0.9 s) in the
vertical plane with mode number of m = 20.
1
-1
-2
-3
0
10
20
m
30
40
50
Growth rate vs. mode number
in the vertical plane
47
4
1.1185
3
1.118
1/ t , Hz
1.119
y
y
1/ t , Hz
5
2
1
0
179
1.1175
1.117
179.2
179.4
ny
179.6
179.8
180
Instability growth rate vs. vertical tune
1.1165
-3
-2
-1
0

1
2
3
Instability 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.
Electron cloud instability
KEKB
SuperKEKB
SuperB
CEPC
Beam energy E, GeV
3.5
4.0
6.7
120
Circumference L, m
3016
3016
1370
53600
Number of e+/bunch, 1010
3.3
9
5.74
37.1
Emittance H/V ex/ey, nm
18/0.36
3.2/0.01
1.6/0.004
6.79/0.02
Bunch length z, mm
4
6
5
2.66
Bunch space Lsp, ns
2
4
4
3575.8
Single bunch effect
Electron freq. e/2, GHz
35.1
150
272
183.9
Phase angle ez/c
2.94
18.8
28.5
10.3
Threshold density re,th, 1012m-3
0.7
0.27
0.4
1.1
Multi-bunch effect
p-e per meter n, p/(m)
5.0E8
1.5E9
3.6E9
1.1E10
Characteristic frequency G, MHz
62.8
87.2
69.6
5.9
Phase angle GLsp/c
0.13
0.35
0.28
21.2
•
•
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.49
Beam ion instability
• Ion trapping
– With uniform filling pattern, the ions with a relative molecular mass
x 10
larger than Ax,y will be trapped.
3
4
Nb rp Sb
y
x
2( x   y ) x, y
2
A /A
Ax, y 
Ax
Ay
2.5
1.5
– The ions will not be trapped by
1
the beam.
0.5
• Fast beam ion instability
0
0
0.5
1
1.5
2
2.5
– With uniform filling, the growth time considering
ion
z, oscillation
m
x 10
frequency spread is 6.9ms, which is lower than the damping time.
– Fast beam ion instability could occur with uniform filling.
X: 1.077e+004
Y: 421.5
4
t [ s ]  5 p[Torr]
1
inst
1
/2
Nb3 / 2 nb2 re rp1 / 2 L1sep
c
 y3 / 2 ( x   y )3 / 2 A1 / 2b
1
1  t inst
t inst
c
2 2 Lsep nB ions
50
Booster bypass design
Booster: Outer of Collider
CEPC
Booster lattice
Version 1
Version 2
Parameters
Collider
Booster
Collider
Booster
Number of super-period in whole ring
16
16
16
16
Number of normal cells in an arc
59
36
60
37
Number of dispersion suppressor cells in an arc
22
22
22
22
Number of straight sells in a super-period
3
3
8
3
Length of a cell (m)
48
73.7
44
72
Length of bending magnets in a cell (m)
410
416
218
88
Length of an arc (m)
3024
2948
2816
2952
Length of straight cells in a super-period (m)
144
221.1
352
216
Length of a super-period (m)
3168
3169.1
3168
3168
(Arc) Ring circumference (m)
50688
50705.6
50688
50688
FODO Lattice functions: booster vs. collider
Version 1
Version 2
A SUP Lattice functions: booster vs. collider
Version 1
Version 2
Dynamic aperture
dp p
2
dp p
1
dp p 0
dp p 1
dp p 2
Main Parameters
Main Collider
Booster
Energy (GeV)
120
10~120
Circumference (Km)
50
50
Bunch Number
50
50
Emittance x/y (nm)
6.8/0.02
24/
Life time (min)
30
Beam Current (mA)
16.9
0.84
Injection Options
Geometrical Arrangement
Booster
2m
Main Collider
Injection linac
6GeV Conventional Linac (option I)
Injection linac
• Main parameters
Parameter
Symbol
Unit
Value
E- beam energy
Ee-
GeV
6
E+ beam energy
Ee+
GeV
6
Pulse width
Δt
ns
0.7
Repetition rate
frep
Hz
100
E- bunch population
Ne-
2×1010
E+ bunch population
Ne+
2×1010
Energy spread (E+/E-)
σE
<1×10-3
 Challenge
1. Nbunch e+=21010
2. Polarization
3.2nC/bunch e+
Injection linac
 Linac Frequency: 2856MHz Normal conducting
 Conventional Positron Source and a 0.2GeV Positron Beam
Transport Line
Electron source
• Unpolarized Electron Source (Baseline)
Electron Gun
Gun type
Thermionic Triode Gun
Cathode
Y824 (Eimac) Dispenser
Beam Current (max.)
A
10
High Voltage of Anode
kV
150-200
Bias Voltage of Grid
V
0 ~ -200
Pulse duration
ns
0.7
Repetition Rate
Hz
50~100
• Polarized Electron Source (R&D)
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 target
GeV
4
E- bunch charge on the target
nC
10
Target material
W-Re
Target thickness
mm
14
Focus device
Flux Concentrator
5Tesla
E+ Energy pre-accelerate
MeV
200
E+ Yield
SppC Layout
High Energy Booster(7.2Km)
Medium Energy Booster(4.5Km)
Low Energy Booster(0.4Km)
IP4
Proton Linac
(100m)
IP3
SppC main parameters
Parameter
Value
Unit
Circumference
52
km
Beam energy
35
TeV
Dipole field
20
T
Injection energy
2.1
TeV
Number of IPs
2 (4)
1.2E+35
cm-2s-1
Beta function at collision
0.75
m
Circulating beam current
1.0
A
Peak luminosity per IP
Max beam-beam tune shift per IP
0.006
Bunch separation
25
Bunch population
2.0E+11
SR heat load @arc dipole (per aperture)
56
ns
W/m
Beam-beam tune shift limit analytical calculations
For lepton collider:
 y,max 
J. Gao, Nuclear Instruments and Methods in Physics
Research A 533 (2004) 270–274
2845 
1
re
6RN IP
 0.072 (CEPC )
r_e is electron radius
γ= is normalized energy
R is the dipole bending radius
N_IP is number of interaction points
 x,max  2 y ,max  0.11(CEPC)
J. Gao, Nuclear Instruments and Methods in Physics
Research A 463 (2001) 50–61
For hadron collider:
 max
where
f(x )  1 
x
2

4f(x )
max N IP
2
2
x
 exp( 
0
4f 2(x )

2845
t2
2
2845

f  x
)dt
6R
rp N IP
Formulae from private note of J. Gao
rp
6 RN IP
r_p is proton radius
SppC (actual parameter list)
x  2.03656
f(x )  0.0417
 max  0.0064
FCC (pp) 0.005 (theory and design)
Injector chain (for proton beam)
p-Linac: proton superconducting linac
p-RCS: proton rapid cycling synchrotron
MSS: Medium-Stage Synchrotron
SS: Super Synchrotron
Ion beams have
dedicated linac (I-Linac)
and RCS (I-RCS)
Main features on accelerator physics
• Very high luminosity: 1.21035 cm-2s-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 W/m @dipole
– High circulation current: 1 A (similar to HL-LHC)
• Machine protection by sophisticated collimation system
(6.3 GJ per beam; inefficiency: 10-7)
• 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: 14-20 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
(Very Preliminary)
• 2015-2020: Development of a 12 T operational field Nb3Sn
twin-aperture dipole with common coil configuration and 10-4
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).
• 2020-2025: Development of a 15 T Nb3Sn twin-aperture dipole
and quadrupole with 10-4 field uniformity; Fabrication and test
of 4~5 T HTS (Bi-2212 or YBCO) coils in a 15 T background field.
• 2025-2030: 15 T Nb3Sn coils + HTS coils (or all-HTS) to realize
the 20 T dipole and quadrupole with 10-4 field uniformity;
Development of the prototype SppC dipoles and quadrupoles
and infrastructure build-up.
69
CEPC+SppC Layout
e+
e-
IP1
LTB
High Energy Booster(7.2Km)
BTC
Medium Energy Booster(4.5Km)
Low Energy Booster(0.4Km)
IP4
IP2
LTB : Linac to Booster
BTC : Booster to Collider Ring
e+ e- Linac
(240m)
Proton Linac
(100m)
BTC
IP3
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
Acknowledgements
Thanks go to the speakers who provide me their
presentations and all participants during discussion
Thank you for your attention