CEPC Booster Design

FCC Week 2015, 23-27 March, 2015

Marriot Georgetown Hotel

Huiping Geng Presented for Chuang Zhang

The CEPC Booster

General description

Lattice

Low injection energy issues

Beam transfer

Summary

1. General DescriptionBooster is in the same tunnel of the CEPC

collider, and will be installed on its up-side with about the same circumference as the collider, while bypasses are arranged to keep away from detectors.

Providing beams for the collider with top-up frequency up to 0.1 Hz.

Using 1.3 GHz RF system;

The injection energy of the booster is 6 GeV;

Magnetic Field is as low as 31 Gs at injection.

The CEPC Layout

P.S.

P.S.

P.S.

IP1

IP4

IP3

IP2

D = 17.428 km

½ RF

RF

RF

RF

RF

½ RF

½ RF

½ RF

RF RF

One collider RF station:

650 MHz five-cell SRF cavities;

4 cavities/module 12 modules, 8 m

each RF length 120 m

(4 IPs, 1132.8 m each)

4 arc straights849.6 m each

8 arcs 5852.8 m each

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

BTCe+ BTCe-

Linac

LTB

Main parameters of CEPC booster

Single bunch injection from linac (E=6 GeV, Ip=3.2nC, frep=50 Hz,

ex,y=0.1-0.3 mmmrad) to booster;

Assuming 5% of current decay in the collider between two top-ups ;

Booster operates with repetition frequency of 0.1 Hz.

Overall efficiency from linac to the collider is assumed as 90 %.

SR power density of 45W/m is much lower than in BEPCII of 415W/m.

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0.0 2.0 4.0 6.0 8.0 10.0 12.0

F(t

)/F

ej

t (s)

0.0

1.0

2.0

3.0

4.0

5.0

6.0

6 12 18 24 30 36 42 48 54 60 66 72 78 84 90 96 102

108

114

120

Vrf

(GV

)

E (GeV)

Parameter Symbol Unit Value

Injection energy Einj GeV 6

Ejection energy Eej GeV 120

Circumference C km 54.7528

Bending radius km 6.519

Main bending field Bej/Binj T 0.0614/0.00307

SR loss/turn U0 GeV 2.814

Bunch number nb 50

Bunch population Nb 1010 2.0

Beam current Ibeam mA 0.87

SR power @ 120GeV PSR MW 2.46

SR Power density @120GeV PSR/C W/m 45

6

2. Lattice Similar arc arrangement to the collider

Simple structure:

FODO cells + Disp. Suppr. + Straight / bypass

Cell length：To optimize cell number, emittance and aperture

Straight sections

For RF cavities, injection, extraction, etc.

Arc straight -DIS 78 FODO cells DIS IR2/IR4 straight

Arc straight -DIS 75 FODO cells DIS Bypass

FODO cell Length L 47.2 71.3 94.4 m

Quadrupole strength |kQlQ| L-1 0.044 0.029 0.022 m-1

Maximum beta function in a cell max L 81.2 122.6 162.3 m

Maximum dispersion in a cell Dx L2 0.38 0.86 1.52 m

Betatron tune x,y L-1 189.2 125.3 94.6

Momentum compaction factor p L2 3.43 7.83 13.72 10-5

Chromaticity L-1 86.4 57.2 43.2

Sextupole strength SF/SD |ksls| L-3 0.15/0.24 0.044/0.070 0.019/0.030 m-2

Nature emittance x0 L3 6.8 23.44 54.40 nm

Synchrotron tune (VRF=5 GV) sL 0.204 0.31 0.41

Maximum Betatron beam size x/y L2 0.74/0.53 1.70/1.20 2.97/2.10 mm

Maximum Beam orbit spread xE L2 0.49 1.12 1.97 mm

Maximum horizontal m beam size x L2 0.89 2.03 3.57 mm

Bunch length (VRF=5 GV) z L 1.84 2.78 3.68 mm

2.1. Choice of cell length

2.2 Lattice functions: booster vs. collider

ARC

FODO cell

SUP and Ring Lattice: booster vs. colliderSUP

Ring

10

2.3 Bypasses Two bypasses are arranged to skirt the detectors at IP1

and IP3 of the collider.

P.S.

P.S.

P.S.

IP1

IP4

IP3

IP2

½ RF

RF

RF

RF

RF

½ RF

½ RF

½ RF

RF RF

(4 IRs, 1132.8 m each)BTCe+ BTCe-

Linac

LTB

CEPC &Booster

11

Bypasses

Length of half bypass: L=(4+4f1+1.5f2)Lc

Width of the bypass: W=(9.5+9f1) cLc

L = 10.5Lc= 752.482 m (f1=1.0, f2=1.0)

W 18.5cLc = 13.0m (f1=1.0) (MAD: 12.662 m)

By adjusting f1 and f2, both length and width of bypass

can be adjusted to fit the FFS length and detector width.

No additional bending cell is required!

-3*FODO

-3Lc

DIS

2Lc

BPI1

4f1Lc

-DIS

2Lc

FODO

Lc

DIS

2Lc

BPI2

1.5f2Lc

The bypass latticeBPI1 -DIS FODO DIS BPI2

RFC

ARC DIS

Orbit length change

LBP = LAS+SS+8Dl =21LC + DL

DL=8Dl =LC d =Lc(1/cos3qC-1) DL=0.25 m

s3Lc

3Lc

4(Lc+Dl)

4(Lc+Dl)15Lc

3Lc 3Lc7Lc

4Lc 4Lc7Lc

To increase the straight length from 7Lc to 7Lc+2DL

LBooster=Ccollider+2DL = 54752.7936 m

MAD calculation: DL = 20.1934 = 0.3868 m

2.4 Dynamic aperture

30 20 10 10 20 30 40x x

50

100

150

200

250

300

350

y y

T he dy namic ap erture by t racking of 3 damp ing t imes

dp p 2

dp p 1

dp p 0

dp p 1

dp p 2

30 20 10 10 20 30 40x x

50

100

150

200

250

300

350

y y

T he dy namic ap erture by t racking of 3 damp ing t imes

dp p2

dp p1

dp p0

dp p1

dp p2

With two family sextupoles, xc=0.5

r = ey/ex = 0.01 Dp/p = +2%

Dp/p = +1%

Dp/p = 0

Dp/p = -1%

Dp/p = -2%

nx (s)x

ny (sy)

Lattice ParametersParameter Unit Value

Circumference m 54752.7936

Bending radius m 6519

Horizontal/vertical tunes 127.18/127.28

Total FODO structures in a ring 768

FODO cell length m 71.665

Phase advance in a cell (H/V) 60°/60°

Maximum horizontal/vertical m 123.84/122.97

Maximum dispersionfunction m 0.879

Length of bypass m 2752.482

Width of bypass m 13.0

3. Low injection energy and low field issue

The bending field of CEPC booster is 614Gs at 120 GeV; To reduce the cost of linac injector, the injection beam energy for booster is chosen as low as 6 GeV with the magnetic field of 30.7 Gs.

It needs to be tested if the magnetic field could be stable enough at such a low field against the earth field of 0.5-0.6 Gs and its variation? Try to do magnetic measurement using existing magnet at low field strength.

3.1 Low field stability test

A BEPC bending

magnet:B0=9028Gs @ IB=1060A;

B0=30Gs @ IB=3A 。

Power supplies for ADS:

3A/5V, 15A/8V ;

DI/I < 110-4。

Hall probe system will be used for field measurement; DB= 0.1 Gs DB/B0~310-3。

Magnetic field stability measured in 24 hours3A—温度值与磁场值对比

2424.224.424.624.825

25.225.425.625.8

1 71 141 211 281 351 421 491 561 631 701 771 841 911 981 1051 1121 1191 1261 1331 1401

测量点数

℃温

度值

（）

33.35

33.4

33.45

33.5

33.55

33.6

33.65

磁场

值（Gs ）

3A-温度3A-磁场值

6A—温度值与磁场值对比

25

25.2

25.4

25.6

25.8

26

26.2

26.4

26.6

1 71 141 211 281 351 421 491 561 631 701 771 841 911 981 1051 1121 1191 1261 1331 1401

测量点数

℃温

度值

（）

59.5

59.6

59.7

59.8

59.9

60

60.1

60.2

磁场

值（Gs ）

温度值磁场值

IB=3A, B30Gs, sB=710-4

9A—温度值与磁场值对比

25

25.2

25.4

25.6

25.8

26

26.2

1 71 141 211 281 351 421 491 561 631 701 771 841 911 981 1051 1121 1191 1261 1331 1401

测量点数

℃温

度值

（）

86.25

86.3

86.35

86.4

86.45

86.5

86.55

86.6

86.65

磁场

值（Gs ）

温度值磁场值

sB=1.810-3

IB=6A, B 60Gs, sB=1.310-3

IB=9A, B90Gs, sB=1.810-3

Low field stability test

The earth field outside the magnet: Bx=0.550.026Gs, By=0.450.027Gs, Bz=0.250.03 Gs B= 0.80.04Gs

Inside the magnet, By=7.00.05Gs is dominated by residual field, Bx=0.40.04Gs reduced due to the shielding while Bz=0.250.03 Gs.

The reason of the measured field variation (field itself or measurement error) is being investigated;

The 24h field stability (sB) for 30 Gs-150 Gs is about (1-2)10-3;

The magnet ramps smoothly around the low fields with accuracy better than 110-3;

The field error DBy/By 10-4 for x(-60, 60) mm and By(30-150) Gs

The injected beam energy for booster of 6 GeV could be feasible in view of magnetic field stability.

Mitigation

Wiggling band scheme

Increase linac energy

10 GeV, 12 GeV

Accumulating pre-booster

3.3 Instability issuesBeam stability at injection is concerned

Ebooster, inj=0.05Ecollider vs. Ibooster,=0.05Icollider;

Almost no synchrotron radiation damping;

HOM of 1.3 GHz SC cavities, CB instability;

Resistive wall instability;

Transverse mode coupling instability;

ECI and ion effects?

Bunch-by-bunch feedback to stabilize beams.

Instability issues (N. Wang)

The transverse mode coupling

Considering the impedance generated from the resistive wall and the RF cavity, the single bunch threshold current of 27A, higher than the design bunch current of 18A, but doesn’t leave much margin.

The resistive wall instability

The growth time for the most dangerous mode is 34 ms in the vertical plane. The growth rate is much shorter than the radiation damping time, transverse feedback system is needed to stabilize the beams.

The growth rate of the first few HOM’s

* k ∥mode= 2πf·(R/Q)/4 [V/pC] ** k⊥ mode = 2πf·(R/Q)/4 [V/(pC·m)]

Monopole Mode f (GHz) R/Q ()* Q f (MHz) (s)

TM011 2.450 156 58600 9 1.5

TM012 3.845 44 240000 1 0.5

Dipole Mode f (GHz) R/Q (/m)** Q (ms)

TE111 1.739 4283 3400 5 218

TM110 1.874 2293 50200 1 44

TM111 2.577 4336 50000 1 22

TE121 3.087 196 43700 1 497

Longitudinal (td < 0.5 s) and transverse (td< 20 ms) feedback systems should be equipped to stabilize beams.

4. Beam transfere+ inj. e- inj.

e+ arc Match to booster for e+

Linac Match to linac Vertical slope line Switch

e- arc Match to booster for e-

4.1 Transfer From Linac to Booster

Match and Switch

Booster

Match to the booster

Matching section

Arcs

Vertical slope line

Vertical slope lineSlope = 1:10, L~500m,Dx,max~2m

4 FODO match from linac

Match to e arcs

Vertical slope line

Match from linac to booster

From linac to the end of VSL Match and switch to e Arc

Match to booster MTB From Linac to Booster

MatchingSwitch e+ (or e-) arc

4.2. Beam injection to booster

Component Length (m) Waveform Deflection angle(mrad) Field (T)

Aperture

H (mm) V (mm)

Septum 2.0 DC 9.1 0.18 41.4 13.4

Kicker 0.5 1.5 s half-sine wave

0.40 0.032 41.4 13.4

xk = 12x,ej +3x,inj+d

x,inj x,inj

Injected bunch

x

y Septum

Injecting bunch

d

2x,inj

12x,ej

e beams are injected from outside of the booster ring;

Horizontal septum is used to bend beams into the booster;

A single kicker downstream of injected beams kick the beams into the booster orbit.

Tunnel

Arrangement

Septum Kicker

Booster CCoolllliiddeerr Booster CCoolllliiddeerr

Copper, H CCooppppeerr,, HH H HH

Iron, H IIrroonn,, HH V VV oorr NNoo

Copper, V CCooppppeerr,, VV V VV

Iron, V IIrroonn,, VV H HH

C. S., H I. S., H C. S., V I. S., V

4.3 . Transfer from booster to collider

Booster ejectionSingle kicker + 4 orbit bumps are used for beam extraction vertically from the booster;

Septum magnets are applied to bend beams vertically into BTC;

Maximum extraction rate is 100 Hz.

Component Length (m) Waveform Deflection angle(mrad) Field (T)

Aperture

H (mm) V (mm)

Lamberstson 10.0 DC 9.1 0.41 41.4 18.6

Kicker 2.0 1.5 s half-sine wave

0.33 0.046 41.4 13.6

Vertical transfer

V. Septum (Cop. or Iron)

Lc

22 SSeeccttiioonn 4Lc

V. Septum (Cop. or Iron)

Lc

Summary Conceptual design study on CEPC-Booster has been carried out;

There is no showstopper found in the design, from the point of view of lattice, bypasses, dynamic aperture, beam transfer and requirement to technical systems.

The issues related to the low energy injection remain a central concern in the design. The schemes of extending the linac injection energy and/or adding a pre-booster are being considered.

There are some technical challenges, such as the low HOM in 1.3 GHz SC cavities, supports & alignment etc.

The design study will keep moving on.

Our Pre-CDR is available at:

• http://cepc.ihep.ac.cn/preCDR/volume.html

Thank you !