a brighter future

Salim Ogur
FCC-ee Injector Design Study& on behalf of K. Oide, F. Zimmermann

KEK, Tsukuba, Ibaraki 30-Oct-2016

Outline
0. Review of Accelerators and Baseline Parameters
1. Linac Design< Positron Parameters >2. Damping Ring Design
3. Conclusions

22

Motivation:
FinalOperation Type

Energy[GeV]

Bunches

Bunch

Horizontal

Vertical/BeamPopulation

Emittance

Emittance

Z

45.6

91500

3.3E+100.09 nm

1 pm

W

80

5260

6E+100.26 nm

1 pm

H120780

8E+100.61 nm

1 pm

tt

175

81

1.7E+111.3 nm

1 pm❖ FCC ee has 4 different operations, especially Z operation is challenging in terms ofpre-injection since it requires the highest total charge and the lowest emittance.
❖ Therefore, the fulfilling the requirements of Z-operation is to cover all otheroperations in terms of total charge and final geometric emittance in the collider.
30. Electron Flow Scheme
electron

6 GeV Linac
100 km - Collider
45.6 GeV
100 km - Booster
45.6 GeV
not to scale!

0.4407 x 3.5 = 1.54 GeV e+ Damping Ring
The energy is chosen regarding the spin tune polarisation

0. Positron Flow Scheme
electronpositron

Booster

6 GeV Linac
100 km - Booster

0. Positron Flow Scheme
electronpositron

Booster

100 km - Booster

0. Positron Flow Scheme
electronpositron

Booster

100 km - Booster@4.46 GeV

0. Positron Flow Scheme
electronpositron

Booster

100 km - Booster@4.46 GeV

1.54 GeV e+ DR

0. Positron Flow Scheme
electronpositron

Booster

100 km - Booster@4.46 GeV
1.54 GeV
1.54 GeV e+ DR

0. Positron Flow Scheme
electronpositron

Booster

100 km - Booster

1.54 GeV
1.54 GeV e+ DR

0. Positron Flow Scheme
electronpositron

Booster

100 km - Booster

1.54 GeV
1.54 GeV e+ DR

0. Positron Flow Scheme
electronpositron

Booster

100 km - Booster

1.54 GeV
1.54 GeV e+ DR

0. Positron Flow Scheme
electronpositron

Booster

100 km - Booster

1.54 GeV
1.54 GeV e+ DR

0. Positron Flow Scheme
electronpositron

Booster

100 km - Booster

1.54 GeV
1.54 GeV e+ DR

0. Booster- the first Fill-up of the Collider❖The Booster fill time is suggested as 4 seconds and 6 more seconds for the acceleration of theavailable bunches. The electrons are injected with f=100 Hz from the linac with 2 bunches per RF
Pulse (we are working on SLED acceleration scheme to check the possibility of accelerating 4bunches per RF pulse or more). Therefore,
4 [seconds]*100 [Hz]* 2 [Bunches/RF Pulse] = 800 Bunches60. Booster- the first Fill-up of the Collider❖

The Booster fill time is suggested as 4 seconds and 6 more seconds for the acceleration of theavailable bunches. The electrons are injected with f=100 Hz from the linac with 2 bunches per RF
Pulse (we are working on SLED acceleration scheme to check the possibility of accelerating 4bunches per RF pulse or more). Therefore,

Collider4 [seconds]*100 [Hz]* 2 [Bunches/RF Pulse] = 800 Bunches

Booster
t=10 seconds,
the booster has 800 bunches
the collider has 0 bunch60. Booster- the first Fill-up of the Collider❖The Booster fill time is suggested as 4 seconds and 6 more seconds for the acceleration of theavailable bunches. The electrons are injected with f=100 Hz from the linac with 2 bunches per RFPulse (we are working on SLED acceleration scheme to check the possibility of accelerating 4bunches per RF pulse or more). Therefore,

Collider4 [seconds]*100 [Hz]* 2 [Bunches/RF Pulse] = 800 Bunches

Booster
t=10 seconds,
the booster has 800 bunches
the collider has 0 bunch

t=20 seconds,
the booster has 800 bunches
the collider has 800 bunches60. Booster- the first Fill-up of the Collider❖

The Booster fill time is suggested as 4 seconds and 6 more seconds for the acceleration of theavailable bunches. The electrons are injected with f=100 Hz from the linac with 2 bunches per RFPulse (we are working on SLED acceleration scheme to check the possibility of accelerating 4bunches per RF pulse or more). Therefore,Collider

4 [seconds]*100 [Hz]* 2 [Bunches/RF Pulse] = 800 Bunches

Booster
t=10 seconds,
the booster has 800 bunches
the collider has 0 bunch

t=20 seconds,
the booster has 800 bunches
the collider has 800 bunches

t=1150 seconds (~19 mins),
the booster has 800 bunches
the collider has 92000 bunches60. Overview of Emittance Evolution★Aim: Linac is optimised to accelerate 4E10 particles. The expected beam population at
the end of linac is 3.3E10 at 6 GeV. Therefore, the Linac should at least have 83% oftransmission. Meanwhile the exiting beam emittance should match the requirements:

e- Accelerators

EnergyRel. Gamma
Ratio

EmitX

EmitY

Collider Aims

45.6-

0.09 nm

1 pm

Collider Accepts

45.6

-

27.3 nm

2 nm

Booster Exit

45.6

-

0.09 nm0.13 nm

Booster Entrance

67.6

0.7 nm

1.0 nmLinac Exit

6-

0.7 nm

1.0 nmLinac Entrance

0.012

500

0.35 !m

0.5 !m❖ Assuming normalised emittance kept constant at 8/12 μm (h/v) throughout the re-entrance
7of the linac, thru transfer to the booster, inside the booster and injection to the collider.

1. Linac - Basics❖ The Linac is deploying cavities of ~2.97 m length with 10mm aperture size at frequency 2855.98 MHz (S-band).
❖ The Wakefields have been turned on through the linac
simulations.
❖ Normal conducting linac with 100 Hz repetition, it is
optimised to accelerate 4E10 particles per bunch which isintentionally above full-charge(3.3E10) concerning theprobable transmission loss.

81. Linac - Optics
Parameter
Initial Energy[MeV]
Final Energy[GeV]
Length [m]Value126257.3

InitialEmittance

0.35/0.5(h/v) [μm]FinalEmittance

0.7/1.0(h/v) [nm]# of cavities
Gradient[MV/m]
Grad. thru acc.
[MV/m]❖

Gaussian Random Beam with 1 mm bunch length and 1%
energy spread

8025239

1. Linac - Beam Profile101. Linac - Misalignments❖ Realistic errors have been introduced to study transmission
and orbit correction. Each error refers to 1 sigma in Monte Carlosimulation (Gaussian distribution).
❖ About 3 m long 2.856 GHz cavities with 10 mm aperture size
are used.
11

1. Linac - Misalignments

Transmission drop to 33% !!
❖ Realistic errors have been introduced to study transmission
and orbit correction. Each error refers to 1 sigma in Monte Carlosimulation (Gaussian distribution).
❖ About 3 m long 2.856 GHz cavities with 10 mm aperture size
are used.
11

1. Linac- Orbit Correction(First Step)❖ Beam envelope oscillations have not been changed dramatically after
deploying a steerer magnet for each cavity.
122. Linac- Orbit Correction(First Step)• The gradients of the steerers are dynamically set to re-center the misaligned
incoming beam to the cavity center by the code written by K.Oide.

• Physically, this script corresponds to a readout of BPM, and then to
determine the gradient of the steerers depending on that.
131. Linac- Orbit Correction(First Step)• The transmission is 69%.
14

1. Linac- Orbit Correction(Second Step)• Half length cavities with 20 mm aperture have been deployed
to reduce the impact of the wakefields in the low energy part.
15

1. Linac- Orbit Correction(Second Step)• Thanks to shorter cavities and larger aperture, the impact of
the wakes decreased. Besides, we can steer the beam in ashorter distances.
16

1. Orbit Correction- Beam Profile

Simulations
with
1M particles

17

1 . Linac - Results@ the end of Linac

Results

Transmission Required

83%

Transmission Provided

88%

Emittance (h/v) Required

0.7/1.0 nm

Emittance (h/v) Provided

60/51 nm• Wakefields cause the beam toshape like “banana”, and thisinevitably makes the emittancemuch bigger.
• Deploying half-length cavities (14.3wavelengths=1.5 m) reduce theeffect of the wakefields in low
energy part. Aperture size doubled;
meanwhile the gradient is kept
below 27 MV/m.
• As on-going study, the emittancegrow, and getting rid off “banana”
shape is under consideration.

18

<Overview of Damping Necessities>
e+ Accelerators

Energy [GeV]

Damping Ring

1.54

Damping Ring exit
Booster exit

Rel. Gamma

EmitX

EmitY

-0.76 μm *0.71 μm *1.54-2.66 nm

3.9 nm

45.6

29.6

0.09 nm0.13 nm

Ratio➡ Assuming no normalised emittance shrink or blow throughout the re-entrance of thelinac, thru transfer to the booster, inside the booster and injection to the collider.
* KEK positron data is adapted to the FCC-ee selection of energy and bunchcharge !
19

2. Damping Ring - Overview❖ Circumference of the DR 216 meter ⬌ 720 ns for the speed of light.
— 3 trains x 2 bunches

120 ns spacing;

Beam Enters:=Positron Bunch
RF Section:
2 Cavities
with ~ MV
voltage

Beam Exits
20

< Positron Acceleration- Time Schedule>
RF time [ms]LinacDamping RingBooster0-20

accelerates 2 bunches of e-

damps 2 bunches of e+

empty

20-40

accelerates 2 bunches of e-

damps 4 bunches of e+

empty

40-50

accelerates 2 bunches of e-

damps 6 bunches of e+

empty

50-60

accelerates 2 bunches of e+

damps 4 bunches of e+

accumulates 2 e+ bunches

60-70

accelerates 2 bunches of e-

damps 6 bunches of e+

accumulates 2 e+ bunches

70-80

accelerates 2 bunches of e+

damps 4 bunches of e+

accumulates 4 e+ bunches

80-90

accelerates 2 bunches of e-

damps 6 bunches of e+

accumulates 4 e+ bunches

90-100accelerates 2 bunches of e+

damps 4 bunches of e+

accumulates 6 e+ bunches

100-110accelerates 2 bunches of e-damps 6 bunches of e+

accumulates 6 e+ bunches(T= 20 ms periodic)
1200+50 ms

accumulates 60 x 2 e+bunches

at the end of 4 s

400 e+ bunches❖ 100 Hz i.e.10 ms Linac repetition with 2 bunches per RF pulse where bunch population
is 4E10 e- or e+.
➡ This scheme enables positron bunches 50 millisecond inside the damping ring !

2 . Damping Ring - Optics
Parameter
tau_x[millisecond]
tau_y[millisecond]
emit_x[nm]
emit_yCircumference[m]# of bends
Dipole Field[T]
Wiggler Field[T]

ko7.sad

Value
11.0
11.4
1.3
216
192
0.67
1.65

Cell_tune_x [rad]0.193

Cell_tune_y [rad]

0.183
22

2 . Damping Ring - DA
❖ 234 sigmas intransverse❖ 110 sigmas inlongitudinal

Ring is tuned:★ nxcell = 0.193★ nycell = 0.183★ NX = 20.087★ NY = 19.163★ Cavity Voltage: 2 MV23

ko7.sad2 . Damping Ring - Results❖ The performance of the Damping Ring in the transverse directions:e+ Accelerators

Energy [GeV]Emittance_X

Emittance_Y

Damping Ring entrance

1.54

0.76 μm

0.71 μm

Damping Ring exit (target)

1.54

2.66 nm

3.9 nmDamping Ring exit (t=50 ms)

1.54

1.36 nm

0.1 nm❖ Hence, we reach the target at t_x=35 ms, t_y=29 ms; meanwhile the allocatedtime is 50 ms.

24

2 . Damping Ring - Results❖ The performance of the Damping Ring in the transverse directions:

Natural EmittanceDA NeededDA Created

1.3 nm

73 sigmas

234 sigmas

AcceptanceAcceptance

Needed [3 sigma]

Provided

6.84 μm69.5 μm

PS: 1-sigma emittance is 0.76 μm

25

2 . Damping Ring - Results❖ The performance of the Damping Ring in the longitudinal direction:— Natural emittance : 3.56 μm for 2 MV cavity voltage
2

3.56 µm ⇤ (110) = 43.1 mm

which is surpassing the acceptance which is at least 9 times of theadapted KEKB initial positron emittance in z-axis:
21 mm ⇤ (3) = 9 mm

26

2 . Damping Ring - Results❖ The performance of the Damping Ring in the longitudinal direction:— Bucket Height— Energy Spread: 0.0838: 6.71E-4—> Dynamic Aperture : 110 σ < 125 σ

27

2 . Damping Ring - Results❖ The performance of the Damping Ring in the longitudinal phasespace:— Natural emittance : 3.56 μm for 2 MV cavity voltage— Bunch Length: 5.30 mm
2z(5.30 mm)2== 7.9 m which is bigger than thez =✏z
3.56 µm

beam size provided by the KEKB positron data:2z(0.041 m)2== 1.7 mz ="z0.001 menergy compressor !!

28

Conclusions-Linac❖ 6 GeV S- Band Linac has become 299 meters with 28 half-lengthand 64 full-length (i.e. 3 m) cavities. There are 22 quadrupoles,and 92 steerer magnets.
❖ The acceleration gradient is around 25 MV/m and 2 bunches per
RF pulse are sent. These are quite feasible with the recenttechnology.
❖ The linac transmission is 88%, which can be increased evenmore. Yet, the emittance blow has to be cured.
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Conclusions-DR❖ Damping Ring consists of standard FODO lattice (with sextupoles),and normal conducting wigglers. DR also has additional 16quadrupoles in straight sections to control the ring tune. All magnets(except wigglers with 1.65 T ) are below 0.8 T.
❖ Damping Ring totally covers the FCC-ee positron damping
requirements.
❖ Collider for Z-operation will be filled from the scratch with 91500
bunches of e- in 19 mins, and same number of e+ in 27 mins. Suchthat in 46 mins, the collisions can start.
❖ Accelerating more than 2 bunches per RF pulse is underconsideration to reduce the time for the first fill of the collider.

3030