Capture Simulation for ILC Electron-Driven Positron Source

Y. Seimiya, M. Kuriki, T. Okugi, T. Omori, M. Satoh, J. Urakawa, and S. Kashiwagi

14 May 2014

• ILC is an international big project.• It should be “fail-safe”.• It should be implemented by the latest technology

which is sometimes with unexpected risks. • To control the risk, a technical back up is necessary. • The e-driven e+ source is the backup.

Why do we need e-driven e+?

• The electron driven e+ source is however not “conventional”. Amount of e+ is 50 times larger than that for SLC.

• To implement the e+ source with the minimum risk, it should be designed in operable regime, 35 J/g PEDD (Peak Energy Deposition Density) on target.

• In this study, we demonstrate that an enough amount of e+ can be generated with this condition.

Purpose of this study

Chart of Positron Source for ILC

DR

Capture Section Booster Linac

e- e+

ECS

• Capture Section: AMD and solenoid up to several hundreds MeV (L-band).

• Booster Linac: Acceleration up to 5GeV (L-band+S-band).

• ECS （ Energy Compression System ） : matching in longitudinal phase space.

Chart of Positron Source for ILC

DR

Capture SectionBooster Linac

e- e+

ECS

Yield(e+/e-): The number of e+/ The number of e- at the target

Design guideline is Yield 1.5 (3.0e+10 e+) in DR acceptance (50% margin).

Capture SectionBeam parameters & Target

Drive beam energy 6 GeV

Beam size 4.0 mm (RMS)

Target thickness 14 mm

AMD

Solenoid

e-

Target (rotate)

e+

Accelerating Structure

Accelerating Structure

RF Gradient 25 MV/m

RF frequency 1.3 GHz (L-band)

Length 10m

Aperture (radius) 20mm

AMD parameters

Max AMD field 7 T

Taper parameter 60.1 /mm

AMD length 214 mm

Solenoid

Solenoid Field 0.5 T

Positron distribution at the exit of Capture Section

• Positron distribution simulated by GEANT4 just after the Target. (T. Takahashi)

• The number of e-: 1000, The number of e+: 12696

Booster Linac

Booster Linac

RF Peak Gradient 40 MV/m

RF frequency 1.3 GHz (L-band)

Length 323.6 m

Aperture (radius) 17mm

Basic structures are FODO cells consisted of 4 QMs and some RF.

Positron distribution at the exit of Booster Linac

Energy Compression System (ECS)

ECS

RF Peak Gradient 38 MV/m

RF frequency 1.3 GHz (L-band)

Length 90.5 m

Aperture (radius) 17mm

Base structures are 3 chicanes and some RF.

Positron distribution at the exit of ECS

Parameters for optimization

1. RF phase at Capture Section2. RF phase at Booster Linac, ECS3. Aperture at Capture Section4. Aperture at Booster Linac, ECS5. Aperture and magnetic strength at AMD, and distance

between AMD and target6. Drive beam energy, target thickness, and beam size7. RF gradient at Capture Section8. Positron energy at the exit of Capture Section

Fix at the realistic largest aperture

Optimized automatically

small impact

Capture RF phase

• Aperture at Capture Section (X2+Y2)1/2 < 20 mm• Aperture at Booster Linac (X2+Y2)1/2 < 17 mm• Acceptance at DR

Longitudinal Acceptance: (E-E0)/E0 < 0.75 %, (z-z0) < 37.5 mm

Transverse Acceptance: (Wx+Wy)*γ < 70 mm

Dec. capture

Acc. capture

Yield is Max. at 270 〜 310°

Adiabatic Matching Device (AMD)

dZ

• AMD Aperture (≡RAMD) ： 6mm(radius)

• AMD Max. field strength (≡BAMD) : 7T

• Place of BAMD and end surface of Target (≡dZ) : 5mm (giving 3.5T)

Z (m)

Bz (T

)

AMD and Target configurations

• Yield is greatly depended on RAMD and dZ.• But not so much on peak BAMD. • Yield is saturated at dZ<3mm and RAMD > 8mm.• BAMD=7T, dZ=3mm, and RAMD=8mm are a feasible parameter set.

dZ=5mm dZ=3mm

RAMD(mm) RAMD(mm)

Aperture in Booster Linac

Capture eff. is saturated at 17mm . 17mm is optimum.

c

Drive beam and Target configuration （ 1 ）E=6GeV, T=20mm E=6GeV, T=14mm E=3GeV, T=14mm

RAMD(mm) RAMD(mm) RAMD(mm)

• Ne=2.0e+10 (fixed).• Yield is better for smaller spot size.

Drive beam and Target configuration （ 2 ）

Energy Thickness Beam size PEDD Yield Total deposit

3 GeV 14 mm 4mm 15 J/g 0.7 1.8 J

6GeV14 mm 4mm 23 J/g 1.3 2.6 J20 mm 4mm 27 J/g 1.5 4.9 J

3 GeV 14 mm 6mm 7 J/g 0.4 1.8 J

6GeV14 mm 6mm 10 J/g 0.8 2.6 J20 mm 6mm 12 J/g 0.9 4.9 J

• Ne- =2.0e+10• RAMD=8mm

• Larger spot size gives larger # of e+.• 6GeV-thickness14mm might be optimum.

Drive beam and Target configuration （ 3 ）

E=6GeV, T=20mm E=6GeV, T=14mm E=3GeV, T=14mm

RAMD(mm) RAMD(mm) RAMD(mm)

# of positron giving PEDD 23 J/g.

Drive beam and Target configuration （ 4 ）

Energy Thickness Beam size # of cap. e+ Total deposit3 GeV 14 mm 4mm 2.1×1010 2.7 J

6GeV14 mm 4mm 2.6×1010 2.6 J20 mm 4mm 2.6×1010 4.2 J

3 GeV 14 mm 6mm 2.9×1010 6.1 J

6GeV14 mm 6mm 3.4×1010 5.9 J20 mm 6mm 3.3×1010 9.5 J

• PEDD=23 J/g, Ne- is scaled. • RAMD=8mm

1-6 Cell = (2FODO +RF)7~18Cell = (2FODO+2RF) 19~40Cell = (2FODO+ 4RF)

19Cell

20Cell (starting point of S-band)

Exit of Booster Linac

L-band(1~19) S-band(20~40)

Replacing L-> S-band （１）

• Capture Section L-band RF Aperture: 20 mm

• Booster Linac L-band RF Aperture: 17 mm S-band RF Aperture: 10 mm

• ECS Aperture: 17mm

L-band RF= 6+12*2+(Nc-18)*4 S-band RF= (40-Nc)*4Nc=26 giving L-band: 62 and S-band: 56

• Red: considered only S−band Aperture (1.3GHz)

• Green: considered S-band Aperture and RF frequency

Replacing L->S-band （２）

1-6 Cell = (2FODO +RF)7~18Cell = (2FODO+2RF) 19~40Cell = (2FODO+ 4RF)

Nc :Cell number where S-band starts

Magnetic field distributions of FC

Bz(T)

Z(m)

A=-1/6 ~ 1

• Many electrons are also generated by the target.• These electron are captured in RF phase opposite to

that for positron .• Total beam loading becomes roughly twice of that by

positrons.• The electrons can be eliminated by a chicane. • However, the chicane at low energy causes a

significant loss on the capture efficiency. • The position of the chicane is compromised between

the beam loading and the capture efficiency.

Beam loading by electron

• Positron Capture for ILC Electron-Driven Positron Source is simulated.

• Yield(e+/e-) is greatly depended on AMD aperture, target position, and beam size. When E=6GeV, T=20mm, σ>5mm, dZ=5mm, RAMD >7mm, and BAMD=5T, enough e+ is obtained.

• Yield is reduced greatly when FC field is distorted. Time variation should be carefully investigated.

• The chicane position should be optimized.

SUMMARY

backup

RF phase dependence （ After Booster Linac ）

• Aperture of Capture Section (X2+Y2)1/2 < 0.02 m• Aperture of Booster Linac (Transmitted): (X2+Y2)1/2 < 0.017 m• Longitudinal Cut: (E-E0)/E0 < 0.75% (z-z0) < 37.5 mm• Transverse Cut: (Wx+Wy)*γ < 0.07 m

• Target is placed in maximum field of AMD (7T).

• Ignore AMD aperture

20 triplets, rep. = 300 Hz • triplet = 3 mini-trains with gaps • 44 bunches/mini-train, Tb_to_b = 6.15 n sec

DRTb_to_b = 6.15 n sec

2640 bunches/train, rep. = 5 Hz • Tb_to_b = 369 n sec

e+ creation go to main linac

Time remaining for damping = 137 m secWe create 2640 bunches in 63 m sec

Booster Linac5 GeV NC300 Hz

Drive LinacSeveral GeV NC300 Hz

TargetAmorphous Tungsten

Pendulum or Slow Rotation 2640 bunches60 mini-trains

Stretching

Conventional e+ Source for ILCNormal Conducting Drive and Booster Linacs in 300 Hz operation

Beam after DR

Extraction: fast kicker ( 3 ns kicker: Naito kicker) the same as the baseline

35J/g

500k

100k

Parameter Plots for 300 Hz schemePEDD J/g

colored band accepted e+/e-

there seems to be solutions

dT max by a triplet

１ ２ ３ ４ ５

e- directly on to Tungsten

s=4.0mmNe-(drive) = 2x1010 /bunch

• 3-5m/sec required (1/20 of undulator scheme)• 2 possible schemes being developed at KEK

Moving Target

2013/8/30 ILC monthly, Yokoya32

bellows seal

vacuum

airferromagneticfluid seal

air vacuum

5Hz pendulum with bellows seal rotating target with ferromagnetic seal

main issue: life of bellowsmain issue: vacuum

First step prototype fabricated

今年度：既存のＸ線発生装置の基本構造を利用して真空度（リークレート、到達真空度）など基礎実験を行い、データを取る。オイルの対放射線特性データーも測定H ２６−２７： ILC の実機とほぼ同じターゲットの制作し真空試験。

KEK 工作センター、広大リガク、原研高崎

KEK 、広大、 DESY, CERN, IHEP

Dependence on Drive beam size

s of the Drive e- Beam (mm)

35J/g

e+/e- =1.5

, Ne-/bunch = 2x1010