Capture Simulation for ILC Electron -Driven Positron Source
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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
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