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 Section Booster 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 Section Beam parameters & Target Drive beam energy6 GeV Beam size4.0 mm (RMS) Target thickness14 mm AMD Solenoid e-e- Target (rotate) e+e+ Accelerating Structure RF Gradient25 MV/m RF frequency1.3 GHz (L-band) Length10m Aperture (radius)20mm AMD parameters Max AMD field7 T Taper parameter60.1 /mm AMD length214 mm Solenoid Solenoid Field0.5 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 RF Peak Gradient40 MV/m RF frequency1.3 GHz (L-band) Length323.6 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 Gradient38 MV/m RF frequency1.3 GHz (L-band) Length90.5 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 Section 2.RF phase at Booster Linac, ECS 3.Aperture at Capture Section 4.Aperture at Booster Linac, ECS 5.Aperture and magnetic strength at AMD, and distance between AMD and target 6.Drive beam energy, target thickness, and beam size 7.RF gradient at Capture Section 8.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 (X 2 +Y 2 ) 1/2 < 20 mm Aperture at Booster Linac (X 2 +Y 2 ) 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 (≡R AMD ) ： 6mm(radius) AMD Max. field strength (≡B AMD ) : 7T Place of B AMD and end surface of Target (≡dZ) : 5mm (giving 3.5T) Z (m) Bz (T)

AMD and Target configurations Yield is greatly depended on R AMD and dZ. But not so much on peak B AMD. Yield is saturated at dZ 8mm. B AMD =7T, dZ=3mm, and R AMD =8mm are a feasible parameter set. dZ=5mm dZ=3mm R AMD (mm)

Aperture in Booster Linac Capture eff. is saturated at 17mm. 17mm is optimum. c c

Drive beam and Target configuration （ 1 ） E=6GeV, T=20mm E=6GeV, T=14mm E=3GeV, T=14mm R AMD (mm) Ne=2.0e+10 (fixed). Yield is better for smaller spot size.

Drive beam and Target configuration （ 2 ） EnergyThicknessBeam sizePEDDYieldTotal deposit 3 GeV14 mm4mm15 J/g J 6GeV 14 mm4mm23 J/g J 20 mm4mm27 J/g J 3 GeV14 mm6mm 7 J/g J 6GeV 14 mm6mm10 J/g J 20 mm6mm12 J/g J Ne- =2.0e+10 R AMD =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 R AMD (mm) # of positron giving PEDD 23 J/g.

Drive beam and Target configuration （ 4 ） EnergyThicknessBeam size# of cap. e+Total deposit 3 GeV14 mm4mm2.1× J 6GeV 14 mm4mm2.6× J 20 mm4mm2.6× J 3 GeV14 mm6mm2.9× J 6GeV 14 mm6mm3.4× J 20 mm6mm3.3× J PEDD=23 J/g, Ne- is scaled. R AMD =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)*4 Nc=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, R AMD >7mm, and B AMD =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

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RF phase dependence （ After Booster Linac ） Aperture of Capture Section (X 2 +Y 2 ) 1/2 < 0.02 m Aperture of Booster Linac (Transmitted): (X 2 +Y 2 ) 1/2 < 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, T b_to_b = 6.15 n sec DR T b_to_b = 6.15 n sec 2640 bunches/train, rep. = 5 Hz T b_to_b = 369 n sec e+ creation go to main linac Time remaining for damping = 137 m sec We create 2640 bunches in 63 m sec Booster Linac 5 GeV NC 300 Hz Drive Linac Several GeV NC 300 Hz Target Amorphous Tungsten Pendulum or Slow Rotation 2640 bunches 60 mini-trains Stretching Conventional e+ Source for ILC Normal 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 scheme PEDD J/g colored bandaccepted e+/e- there seems to be solutions dT max by a triplet １２３４５ e- directly on to Tungsten  =4.0mm Ne - (drive) = 2x10 10 /bunch

3-5m/sec required (1/20 of undulator scheme) 2 possible schemes being developed at KEK Moving Target 2013/8/30 ILC monthly, Yokoya 32 bellows seal vacuum air ferromagnetic fluid seal airvacuum 5Hz pendulum with bellows sealrotating target with ferromagnetic seal main issue: life of bellows main 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  of the Drive e- Beam (mm) 35J/g e+/e- =1.5, Ne - /bunch = 2x10 10