KEKB/SuperKEKBpositron source
a review and the status
KEK M. Fukuda
1AWLC2017
Contents
• Positron source for the KEKB and the SuperKEKB• Positron target
• Matching device (QWT, FC)
• Commissioning of FC
• Calculation of the magnetic field of the QWT for ILC
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Positron source for the KEKB and the SuperKEKB
3
IPAC10, THPD004, N. Iida
OHO07, KamitaniAWLC2017
Primary e- beam
DC solenoid
Phase spaceMatching device
Target
Accelerator
Positrons
Target material
4
RequirementsHigh Z (Cross section of Bremsstrahlung ∝ Z2/A)High melting pointTantalum(73Ta),
Tungsten(74W), Tungsten- rhenium alloy (W-Re)
KEKB, SuperKEKBTarget material: W 14mm (4c0)Primary e- beam energy: 4.0 GeV(KEKB), 3.3GeV(SuperKEKB)
Joining of tungsten crystal to a copper body by a hot isostatic pressing (HIP)
AWLC2017
T. Suwada et al., Phys.Rev.STAB 10 073501
Target destruction limit
5
Positron production for CLIC(CLIC note 465)
Threshold: 0.93x1010 [GeV/mm3] 76J/g(Peak energy-deposition density per volume)
After the target destruction was occurred in the SLC,This threshold : 76 35J/g (slac-r-571)
Threshold:2.0x1012 [GeV/mm2](Incident beam energy density per area)
B1: 24.4GeV, σx: 0.91mm, σy: 0.35mm, 8x1010 e-/pulse, Area 1.0mm2
1.95x1012[GeV/mm2]
CLIC note 465
Material: W75Re25 alloyTarget thickness5.4X0
Positron target material test @ SLACIncident beam energy:20.5-24.4GeV
SLAC-TN-15-006(CN-128)
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Matching Device
6
QWT
QWT(Quarter wave transformer) AMD(Adiabatic matching device)
AWLC2017
Primary e- beam
DC solenoidPhase spaceMatching device
Target
Accelerator
Positrons
The generated positrons have the small beam size and the large divergence.The matching device converts them to parallel beam.
QWT(Quarter wave transformer)
7
(Pz = 10MeV/c in the KEKB)
OHO07, Kamitani
Magnetic field: BiQWT length: Li Momentum: pz
The QWT transforms 90deg in the phase space.It captures the positrons satisfying this condition.
Energy acceptance
AWLC2017a: Diameter of an accelerator iris
Transverse acceptance
Energy acceptance
CERN-94-1 Positron source, R. Chehab
AMD(Adiabatic matching device)
8
OHO07, Kamitania: Diameter of an accelerator iris
(B0 = 7.0 [Tesla], μ = 60[1/m])
AMD field is produced by a flux-concentrator.The eddy current is induced in the tapered conductor by a changing magnetic field which is made by the primary coil.The magnetic field is concentrated due to the tapered shape of the FC head.
Transverse acceptanceadiabatic condition
AWLC2017
Adiabatic invariance is constantduring the motion.
Kamitani20061101.pdf
Primary coil
Conductor
e+e-
CERN94-1, R. Chehab
Debunching
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Because the positrons have the large energy spread, the debunching is caused.
Debunching caused by speed differenceβ of positrons is small before acceleration.
Debunching caused by spiral orbitThe positron has the spiral orbit in the solenoid field.The diameter depends on the energy.
OHO07, T. KamitaniAWLC2017
Matching device
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OHO07, Kamitani
2017/05/22 Posipol2016 “SuperKEKB positron source status” KamitaniOHO07, Kamitani
4GeV
Pulse coil: 2.3T @ 10kAFlux ConcentratorQuarter wave transformer
KEKB SuperKEKB
AWLC2017
The Matching device is the QWT in KEKB.It has been changed to the flux concentrator to increase the positron intensity in the SuperKEKB.
QWT
11
Pulse coil
Bridge coil
Current shape is a half sinusoidal waveOHO07, T. Kamitani
Target
accelerator
Bridge coils compensate for the field gapsbetween the pulsed coil and the accelerator.
Field strength: 2.3 TCoil length: 42.5mmInside diameter: 11mmNumber of turns: 8 turnPeak current: 10kAPulse width: 100us
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Flux concentrator
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Field strength: 3.5TLength: 100mmOutside diameter: 108mmAperture diameter: 7mm(min), 52mm(max)Number of turns: 12turnSpiral gap: 0.2mmPeak current: 12kAPulse width: 6us
Target: W 14mm(4X0)Beam size on the target: σx,y 0.7mm(The size is expanded by the spoiler)
AWLC2017PASJ2016 MOP063 Y. Enomoto et.al
Flux concentrator
13POSIPOL2016, T. Kamitani
Work-hardening Procedure1. Press FC-head till the gaps are contacted.2. Insert spacers into the slit.3. Remove the spacers.4. Measure the gap size.5. Repeat them from (1)
PASJ2016, MOP063,T. Kamitani et. al.AWLC2017
FC power supply
14
The 12kA modulator is developed based on the modulator for the S-band klystron.To reduce the cost, the modulator is consists of the common device(Switching power supply, thyratron and so on).
Charging voltage: 17kVPulse width: 5usPeak current: 12kARepetition rate: 50Hz
PASJ2013, SUP057, M. Akemoto et.alAWLC2017
Positron capture section
15
IPAC14, THPRI047, T. Matsumoto et.al.
Large Aperture S-band structure: LASIris diameter: 30mm(SuperKEKB)
POSIPOL2016, T. Kamitani
DC solenoid (KEKB, SuperKEKB)Field strength: 0.4 TCoil length(1 module): 450mmNumber of turns(1 module): 301 turnCurrent: 650A
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OHO07, T. Kamitani
Commissioning
16POSIPOL2016, T. Kamitani
Positron yield optimization In 2015 Oct – Dec FC Peak current: 6kAIncident beam charge: 6.3nC (e-)Positron 1.9nC , Yield: 30%
Design: 50%(at Sector2-end, FC 12kA)(Yield 10% (at Linac end, QWT 10kA))
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Summary of the positron source for the KEKB and the SuperKEKB
• Target• Material: W 14mm (4χ0)• Incident e-beam: 4GeV(KEKB), 3.3GeV(SuperKEKB),
σe- : 0.7mm
• Flux concentrator (SuperKEKB)• In 2015, the commissioning of the FC was carried out. Y(e+) = 30% at 6kA.• The peak current is limited by the breakdown in FC head.• Work-hardening is important to avoid the discharge.
• Capture section• DC Solenoid: 0.4T (KEKB, SuperKEKB)• Large Aperture S-band structure: LAS, Iris diameter: 30mm (SuperKEKB)
• Positron yield• KEKB: QWT(10kA): Y(e+) = 10% (Q(e+): 0.6nC, Q(e-): 6nC),• SuperKEKB: FC(6kA): Y(e+) = 30% (Q(e+): 1.9nC, Q(e-): 6.3nC), (in 2015)
FC(12kA): Y(e+) = 50% (Q(e+): 5nC, Q(e-): 10nC), (Design)
17AWLC2017
Acknowledgement
• I would like to thank Prof. T. Kamitani for giving useful information of the positron source in KEKB and SuperKEKB.
• Next :Calculation of the QWT magnetic field by POISSON
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Calculation of the QWT magnetic field
KEK M. Fukuda
AWLC2017 19
Motivation
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The aim is to reproduce the magnetic field of the QWT for ILC.It was calculated by Wanming Liu
Procedure ・Read the geometry from the below picture.・Calculate the magnetic field in the case of the geometry by POISSON.
Preliminary conceptual designing works regarding positron capture magnets.pdfW. Liu AWLC2017
93
75 162
180
193
224
206 293
311
346
381
818
853
630
609
518
427
391
357
619
348
382
514
Calibration: X: 50cm/(630-193)px = 0.1144 cm/pxY: 30cm/(619-357)px = 0.1145 cm/px
Origin: 193px, 619px
Pixel value picked up from the picture
21AWLC2017
-11.4
-13.5-3.5
-1.5
0
3.5
1.5 11.4
13.5
17.5
21.5
71.5
75.5
50
1.1
11.6
22.0
26.1
30
0
31.0
27.1
12.0
Conversion from the pixel value to the length (cm)
The pixel value is converted to the real length by using the calibration.The origin is the middle between the backing coil and the focusing coil.This geometry is inputted to the POISSON. 22AWLC2017
Comparison of the geometries
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Reproduced picture
Liu’s picture
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Calculation by the POISSON
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Mesh: 0.5mmReturn yokes of Solenoids: Iron (Default: Steel 1010)Ampere turn: Focusing, backing: 121121, -121121 AT
Matching: 210800 AT
These ampere turns were tuned so that these peaks were reproduced.
Backing FocusingMatching
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10345 Gauss
5093 Gauss
FocusingMatching
Magnetic field on the Z-axis
25
Z = 0 is the position of the target.
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Backing
Focusing
Matching
10448 Gauss
5114 Gauss
4386 Gauss
Comparison of the strength of the magnetic field on the z-axis
26
The field strength at the focusing and the matching coils is identical within 1%.The strength of the middle part between these coils is different about 8%.
Liu’s result Reproduced result
AWLC2017
4386 Gauss4747 Gauss
10345 Gauss
5093 Gauss
10448 Gauss
5114 GaussFocusing
Matching
Summary
• I was able to almost reproduce the QWT magnetic field calculated by Liu-san.
• The field strength and the Ampere tune:• Focusing coil: 1.05T (121121AT)
• Matching coil: 0.51T (210800AT)
• The field strength at the middle part between the focusing and the matching coil is slightly different about 8%.
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28AWLC2017
Flux concentrator
29
The positron yield is decreased due to the offset.Yield: 0.87(ideal) 0.53
After the optimization of the slit position and the e- beam position on the target, the Yield is improved.Yield: 0.53 0.79
IPAC14, MOPRI003, L. Zang
IPAC13, MOPFI017, L. Zang
The FC is placed on the beamline with the offset of 2mm.
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