Belle2 GM (2014.06.18)

Injector Status[Positron Source Upgrade]

KEKB injector linac
Takuya Kamitani

2SuperKEKB Injector
SuperKEKB injector

1.1 GeV
Damping Ringcirc. 136 m

low emittanceRF gun3.5 GeV
10nC x 2 (prim. e-)
5nC x 2 (inj. e-)

Bunch
Compressor

S-bandlinac

Energy-spread
Compression System
3TRF gunPF

50 Hz (e+ or e-)pulse-by-pulse
mode switching

2.5 GeV e0.1nC x 1

LER

4.0 GeV e+
4nC x 2

HERe+ target &LAS capture section

ECS

7.0 GeV e5nC x 2AR
6.5 GeV e-Key issues in Positron Source Upgradel Damping ring for lower emittance (2000 -> 92[H]/7[V] µm)
l Capture section upgrade for higher intensity (1 -> 4 nC)
v flux concentrator (e+ focusing pulsed solenoid)v LAS [Large Aperture S-band accelerating structure]
Belle2GM (2014.06.18)

Injector Status [Positron Source Upgrade] (Takuya Kamitani)

3SuperKEKB positron station
flux concentrator

primary
e- beamtargetpositronproduction
TargetBridgeCoils

FluxConcentrator
e+ beam
Belle2GM (2014.06.18)

Injector Status [Positron Source Upgrade] (Takuya Kamitani)e+/e- beam switching & target holeside viewprimary e-bridge coils

DC QM

spoilertargetrear viewsolenoid

Accel.
structuretargetdiameter
4.0 mmtargetoffset
3.5 mm

e+
beam
hole

injection eFlux
Concentrator

pulse ST
pulse QM

42.0 mm
FC offset

holediameter
2.0 mm
7.0 mm
FC aperturel injection e- beam ON-axis for low emittance preservationl primary e- beam OFF-axis with positron yield degradation
Belle2GM (2014.06.18)

Injector Status [Positron Source Upgrade] (Takuya Kamitani)

Positron production targetn target material selection
u high Z material

beamhole5tungstentargetu high melting pointu high tensile strengthn => tungsten

14 mm long = 4.0 X04 mm diametern beam hole for injection ecooling waterpipe
primary
e- beam

Belle2GM (2014.06.18)

Injector Status [Positron Source Upgrade] (Takuya Kamitani)Beam spoiler for target protection
3m distancen beam spoiler to enlarge beam

spot on target to be sx ,sy> 0.7 mm
to avoid target destructionn spot size monitoring screen Al2O3(0.14 mm thick)+ scattering Al foil (0.25 mm thick)[total material thickness = 0.05 X0]
n beam hole for injection eFront

Belle2GM (2014.06.18)

6screen & scatterer

targete+primary einjection
e- beamholeholespot size
cameraRearInjector Status [Positron Source Upgrade] (Takuya Kamitani)flux concentration concept          l DC current in primary coil produce uniform solenoidal fieldl Pulsed current & Conductor with slit=> eddy current flows inner surface
to generate high magnetic flux density (flux concentration !)but with non-axial symmetric transverse field !
=> transverse kick to positrons ! beam loss !

7

e+ yield degradation by target offset

8

n e+ yield degrades ~50 %by offset e+ generationn it can be improved to 78 % byu utilizing transverse kick byproper orientation of FC slit
u e- incident position optimization
FC field map (Bx)
0.010

Bx

0.005

Bx [T]

0.000-0.005-0.010targetcenterposition

FC2 data Bx
CST BxBx-max =0.15 T @ 12 kA-0.015-0.020-20020406080

10 0Longitudinal Position [mm]Belle2GM (2014.06.18)

Injector Status [Positron Source Upgrade] (Takuya Kamitani)

Positron Capture Section
SLEDSLEDKLY
1-59KLY
1-6target+FC

LAS : Large Aperture
S-band structure

LAS 14 MV/m
deceleration & phase slip
& acceleration

LAS 10 MV/m
acceleration

Solenoids

DC solenoid

LAS
acceleratingstructure
Belle2GM (2014.06.18)

Injector Status [Positron Source Upgrade] (Takuya Kamitani)positron capture animation

10from target to capture section exit (120 MeV)
Deceleration capture

Energy (MeV)

Energy (MeV)

Acceleration capture

longitudinal position (mm)You are watching longitudinal particle motion(z-position vs energy) in a moving frame
riding on a microwave !

longitudinal position (mm)Positrons with deceleration capturefavored for less halo and satellites !
KEKB Review Comittee (2012.02.21)

e+/e- separator chicane

11

e- stopper blockl both secondary e+/e- are captured
l to avoid disturbance ofbeam position monitors
by mixture of e+/e- signals,
only secondary e- are absorbed
l pure e+ beam is transmitted

Belle2GM (2014.06.18)

Injector Status [Positron Source Upgrade] (Takuya Kamitani)

12

The first positron beam after the upgrade

positron signal !!

BPM: SP_15_T in front of target
negative charged particles (e- beam)
give (-)(+) bipolar signal

BPM: SP_16_5 after e+ capture section
positive charged particles (e+ beam)
give (+)(-) signal

observed positron intensity

orbit-X[mm]orbit-Y[mm]beam
intensity[nC]

Primary Electron
intensity at target
Q(e-) = 0.500 nC

GunJ-arctarget

Positron intensity
at positron line end
Q(e+) = 0.02 nC

Sector-2 end

1314Summary1) Positron source components have been installedin the beam line
(a target, a beam spoiler, a flux concentrator, bridge coils,
DC solenoids, LAS accelerating structures, e+/e- separator
chicane, plenty of quads)

2) Still in low spec. operation due to various constraints
uuuu

flux concentrator
bridge coils
DC solenoids
LAS field gradientdesign full spec.
12 kA
750 A
650 A
14, 10 MV/machieved
6 kA
600 A370 A
10, 7 MV/m

3) We have observed the first positron beam
after the upgrade !
2014.06.09(Qe+ = 0.02 nC @sector-2 end for Qe- = 0.5 nC @target)x200(Qe+ = 4 nC

x20

SuperKEKB@sector-2 end for Qe- = 10 nC @target)
full spec.

Belle2GM (2014.06.18)

Injector Status [Positron Source Upgrade] (Takuya Kamitani)