KEKB Review 2016

Positron Source Status(2016 June 14)
KEKB injector linac
Takuya Kamitani

Positron source members

2n KEKu Y. Enomoto, Yokoyama, Zang, Fukuda, Kamitaniu Tanaka, Ikeda, Kakihara, Arakida, Ohsawa, A. Enomotou Nakajima, Akemoto, S. Matsumoto, Higou Miura, Miyahara, Sugimoto, Seimiya, Iida, Ohnishiu Okada, Takatomi, Someya, Kazaman Mitsubishi Electric System Service Co.
u Ushimoto, Suzuki, Kimuran Toyama Co.
u Iino, Morota, Sakai, Satoh
KEKB Review (2016.06.14)

Positron Source Status (Takuya Kamitani)

3SuperKEKB Injector
SuperKEKB injector

low emittancephoto-cathodeRF gun+ thermionic gun
for primary e-

3.5 GeV
10nC x 2 (prim. e-)
5nC x 2 (inj. e-)

BunchCompressor

S-bandlinac

1.1 GeV
Damping Ringcirc. 136 m
Energy-spread
Compression System
3TRF gun

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

PFAR

2.5 GeV e- 3.0 GeV e0.1nC x 1 (-> 6.5 GeV)

LER

4.0 GeV e+
4nC x 2ECSe+ target &LAS capture section

HER 7.0 GeV e5nC x 2

Upgrade items in positron source
Low emittance e+n positron damping ring introduced
e+ intensity (x4)n new positron focusing lens: flux concentrator (3.5 T) + bridge coils (1.0 T)
n large-aperture (2a=30mm) accelerating structure (LAS) in capture sectionn positron focusing beam line layout reorganized with 100 new quad. magnets
KEKB Review (2016.06.14)

Positron Source Status (Takuya Kamitani)

SuperKEKB positron source4

primary
e- beam
3.3 GeVpositron
production
TargetBridgeCoils

FluxConcentrator
e+ beam
KEKB Review (2016.06.14)

Positron Source Status (Takuya Kamitani)

5target offset & beam 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

2.0 mmFC offset

holediameter
2.0 mm
7.0 mm
FC aperture

pulse QM

l injection e- beam : on axis to preserve low emittancel primary e- beam : 2.5 mm off axis to minimize e+ yield degradation(target offset 3.5 mm, FC offset 2.0mm)KEKB Review (2016.06.14)

Positron Source Status (Takuya Kamitani)

Positron Capture Section
SLEDSLEDKLY
1-56KLY
1-6target+FC

LAS : Large Aperture
S-band structure

LAS 10 MV/macceleration

LAS 14 MV/m
deceleration & phase slip
& acceleration

Solenoids

operated at 10 MV/mwith SLED detuned
Large Aperture
S-band structure(LAS)n LAS with SLEDs for sufficient field gradientn breakdown issue of LAS in solenoid fieldn needs careful RF conditioning

KEKB Review (2016.06.14)

Positron Source Status (Takuya Kamitani)e+ capture section in linac tunnel
Flux concentrator,target, bridge coil(inside)KEKB Review (2016.06.14)

7DC solenoids& LAS accel. structures

Positron Source Status (Takuya Kamitani)e+ status at previous Review (2015/02/24)

8n e+ source components had been installed andoperated at limited performanceu FC : IFC = 6 kA (spec. 12 kA) with temporary pulse modulator
u BC : IBC = 600 A (=full spec)u DC Solenoids : IDC = 370 A (spec. 650 A)
u Acc. field : EACC = 10, 12 MV/m (spec. 14, 10 MV/m)
u DR not yet availablen (Linac stand-alone) e+ initial commissioning (first e+ for SuperKEKB)u Q(e+) = 0.12 nC@SY2 with Q(e-) = 0.60 nC, E(e-) = 3.1 GeV
spec. (5.0 nC after DR -> 4.0 nC)(10.0 nC)
(3.3 GeV)u Y(e+) = (0.12 nC / 0.60 nC) = 20% @SY2 (= at entrance to DR)
n FC coaxial feeder cable accident

higher voltage tolerance-> renewal planned for thicker cable (insulator 2.3 -> 7.4 mm)
and parallel plate feeder line (two plates -> triplate)
lower induced voltage
KEKB Review (2016.06.14)

Positron Source Status (Takuya Kamitani)9

FC test stand (2015 July)n test operation performed withu spare FC-base (#4)
u 12-kA pulse modulator
u new coaxial cables
u new triplate feeder line
u snubber circuit
u but w/o bridge coils
n full-spec (12 kA) operation forcontinuous 200 hours achieved withno serious breakdowns and problems

triplate
feeder line

snubbercircuit
FC-base (#4)

coaxialcables

cable connection
inside modulator
KEKB Review (2016.06.14)

Positron Source Status (Takuya Kamitani)

Installation in linac tunnel (2015 August)n Installed for beam operation
u 12-kA pulse modulator
u new coaxial cables
u new triplate feeder line
u snubber circuit

1012 kApulsemodulatorn Same as before
u FC assembly #1 (FC-base #3)
u Bridge Coilsu DC solenoids & accel. structures

radiation shield
triplate
feed line

FC &target

KEKB Review (2016.06.14)

Positron Source Status (Takuya Kamitani)

Double-deck pre-injectors

11

Upper deck (former KEKB pre-injector, reconstructed !)thermionic gun + RF bunching section
Gun 200 kV (=> 5 MV/m)
Sub Harmonic Buncher 1 (114 MHz)Sub Harmonic Buncher 2 (571 MHz)
Prebuncher (2856 MHz)
Buncher (2856 MHz)

1300 ps
500 ps
330 ps
70 ps
10 ps

bunch
lengthshieldwallLower deck
photo-cathode RF gun+ magnetic bunching

e- beam fore+ generation

bunchlength

e- beam for
HER injection

KEKB Review (2016.06.14)

Positron Source Status (Takuya Kamitani)

RF gunChicane

25 ps
10 ps

FC processing with BC field
2015.09.24
FC stable at IFC = 11.5 kA
w/o BC field

12

2015.09.28
2015.09.29
Huge gas burst occurred
Gas bursts occurredat IFC = 9.8 kA @IBC = 750A
even w/o BC field
Irreversible damage in FC
Operable current
by breakdown !!
lowered -> 6 kACurrentsof FC and of BC

Vacuum Pressures [Pa]at FC and at LASKEKB Review (2016.06.14)

Positron Source Status (Takuya Kamitani)FC copper block work hardening

13n Y. Enomoto and T. Higo visited SLAC and discussed with the positron

experts (A. Kulikov and E. Bong) on the FC gas bursting issue.
n They suggested that the work hardening of the OFC block of FC isessential against the damage by breakdown. (We neglected this process!)n "Work hardening (strain hardening)" is a method of strengthening of ametal by repeated plastic deformation.
n When a breakdown occurs in FC,

the spiral structure is deformed but
it springs back to the original shape
if it is work hardened.
n Unless work hardened, deformation
remains permanently and makes
very narrow gap in the slit.

KEKB Review (2016.06.14)

Positron Source Status (Takuya Kamitani)

Hardening test

14

Hardening Procedure
Press FC-head till the gaps are contacted.
Insert spacers into the slit.
Remove the spacers.
Measure the gap size.
Repeat them from (1) (~ 100 times)

1.
2.
3.
4.
5.

natural gap size (mm)0.6

# of trials

0.5

1回目
0.4

2回目
3回目

0.3

4回目
0.2

5回目
6回目

0.1
0
0

2

4

6

8

10

12

slit position (downstream <- upstream inside FC)

The natural gap size transfers to the spacer thickness(0.3 mm) by repeated hardening.
KEKB Review (2016.06.14)

Positron Source Status (Takuya Kamitani)FC assembly #2 & test stand15

n Operation test with BC field isessential.
n FC assembly #1 is radio-activatedin the beam line.
n Construct assembly #2 foroperation with BC field at test stand.
n Test-1: operation with FC-head #4(not work-hardened model) to see
what happens in the same situation
as the damaged FC.
[2016 June, soon]n Test-2: operation with FC-head #5(well work-hardened model) tocheck the operability at full current(12 kA) under the BC field.
[2016 August ~]KEKB Review (2016.06.14)

Positron Source Status (Takuya Kamitani)e+ beam performance (2015 Nov.)

16n Beam tuning to optimize e+ yieldperformed in 2015 Oct ~ Dec.
n IFC = 6 kA (design 12 kA)
enhancement by FC ~ 1.8n Q(e-) = 6.3 nC @ target
Q(e+) = 1.9 nC at SY2Y(e+) = 1.9/6.3 => 30 % (design 50 %)Primary Electron
intensity at target
Q(e-) = 6.3 nC
beam
intensity [nC]targetY(e+) upon capture RF phase

Sector-2 end

Y(e+) upon FC pulse timing

operationphase

FC ontiming
Deceleration
CaptureQ(e+) = 1.9 nC
at entranceof DR LTR line

Acceleration
CaptureFC offtiming

Yield enhancement by FC (6 kA) ~ 1.8
KEKB Review (2016.06.14)

Positron Source Status (Takuya Kamitani)Is achieved e+ charge consistent with simulations ?
(committee member’s question)

17n We do not have a simulation result which reflect all theoperation condition.
(GEANT simulation [e+ generation at target]+GPT simulation [e+ capture simulation]+SAD tracking simulation [e+ transport in linac & BT line)
u precise beam spot size on the target is unknown-> planning to install thin screen monitor and triggered camerain this summer shutdown
u DC solenoid field distribution modified to optimize e+ intensity
u FC 6 kA situationu Lower LAS acceleration field situationn Possible comparison

simulation expectation now is Y(e+) ~ 45 % at capture
section exit and the observed Y(e+) ~ 30 % at after the 1-6chicane.
n It is my homework for next KEKB Review.
KEKB Review (2016.06.14)

Positron Source Status (Takuya Kamitani)

SuperKEKB e+ injection beam

18

orbit-Y[mm]orbit-X[mm]

Typical e+ injection beam at linac and BT-line

beamintensity [nC]

Primary Electron
intensity at targetQ(e-) = 7.0 nC

GunJ-arc

Q(e+) = 1.3 nC at SY2[2.0 nC if no collim.]targetQ(e+) = 0.75 nC
at linac-end

Linac end

Beam collimators inserted to localize
beam loss in low energy region.

Q(e+) = 0.3 nC
at BT-line end

BT endDue to limited beam acceptance, inevitable beam loss
occurs in linac & BT-line in direct injection w/o DR.

KEKB Review (2016.06.14)

Positron Source Status (Takuya Kamitani)

SuperKEKB e+ beam performance

19e+ beam intensity history (2016 Jan ~ June)
IFC = 5.2 kA

IFC = 2.2 kA
with temporarypulse modulator
FC OFFKEKB Review (2016.06.14)

Positron Source Status (Takuya Kamitani)Diamond beam loss monitor

20

n Radiation-hard diamond beam loss

monitor was developed by S. Kazama
in collaboration with V. Kubytskyi andP. Bambade (LAL Orsay)
n single crystal CVD diamond
2.0 mm x 2.0 mm x 0.5 mm
with electrode (Ti, Pt, Au)
operated at 400 V.
n Detect beam hit/no-hit(1) on beam spoiler and (2) on target
signal:charge {charge>3.4}
collected charge [pC]

Voltage [V]20nsec0−0.05

typicalsignal

−0.1
−0.15

50454035−0.2−0.25

linearity to
beam charge

30−64.96 4.98

52mm

5.02 5.04 5.06 5.08

5.1 5.12
time [sec]

×1025

3.5

4

4.5

55.5

KEKB Review (2016.06.14)

66.5
beam charge [nC]

Positron Source Status (Takuya Kamitani)Summary211) Though test operation of spare FC (#4) with new modulator, newcables, new triplate feeder but w/o BC was successful up to 12 kA,a serious damage occurred in FC (#3) with BC field (2015 Sep.) andoperable current has been 5 ~ 6 kA.
2) Importance of work-hardening process of FC-head was recognized.
Test stand with FC assembly #2 has been constructed to perform
tests of not-hardened and well-hardened models with BC field.
(2015 June ~)3) Positron yield Y(e+) = 30% (Q(e+)=1.9nC/Q(e-)=6.3nC) achieved with
6 kA FC current at entrance of DR-LTR line. Stable e+ injection toLER has been achieved (Q(e+)@BT-end ~ 0.3nC x 2-bunch) since2016 Feb. Beam loss in linac and BT line is due to operation w/o DR.
4) After finishing operation at test stand, FC assembly #2 will be
installed in the beam line in 2016 Dec. ~ 2017 Jan.
DR commissioning and LER injection in Phase-2 will be started in2017 Nov.
KEKB Review (2016.06.14)

Positron Source Status (Takuya Kamitani)