Injector upgrade
23 Oct. 2015
Toshi Higo (on behalf of Injector linac group)Contents• Beam requirement• Schedule and upgrade scenario• Positron status and near future plan
• Emittance related issues• Conclusion

23 Oct. 2015

B2GM2

Based on Miura-Furukawa,
B2GM in June 2015

SuperKEKB scheduleCommissioning is divided into three stages.
(phase1, phase2, phase3)
Calendar2015

2016

Power restriction
in summer

LinacCurrent plan on going

2017

Power restriction
in summer

2018

Power restriction
in summer

Power restriction
in summer

Phase 1Phase 2

w/o QCS QCS, Belle II install
w/o Belle II

VXD install
w/ QCS
w/ Belle II (no VXD)

w/ full Belle II

L= 1´1034cm-2s-1(KEKB design)

L= 8´1035cm-2s-1

Vacuum Scrubbing
Basic machine tuning
Current=1A

Phase 3
Add more RF

Full Current

Injection Beam
1 nC/bunch
w/o DR

DR commissioning

no Top-up inj.

23 Oct. 2015

w/ DR

low emittance
4~5 nC/bunchw/ DR

Top-up injection

Top-up injection

low emittance
2 nC/bunch

B2GM3

Required beam parameters
StageKEKB

Phase-I

SuperKEKB

Iteme+e-e+e-e+e-Energy

3.5 GeV8.0 GeV

4.0 GeV

7.0 GeV

4.0 GeV

7.0 GeV

Primary e-10nC

Primary e- 4nC

Bunch charge→ 1 nC

1 nC→ 0.2 nC

Norm.Emittance (gbe)(µrad)

2100

100

2400

Energy spread

0.125%

0.125%

Num. of Bunch / Pulse

221 nCPrimary e-10nC→ 4 nC

5 nC

150

100/20(Hor./Ver.)

50/20(Hor./Ver.)

0.5%

0.5%

0.1%

0.1%

2222

Repetition rate

50 Hz

50 Hz

50 Hz

Simultaneous top-up
injection

3 rings(KEKB e-/e+, PF)

3 rings(KEKB e-/e+, PF)

4 rings(SuperKEKB e-/e+, PF, PF-AR)

23 Oct. 2015

B2GM4

What and when to be improved
from KEKB to SuperKEKB• Present in late 2015
– Prepare low-emittance electron & positron to be cooled at DR• Phase-I in early 2016
– Supply for initial ring tuning and beam-duct baking– Investigate the strategy for emittance-preserved high charge• Phase-II in 2017
– Gradually improve emittance preservation– Make effort for higher charge• Phase-III in late 2017
– Emittance to be fully minimized with maximum charge
23 Oct. 2015

B2GM

5

Thermionicgun @A1

Upgrades of Injector LINACPhoto-cathode RF gun system< e- beam>
Low emittance (ge £ 20 mm×mrad)
high bunch charge ( ³ 5nC)

Positronproduction@14

Positron Damping Ring (DR)Low emittance e+ beam

Alignment error tolerance

1.5 GeVs(local)=0.1mm
s(global)=0.3mm

Low emittance preservation

BCS

ECS

PF
ECS PF-AR

chicanee+targetPulsed Quads & Pulsed Steering Magnets

HER LER

Event Timing System and Pulsed Modules• Synchronization for 5-rings including DR• 200 parameters are switched at 50Hz each mode
• Optics at the downstream of DR is switched byusing pulsed magnets

Positron Capture Section- Flux concentrator (FC)- Large aperture S-band accel.
Structures (LAS)
4 times higher e+ yield
23 Oct. 2015

1.1 GeV e+
Damping Ringcirc. 136 m

RF gunThermionic gun(10nC primary e-)

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

Collimation
@18

B2GM

6Electrons• Electrons– for HER
– for making positrons• Development on RF gun for electrons has been muchadvanced– Targeting ultimately low-emittance, high-charge beam
– RF gun cavity seems well developed but operation in full spec isrequired for actual use.
– Considerable work is needed to make stable laser system.

• We decided to bring thermionic gun for Phase-I to life
– For positron generation and possibly for electrons in phase-I– Thermionic gun and RF gun were set in parallel at A1
23 Oct. 2015

B2GM

7

Miura, Furukawa in
B2GM in June 2015

Beam Commissioning of RF Gun
Operation Condition• Laser: 2bunch, 25 Hz• RF gun acc. voltage: limited to 6.5 MV bybreakdown (13.5 MV@design)

Target : 5nC
gex=50 mm×mrad, gey=20 mm×mrad @ LINAC end
gex , gey = 10 mm×mrad @ Gun

Bunch charge just after RF GUN (A1_C5)

Emittance measurement by Quad-scan(m)1 weekRF GUN

4nC/bunch

Sort for 3h

Bunch charge: 3nC@Screen
Beam size was measured shot by shot.
=> Position jitter is not included
gey=26.2 mm×mrad±10%gex=49.2 mm×mrad±10%






(Y,M,D)

Screen monitor (t=30µm)  

Archived 1/10s

Bunch charge stability depends on the laserstability.
Ø Measured emittances were higher than target values.
Ø Higher horizontal emittance is due to laser incidentangle.

Yb:YAG Thin-disk cooling by soldering Cu plate
was Improved.
R. Zhang, TUPWA071
Laser power increased and stability was also improving.
23 Oct. 2015

Need high acc. voltage of RF gun for small emittanceB2GM8

A1 electron gun areain double-deck configuration
Two lines merge

23 Oct. 2015

GR-A1GU-AT

B2GM

9

Out of 6nC, 2 nC was transported
through target center hole to linac end

Recent electronbunch charge
6 nC was delivered to targetIn late January, 2016
Radiation shield at target area will be reinforced
Target drive current of 200nA at present will be increased to 800nA with adding iron shield around target area
It allows drive electron with 8nC/bunch in 2 bunched at 50Hz.
23 Oct. 2015

B2GM10Positron system• For phase-I (without DR)––––––

Primary drive electron intensity will be increased
Radiation safety under 800 nA for phase-I will be allowed in late Jan. 2015
Production rate will be increased with using
flux concentrator, high solenoid field and large aperture accelerator tube
Emittance will be reduced by collimation
Big shield is being prepared for radiation safety

23 Oct. 2015

B2GM11Schematic of positron Capture Section
SLEDSLEDKLY
1-5KLY
1-6

target+FC

LAS : Large Aperture
S-band structure

LAS 14 MV/m
deceleration & phase slip& acceleration
Large Aperture
S-band structure(LAS)

Solenoids

LAS 10 MV/m
accelerationn LAS with SLEDs for sufficient field gradientn breakdown issue of LAS in solenoid fieldn needs careful RF conditioning

23 Oct. 2015

B2GM12

Kamitani, POSIPOL 2015

Positron intensity achieved in 1 July, 2015

e- 4nCe+ 0.4nC

Reached h=0.1 before summer shutdown in this year
23 Oct. 2015

B2GM

13

Boosting positron yieldand intensity

Done withelectricity powerup

Under processing
with magnetic
field

Under processing
with magnetic
field

For Phase-I
23 Oct. 2015

B2GM

14

Target / FC / LAS / Solenoid

Radiation
shieldFC & TGTBeam

LAS & Solenoid• FC drive current capacity was doubled
in summer 2015
• Radiation shield will further increased
before phase-I in Jan. 2016

FC & TGT
23 Oct. 2015

B2GM15Struggling against gas burst
ESGas pressure

RF powerPressure

Drive voltage

24 hours
Frequent gas burst prevents FC withsolenoid field from higher current operation
than half-design.
23 Oct. 2015

Frequent gas burst and vacuum breakdown
prevents LAS in solenoid field from higher
field operation than 10 MV/m.

For both, processing
is kept under way.
B2GM

16

Breakdown(?) to be understood and suppress
RF power for LAS
RF Input

FC current pulse

NormalRF reflected
RF transmittedAbnormalA few microsec

Normal pulse

Trailing half was reduced,
showing reduction of inductance.
23 Oct. 2015

Abnormal pulse

RF power was reflected back to klystron andinterrupting transmission throughaccelerator tube.
B2GM

17

Further development on FC
FC chamber

TGT+FC• Replacement of TGT+FC is under consideration for phase-I.
• Complete exchange mechanism of the TGT + FC + LAS may be in hand
before Phase-II.
23 Oct. 2015

B2GM

18

Positron at present and near future• Positron yield of 10% of drive electron was established.
• Higher-charge drive electron makes more positrons.
• High voltage cabling and other peripheries are approaching to theirfinal ones.
• Frequent gas burst is observed especially with solenoid magnetic
field at more than 6kA current for FC.
• Processing is a bit slow and we need to understand what ishappening to overcome this phenomenon and operate at design
current.
• LAS (Large-aperture S-band) accelerator tubes are also subject togas burst and sometimes with RF breakdown. More conditioning timeis needed to reach the full accelerator field with SLED.
• Exchange mechanism of target and FC was designed.
• Exchange mechanism of fully replacing FC system is underway forfinal phase. This makes possible to replace any of theTGT/FC/LAS/Solenoid hard wares.
23 Oct. 2015

B2GM

19

Collimation for phase-I• A set of three collimators wereprepared for cutting beam tailfor DR injection at the end ofsector 1.
• These can be used for cutting
positron beam tail for Phase-I
without DR.
• Additional shield is being
prepared.

23 Oct. 2015

B2GM

20

Emittance issue for phase-II and beyond
1. Hard wares aligned on a girder by measuring positon bylaser tracker
2. Girder are aligned by using laser PD referred to laser
light passage
3. Hard ware alignment are to be smoothly improved bymeasuring with laser tracker
4. Beam evaluation and evaluation to be integrated in thealignment process
5. Suppression of emittance growth due to the floor
movement
23 Oct. 2015

B2GM

21

J-ARCAlignment Requirement
120m
B
ACRings
12500m345s < 0.1 mm: bge 20 mm·mrad is almost
satisfied.
s > 0.1 mm: emittance preservation isrequired by some methods.

Requirement
Local s < 0.1mm
Global s < 0.3mm
23 Oct. 2015

H. SugimotoB2GM22

Laser PD system as areference to align girders
500m laser line

4-segmented silicon
PD (dia.=10mm)

Manual ON/OFF
23 Oct. 2015

Automatic ON/OFFLinear type
2+8 installed now
B2GM

Foresee more installationconsidering pendulum type
and/or present type ascandidate23

Laser PD measurement
Mostly aligned by a year ago, summer in 2014
Horizontal

VerticalPD in automatic measurement system are installed
two in autumn last year and eight in Summer this year
and more to be installed in this fiscal year
23 Oct. 2015

B2GM

PD_28
_G6DA
P D_2
8_RE
FUAVer.

24

Laser PD more near expansion joint
Horizontal

VerticalVer. Same data
as left figure

Movement near joint is big.
Mover or some passive support structure to be developed.
23 Oct. 2015

B2GM

25

Hard ware initial alignment on a girders in sector 3 - 5
Horizontal
VerticalFirst round done to install/assign/measure.
From now on, we try to find a series ofalignment chances to improve smoothness.
the stability of this alignment should be confirmed.

Horizontal
s=34µm23 Oct. 2015

2015/2/24

Vertical
s=47µm

B2GM

2626

Floor configuration

BAGunDRBCSExpansion jointC1

ECS2345PFe+ target

ECS PF-AR

HER LER

Laser PD continuous measurement devices
Half a year data in next page
23 Oct. 2015

B2GM27

Movement in half a yearß Upstream PD_28_G6DA

4.25 m

PD_28_REFUA Downstream àCorrelation between these two positions.
1. Movement of 1mm order wasobserved in half a year.
2. Daily movement is of the orderof +/- 0.15mm.
3. Positive correlation wasobserved.
23 Oct. 2015

B2GM28

Status and near future strategy• Monthly measurement of relevant PD’s are kept in best effort
base for more than a year.
• Continuous PD measurement at 10 points are in progress andacquire data over a year.
• More automatic PD’s will be made and installed.
• Movement at joint is underway to understand movement.
• Beam study will be performed to acquire the feasibility of floor
movement information by beam.
• Feasibility of mover will be studied in mechanism, time, cost.
• These efforts should be integrated to make a system before
Phase-III, in two years from now.
23 Oct. 2015

B2GM29

Conclusion• Phase-I beam, both electrons and positrons, can bedelivered in time in 2016.
– Thermionic gun, positron production, shield reinforcement, ….

• Preparation for DR will be made by next summer and supply“low” emittance beam will be delivered in Phase-II from2017.
– RF-gun, LTR/RTL, pulse magnet, …..

• Floor movement should be understood and we develop asuppression / compensation scheme to meet Phase-III
operation in 2018.
– Floor movement and emittance control, ultimate laser RF-gun, …
23 Oct. 2015

B2GM30Mt. Tsukuba

Thank you
SuperKEKB
dual rings
PF-ARPF

23 Oct. 2015

Injector
Linac

B2GM31