Positron source

Yoshinori Enomoto1OutlineOperation in phase 3
 Positron source setup
 Requirement and achievement
Present status and development
 Magnetic filed in solenoid section
 Discharge of FC Upgrade plan Collaboration
Summary
Answer to the previous review comments

2

Positron source setup 1
Positron target and capture section

3

Positron source setup 2
FC head + BC + target = FC assembly
BC (bridge coil)targetLAS (large aperture S-band)FC(flux concentrator) headsolenoid4

Positron source setup 3
beam

W targetΦ2 mm hole for electron
Temp sensor
Cooling water pipe

5x2.25

1/25

2018.5.29

ALCW2018

6

Injection requirement
Present working assumption (final)𝑑𝐼 3.6 [A]Life360 s== 10 [𝑚A/s]
Current
3.6 A
𝑑𝑡 360 [s]Injection bunch charge

4 nC

Injection rate

25* Hz x 2 bunch

Injection efficiency

50 %Circulation frequency

105

4 nC × 25 Hz × 2 bunch × 50 % × 105 Hz= 10 [𝑚A/s]

7

Injection requirement
Present working assumption (final)𝑑𝐼 3.6 [A]Life360 s== 10 [𝑚A/s]
Current
3.6 A
𝑑𝑡 360 [s]Injection bunch charge

4 nC

Injection rate

25* Hz x 2 bunch

Injection efficiency

50 %Circulation frequency

105

4 nC × 25 Hz × 2 bunch × 50 % × 105 Hz= 10 [𝑚A/s]

Typical Phase 3 operation
Life2500 sCurrent

0.5 A

Injection bunch charge

0.6 nCInjection rate

6.2 Hz x 1 bunch

Injection efficiency

50 %Circulation frequency

105𝑑𝐼
0.5 [A]== 0.2 [𝑚A/s]
𝑑𝑡 2500 [s]0.6 nC × 6.25 Hz × 1 bunch × 50 % × 105 Hz= 0.2 [𝑚A/s]*total rep. rate is 50 Hz
The other 25 Hz will be used electron injection

Due to limitation by Belle2 detector and SuperKEKB ring
Required injection amount is still low.
8

Positron charge and injection efficiency
Primary e- 7 nC@target

Primary e- 10 nC@e-gun

Positron 1 nC@DR

Positron 0.55 nC@BT end dump

Positron 1.5 nC@first BPM

Positron current in the ring (LER)

Injection efficiency

9 hours
9

Operation in phase 3

FC used in phase 2 was removed in Sept. 2018
With work hardened
Tested up to 12 kA at test benchDamaged by discharge after installation in tunnelMaximum current was limited to 6 kA in phase 2
operationNew exchange jig works well
New FC was installed in Jan. 2019
Without work hardened (old one)
Tested up to 12 kA at test benchOperated 3.5 kA in tunnelNot damaged till now

Safe and stable operation in phase 3→play for time
→push R & D at test bench
10OutlineOperation in phase 3
 Positron source setup
 Requirement and achievement
Present status and development
 Magnetic filed in solenoid section
 Discharge of FC Upgrade plan Collaboration
SummaryAnswer to the previous review comments

11Design and present status
Simulation by F. Miyahara

designParameter

simulation

Experiment

BC600 A

600 A

SL_15_11

650 A

600 A

SL_16_11

650 A

400 A

SL_16_22

650 A

400 A

SL_16_33

650 A

650 A

ACC_15_1/2

10 MV/m

8.5 MV/m

ACC_16_1/2/3/4

12 MV/m

12 MV/mWhy yield is low compared to the design value?
How to increase the FC current?
12Solenoid field issue

Design 600 A
present 600 A

650 A
600 A

650 A
400 A

650 A
400 A

650 A
650 A

Solenoid section consists of 30 solenoid coils.
They are connected in 5 groups.
Each group is energized by independent power supply.

Design value and present value tuned to maximize positron yield is different
13Solenoid field issue

Measured by T. Kamitani

Measurement of deflection amount of
3 GeV electron beam
by asymmetric field in solenoid
section
1,Prepare ballistic beam between
SP_15_T and SP_16_5
2,Energize a part of solenoid by
1/10* max. value step.
3, Monitor beam position at SP_16_5
14

Solenoid field issue

Steering coils

BPM

Install steering coils and BPM in solenoid section.
Measure magnetic field in the solenoid section using electron beam.
Detailed simulation of magnetic field by CST is also in progress
400-6

B (10 T)

200

Bx
By

0-200-400

15051015

Fight against discharge
Why we can not apply 12 kA to the FC?
 Because it discharges!
16

17

18

After large discharge…
After large discharge

Slit gap got narrow.
Not possible to apply
high voltage unlessthe gap will beexpanded.
19

Fight against discharge
Why we can not apply 12 kA to the FC?
 Because it discharges!
To suppress discharge Reduce voltage by snubber circuit Cu-alloy material for FC head
 Insertion of insulators in the slit
 Optimization of gap width20

CT𝑑𝐼𝑉~𝐿𝑑𝑡
High voltage probe

𝐴 = 𝜋𝑟 2

High voltage probe～3MHz
Due to resonance by
capacitance of thecable and inductanceof the load

dI/dt]

I[kA]

Vsupply[kV]
Vreturn[kV]

ALCW2018

Vsupply-Vreturn[kV]21

Snubber circuit
Avoid discharge→Reduce electric field between gap→Reduce voltage keeping current→suppress rapid current change𝑑𝐼𝑉~𝐿𝑑𝑡

Resister 3 ΩCapacitor 100 x 4 nF

22

Current and voltage waveform w or w/o snubber circuit

w/o snubber circuit
w snubber circuit

23Frequency response of capacitors
1010Z (ohm)

1010

5
432
1

10
1004 nF/ ceramic
1400 nF / film
250 nF / film
100 nF / ceramic

-1

10-2

10
2
10R (ohm)

10
10

10-1

10-2

10-3

10-4

10-4
10

previous-5

10

newC (F)

-6

10-7

10-8

10-9

10

310

10

410

510

6710

frequency (Hz)24

Optimization of the snubber circuit
Es = 5 kV
IFC = 3.5 kA

25

Optimization of the snubber circuit
1R1

Simulation by T. Natsui

6Circuit simulation

D1100k2DC 10k AC 0 01

LEN=10 R=0.01 C=1e-9 L=0.025e-6

Rps5

1.4u C1

Lsy
0.5u/2

9T1

L2
2.5u

L3
1.0u

8

100.1
Rfc

40.1
Rs
11

V1
0.01
Rsy

7

Lfc
1.7u

3SW1

ALCW2018

26

1000nCsOptimization of the snubber circuit
スナバー全体LCR measurement

4

10Z (ohm)

3102101100R (ohm)10108642

1-610C (F)42-7

1042-8103101045671010
frequency (Hz)1027

New material for FC head
Avoid discharge→Reduce electric field between gap→manage slit distance→avoid deformation

𝑑𝑉𝐸~𝑑𝑥Increase yield strength of thematerialWork hardening process wastested

Result was not clear
Another approach using Cu-alloy

Requirements for material of the FC head are• Good brazing characteristic• High yield strength even after brazing• High electric and thermal conductivity

28

Cu alloys

Cu
Cu-Zr
Cu-Cr
Cu-Ni-Si
were tested

29Evaluation of brazing characteristic

Cu-Zr(SH-2)

Cu-Cr(SH-1)

P:Palladium
C1020

Cu-Ni-Si(NC50)

A:Silver30Measured properties of materials
Material

Cu (C1020)

Cu-Cr (SH-1)

Afterbrazing

Thermal cycle

Cu-Zr (SH-2)

Afterblazing

Cu-Si-Ni (NC50)

After
blazingAfterblazing

After aging

conductivity
%IACS

102.2

102.1

90.8

76.0

81.1

68.5

50.3

25.1

48.8

Hardness

87.4

30.4

71.6

60.0

45.9

55.8

95.3

61.2

95.4

Tensilestrength
Mpa

327.4

232.1

402.6

237.2

443.1

238.3

648.7

323.7

658.8

Elongation%

21.654.4

36.8

56.8

32.6

51.4

14.8

46.6

10.6

Yield strength
Mpa

322.3

12.9

293.6

57.9

348.2

40.8

551.8

109.7

513.1

31

Strain-stress curve for C1020 and NC50
NC50

C1020

32

Strain-stress curve for C1020 and NC50

NC50 after brazing

C1020 after brazing

33

Strain-stress curve for C1020 and NC50

NC50 after aging(precipitation hardening)34

Strain-stress curve for C1020 and NC50
NC50
NC50 after aging(precipitation hardening)

C1020

NC50 after brazing

C1020 after brazing

35

Yield strength
600

x40

Yield strength (Mpa)

500

400

300

200

1000
before brazing
after brazing
brazing + aging

C1020
322.3
12.9

SH-1
293.6
57.9
before brazing

after brazing

SH-2
348.2
40.8

NC50
551.8
109.7
513.1

brazing + aging

36

Production and simulation


New FC head is in production using
NC50.
 Assembly will be delivered in Oct.
To evaluate mechanical stress,
combined electromagnetic andmechanical simulation by ANSYSMaxwell has just started.

37

Insertion of insulator plates in the slits

20mm x 25mm x 0.2mm Zirconia (ZrO2) plates are inserted from 3 direction

It works but not perfect→discharge decreased but happened→further investigation is needed38

Optimization of slit gap


Presently 0.2 mm (same value as the one used inSLAC)
Simulation suggest wider gap makes stronger Bx andBy
To confirm simulation, magnetic field measurement
using pick-up coil is under preparation
It is easy to change the gap by inserting insulator
plates 0.3 mm thickness plates will be delivered soon

39Upgrade plan - items

FC
New one made of Cu-alloy (NC50)
 Insertion of insulator plates?
 Optimization of slit gap?
Pulsed power supply Optimization of snubber circuit Longer pulse operation?
Beam tuning in solenoid section
 Steering magnet
 BPM



40

Upgrade plan - schedule
2019
12

3

4

5

67

2020
8

9

10

11

12

1

2

3

4

5

6

7

8

9

10

11

FC (present)
FC (new material)
FC (optimizeddesign)
Snubber circuitLonger pulse
operation
Steering coils
BPM
Magnetic fieldmeasurement

Operation
DesignTest
BidingManufacturing
Installation

We are planning big upgrade of positronsource in 2020 summer shutdown.
budget is one of the concern…..
4112

collaboration
Most important problem is lack of manpower (less than 1 now…)
ILCKEKAttend weekly meetingStart working together
FCC-ee
LAL and BINP

Collaboration in the frame work of FJPPL
Share 3D model for simulation

Visit us in Feb. 2019
CEPC

IHEP

Provided FC head last year
Visit us in Jan. 2019, joined installation of the FC
CLIC

CERN

Share 3D model for simulationcollaboration with people in charge offuture positron source is expanding

42summaryPhase 3 operation of positron source was stable
Very low current (3.5 kA)
FC is not damaged now
Beam study with 3 GeV electron beam in solenoid section was done toinvestigate low positron yieldConfirm electron beam was deflected
Steering coils and BPMs will be installed for compensation and monitor
To avoid discharge of FCOptimization of the snubber circuit is in progressNew FC made of Cu-alloy is in production
Insertion of insulator plates are tested

Optimization of Slit gap distance is under consideration
Major upgrade is planed in summer shutdown 2020
Collaboration with other projects is rapidly expanding

43

Answer to previous review 1R7.1: Continue to build-up of a realistic simulation of the positron production
and collection. This is needed for a realistic prediction of the gain available
from any FC improvements.
Simulation is in progress but man power is limited.
Collaboration with people in charge of future positron source is expanding.

R7.2: The Committee suggests to study whether an increase of the coil gaps,
to, say, about 250 microns or so, can significantly increase the break downvoltage. The resulting central magnetic field will likely be lowered by about
20% for the same current, but with the increased voltage limit the overallmagnetic field may go up significantly.
Gap management with insulator plates was tested and worked well.
Magnetic field measurement is in preparation.

R7.3: Perform a new study to improve the work hardening process of thecopper FC coils. Compare with the experience at other laboratories, e.g. at
SLAC and BINP.
Mechanical properties of the material for the FC were evaluated.
Promising Cu-alloy was found. New FC is in production.
44Answer to previous review 2


The Committee would also like to draw attention to the findings andrecommendation of the last Domestic Review as of September, 8, 2017,
concerning the Positron Source (see Appendix C).
The exchange of the flux concentrator(FC) should be done regularlyeven without damage to reduce the radiation exposure.
The exchange jig works well. It is possible from the technical point of view.
Residual radioactivity is monitored. There is no need to do that presently.
There is not enough budget.
Reconsidering the material of the FC can be necessary. Review thematerial choice by reevaluating the data in the past.
Mechanical properties of the material for the FC were evaluated.
Promising Cu-alloy was found. New FC is in production.
A coil with a larger gap width may be possible.
Gap management with insulator plates was tested and worked well.
Magnetic field measurement is in preparation.

45

Answer to previous review 3This time the FC caused discharging after installing into the tunnel,
despite the success in the tests on surface. The actual pulse form could
differ between them.
In addition to current, voltage pulse shape evaluation was established.
We will try to compare the pulse shape at test bench with that intunnel in detail.

The conditioning should be performed at a voltage higher than the specby 20%.
Preparation of the power supply at test bench is in progress.

It is important to know whether the discharge at the large aperture S
band (LAS) structure was due to the placement nearby the positronsource.
Dummy load and contact of the wave guide flanges were suspicious.

46

Answer to previous review 4
The validness of “hardening” needs more investigation including on thediagnostics.
Did it really improved the entire elasticity or just for the surface?
Mechanical properties of the material for the FC were evaluated.
Promising Cu-alloy was found. New FC is in production.
The estimated improvement on the amount of charge is 20% byincreasing the voltage from 6kV to 12 kV. Consider the priority of thehigher voltage plan taking the necessary resources and the effect.
Beam transport in the solenoid section was evaluated.
Total upgrade work is scheduled in 2020.

Even a non-FC scheme such as at the previous KEKB is thinkable.
Presently, no man power.



Establish an interlock system against discharging to stop operation in asingle pulse to prevent a fatal damage.
Done.

47

Assembly, base management
Phase 1

Phase 2Phase 32019 Q4

2020 Q1,Q2

2020 Q4

deliveredremovedpresenAssembly 1<2015

2017/3In tunnel

Assembly 2

2016/3In operation

Assembly 3

2017/11

Test bench

FC base 1

<2015

Test

FC base 2

<2015

Test

FC base 3<2015

FC base 4

2017/3

With Assembly 1

2018/9In tunnel

NoteFC base 5

2016/7

In operationFC base 6

2017/11

Test bench

FC base 72019/10

In production

FC base 8

2020/7

Final version
In design

FC base 9

2020/10Saper for Finalversion

in operation
sparetest bench48

Observation of FC used in phase 1
FC used in phase 1
operation, which isstored in the shieldcase was extracted
for investigation
since radiation level
got low.

35.7 uSv/h49

Positron source setup 4Bridge coil
DC magnet
I = 600～750 A

How the FC works?

e•••targete+

Flux Concentrator
pulsed magnet
I = 6000～12000A

Electron hit small point of the target.
Positron comes from small spot.
Angle distribution is large.
Calculated by T. Kamitani

targete+•••Adiabatically expand position distribution.
Angle distribution decrease.
Matched to the aperture of the following LAS.

Ratio B @ target / B @ entrance of the LAS is importantstronger field is preferred in the following solenoid section
much stronger field is required @ target50