Overview of Positron Sources and High-Power Targets at KEK

undefined
 
2023/1
1
/7
Y. Enomoto
 
Positron source and target in KEK
 
 
1
 
 
KEK and positron
 
From TRISTAN to ILC
KEK LINAC has keep providing
positron beam to e
+
e
-
 collider
experiment since 1980s.
Positron source for SuperKEKB is
world’s most intense positron source in
operation.
We play an important role to develop
future positron source for ILC.
 
 
 
2
TRISTAN
KEKB
SuperKEKB
 
Comparison of high-power targets in Japan
 
 
 
3
 
Power (kW)
 
beam power
deposited power
 
ILC
 
RIBF
 
n
 
H
 
μ
 
ν
 
ILC
 
RIBF
 
n
 
H
 
μ
 
ν
 
SKEKB
 
SKEKB
 
Particle sources and positron source
 
 
 
4
Neutron source
Muon source
Neutrino source
Electron source
Ion source
 
Primary particle source
 
secondary particle source
 
Positron source is installed in the middle
of accelerator
Collection and acceleration of secondary
particles
need high power primary beam for full
test
Usually impossible before
construction
Positron source
source
 
 
Accelerator
 
High quality beam for
acceleration
Stand alon
e test is
possible
No radiational, thermal
requirement
 
Low beam quality is
acceptable
Need high power
primary beam
Severe radiational,
thermal requirement
 
Positron source for SuperKEKB
 
 
 
5
Originally developed by SLAC
Almost all the other positron
sources follows this design
Surrounded by solenoid 
limited space
Need UHV
<10
-6
 Pa
FC = pulsed coil (20 kV, 12 kA) installed close to target (2mm)
 
SuperKEKB target
 
 
 
6
W
Φ4 
 
L14
)、
HIP to 
Cu block for cooling
Hole for electron
Beam
 
power
 
3 kW (3 GeV 
 
10 nC 
 
2 bunch
 
 
50 Hz)
Deposition ~ 0.7 kW
PEDD
 
:
 
27.5 J/g
 
temperature
 
 
 
7
 
Pulsed heating every 20 ms by beam
Amplitude
 
~
 
200
 
20 ms
Y. Morikawa
 
stress
 
 
 
8
Caused by difference of thermal expansion
coefficient and edge geometry (580MPa)
Beam heat peak
(140 MPa)
Caused by difference of thermal expansion
coefficient and edge geometry (610MPa)
Beam heat peak
(30 MPa)
 
Thermal stress by pulsed beam
High at Cu-W contact surface
Care must be taken to fatigue
50 Hz =
 
4 
 
10
6
 /day
Y. Morikawa
 
Withstanding heat load
 
 
 
9
 
~3700 K
(456 J/g)
 
~2160 K
(250 J/g)
*
 
~1500 K
(161 J/g)
 
~870 K
(77 J/g)
 
Melting point
 
Single pulse
destruction
 
emb
rittlement by
recrystallization
 
fatigue
 
Value in 
() 
varies design of target.
Here target of SuperKEKB is assumed for reference.
*
thermal stress reach 1 GPa
 
Melting point
Unavoidable Limit
Single
 
pulse
 
destruction
Thermal stress exceed material yield
strength
Short pulse beam 
 instantaneous
temperature rise
Embrittlement by recrystallization
W-Re alloy shows better value
Difficult to obtain large size
Advanced W alloys are one of research
field
J
P
S
 
C
o
n
f
.
 
P
r
o
c
.
 
2
8
,
 
0
3
1
0
0
2
 
(
2
0
2
0
)
Fatigue
limit by repetitive thermal load by pulsed
beam
 
From SuperKEKB to ILC
 
Based on SuperKEKB
Big jump from
SuperKEKB
3 x SLC in beam
power (74 kW)
4 x SuperKEKB in
capture efficiency
 
 
 
10
past
present
future
 
ILC e-driven
High power
High efficiency
 
SLC
 
SuperKEKB
 
FCCee
 
ILC undulator
 
CLIC
 
CEPC
 
KEKB
 
BEPC
 
DAFNE
 
VEPP-5
 
Latest 3D model for ILC positron source
 
 
 
11
Rotating target
RF cavity
solenoid
Flux concentrator
 
Rotating target in Japan
 
 
 
12
 
Thanks to
   J-PARC Muon: Matoba, Makimura
   J-PARC hadron: Sawada, Takahashi, Watanabe
   RIKEN RIBF: Yoshida, Yanagisawa
 
To do
 
Water cooled UHV compatible rotating mechanism
Robust W-Cu connection
RF cavity after the target
~a few 10 kW heat load from shower
Flux concentrator compatible with rotating target
Exchange mechanism of
 highly activated materials in
accelerator tunnel
Not in 
special target area
Deep underground (~100 m) and limited space
 
 
 
13
Grant from MEXT
FY2023
 
~ FY2027
Development started 2022/Q4
 
5 years-plan
 
 
 
 
14
Design
Manufacuring
test
 
Test bench for ILC positron source
 
 
 
15
 
Summary
 
Say hello to the high-power target community
from positron group
Different requirement and limitation from proton
machine
Most of the technologies are still useful for us
Requirements of the ILC, linear collider
, are
very high
We started development for ILC recently
Details about rotating target 
next talk
 
 
 
16
 
 
 
 
 
17
 
Bunch structure
 
Create positron for 66 ms
Store them in the DR for 199.3 ms
Extract them to main linac for 0.7 ms
20 pulse / train
66 bunch / pulse
1320 bunch / train
Repetition 5 Hz
 
FC must keep field variation below the
requirement to keep bunch-by-bunch
charge variation
Minimum current pulse width is about
500 ns
 
 
 
18
M. Kuriki, OHO seminar 2021
 
3.3 ms
20
 
= 66 ms
66
train
pulse
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Comparison of the positron source at KEK, from the TRISTAN era to current SuperKEKB operations, along with details on high-power targets used in various experiments. The discussion covers the development of positron sources for the ILC, the significance of SuperKEKB, and the challenges associated with maintaining and utilizing high-power targets. Additionally, insights are provided on the design and functionality of the positron source for SuperKEKB, key specifications of the SuperKEKB target, and considerations for particle sources related to the acceleration of high-quality beams.


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  1. Positron source and target in KEK 2023/11/7 Y. Enomoto 1

  2. KEK and positron TRISTAN From TRISTAN to ILC KEK LINAC has keep providing positron beam to e+e-collider experiment since 1980s. Positron source for SuperKEKB is world s most intense positron source in operation. We play an important role to develop future positron source for ILC. SuperKEKB KEKB 2

  3. Comparison of high-power targets in Japan e+ e+ n Neutrinos Hadrons RIBF Institute KEK (SuperKEKB) ILC (e-driven) J-PARC J-PARC J-PARC J-PARC RIKEN Primary particle e- e- p p p p C~U Target material W W C Hg C Au Be, W Energy [GeV] 3 3 3.5 3 30 30 0.345/u Charge/pulse [nC] 13300 13300 52900 16470 CW 10 2 3.7 66 Repetition [Hz] 50 100 / 300 25 25 0.47 0.19 CW (1puA) Beam Power [kW] 3 74 1000 1000 750 95 82 Beam size x y[mm] Thickness [mm] 0.5 0.5 2 2 3.5 3.5 37 17 4.2 4.2 2.5 1.0 0.42 0.42 14 16 20 2000 909 ~mm 66 (6 11) Deposited power [kW] 0.5 18.8 3.1 480 20 7.4 18 PEDD [J/g] 27.5 33.6 20 1.1 190 Slow extraction CW Cooling Water Water Radiation Water He Water Water structure Fixed Rotating Rotating Liquid Fixed Fixed Rotating beam power deposited power 50 1000 40 Power (kW) 30 500 20 10 0 0 3 RIBF SKEKB ILC n H RIBF SKEKB ILC n H

  4. Particle sources and positron source secondary particle source Primary particle source Accelerator Neutron source Muon source Neutrino source Electron source Ion source High quality beam for acceleration Stand alone test is possible No radiational, thermal requirement Positron source source Low beam quality is acceptable Need high power primary beam Severe radiational, thermal requirement Positron source is installed in the middle of accelerator Collection and acceleration of secondary particles need high power primary beam for full test Usually impossible before construction 4

  5. Positron source for SuperKEKB Originally developed by SLAC Almost all the other positron sources follows this design Surrounded by solenoid limited space Need UHV <10-6Pa FC = pulsed coil (20 kV, 12 kA) installed close to target (2mm) 5

  6. SuperKEKB target W 4 L14 HIP to Cu block for cooling Hole for electron Beam power 3 kW (3 GeV 10 nC 2 bunch 50 Hz) Deposition ~ 0.7 kW PEDD : 27.5 J/g 6

  7. temperature Y. Morikawa 20 ms Pulsed heating every 20 ms by beam Amplitude ~ 200 7

  8. stress Y. Morikawa Thermal stress by pulsed beam High at Cu-W contact surface Care must be taken to fatigue 50 Hz = 4 106/day Beam heat peak (140 MPa) Beam heat peak (30 MPa) Caused by difference of thermal expansion coefficient and edge geometry (580MPa) Caused by difference of thermal expansion coefficient and edge geometry (610MPa) 8

  9. Withstanding heat load Melting point Unavoidable Limit Single pulse destruction Thermal stress exceed material yield strength Short pulse beam instantaneous temperature rise Embrittlement by recrystallization W-Re alloy shows better value Difficult to obtain large size Advanced W alloys are one of research field JPS Conf. Proc. 28, 031002 (2020) Fatigue limit by repetitive thermal load by pulsed beam ~3700 K (456 J/g) Melting point Single pulse destruction ~2160 K (250 J/g)* embrittlement by recrystallization ~1500 K (161 J/g) ~870 K (77 J/g) fatigue Value in varies design of target. Here target of SuperKEKB is assumed for reference. *thermal stress reach 1 GPa 9

  10. From SuperKEKB to ILC 0.5 Based on SuperKEKB Big jump from SuperKEKB 3 x SLC in beam power (74 kW) 4 x SuperKEKB in capture efficiency past present future 0.45 ILC e-driven 0.4 0.35 Ne+/Ne-/GeV 0.3 High efficiency CLIC 0.25 0.2 0.15 SuperKEKB FCCee 0.1 BEPC DAFNE VEPP-5 0.05 CEPC KEKB SLC ILC undulator 0 0 20 40 60 80 e- beam power (kW) High power 10

  11. Latest 3D model for ILC positron source Rotating target RF cavity solenoid Flux concentrator 11

  12. Rotating target in Japan e+ Hadrons RIBF Institute ILC (e-driven) J-PARC J-PARC RIKEN Primary particle e- p p C~U Target material W C Au or W Be, W Repetition [Hz] 100 / 300 25 0.19 CW (1puA) Beam Power [kW] 74 1000 150 82 (design) Deposited power [kW] 18.8 3.1 11 18 (design) PEDD [J/g] 33.6 20 Slow extraction CW status Prototype In operation Prototype In operation Cooling Water Radiation He Water Thanks to J-PARC Muon: Matoba, Makimura J-PARC hadron: Sawada, Takahashi, Watanabe RIKEN RIBF: Yoshida, Yanagisawa 12

  13. To do Water cooled UHV compatible rotating mechanism Robust W-Cu connection RF cavity after the target ~a few 10 kW heat load from shower Flux concentrator compatible with rotating target Exchange mechanism of highly activated materials in accelerator tunnel Not in special target area Deep underground (~100 m) and limited space Grant from MEXT FY2023 ~ FY2027 Development started 2022/Q4 13

  14. 5 years-plan 2022 2023 2024 2025 2026 2027 FY year 2023 2024 2025 2026 2027 Quarter Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Test bench High power test bench W-Cu connection Target unit 1stunit 2ndunit 3rdunit FC base 1stunit 2ndunit magnet Solenoid + ST Power supply Chamber, vacuum, support Acc. Structure Dummy 1stunit 2ndunit FC power supply RF power supply Design Manufacuring test 14

  15. Test bench for ILC positron source 15

  16. Summary Say hello to the high-power target community from positron group Different requirement and limitation from proton machine Most of the technologies are still useful for us Requirements of the ILC, linear collider, are very high We started development for ILC recently Details about rotating target next talk 16

  17. 17

  18. Bunch structure M. Kuriki, OHO seminar 2021 Create positron for 66 ms Store them in the DR for 199.3 ms Extract them to main linac for 0.7 ms 20 pulse / train 66 bunch / pulse 1320 bunch / train Repetition 5 Hz 66 . train FC must keep field variation below the requirement to keep bunch-by-bunch charge variation Minimum current pulse width is about 500 ns 3.3 ms 20 = 66 ms pulse 18

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