1. Current Status of Electron-RI Collision Project at RIKEN
COOL2015 JLab
Current Status of Electron-RI Collision Project at RIKEN
M. Wakasugi
COOL15 Workshop, JLab, USA, Sep. 28, 2015
SCRIT Collaboration
RIKEN Nishina Center for Accelerator-Based Science
T. Ohnishi, M. Watanabe, S. Ichikawa, M. Hara, T. Hori
Department of Physics, Rikkyo University
M. Togasaki, K. Yamada, T. Hujita, K. Adachi, M.Hori, A. Enokizono, K. Kurita
Research Center for Electron Photon Science, Tohoku University
K. Tsukada, T. Tamae, T. Suda

2. Current Status of Electron-RI Collision Project at RIKEN
COOL2015 JLab
Current Status of Electron-RI Collision Project at RIKEN
Charge density distribution from elastic scattering
Differential Cross Section (ds/dW)
Scattering angle (deg.)
Luminosity
> 1026 /(cm2s)
Cross section
measurement until
second maximum
Sn isotope
Ee=300MeV
L=1026/(cm2s)
q=20°-65°
Df=90°
1 week meas.
Determination of
radii and diffuseness
with a few % accuracy

3. Current Status of Electron-RI Collision Project at RIKEN
COOL2015 JLab
Current Status of Electron-RI Collision Project at RIKEN
Brief history of the project
In 1995, the project was proposed.
Design study of e-RI collider ring was started.
In 2002, experimental scheme was changed to the SCRIT method.
In 2007, feasibility study of the SCRIT method was succeeded.
In 2009, the SCRIT facility construction was started.
In this year, the construction has been almost completed.
The facility is now under comprehensive test.

4. SCRIT (Self-Confining RI Ion Target)
SCRIT is internal-target-forming technique in an electron storage ring.
Target ions are confined in the beam orbit by periodic focusing force.
Recoiled ions
Trapped RI ions
injected from out side
scattered
electrons
Mirror potential for
longitudinally localizing
trapped ions
Bunched e-beam in storage ring
~1010 electrons/bunch

5. Location of the SCRIT Facility in RIKEN RI Beam Factory
SRC
IRC
fRC
RRC
Rilac
ECR
CSM
GARIS
AVF
Rilac2
RIPS
BigRIPS
ZeroDegree
SAMURAI
SHARAQ
SCRIT
Rare-RI Ring

6. The SCRIT Electron Scattering Facility
Electron beam 150MeV
ERIS
Electron beam
100~700MeV
300 mA
Cooler
Buncher
Luminosity
Monitor
SCRIT 2 4
6 m
SR2
High-resolution
spectrometer (WiSES)

7. The SCRIT Electron Scattering Facility
RI ion beam
from ERIS
e-beam
Scattered
electrons
WiSES
SR2 (SCRIT-equipped RIKEN Storage Ring)
Energy – 700 MeV
Stored current 300 mA
Circumference m
Tunes / 1.58

8. SCRIT and its Performances

9. Simple Estimation of Achievable Luminosity
Current~ 160mA
Cross section ~ 1mm2
Number of target ions Ni
Luminosity ~ Ni × 1020 /(cm2s)
Required luminosity
1026 /(cm2s)
Number of target ions
~106 ions
Actually, we have : Charge state multiplication
Decay of target ions due to interactions with
electron beam, residual gas ions, wake field.....
Decay of electron beam current
Luminosity is not stable

10. SCRIT Devise Installed in SR2
e-Beam

11. Performance of Ion trapping in the SCRIT
At 250mA:
Trapping efficiency ~90 %
Collision luminosity ~1027/cm2/s
(with 3x107 ions)
Trapping lifetime > 1s

12. RI Production and Buncher for Ion Injection to SCRIT

13. ERIS (Electron-beam-driven RI separator for SCRIT)
UCx Target in
FEBIAD ion source
UCx target
Ta converter
～2000℃
M/DM 1660
Overall eff. 21 %
Electron beam

14. RI Beam Production at ERIS
Production rate
Upgrade of
RTM e-Beam
5mApeak
8μs pules
400Hz repetition
L~1027/(cm2s)
109
Expected
U 30g, e-Beam 2kW
Planned
108
5mApeak
4μs pules
20Hz repetition
Expected
U 30g, e-Beam 50W
In progress
L~1025/(cm2s)
Extraction rate (/s)
107
Achieved in 2014
U 15g, e-Beam 10W
1.5mApeak
4μs pules
10Hz repetition
Current
106 Xe Sn
105
130
135
140
Mass Number

15. Cooler Buncher Device for Ion Injection to SCRIT
Cooler Buncher converts DC beam to 500ms pulsed beam
Based on RFQ linear trap
Einzel lens
Length
Bore
Freq.
VRF
950 mm
16 mmf
0.3~3 MHz
< 500 V
Extraction electrode
RFQ electrodes
Barrier electrodes
Injection electrode
Einzel lens

16. Buffer-Gas Free Cooler Buncher for Low-Energy Ion Beam
DC beam is stacked in RFQ by flinging RF field effect at the entrance
Injected ions are decelerated by flinging
field and they are stacked in the RFQ
DC beam input
Pulsed beam output
with appropriate
frequency (<10Hz)
Stacking
Barrier1
Barrier2
RFQ
Ion
Source
Vacc
Vbar1
Vbar2
VRFQ
Vacc > Vbar1 ≈ Vbar2 > VRFQ
( V ) ( -7V )

17. Buffer-Gas Free Cooler Buncher for Low-Energy Ion Beam
Stacked ions slowly decay
DC-Pulse conversion efficiency
Number of stacked ions N(t) :
10Hz (0.1s Stacking)
2 Hz (0.5s Stacking)
1Hz (1.0s Stacking)

18. Luminosity Monitors and Scattered Electron Detectors

19. On-line Luminosity Monitor
Bremsstrahlung gamma ray created by target ions :
Absolute value of luminosity is obtained from the counting rate.
It is ensured by measuring the energy spectrum and the spatial distributions.
Pb collimator
1/γ cone
Veto scintillator
γ→e-e+
Al converter
Fiber scintillator
Pure-CsI
calorimeter
Target ions
in SCRIT
two-dimensional spatial
distribution of gamma ray
gamma ray
spectrum

20. On-line Luminosity Monitor
Counting rate is 40kHz at L=1027 /(cm2s) and 150MeV
Accuracy is a few %
Spatial distribution of
Bremsstrahlung gamma ray
from 132Xe target at Ee=150MeV
Absolute value of luminosity
Horizontal position (mm) 50 40 30 20 10
Vertical position (mm)
Bremsstrahlung γ-ray
from trapped 132Xe ions
at Ee=150MeV
Energy (MeV)
105
104
103
102 10 1
Counts

21. Window-frame type SCRIT Electron Spectrometer (WiSES)
in combination with drift chambers and trigger scintillators
Window frame type
for field uniformity
Large aperture to enlarge solid
angle for 500-mm long target
0.8 T
848 A
< 0.2 %
1710 x 290 mm
30 ~ 55 deg.
80 msr
50 ~ 300 MeV/c
100 ~ 300 MeV
Designed
Magnetic field (max)
Current (max)
Uniformity
Aperture (hor. ver.)
Angle coverage
Solid angle
Momentum transfer
Electron energy
Field clamp for small
field leakage
Momentum resolution 0.1 % ( 300keV/c at 300MeV)

22. Preliminary Performance of WiSES
Measurement of elastic scattering from W wire target
with luminosity ~1028 /(cm2s)
Studies for evaluating :
momentum resolution
⇨ ~2.5x10-3 at 300MeV
vertex resolution
⇨ 2~3mm/z, 4mm/y
acceptance distribution,
⇨ well agree with simulation
and the other characteristics
Wide range of momentum transfer
is covered by changing electron
beam energy.
L (ds/dW) (sr-1s-1)
△ 100MeV
○ 200MeV
● 150MeV
Effective momentum transfer (fm-1)
W-wire target
inserted at the center of SCRIT
Preliminary

23. Preliminary Performance of WiSES
Elastic scattering from trapped 132Xe ion with the luminosity 2.5x1026 /(cm2s)
Trapped 132Xe
e-beam
Effective momentum transfer (fm-1)
L (ds/dW) (sr-1s-1)
Vertex-momentum distribution
Angular distribution of elastic events
Longitudinal vertex (mm)
Momentum (MeV/c)
Elastic components
from trapped 132Xe
Ee=150MeV
e-beam
Preliminary
1.5 h measurement

24. COOL2015 JLab
Summary
SCRIT facility construction has been almost completed.
The facility is now under comprehensive test.
Works in progress are :
bug hunting in all system
improvement of RI beam extraction efficiency at ERIS
improvement of CD-Pulse conversion efficiency at buncher
RTM beam power upgrade
study of detector characteristics of WiSES
In this fiscal year :
elastic scattering cross section measurement for Xe isotopes
experiments for RI will be started.

25. Thank you for your attention