1. Carbon Injector for FFAG
M. Okamura 1

2. Keys
Direct Plasma Injection Scheme (DPIS) with RFQ is well suit for FFAG
Fully stripped carbon ions can be provided with 100 mA of beam current.
Pulse duratioin is about 1 to a few micro second
Repetition rate just depends on laser driver system 2

3. Content: Introduction of DPIS Experiment at TIT
CO2 and YAG laser sysmtems
RIKEN‘s new project (next step)
Linacs for FFAG

4. Low energy transport line for high current heavy ion beams
RFQ LINAC
Established structure for LEBT
Ion source
High voltage
stage
Difficulties about the LEBT for Heavy Ions
Strong space charge effect : Due to the low energy and highly charged states.
Matching to the RFQ : Time variation of the beam emittance from the pulsed source.
Multiple charged states : Effects from un-wanted charged state particles. 3

5. Direct Plasma Injection Scheme
From the source to the RFQ, ions are transported being included by plasma.
Free from the strong space charge effect.
Beam emittance of the plasma can be conserved up to the entrance of the RFQ
Overcome Space Charge Effect
No need to build a high voltage stage.
Works W/O any focusing devices or complicated extraction system.
Extremely Simple
Laser Ion Source 4

6. Experimental Set-Up for Direct Injection Method
Floor layout
PF power supply
F. C. 1
TiTech RFQ
Target Chamber
Laser Beam
Analyzing magnet
Beam envelope after the RFQ
CO2 laser
Q-magnets
F. C. 2
FDF
Field strenth for C1+
Input emittance
X=2.78 mm
X’=18.5 mrad
Epsx=24.4 mm mrad
Q1: kG
Q2: 3.53 kG
Q3: kG
D: 9.25 kG 5

7. TEA CO2 laser system Total laser power 100±30 MW
Wave form of the laser pulse
Gas mixture ratio
Laser Beam Profile
Gas mixture ratio CO2:N2:He = 1:2:4
Peak Energy ±0.6 Joule
Pulse width ±5 ns
Total laser power 100±30 MW
50 mm 6

8. Plasma Target Chamber 3.35 1012 W/cm2 Insulator C Target (MC nylon)
Laser Wavelength: l = 10.6 mm
Focusing Mirror: f = 250 mm
Diameter of Laser Beam: D = 50 mm
C Target
(Rotateable)
Focal Spot Size on Target Surface:
d = 1.22f l/D = 64.7 mm
RFQ
Laser Beam
Power Density:
P = W/(p(d/2)2)
W/cm2
Na Cl
H. V.
Lens
Slit 4mm
Properties of the laser plasma
Energy of the ions : about 100 eV/u
Emission angle : less than ±20 degrees 7

9. TITech RFQ LINAC TITech 80 MHz Heavy Ion RFQ M. Okamura et al.,
Nucl. Inst. And Meth., B
(1994) p
Designed Values
Table: The main parameters of the TITech RFQ
Charge to mass ratio ≥1/16
Operating frequency (MHz)
Input energy (keV/amu)
Energy spread (%) ±5
Output energy (keV/amu)
Normalized emittance (100%) (cm·mrad) p
Vane length (cm)
Total number of cells
Characteristic bore radius, r0 (cm)
Synchronous phase, fs ˚ to -20˚
Transmission
for q/A=1/16 beam 10 mA input mA 8

10. Photo album of the experiment9

11. Measurement of the accelerated beam -just after the RFQ
Current [mA]
H. V. 16 kV
Peak Current: 25mA
Averaged Current: 8mA
Pulse Width (90%): 1.24 ms
Time [s]
C ion beam
214 keV/u
Bunched Structure !! 10

12. Measurement of the accelerated beam -after analyzing magnet
C4+ ion beam
Peak Current: 4.0mA
Pulse Width (90%): 0.41 ms
Beam Energy: 214 keV/u
Fine structure
Current [mA]
Time [s]
F. C. 2
C3+
C3+ ion beam
Peak Current: 0.8mA
Pulse Width (90%): 0.35 ms
Beam Energy: 214 keV/u 11

13. PARMTEQ simulation with multiple charged states
Laser Ion Source at RIKEN
L=250mm ɔ4mm
Total current: 94 mA
C3+: %
C4+: %
C5+: %
PARMTEQ-HI for multiple charge state ions
(R. Jameson)
Input emittance (x,y): a = -3.94
b = 1.00 mm/mrad
e = 9.80 p mm mrad
Vane voltage factor: vfac = 0.7
Buncher
Section
Booster
Current [mA]
Input energy [keV] Predicted current [mA]
C3+
C4+
C5+ 45 60 75
0.45
1.85
0.03
cell 12

14. Results of the experiment
9.2 mA of Carbon beam was detedted after the RFQ.
-> Direct Injection works very well
Ions are extracted within slit.
Tracking with 3D field map is useful.
pteqHI simulation can reproduce measured results well.
Beam current was lmited by the RFQ
We are now ready to proceed to next step
New RFQ for higher current acceleration 13

15. Measurement of Plasma Property
CO2 laser and Nd-YAG laser are used.
Charge states distributions were obtained from two types of lase plasmas.

16. Experimental equipment
Nd-YAG Laser
TEA CO2 Laser
Detector
NaCl Window
4.6m
3.1m
Analyzer (ITEP)
FC Chamber
Target Chamber (ITEP)

17. Target Chamber
Laser
Plasma
Carbon Target
Chamber

18. Comparison with laser wave form
Pulse width :YAG<CO2
Energy:YAG<CO2
Most of all energy gather in one wave form in Nd-YAG laser.
Energy is separated into two parts, peak part and tail part in CO2 laser

19. Power density calculation
Divergence angleθ=1.22・λ/D
Spot size d=θ・F
Power density calculation
（D: beam size　F：focal length of lens 135・10-3m）
Nd-YAG laser
CO2laser
λ=1.06・10-6m
D=8・10-3m
E=0.26J
P=2.3・1012 W/cm2
λ=10.6・10-6m
D=50・10-3m
E=1.2 J
P=3.7・1011 W/cm2

20. Result （by F.C.） CO2 laser YAG laser Two peaks in CO2 laser
　　→depends on power 　　　　　　distribution of laser
(peak and tail)?
Beam velocity :YAG>CO2
→power density
CO2 laser
Total currrent:YAG<CO2
→Laser power
YAG laser

21. Result (by analyzer)
Current measured by analyzer is estimated by integrating
（Signal from Analyzer）/γ and current at F.C. and comparing them
γ：secondary electron emission coefficient
More high charge state was produced by Nd-YAG than by CO2
→power density

22. Energy YAG＞CO2 ⇒power density Charge state YAG>CO2 ⇒power density
Summary
Energy　YAG＞CO2　⇒power density
Charge state YAG>CO2 ⇒power density
Current　YAG<CO2 ⇒total power

23. High laser power -> Fasr ions
Currents from YAG laser Plasma
Various laser power
High laser power -> Fasr ions

24. CO2 laser C4+ beam Long pulse
Nd-YAG laser
C6+ beam
Easy to handle

25. RIKEN new RFQ for 100mA Carbon beam
Proposed Specs for the new RFQ
Output Current : 100 mA
Target Particle : C4+, C6+
Length : up to 2 m
Output Energy : 1.2 MeV 14

26. Linacs for FFAG
Injector will be used for proton and carbon acceleration
Use commercially available DTL (Accsys?) Proton DTL can be operated 4 pi mode for carbon beam. q/A must be 1/2.
4 rod type RFQ or 4 vain type RFQ?

27. RFQ design (30 mA of injection current)
212 MHz (doubled frequency of Accsys‘s DTL), 4 rod structure, 3.3 m (length), 98 % transmission. (New IH DTL?)
425 MHz, 4 vain type, 4.83 m, 86%