Carbon Injector for FFAG

M. Okamura

Keys Direct Plasma Injection Scheme (DPIS) with RFQ is w

ell 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

Content:

Introduction of DPISExperiment at TITCO2 and YAG laser sysmtemsRIKEN‘s new project (next step)Linacs for FFAG

Low energy transport line for high current heavy ion beams

Established structure for LEBT

High voltagestage

Ion source

RFQ LINAC

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.

•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

Direct Plasma Injection Scheme

Laser Ion Source

Experimental Set-Up for Direct Injection Method

F. C. 2

CO2 laser

Laser Beam

PF power supply

TiTech RFQ

Analyzing magnet

Q-magnets

F. C. 1

Target Chamber

Q1

-1.704

Q2

3.527

Q3

-2.396

D1

9.245

Beam envelope after the RFQ

Floor layout

Q1: -1.70 kGQ2: 3.53 kGQ3: -2.40 kGD: 9.25 kG

X=2.78 mmX’=18.5 mradEpsx=24.4 mm mrad

Input emittance Field strenth for C1+

FDF

TEA CO2 laser systemWave form of the laser pulse

Laser Beam Profile

CO2:N2:He Mean Energy (J) Standard Deviation (J) (%) 1:1:8 6.71 0.51 7.56 1:1:4 7.41 0.73 9.90 2:1:4 6.96 0.58 8.43 1:2:4 8.16 0.80 9.80

50 m

m Gas mixture ratio CO2:N2:He = 1:2:4Peak Energy 8.4±0.6 JoulePulse width 85±5 ns

Total laser power 100±30 MW

Gas mixture ratio

Plasma Target Chamber

RFQ

Slit 4mm

Insulator(MC nylon)

C Target(Rotateable)

Na Cl

Laser Beam

Properties of the laser plasmaEnergy of the ions : about 100 eV/uEmission angle : less than ±20 degrees

Lens

Focal Spot Size on Target Surface:

d = 1.22f l/D = 64.7 m

Laser Wavelength: l = 10.6 mm

Focusing Mirror: f = 250 mm

Diameter of Laser Beam: D = 50 mm

Power Density:P = W/(p(d/2)2)

3.35 1012 W/cm2

H. V.

TITech RFQ LINAC

Table: The main parameters of the TITech RFQ

Designed Values

Charge to mass ratio ≥1/16Operating frequency (MHz) 80 Input energy (keV/amu) 5Energy spread (%) ±5Output energy (keV/amu) 214Normalized emittance (100%) (cm·mrad) 0.05Vane length (cm) 422Total number of cells 273Characteristic bore radius, r0 (cm) 0.466Synchronous phase, s -90˚ to -20˚Transmission for q/A=1/16 beam 10 mA input 6.84 mA

TITech 80 MHzHeavy Ion RFQ

M. Okamura et al.,Nucl. Inst. And Meth., B(1994) p. 38-41.

Photo album of the experiment

Measurement of the accelerated beam-just after the RFQ

012345673.97 10-63.98 10-63.99 10-64 10-6

Faraday Cup 1Bunched Structure !!

Curr

ent [

mA]

Time [s]Peak Current: 25mAAveraged Current: 8mAPulse Width (90%): 1.24 s

C ion beam214 keV/u

H. V. 16 kV

Measurement of the accelerated beam-after analyzing magnet

C4+ ion beam

Peak Current: 4.0mAPulse Width (90%): 0.41 sBeam Energy: 214 keV/u

C3+ ion beam

Peak Current: 0.8mAPulse Width (90%): 0.35 sBeam Energy: 214 keV/u

F. C. 2

Fine structure

Curr

ent [

mA]

Time [s]

C3+

C4+

PARMTEQ simulation with multiple charged statesL=250mm ɔ4mm

Total current: 94 mAC3+: 30%C4+: 60%C5+: 10%

PARMTEQ-HI for multiple charge state ions (R. Jameson)

02468101214050100150200250300tapengood(vfac=0.7)C3+(30mA)C4+(60mA)C5+(10mA)

cell

Curr

ent [

mA] Input emittance (x,y): a = -3.94

b = 1.00 mm/mrade = 9.80 mm mrad

Vane voltage factor: vfac = 0.7

C3+

C4+

C5+

Input energy [keV] Predicted current [mA]456075

0.451.850.03

BuncherSection

Booster

Laser Ion Source at RIKEN

New RFQ for higher current acceleration

Results of the experiment

9.2 mA of Carbon beam was detedted after the RFQ. -> Direct Injection works very wellIons are extracted within slit.Tracking with 3D field map is useful.pteqHI simulation can reproduce measured results well.

Beam current was lmited by the RFQWe are now ready to proceed to next step

Measurement of Plasma Property CO2 laser and Nd-YAG laser are us

ed.Charge states distributions were obtained from t

wo types of lase plasmas.

Target Chamber (ITEP)FC ChamberAnalyzer (ITEP)

Experimental equipment

3.1m

Detector

4.6m

NaCl Window

Nd-YAG Laser

TEA CO2 Laser

Plasma

Laser

Carbon Target

Chamber

　　　　　　　　　Target Chamber

0 200 400 600 800 100012001400160018002000-0.01

0.00

0.01

0.02

0.03

0.04

0.05

0.060 20 40 60 80 100

0.000

0.005

0.010

0.015

0.020

0.025

0.030

50% of total energy λ=10.6 m=1.2 E J

=85 FWHM ns

Laser pulse shape

, Time ns

CO2 Laser

λ=1.06 m=0.26 E J

=15 FWHM ns

, Time ns

- Nd YAG LaserComparison 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

Power density calculation

Divergence angleθ=1.22 ・ λ/DSpot size d=θ ・ F

（ D: beam size 　 F ： focal length of lens 135 ・ 10-3

m ）

λ=1.06 ・ 10-6mD=8 ・ 10-3m

E=0.26J

P=2.3 ・ 1012 W/cm2

λ=10.6 ・ 10-6mD=50 ・ 10-3m

E=1.2 J

P=3.7 ・ 1011 W/cm2

CO2laserNd-YAG laser

-10 -5 0 5 10 15 20 25 30 35 40 45 50 55 60

0

2

4

6

8

Current, mA

Time, s

2CO -Nd YAG

Two peaks in CO2 laser

　　→ depends on power 　　　　　　 distribution of laser

(peak and tail)?

Beam velocity :YAG>CO2

→power density

Total currrent:YAG<CO2

→Laser power

Result （ by F.C. ）

CO2 laser

YAG laser

Result (by analyzer)

10 15 20 25 30 35 40 45 50 55 60

0

1

2

3

4

5

6

7

L=3.1 md

FC=30 mm

CO2 laser produce plasma

Current of the different charge states

Current, mA

Time, s

C+1 2.6 10x 10

C+2 2.9 10x 10

C+3 4.5 10x 10

C+4 8.2 10x 10

C+5 2.1 10x 10

8 10 12 14 16 18 20 22 24 26 28 30 32 34-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

L=3.1 md

FC=30 mm

Nd-YAG laser produce plasma

Current of the different charge states

Current, mA

Time, s

C+2 1.6 10x 9

C+3 3.1 10x 9

C+4 6.3 10x 9

C+5 6.0 10x 9

C+6 3.8 10x 9

More high charge state was produced by Nd-YAG tha

n by CO2

→power density

Current measured by analyzer is estimated by integrating

（ Signal from Analyzer ） /γ and current at F.C. and comparing th

em γ ： secondary electron emission coefficient

0 1 2 3 4 5 6 7 8 9 10

104

105

106

107 Energy distribution of ionsTime-of-flight spectrum

Nd-YAG laser produce plasma

L=3.1 md

FC=30 mm

dN/dE

E, keV

C+2 C+3 C+4 C+5 C+6

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5

105

106

107

108

L=3.1 md

FC=30 mm

Time-of-flight spectrumEnergy distribution of ions

CO2 laser produce plasma

dN/dE

E, keV

C+1 C+2 C+3

C+4 C+5

Energy 　 YAG ＞ CO2 　⇒ power density

Charge state YAG>CO2 ⇒power density

Current 　 YAG<CO2 ⇒total power

Summary

-10 -5 0 5 10 15 20 25 30 35 40 45 50 55 60-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4L=3.1 mU

supreshion=5 kV

dFC

=30 mm

Nd-YAG laser produce plasma FC signal.

Current, mA

Time, s

340 mJ 305 mJ 250 mJ 185 mJ 110 mJ

High laser power -> Fasr ions

Currents from YAG laser Plasma

Various laser power

CO2 laserC4+ beamLong pulse

Nd-YAG laserC6+ beamEasy to handle

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

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?

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%