Improvement of Beam Quality of the JAEA AVF Cyclotron for Heavy-ion Microbeam Formation

Satoshi KURASHIMA

Takasaki Advanced Radiation Research InstituteJapan Atomic Energy Agency (JAEA)

930 AVF Cyclotron

Resonator

MembersMembersCyclotron R & DS. Okumura, W. Yokota, S. Kurashima, N. Miyawaki, T. Nara, I Ishibori, K. Yoshida, H. Kashiwagi, Y. Yuri, T. Yuyama, T. Ishizaka

OperatorsT. Yoshida, K. Akaiwa, S. Ishiro, T. Yoshida, S. Kano, A. Ihara, K. Takano, S. Mochizuki

Microbeam R & DT. Kamiya, M. Oikawa, T. Satoh

Outline1. Introduction

2. Microbeam Formation System

3. Required Developments for High Quality Beam

4. Development of Flat-top (FT) Acceleration System

5. Beam Tuning for Reduction of the Energy Spread

6. Microbeam Formation Experiment

7. Quick Change of Ion Species of Heavy-ion Microbeam

8. Summary

1. IntroductionTIARA Facility

Takasaki Ion Accelerators for Advanced Radiation Application

Ener

gy (M

eV)

0.01

0.1

1

10

100

1000

AVF Cyclotron

Ta nde m Acce lera tor

Ion Implante r

Mas s Num ber (amu )1

Single-e nde d

10 200100

Energy Range Covered by the Four Accelerators

・K110 AVF Cyclotron

・3 MV Tandem Accelerator

・3 MV Single-ended Accelerator

・400 kV Ion Implanter

Ion Beam

RF Amplifier

Deflector

Magnetic ChannelRF Resonator

Flat-topResonator

Dee Electrode

Main Coil GradientCorrector

Phase Probe

Cyclotron Magnet(Side & Lower Yoke)

Specification of the JAEA AVF cyclotron

Kb 110Kf 95

Extraction radius (m) 0.923Max. Average Field (T) 1.64

RF (MHz) 11-22Acceleration Harmonics 1, 2 and 3Span Angle of Dee (deg.) 86

Maximum Dee Voltage (kV) 60Proton Energy (MeV) 10 to 90

Heavy-ion Energy (MeV/n) 2.5 to 27

・K110 AVF Cyclotron

・3 MV Tandem Accelerator

・3 MV Single-ended Accelerator

・400 kV Ion Implanter

Microbeam by a collimation aperture.

Beam size of 5-10 um.A few ions per minute.

10 μ m核

イオンの

ヒット位置

10 μ m10 μ m

Hit position

Cell nucleus

Microbeam by a focusing lens system.

Beam size of 1um.600 ions per minute.

Hyper Nanogan14.5 GHz,Metal Ions by MIVOCSi, Fe, Ru, Au

Octopus6.4 GHz and 14.3 GHz,The oldest ECRIS

operating in the world ?

0

1

2

3

4

5

6

7

8

0 5 10 15 20 25

Energy Spread dE/E = 0.1 %

x_div 0.2 mrady_div 0.2 mradx_div 0.5 mrady_div 0.5 mradx_div 1.0 mrady_div 1.0 mrad

Beam

Size (u

m)

Object Size (um)

Designed line with a demagnification of 1/5

0

1

2

3

4

5

6

7

8

0 5 10 15 20 25

Energy spread dE/E = 0.02 %

x_div 0.2 mrady_div 0.2 mradx_div 0.5 mrady_div 0.5 mradx_div 1.0 mrady_div 1.0 mrad

Beam Size (um)

Object Size (um)

Designed line with a demagnification of 1/5

Estimation of the beam size at the focusing microbeam line calculated by the TRANSPORT code. <x|θδ>=71.3 µm/mrad%、<y|φδ>=103.1 µm/mrad%

Requirement for 1 µm !

Challenging Development for the Cyclotron

Flat-top Acceleration

Micro slits

Divergence defining slits

Quadruplet quadrupole

magnets

Target position

Beam shifter

Beam diagnostic station 1

Beam line mount

Beam scanner

90 deg. bending magnet

C

CD

D

3600

mm

4930

mm

Beam

Beam diagnostic station 2

103 µm/mrad%<y|φδ>

71 µm/mrad%<x|θδ>Chromatic Aberration

1/5<y|y0>

1/5<x|x0>Magnification Factor

103 µm/mrad%<y|φδ>

71 µm/mrad%<x|θδ>Chromatic Aberration

1/5<y|y0>

1/5<x|x0>Magnification Factor

Beam optics

5 um

1 um

2. Microbeam Formation System

3. Required Developments for High Quality Beam

Requirement Target

5th Harmonic Flat-top Acceleration System 55 - 110 MHz

Stability of cyclotron magnetic field B/B ≤ 0.002 %

Control of Beam phase width ∆φ ≤ 10 deg. RF

Stability of acceleration voltage V/V ≤ 0.02 % for fundamentalV/V ≤ 0.1 % for harmonic

High performance beam buncher high compression of injected beamwithin 10 deg. RF

4. Development of Flat-top Acceleration SystemTasks・Wide range of the resonance frequency

from 55 to 110 MHz (f1: 11 to 22 MHz).・Compactness of the resonator due to the limited space for installing.

・Low power consumption at the resonator.

Goal:Accelerate all ion beams

available at our facility with the FT system

Relation between the resonant frequency and the parameters in the actual test.

C5

Dee VoltagePick up

L5

。

。

Power inlet for the

fifth-harmonics（Capacitive coupling)

Amplifier for the fundamentals(Inductive coupling)

C5 : Position of the coupling capacitor

L5 : Position of the movable short

Dee Electrode

Movable short of f1

Flat-top resonator

Main resonator

Acce

leratio

n Gap

C5

Dee VoltagePick up

L5

。

。

Power inlet for the

fifth-harmonics（Capacitive coupling)

Amplifier for the fundamentals(Inductive coupling)

C5 : Position of the coupling capacitor

L5 : Position of the movable short

Dee Electrode

Movable short of f1

Flat-top resonator

Main resonator

Acce

leratio

n Gap

Outline of the RF Resonator (including FT resonator)

100

150

200

250

300

350

400

0

5

10

15

20

25

30

35

40

50 60 70 80 90 100 110

L5 C5

Posi

tion

of L

5 (m

m)

Gap of C

5 (mm

)

5th-harmonic Frequency (MHz)

FT resonator installed to the main resonator

“Flat-top” waveform observed at the dee voltage Pick-up in the power test. The fundamental frequency and the voltage are 17.475 MHz and 25 kV, respectively.

The required region of the 5th-harmonic frequency is fully covered by the FT resonator.

RF Amplifier

Main Coil

Flat-top Cavity

Main Resonator

RF Amplifier

Main Coil

Flat-top Cavity

Main Resonator

Power Test

Preparation for the FT acceleration

0

0.2

0.4

0.6

0.8

1

1.2

0 200 400 600 800 1000

59.2 MHz80.7 MHz95.9 MHz105.2 MHz

Dee

Vol

tage

(a.u

.)

Diatance from the Tip of the Dee (mm)

14

16

18

20

22

24

26

28

30

10 12 14 16 18 20 22

h = 1h = 2h = 3

Vol

tage

Rat

io V

1/V

5

Frequency (MHz)

Key points

・Isochronous field tuning within ±5deg.

・Precise control of the beam phase width by phase slits.

・fine-tuning of trim coil current at the center region.

・Estimation of the optimum voltage ratio of the fifth-harmonic frequency to the fundamental one.

Deflector electrode

Deflector

probeMoving direct

Beambunch

probe head

The turn separation can be seen by the scanning current probe with thin probe head when beam width is reduced by the FT acceleration.

0

20

40

60

80

100

0 10 20 30 40 50 60 70

Flat-top ON

Bea

m C

urre

nt (n

A)

Probe Position (mm)

V1 = 32.7 kVV5 = 1.2 kV

0

0.05

0.1

0.15

0.2

0.25

0.3

0 10 20 30 40 50 60 70

Flat-top Off

Bea

m C

urre

nt (u

A)

Probe Position (mm)

V1 = 36.502 kVV5 = 0.0 kVN = 265 (h=2)

Ion Beam: 260 MeV 20Ne7+

5. Beam Tuning for Reduction of the Energy Spreadnio

Energy Spread MeasurementThe energy spread ∆E/E was measured by analyzing magnet with a micro-slit system.

0

50

100

150

200

250

300

350

400

-2 -1.5 -1 -0.5 0 0.5 1 1.5 2

Counts

TS2_POS.(mm)

dX_FWHM = 1.665 * m4 = 1.07 mmdE/E = dX_FWHM * 0.1%/1mm = 0.107 %

0

50

100

150

200

250

-1 -0.5 0 0.5 1 1.5 2Count

sTS2_POS.(mm)

dX_FWHM = 1.665 * m4 = 0.510 mmdE/E = dX_FWHM * 0.1%/1mm = 0.0510 %

Flat-top OFF (multi-turn extraction) Flat-top ON (single-turn extraction)

∆E/E = 0.1 %∆E/E = 0.05 %

The energy spread of the beam has been reduced with the FT acceleration !

Multi-peakSingle-peak !

6. Heavy-ion Microbeam Formation

10 µm

(b)

SEM Image

10 µm

(b)

SEM Image

10 µm

(a)

Optical Microscope Image

5 µm

5 x 5 Single-ion Hit Pattern

1 um microbeam

7. Quick Change of Ion Species of Heavy-ionMicrobeam

Wide range of linear energy transfer (LET) is required for research in biotechnology and materials science.

M Q M/Q η(M/Q)/(M/Q)

B 11 4 2.75178 -3.633E-02

N 14 5 2.80007 -1.942E-02

Ne 20 7 2.85551 0.000E+00

Si 28 10 2.79714 -2.044E-02

Ar 40 14 2.85391 -5.603E-04

Fe 56 20 2.7962 -2.077E-02

Cocktail beam acceleration

101

102

103

104

0 5 10 15 20 25 30

BNNeSiArFe

LET

(keV

/µm

)

Energy (MeV/n)

100 to 2000 keV/umin water.

260 MeV Ne

Cocktail Microbeam Formation

Cocktail Microbeam Formation

0

0.1

0.2

0.3

0.4

0.5

0

10

20

30

40

50

40 45 50 55 60 65

Ne

ArB

eam

Cur

rent

of N

e (u

A) B

eam C

urrent of Ar (nA)

Probe Position (mm)SEM Image by Ne SEM Image by Ar

Quick change within 30 minutes.(Usually, 6 hours)

Very powerful tool in microbeam research!

・Optimization of ECRIS for each ion.

・Fine-tuning of trim coil of center region and harmonic coils.

Summary

1. The FT acceleration system with fifth-harmonic frequency improved the beam quality and extraction efficiency.

2. Heavy-ion microbeam with a spot size and hitting accuracy of 1 um was successfully formed.

3. Ion species of the microbeam was quickly changed by the cocktail beam technique within 30 minute.

Appendix. Beam Transmission

0

0.2

0.4

0.6

0.8

1

1.2

IS1 IS3 IS5 Inf Mag 0mm Mag 80mm TS1

Spot of Measurement

Tran

smis

sion

H 70 MeV (h=1)Ne 260 MeV (h=2)Ar 150 MeV (h=3)FT Ne 260 MeV

Injection Line

Deflector

Sinusoidal + Saw-tooth buncher1.4 times beam intensity

Thank you very muchfor your attention !

Thank you very muchThank you very muchfor your attention !for your attention !