京大炉におけるビーム利用のための次期中性子源検討 2

2014.1.17

FFAG加速器ビーム増強!現状と今度の展開

京大原子炉　石　禎浩　!森　義治!

　　　　　　上杉智教!　　　　　　栗山靖敏!　　　　　　阪本雅昭!

目次1.FFAGの特徴

2.FFAG加速器システム開発の経緯

3.現在の利用状況

4.ビームスタディー結果

5.ビーム増強

6.FFAG加速器の今後の展開（加速器中性子源）

7.まとめ

FFAG: Fixed Field Alternating Gradient

固定磁場（時間変化しない） サイクロトロン的であるが、軌道の広がりは小さい

速い加速が可能 磁場とRFの同期が不要

高繰り返しが可能 一度に加速する粒子数を減らす事が可能 空間電荷効果やその他の不安定性を軽減

交互勾配ー強収束 ( 6D-focusing i.e. x, px, y, py, s, ps )

シンクロトロン的 コンパクトサイズの電磁石 高エネルギーでの収束が安定 さまざまな RF gymnasticsが可能

Bunching, Stacking etc.

B(r) = B(r0)�

r

r0

�k

School,London,June 24-28, 20002

Cyclotron*isochronous

Synchrotron*const. closed orbit(varying mag. field)

FFAG*varying closed orbit(const. mag. field)

B

f

Bf

B

faccelerating time accelerating time accelerating time

High In

tensity

High En

ergy

High En

ergy &

High In

tensity

Qh3.5 3.55 3.6 3.65 3.7 3.75 3.8 3.85 3.9 3.95 4

Qv

1

1.05

1.1

1.15

1.2

1.25

1.3

1.35

1.4

1.45

1.5

tune diagramtune diagramMain ring operating point

11MeV

37MeV

FFAG – KUCA ADS system schematic diagram ( original ) 2008 - 2010

Ion source

Injector （ion-beta)

Booster

Main ring

Critical Assembly (KUCA)

125 keV 1.5 MeV 11 MeV 100 MeV

TargetH+

FFAG – KUCA ADS system schematic diagram ( upgraded ) from 2011

Ion source

Main ring

Critical Assembly (KUCA)

30 keV 11 MeV 100 MeV

TargetH-

LINACH-

H+charge

exchange

FFAG – KUCA ADS system schematic diagram ( upgraded ) from 2012

Ion source

Main ring

Critical Assembly (KUCA)

30 keV 11 MeV 150 MeV

TargetH-

LINACH-

H+charge

exchange 100 MeV

Irradiation chamber

Summary of Machine Time ( FY 2012 )

Beam study 106 hr

Irrad. exp. 274 hr

ADS. exp. 77 hr

Total 457 hr

unit May. - Oct. Nov. Dec. Jan. Feb. Mar. Apr.

Beam Study hr 77 21 5 3 0 0 0ADS Exp. hr 0 0 28 0 49 0 0Irrad. Exp. hr 0 9 0 14 24 73 153Ext. Energy MeV 100/150 150 100 150 100 150 150

KURRI FFAGのユーザー!

• KUCAでのADS 実験 100MeV / 1nA

•材料照射・放射化学 150MeV / 1nA ( ~10nA max )

• BNCT基礎研究のための生物ハイブリッド照射 100MeV / 1nAを計画中

KUCAでのADS実験

Require ultra low intensity ( but quite stable ) beams to avoid piling up of neutron counting. e.g. 5pA - 10pA 1/1000 ordinary intensity

動特性測定

Fig. Core configuration of 235U-loaded cores (100 MeV protons)

(Protons: 100 MeV, 0.5 nA, 100 ns, 20 Hz)

Fig. Neutron spectra (W vs. W+Be)

Fig. In reaction rates (W, W+Be and Pb-Bi)

放射化を用いた中性子スペクトル測定

1 - 2時間ビームトリップが許されない

Beam Line and Chamber for Irradiation Experiments

150 MeV陽子ビームラインに設置された照射チェンバー。冷凍機と引っぱり試験機が装備され陽子ビーム照射中での測定が可能。

陽電子寿命測定、電気抵抗測定において格子欠陥の生成分布に計算との違いがみられた。電気抵抗測定の追実験により確認を実施中。

100 MeV陽子ビームの照射（240nA-h）により表面ぬれ性の改善 がみられた.

!

Biological experiment of irradiation to mice

Upgrade of control system

The control system of FFAG accelerator at KURRI has been upgraded with EPICS under collaboration with the KEK accelerator control group. Some parts of the system are using LabView on Windows XP, but they are going to be replaced by EPICS based program for more reliable and secure system.

View of Control Room

The FFAG accelerator control room. Only one person can operate whole system. There are two Macs link to Windows and LINUX PCs which command PLCs to control accelerator devices.

Beam diagnostics system upgrade

linac

FFAG-ERIT ring

FFAG main ring

charge exchange foil

H- ion source

H- injectionBeam injection to the main ring

0

1

2

3

4

5

6

0 1 2 3 4 5 6

87mm

0.5°

H-

H+

main magnet

F-mag D-mag

D-mag

charge stripping foil

linac

FFAG-ERIT ring

FFAG main ring

charge exchange foil

H- ion source

H- injectionBeam injection to the main ring

0

1

2

3

4

5

6

0 1 2 3 4 5 6

87mm

0.5°

H-

H+

main magnet

F-mag D-mag

D-mag

charge stripping foil

CT

CTs installed in vacuum

up stream L = 20mH tau = .4ms

down stream L= 50mH tau = 1ms

-1

0

1

2

3

4

5

6

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

"fort.52" using ($1/1000):3"fort.52" using ($1/1000):5

"fort.53" using ($1/1000):(-$7)

foil

βx

path length ( m )

βy

Bzβx (

m ),

βy

( m ),

Bz (

T )

injection point

matching point

Beta functions calculated from backward tracking in the main ring

linac

FFAG-ERIT ring

FFAG main ring

charge exchange foil

H- ion source

H- injectionBeam injection to the main ring

0

1

2

3

4

5

6

0 1 2 3 4 5 6

87mm

0.5°

H-

H+

main magnet

F-mag D-mag

D-mag

charge stripping foil

linac

FFAG-ERIT ring

FFAG main ring

charge exchange foil

H- ion source

H- injectionBeam injection to the main ring

0

1

2

3

4

5

6

0 1 2 3 4 5 6

87mm

0.5°

H-

H+

main magnet

F-mag D-mag

D-mag

charge stripping foil

Faraday cup

secondary electron suppresssion B by permanent magnet

Faraday cup

linac

FFAG-ERIT ring

FFAG main ring

charge exchange foil

H- ion source

H- injectionBeam injection to the main ring

0

1

2

3

4

5

6

0 1 2 3 4 5 6

87mm

0.5°

H-

H+

main magnet

F-mag D-mag

D-mag

charge stripping foil

linac

FFAG-ERIT ring

FFAG main ring

charge exchange foil

H- ion source

H- injectionBeam injection to the main ring

0

1

2

3

4

5

6

0 1 2 3 4 5 6

87mm

0.5°

H-

H+

main magnet

F-mag D-mag

D-mag

charge stripping foil

bunch monitor& Faraday cup

H- beam

Main magnet leakage field can be used for secondary electron

suppressor.

Added a Faraday cup for calibration of the

bunch monitor and to estimate transparency of the first half cell of

the ring.

Iav =�

VFCdt

50� 20

Faraday cup

Faraday cup

bunch monitor

Long tailed decay in bunch monitor signal seems to be back scatter of the secondary electron ( suppression is not perfect ) → RC constant R = 1MΩ ( input impedance of the amp) C = 171pF

faraday cup signal is read thru 50Ω at 20Hz rep. rate　

Beam injection to the main ring

0

1

2

3

4

5

6

0 1 2 3 4 5 6

87mm

0.5°

H-

H+

main magnet

F-mag D-magD-mag

charge stripping foil6

0.10 μA

0.10 μA

The aperture of the up stream Faraday cup might not be sufficient.

Results from beam studies in this summer

Beam signal from the bunch monitort ( us )

outp

ut v

olta

ge (

V)

Bunch monitor signal is amplified by preamp ( x 200 Zin = 1MΩ). In the Straight section S7, the monitor can detect both H- and H+ beam.

Injection Studies in ADSR-FFAG Ring

Survival ratio vs turn number

From the bunch signal in previous slide, survival ratio for each turn is calculated as

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0 5 10 15 20 25 30Turn number

Su

rviv

al ra

tio

Survival ratio = Bunch Area of i-th turnBunch Area of 0-th turn

Emittance growth due to the multiple scattering by charge stripping foil

brand-new foil 20 ug/cm2

after 1.5 years...

ビーム増強の手段• 加速電圧の増強（空洞台数：1台→2台）!

–捕獲・加速効率アップ!–繰り返し（ 20Hz → 100 - 200 Hz )アップ!–共鳴によるビームロスの低減!

• 極薄フォイルの開発（ 20ug/mm2 → 10ug/mm2 )!–ビームとフォイルの衝突によるエミッタンス増大を抑制!–アニール等による強度アップ!

• COD補正（ビーム診断系・補正電源追加）!–アパーチャーの拡大!–共鳴によるビームロスの低減!

• ライナックエネルギー増強!• 空間電荷効果の緩和!!!

PETAL CORE CAVITY1. New installation of another rf cavity to obtain higher accelerating voltage. ( 4kV → 2 x 4 kV )!2. Reuse of damaged circular core for wide aperture cavities.!3. A low-power measurements has been done.!4. With this new cavity, rep. rate 100 Hz can be accomplished.!

Innovation research lab.

The KURRI-FFAG accelerator complex has been constructed in the innovation research lab. ; connected to KUCA to deliver the high energy proton beam.

PETAL CORE CAVITY1. New installation of another rf cavity to obtain higher accelerating voltage. ( 4kV → 2 x 4 kV )!2. Reuse of damaged circular core for wide aperture cavities.!3. A low-power measurements has been done.!4. With this new cavity, rep. rate 100 Hz can be accomplished.!

COD correction by the correction dipoles

-0.08

-0.06

-0.04

-0.02

0

0.02

0.04

0.06

0.08

0 50 100 150 200 250 300 350 400

'cod.xy' u 2:3'cod.xy' u 2:(-$5/100)

-0.08

-0.06

-0.04

-0.02

0

0.02

0.04

0.06

0.08

0 50 100 150 200 250 300 350 400

'cod.xy' u 2:3'cod.xy' u 2:(-$5/100)

-0.08

-0.06

-0.04

-0.02

0

0.02

0.04

0.06

0.08

0 50 100 150 200 250 300 350 400

'cod.xy' u 2:3'cod.xy' u 2:(-$5/100)

!"#$%&'()*+

,M-./)FT-3M+01234

,5005600!

,78090'8

,:;<=>?

,COD@A.B>

C0KEKD34EFGHIJK

Friday, May 18, 2012

!"

Friday, May 18, 2012

measured point R1

measured point R2

cavity i.e. COD source

空間電荷効果によるチューンシフト

運転繰り返し：100 ~ 200 Hz!平均ビーム強度：5uA

加速器中性子源案（Linacベース）

30MeV linac

Neutron target

proton beam E = 30 MeV

I = 1 mA～5 mA duty 10 % ( max )

空間電荷効果の緩和

proton beam E = 150 MeV

I = 1uA→数倍 short pulse ( ~ 40ns )

Neutron target

150 MeV FFAG main ring

3.5MeV RFQ

7MeV DTL

11MeV DTL

700 MeV FFAG

time

beam

int

ensi

ty

at injection energy

at extraction energy

extracted beam

rep. rate : e.g. 100Hz

rf stacking

rep. rate : e.g. 10Hz

RF stacking at the extraction energySome users desire low spill rate ( ∼10 Hz ) for the experiments e.g. neutron radiography using TOF which needs to get rid of contamination from the pulse of different timing. !FFAG rings can provide long interval pulse for users, while the machine operation itself is kept at high repetition rate by using rf stacking after acceleration[1]. !This scheme reduces space charge effects at injection energy.

[1] S.Machida,“RFStackingatExtractionMomentum”,FFAG Workshop 2003,October 13-17, 2003 at BNL, http://www.cap.bnl.gov/mumu/conf/ffag- 031013/Machida2.pdf.

BEAM STACKING FOR HIGH INTENSITY PULSED PROTON BEAMWITH FFAG

Y. Ishi∗, J.-B. Lagrange, T. Uesugi, Y. Kuriyama, Y. Mori,Kyoto University Research Reactor Institute, Kumatori, Japan

AbstractThe reuirement of extremely high intensity pulsed pro-

ton beam with low spill rate has apeared from users in thefield of spallation neutron source. To realize the beam sat-isfies this condition, beam stacking at extraction orbit inFFAG ring has been considered. Feasibility studies of rfstacking using the KURRI FFAG main ring are under con-sideration. Prior to these studies, beam simulations havebeen done.

INTRODUCTIONAs a candidate of high intensity proton driver of spalla-

tion neutron source, potentially, an FFAG accelerator hasadvantage in terms of high repetition rate such as 100 -1000 Hz. However, some users desire low spill rate (∼10 Hz ) for the experiments e.g. neutron radiographyusing TOF which needs to get rid of contamination fromthe pulse of different timing. FFAG rings can provide longinterval pulse for users, while the machine operation it-self is kept at high repetition rate by using rf stacking afteracceleration[1]. This scheme reduces space charge effectsat injection energy. For the machine, charge in each bunchcan be reduced by high repetition rate. In the high energyregion i.e. outer radius, accelerated beams are stacked andcirculating around until necessary amount of charge is ac-cumulated. For users, highly compressed beam with longtime interval can be delivered. Schematic diagram of thismethos is shown in Fig. 1.

time

beam intensity

at injection energy

at extraction energy

extracted beam

rep. rate : e.g. 100Hz

rf stacking

rep. rate : e.g. 10Hz

Figure 1: Schematic diagram of rf stacking at extractionenergy.

∗ ishi@.rri.kyoto-u.ac.jp

SIMULATION STUDIES OF RFSTACKING

To confirm the feasibility of rf stacking at extraction en-ergy, simulation studies have been carried out. The modelmachine used in this study simulates the KURRI FFAGmain ring[2], in which the real beam studies are planned.The machine parameters are summarized in Table 1.

Table 1: Machine Parameters used in the Simulationsfield index k 7.7kinetic energy T 11 - 150 [MeV]momentum p 144 - 551 [MeV/c]circumference C 28.8 - 33.6 [m]momentum compaction factor α 0.115rf voltage Vrf 8 [MV]rf frequency frf 1.6 - 4.4 [MHz]harmonic number h 1

RF Acceleration ScenarioBeam accelerations have been simulated according to the

scenario shown in Figs. 2, 3 and 4. In the real machineoperation, we use similar scenarios in which synchronousphase φs and rf voltage are fixed at 30 degree and 4 kV re-spectively during all the acceleration period. On the otherhand, in the scenario used in this simulation study, φs isdropped off linearly from 30 to zero degree when the en-ergy of the beam is between 145 and 150 MeV for soft-landing. The rf voltage is also reduced in this region so thatthe bucket area AB is constant in order to make momentumspread small at the end of acceleration. The bucket area isthe phase-space area enclosed by the separatrix, i.e.

AB = 16

!eVrf

2πβ2E|h|ηα(φs)β2E

ω0, (1)

where E is the total energy of the beam particle, η is theslippage factor, ω0 is the revolution frequency and α(φs) isthe ratio of the bucket area to the stationary bucket. Herewe use approximated expression of α(φs), i.e.

α(φs) =1− sin(φs)

1 + sin(φs). (2)

Machine parameters used in the simulation

0

5

10

15

20

25

30

35

40

0 2 4 6 8 10 12 0

2

4

6

8

10

q s (d

eg )

Vrf

( kV

)

time ( ms )

qsRF voltage

In the real machine operation, we use similar scenarios in which synchronous phase φs and rf voltage are fixed at 30 degree and 4 kV respectively during all the acceleration period. On the other hand, in the scenario used in this simulation study, φs is dropped off linearly from 30 to zero degree when the energy of the beam is between 145 and 150 MeV for soft- landing. The rf voltage is also reduced in this region so that the bucket area is constant in order to make momentum spread small at the end of acceleration.

0

20

40

60

80

100

120

140

160

0 2 4 6 8 10 12 1.5

2

2.5

3

3.5

4

4.5

5

T ( M

eV )

f rev (

MH

z )

time ( ms )

kinetic energyfrev

RF Scenario

0.09

0.1

0.11

0.12

0.13

0.14

0.15

0 2 4 6 8 10 12

buke

t are

a ( e

Vs )

time ( ms )

bucket area

Vrf

φs

kinetic energy

f rev

bucket area

536

538

540

542

544

546

548

550

552

554

-4 -3 -2 -1 0 1 2 3 4

p ( M

ev/c

)

rf phase

536

538

540

542

544

546

548

550

552

554

-4 -3 -2 -1 0 1 2 3 4

p ( M

ev/c

)

rf phase

536

538

540

542

544

546

548

550

552

554

-4 -3 -2 -1 0 1 2 3 4

p ( M

ev/c

)

rf phase

536

538

540

542

544

546

548

550

552

554

-4 -3 -2 -1 0 1 2 3 4

p ( M

ev/c

)

rf phase

0

50

100

150

200

250

300

-2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5

# of

par

ticle

s

dp/p (%)

0

50

100

150

200

250

300

-2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5

# of

par

ticle

s

dp/p (%)

0

50

100

150

200

250

300

-2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5

# of

par

ticle

s

dp/p (%)

0

50

100

150

200

250

300

350

400

450

-2.5 -2 -1.5 -1 -0.5 0 0.5 1 1.5

# of

par

ticle

s

dp/p (%)

1st batch

2nd batch

5th batch

10th batch

Stacking processes are simulated using 1 000 test particles for each acceleration batch.After first ac- celeration, full width of momentum spread is about 0.5%, the final momentum spread after 10 stacks is 2.5% of full width.

w/ soft-landing

0

50

100

150

200

250

300

350

400

450

-5 -4 -3 -2 -1 0 1 2

# of

par

ticle

s

dp/p (%)

0

50

100

150

200

250

300

350

400

450

-5 -4 -3 -2 -1 0 1 2

# of

par

ticle

s

dp/p (%)

0

50

100

150

200

250

300

350

400

450

-5 -4 -3 -2 -1 0 1 2

# of

par

ticle

s

dp/p (%)

520

525

530

535

540

545

550

555

560

565

-1 -0.5 0 0.5 1 1.5 2 2.5 3

p ( M

ev/c

)

rf phase

520

525

530

535

540

545

550

555

560

565

-4 -3 -2 -1 0 1 2 3 4

p ( M

ev/c

)

rf phase

520

525

530

535

540

545

550

555

560

565

-4 -3 -2 -1 0 1 2 3 4

p ( M

ev/c

)

rf phase

w/ soft-landing

1st batch

5th batch

10th batch

Without soft-landing the final momentum spread after 10 stacks is 5% of full width i.e. twice as large as with soft-landing.

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

1.5 2 2.5 3 3.5 4

dp/p

( %

)

frev ( MHz )

8kV 30deg4kV 30deg8kV 40deg

Check if the acceleration bucket affects the stacked beams coasting around the extraction orbit. Generate zero emittance test beam (100 MeV ) with Δp/p = 0 and uniformly distributed in the rf phase. Check if momentum spread is blowing up, while the accelerating bucket is coming up. There are two steps around 2 MHz and 4 MHz in each case. Step around 4 MHz : direct disturbance of the bucket. Step around 2 MHz : f_drive = 1/2 f_rev(stack) It seems that coasting beam can be affected when the accelerating bucket is passing through the frequency which is half of revolution frequency of the coasting beam.

Perturbation from the rf bucket to the coasting beam

まとめ • 2012年度はビーム運転時間の約3/4をユーザに供給した。この期間は半年以上にわたる。

•ユーザによる成果報告が多数なさる一方、安定したビーム供給が要求されている。

•ビーム診断系および制御系の更新を継続中である。

•先に上げた４つの方法を念頭にビーム増強を推進中である。

•平均ビーム強度5uAをめざす。

Thank you for your attention!