A Study of 150 MeV FFAG Acceralator - Osaka U

FFAGの開発とその応用について

Joe Nakano- KEK FFAG group -

April 5, 2002「中間エネルギービームによる物理」@ RCNP

Contents

• Introduction– Characteristics of FFAG– Applications of FFAG

• PoP　FFAG– The first proton FFAG Accelerator

• 150MeV FFAG– A prototype of the practical machine

• PRISM– FFAG ring as muon phase rotator

• Summary

Introduction – FFAG SynchrotronThe characteristics of FFAG …

• Fixed Field ( cf. Cyclotron)FFAG magnetic Field : B=B0(r0/r)k k>1Satisfying the cardinal condition, “zero -chromaticity”

– High repetition rate – Various acceleration patterns are possible

large beam current, flexibility, low power consumption

• Alternating Gradient Accelerator( cf. Synchrotron）

strong focusing

• Large Horizontal acceptancewide aperture

… Strong focusing accelerator with high duty factor

Introduction - Applications of FFAG

FFAG’s catchphrase…“High current, High repetition rate and High efficiency”

• Medical - Cancer therapy– 3dimensional spot scan method

• Atomic Energy - Accelerator Driven System – High current and efficiency beam, low power consumption and low beam loss

• Physics – Accumulator of secondary beam – Manipulation of the short-lived secondary beam

ex.) PRISM, Neutrino-Factory and Unstable Nuclei• Environmental Hygienics – Sterilizer

– Electron beam or X-ray source for the sanitizing and the sterilizing.

…., etc.

A brief history of FFAG Accelerator　－ ‘PoP FFAG’

~50’s FFAG was proposed by Ohkawa, Symon and Kolomensky.a electron FFAG at MURA project.

“Proton FFAG was difficult.”• Difficulties of designing and manufacturing the large magnet gives

the complex magnetic field• No RF cavity has the large aperture and gives the high gradient

field over a wide-frequency

… Great advancement of technologies in 80’s ~ 90’s • large CPU power to do the calculation and the simulation easily• the invention of a Magnetic Alloy for FFAG RF cavity

1998 PoP (proof of principle) FFAG project, to construct the world first proton FFAG, was started.

PoP FFAG - The first proton FFAG Accelerator in the world

PoP FFAG

1. Basic performance2. Studies of beam dynamics• Acceptance survey• Measurement of betatron

tune with RF knockout• A study of resonance

crossing with fast acceleration

同志社大学　工学部　吉本昌弘

PoP FFAG

T. Adachi, M. Aiba, K. Koba, S. Machida, Y. Mori, R. Muramatsu, A. Muto, C. Ohomori, I. Sakai,Y. Sato,M. Sugaya, A. Takagi, R. Ueno, T. Yokoi, M. Yoshii,

M. Yoshimoto,Y. Yuasa and Joe Nakano - KEK FFAG group -

PoP FFAG

FFAG02 Workshop 2002.02.14(Thu.)

Top View of PoP-FFAG Accelerator

Scale : 1m

0 0.5 1.0

RF cavity

ion sourcetriplet-quadrupolemagnet

steering magnet

solenoid magnet

Faraday cup

turbo molecular pump

cryopump

bump electrode

septum electrode

beam position monitor

movable probe

FFAG magnet

PoP-FFAG parameter table

Particle protonType of magnet radial sector typeNo.of sector 8Field index k=2.5Energy 50keV => 500keVRepitition rate 1kHzMagnetic field

Focus-mag. 0.14 - 0.32 TDefocus-mag. 0.04 - 0.13 T

Radial of closed orbit 0.81 - 1.14mbetatron tune

horizontal 2.17 - 2.22vertical 1.24 - 1.26

RF frequency 0.61 - 1.38MHzRF voltage 1.3 - 3.0kVp

PoP FFAG


Beam Position Monitor (BPM)

In FFAG, beam orbit shifts during the acceleration.

=> BPM must have large horizontal aparture.

inner sideelectrode

outer sideelectrode

oscilloscope PC

proton beam

500mm

100mm

50m

m

horizontal BPM

PoP FFAG


The measurements of the machine parameters.

Basic Performance of PoP FFAG• Betatron tune • Fast acceleration within 1msec• Synchrotron oscillation• Multi turn Injection

PoP FFAG


Betatron Tune (1)

Horizontal beam signal Vertical beam signal

circulating beam signal

FFT spectrum


FFT spectrum

fractional part of betatron tune

µh = 0.199 µv=0.289

revolution freq.

side-bands

for betatron

revolution

freq.

side-bands

for betatron

PoP FFAG


Betatron Tune (2)

0.5

0.4

0.3

0.2

0.1

Fra

ctio

nal

part

of

tune

4.24.03.83.6

F/D ratio in B*L

Horizontal tune (measured) Horizontal tune (calculated) Vertical tune (measured) Vertical tune (calculated)

The vertical betatron tune is adjustable changing F/D ratio !

betatron tune vs F/D ratio

Betatron tune shift as a function of F/D ratio:

- vertical

=> shift !!

- horizontal

=> almost constant !!

PoP FFAG


1050

1000

950

900

850

800

750

po

siti

on

[m

m]

1.00.80.60.40.20.0

time [msec]

measured calculated

Beam Acceleration

The beam is accelerated from 50keV to 500keV within 1msec.

=> The beam orbit shifts from 765mm to 1050mm.

200 µsec/div

500 m

V/d

iv

(a) inner electrode

(b) outer electrode

BPM signals during the accelerationbeam orbit shift

PoP FFAG


Synchrotron Frequency

at 500keV (flat top)

100µsec/div50µsec/div

revolution frequency:

1.379MHz

synchrotron frequency:

18.3kHz

30

25

20

15

10

sync

hrot

ron

freq

. [kH

z]

500400300200100

E_kin [keV]

measured calculated

synchrotron freq. vs Ekin

@flat top


FFT spectrum

The observed synchrotron frequency

agreed with those expected by the

beam simulation.

PoP FFAG

FFAG02 Workshop 2002.02.14(Thu

1050

1000

950

900

850

800

750

posi

tion

[m

m]

1.00.80.60.40.20.0

time [msec]

measured calculated

1000

950

900

850

800

750

700

pos

itio

n [m

m]

1.21.00.80.60.40.2

time [msec]

measured calculated

RF pattern

magnetic field RF pattern

ordinary synchrotron changing with regarding the magnet

FFAG synchrotron constant without regarding the magnet

=> RF pattern can be flexibly designed in FFAG synchrotron !

Vrf = const. ¯

s=const. dr/dt = const. ¯

s=const.

The various acceleration pattern is possible in PoP-FFAG.

PoP FFAG

FFAG02 Workshop 2002.02.14(Thu

Multi-turn Injection System

slow decay time of bump voltage

( decay time >> revolution period )

=> multi-turn injection

The slow decay operation makes the multi-turn injection

in possible.

bunched beam

bump

2.5µsec/Div

Bumpelectrode

Bumpelectrode

central orbit

injection orbit

MovableFaradayCup

Septumelectrode

bump orbit

time

bum

p H

V

PoP FFAG


Multi-turn Injection

1bunch inj. 2bunches inj. 3bunches inj 4bunches inj. 5bunches inj

The beam intensity can be increased with multi-turn injection.

circulating beam

signal

bump signal

PoP FFAG


The Studies of the beam dynamics in the PoP-FFAG.

Large horizontal acceptanceMeasurement of betatron tune with RF knockoutA study of resonance crossing with fast acceleration

PoP FFAG


-200

-100

0

100

200

x' [

mra

d]

-60 -40 -20 0 20 40

x [mm]

10000L mm-mrad

FFAG synchrotron has a large horizontal acceptance.

Horizontal Acceptance

horizontal acceptance @ injection energy

from tracking simulation

PoP FFAG


Septumelectrode

Bumpelectrode

Bumpelectrode

central orbit

injection orbit

MovableFaradayCup

Injection System for Acceptance Survey

fast decay time of bump voltage

( decay time ~ revolution period )

=> working as a fast kicker

At the fast decay operation, the bump works as a fast kicker .

bunched beam

bump

2.5µsec/Div

PoP FFAG


820800780760740720 p

ositi

on [m

m]

180x10-6 1601401201008060

time [µsec]

(e) Vbump=15kV

820800780760740720

(d) Vbump=12kV

820800780760740720

(c) Vbump=9kV

820800780760740720

(b) Vbump=6kV

820800780760740720

(a) Vbump=3kV

Horizontal acceptance survey (1)

The beam oscillations with various betatrom motion at the 2kV no signal !!

=> at the 3kV

the maximum amplitude

=> at the 12kV

the optimum

(obtained with BPM)

PoP FFAG


-200

-100

0

100

200

x' [

mra

d]

-60 -40 -20 0 20 40

x [mm]

bump voltage

3kV 6kV 9kV 12kV 15kV

10000L mmmrad

Horizontal acceptance survey (2)

Horizontal acceptance is about 4000L mm.mrad !

(The limit can be explained by the septum electrode.)

4000L mmmradseptum electrode

PoP FFAG


( = integer)

RF Knockout Resonance & Betatron tune

250keV flat top 250keV flat top after RF knockout

fractional part of betatron tune

§h=0.195 ( 0.199@E_inj )

RF knockout resonance : § §+ = ± ±


FFT spectrum


FFT spectrum

revolution freq. revolution freq.

side-bands

for synchrotron

side-bands

for synchrotronside-bands

for betatron

PoP FFAG


radius

radius

frac

tion

al

part

of

tune

0

º º

¨ = ¨ C

Pole

resonancecrossing

tune=const. tune const.C

In PoP-FFAG1.6x106

1.4

1.2

1.0

0.8

0.6

freq

uenc

y [H

z]

2.0x10-3 1.51.00.50.0

time [sec]

synchronus phase 20Deg 10Deg 4Deg 2Deg

Resonance & Fast Acceleration (1)

accelerating speed can be changed !

In FFAG synchrotron.......

the fast acceleration => the beam can be accelerated

even if the betatron tune crosses the

resonance line during the acceleration !

50keV 500keV

630keV =>710keV => wall

second accelerating

start time

Time [msec]1 20

Freq

uenc

y [M

Hz]

1

1.2

1.4

630keV 以降のRF同期位相を変える

PoP FFAG



¯s=20 Deg ¯

s=10 Deg ¯

s=4 Deg

¯s=2 Deg

the beam was accelerated from 630keV to 710keV

in various accelerating speed !

the time of hitting

the wall

resonance

line !

t h e s e c o n d

accelerated start

time

accelerating speed:

slow => doesn’t cross the resonance line

fast => can cross the resonance line

PoP FFAG



@710keV

stored

@708keV

stored

@705keV

stored

@700keV stored RF off

RF off

RF off

RF off

accelerated

accelerated

accelerated

accelerated

fast acceleration

up to around the resonance!

@resonance !

@wall !

レゾナンス@705keV

チャンバー壁@710keV

@700keV

@708keV

PoP FFAG


Summary

*the measurements of the machine parameters:

- The PoP-FFAG works as designed.

- The proton can be accelerated within 1msec.

- It was ascertaned that

tune is adjustable as a function of F/D ratio,

various acceleration pattern is possible,

and the beam intensity increased with multi-turn injection.

*the studies of the beam dynamics:

- Horizontal acceptance at injection energy is at least 4000L mm-mrad.

- Betatron tunes almost didn’t change between 50keV and 250keV.

- The beam was accelerated even if the betatron tune crosses the resonance.

A Study of 150 MeV FFAG Acceralator - Osaka U

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