a study of 150 mev ffag acceralator - osaka u
TRANSCRIPT
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
FFAG02 Workshop 2002.02.14(Thu.)
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
FFAG02 Workshop 2002.02.14(Thu.)
The measurements of the machine parameters.
Basic Performance of PoP FFAG• Betatron tune • Fast acceleration within 1msec• Synchrotron oscillation• Multi turn Injection
PoP FFAG
FFAG02 Workshop 2002.02.14(Thu.)
Betatron Tune (1)
Horizontal beam signal Vertical beam signal
circulating beam signal
FFT spectrum
circulating beam signal
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
FFAG02 Workshop 2002.02.14(Thu.)
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
FFAG02 Workshop 2002.02.14(Thu.)
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
FFAG02 Workshop 2002.02.14(Thu.)
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
circulating beam signal
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
FFAG02 Workshop 2002.02.14(Thu.)
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
FFAG02 Workshop 2002.02.14(Thu.)
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
FFAG02 Workshop 2002.02.14(Thu.)
-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
FFAG02 Workshop 2002.02.14(Thu.)
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
FFAG02 Workshop 2002.02.14(Thu.)
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
FFAG02 Workshop 2002.02.14(Thu.)
-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
FFAG02 Workshop 2002.02.14(Thu.)
( = 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 : § §+ = ± ±
circulating beam signal
FFT spectrum
circulating beam signal
FFT spectrum
revolution freq. revolution freq.
side-bands
for synchrotron
side-bands
for synchrotronside-bands
for betatron
PoP FFAG
FFAG02 Workshop 2002.02.14(Thu.)
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
FFAG02 Workshop 2002.02.14(Thu.)
Resonance & Fast Acceleration (2)
¯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
FFAG02 Workshop 2002.02.14(Thu.)
Resonance & Fast Acceleration (3)
@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
FFAG02 Workshop 2002.02.14(Thu.)
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.