NonNon--Scaling FFAG Scaling FFAG
CyclotronsCyclotrons
Alessandro G RuggieroAlessandro G Ruggiero
Brookhaven National LaboratoryBrookhaven National Laboratory
Hadron Beam Therapy of CancerHadron Beam Therapy of Cancer
Erice, Sicily, Italy Erice, Sicily, Italy ------ April 24April 24--May 1, 2009May 1, 2009
The title of my presentation was chosen for me as
Non-Scaling FFAG Cyclotrons
FFAG stands for Fixed-Field Alternating-Gradient accelerator.
Cyclotrons were conceived about 70-80 years ago. They are Fixed-Field
accelerators with the good property that the guiding and focusing magnetic
field does not need to vary during the acceleration cycle, simplifying thus the
concept and the construction.
At the start they were Weak Focusing devices. But later when the principle of
Alternating-Gradient that allows Strong Focusing was discovered, they truly
became FFAG accelerators. There is thus the (general) consensus that, to
avoid semantic, Cyclotron and FFAG refer to the same identical device. In
reality there are some major differences like the Momentum Range…
The Alternating Focusing is provided either by Radial-Shaped sectors or by the
alternating edges of Spiral-Shaped elements.
Alessandro G. Ruggiero 2Erice – Sicily April 29, 2009
Fixed-Field Accelerators
Cyclotrons and Microtrons are FF Accelerators.
Originally they were conceived as Weak Focusing with
Constant Field Profile. That is they were not AG
RF
RF
Alessandro G. Ruggiero 3Erice – Sicily April 29, 2009
Constant RF
Fixed-Field Alternating-Gradient
• Spiral Sector FFAG
• Radial Sector FFAG
• FFAG Betatrons
• FFAG Synchrotrons
– Acceleration in Phase (Protons)
– Gutter Acceleration (Muons)
Reverse Bend
Edge Focusing
D F
FD
Alessandro G. Ruggiero 4Erice – Sicily April 29, 2009
There are two types of FFAG Cyclotrons according to their magnet lattice that
provides bending and focusing at the same time:
Scaling Lattice, and
Non-Scaling Lattice
Both were already known half-a-century ago when the first prototypes were built at
MURA. At that time Scaling Lattice was adopted, and even recently few Scaling
FFAG were built in Japan (KEK, Kyoto Univ.).
Scaling FFAG have the good feature that, by arranging the bending/focusing magnet
sequence with a proper profile, it is possible to cancel (to first order) the variation of
betatron oscillation frequency (tune) with beam momentum (Chromaticity). In this
mode it is possible to accelerate at constant betatron tunes, avoiding thus (in principle)
the crossing of major resonances; though the dependence of the betatron tunes with
betatron oscillation amplitude could still be appreciable.
But the required field profile for a Scaling Lattice is achieved with a considerable large
magnet size (aperture), and a high bending field. All existing/operating FFAG in the
world have a Scaling Lattice.
Alessandro G. Ruggiero 5Erice – Sicily April 29, 2009
Scaling FFAG Field Profile: B = ± B0 (r0 / r)k
Non-Scaling FFAG Field Profile: B = ± B0 ( 1 + g r) Linear
FFAG Ring is a continuous unbroken sequence of Periods
FODODoubletsTripletsPimplets (G. Rees)….
Non-Scaling F D F
Scaling D F D
Triplet provides strongest Focusing with minimum Dispersion.It allows most compact MagnetsAlessandro G. Ruggiero 6Erice – Sicily April 29, 2009
Design of a Proton NS-FFAG Accelerator
� Sector Magnets. Parallel Entrance and Exit planes
� Trajectory is made of arcs of circle only on the Reference Orbit
� Sharp Magnet Edges
A. G. Ruggiero “Design Criteria of a Proton FFAG Accelerator”, Proc. of the Intern.
Workshop on FFAG Accelerators, Oct. 13-16, 2004, KEK, Tsukuba, Japan, pages 47-
63
� No Entrance and Exit Angles for Reference Orbit
� It minimizes Magnet Width
� It Allows more Drift between Triplets
F FD
Extraction Trajectory
Injection Trajectory
Alessandro G. Ruggiero 7Erice – Sicily April 29, 2009
Photo of ERIT - taken by A.G. Ruggiero on Nov. 7, 2007 at KURRI
Alessandro G. Ruggiero 8Erice – Sicily April 29, 2009
Boron Neutron Capture Therapy
Because of the lattice simplicity, the smaller magnet size, compactness, and the expectation
of a lower construction cost, Non-Scaling FFAG accelerators have recently received closer
scrutiny, and have been proposed for a variety of applications (Neutrino Factories, Muon
Colliders, Proton and Heavy Ion Drivers, …). Several feasibility studies were done, and
specific proposals were written; nevertheless the study remained mostly academic. There
was concerns about the beam stability and survival in the presence of multiple crossings of
low-order resonances. Thus there are not yet operating Non-Scaling FFAG Cyclotrons,
with the exception of a demonstration device scaled-down in energy and size using
electrons:
EMMA (Electron Model for Muon Acceleration, or
Electron Model for Multiple Application)
EMMA has two main goals:
Experiment with Multiple-Resonance Crossing
Demonstration of Fast Acceleration
The hope is that if the acceleration rate is large enough, when the beam crosses a major resonance, the
resulting growth and loss are kept to a minimum.
Alessandro G. Ruggiero 9Erice – Sicily April 29, 2009
Electrons: 10 – 20 MeV C = 16.65 m 42 periods
Alessandro G. Ruggiero 10Erice – Sicily April 29, 2009
Alessandro G. Ruggiero 11Erice – Sicily April 29, 2009
The 10-MeV Proton Storage Ring for AI
Neutron Beam
Foil
MCS & ELS35-kV 10-mA Ion Source
2 MeV RFQ
2-10 MeV DTLInj. Kicker
Extr. Kicker
Circumference 10 m Kinetic Energy 10 MeV Circulating Protons 1010
(7.2 mA)
Beam Dump
200-300 kVolt 54 MHz RF Cavity
Magnets
p-Beam circulating in 12 bunches
N Spot Size 20-40 mm N Divergence 20-40 mrad N Prod. Rate 2.7 1012 /s
… Space Charge Limit at 10 12 circulating Protons …
Overall Dimensions 5m x 10m
Alessandro G. Ruggiero 12Erice – Sicily April 29, 2009
Dejan Trbojevic
Alessandro G. Ruggiero 13Erice – Sicily April 29, 2009
Dejan Trbojevic and G. Rees
Alessandro G. Ruggiero 14Erice – Sicily April 29, 2009
Non-Scaling FFAG accelerators have of course also been proposed for
medical applications, namely Cancer Hadron Therapy, the topic of this
Workshop. There are two initiatives that I am aware of:
Work resulting from the collaboration Keil-Sessler-Trbojevic (KST), and
PAMELA in United Kingdom (see next Talk)
I like to report here about the KST study. This is at the stage of a feasibility
study with no obvious (to me) outcome (though Sessler may say something
about this). PAMELA project is already at the proposal stage (?) and ready
for funding (?) depending on the result of the EMMA experiment.
The goal of the KST approach is to provide two beams:
Protons at 250 MeV, and
Ions of Carbon at 400 MeV/u
Alessandro G. Ruggiero 15Erice – Sicily April 29, 2009
KST
Alessandro G. Ruggiero 16Erice – Sicily April 29, 2009
KST
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KST
Alessandro G. Ruggiero 18Erice – Sicily April 29, 2009
KST
Alessandro G. Ruggiero 19Erice – Sicily April 29, 2009
KST
Alessandro G. Ruggiero 20Erice – Sicily April 29, 2009
Alessandro G. Ruggiero Erice – Sicily April 29, 2009 21
I
Iron yoke and coil flux density (top), 4T
magnet inside LiHe vessel
2.0 m
straight
5.5 –
6.9 m
12C 6+
Flattening the Tune: NS Non Linear FFAGAdjusted Field Profile (AGR, G. Rees)
Carol Johnstone
KST
Alessandro G. Ruggiero 22Erice – Sicily April 29, 2009
Acceleration of charged particles in a circular accelerator requires the following condition between
the revolution frequency f and the radio-frequency (rf) frf to be satisfied
frf = h f f = ββββ c / C (1)
where h, the harmonic number, is a positive integer. In the case of low-energy protons or heavy-ions the revolution frequency f varies during the acceleration cycle. If the harmonic number h is
kept at a constant value then the radio-frequency frf has to vary accordingly. That can be
accomplished with the use, for example, of ferrite-tuned rf cavities. This method lengthens
considerably the acceleration period because of the limitation on the peak rf voltage that can be
achieved with ferrite.
Faster acceleration can be obtained with higher radio-frequency and, eventually, the use of
superconducting rf cavities that can be operated only at constant frequency. In this case, the
harmonic number h should be allowed to vary also to compensate for the variation of the revolution
frequency f so to maintain frf constant during the acceleration cycle. Nevertheless, the harmonic
number h, being a positive integer, cannot vary continuously, but rather jump from an integer value
to another integer value. This method is called Harmonic Number Jump
(A. G. Ruggiero, Phys. Rev. ST-A&B 9, 100101 (2006) ).
Consider a single rf cavity located in one spot of the accelerator ring. The acceleration cycle is a
two-step process: (1) an energy kick at the cavity location, (2) the ring circumference that takes the
particle back to the cavity. The HNJ method requires that the energy gain ∆En during the n-th traversal of the cavity is adjusted to cause a change in the travel period Tn between consecutive
crossings of the cavity so that the particle is pushed forward or back exactly by ∆h rf harmonics and appears in an exactly identical rf bucket ahead or trailing by ∆h rf wavelengths. In linear
approximation (the exact calculation is done on the computer), this is accomplished by requiring:
∆En = βn2 γn3 E0 ∆h / hn (1 – αp γn2) = (Qe Vn / A) sin φnAlessandro G. Ruggiero Erice – Sicily April 29, 2009 23
Alessandro G. Ruggiero Erice – Sicily April 29, 2009 24
∆h = 1 constant
A. G. Ruggiero, Nucl. Phys. B, Proc. Suppl. 155, 315 (2006)
1.5 – GeV 200 – m NS-FFAG Proton Driver
TM010 + TM011
KST
Alessandro G. Ruggiero 25Erice – Sicily April 29, 2009
KST
Alessandro G. Ruggiero 26Erice – Sicily April 29, 2009
KST
Alessandro G. Ruggiero 27Erice – Sicily April 29, 2009
r=4.81 m
34 cm
dispersion
βy
βx
C = 30.24 m
δp/p=+50%
3.6 m
r=4.28 m
Cavities
Extraction/injection Kickers
C=26.8m
Dejan Trbojevic
Alessandro G. Ruggiero 28Erice – Sicily April 29, 2009
Proton
Carbon
Possible Advantages: 1.Amount of steal in the case of proton machine is smaller than the CYCLOTRON or scaling FFAG - Magnets are relatively small size. (see next…)2.Adjustment of the energy is done by changing the extraction time – reducing the total number of turns.3.Fast repetition rate ~1000 turns 4.Relatively small size – 30–50 meter circumference. (see next…)5.Easier to operate as the magnetic field is fixed (with respect to synchrotrons).6.Better preservation of the emittance than in the CYCLOTRON7.For carbon the superconducting machine is necessary to reduce the size but the orbit offsets are small - the magnets are small
Disadvantages:1.Large total power required for the cavities distributed around the circumference, this probably makes larger operating cost - this might not be true as shown in the poster at the workshop. 2.For protons, orbit offsets are not any more few millimeters (this was a compromise between the size, number of cells-periods) but +12 and – 6 cm for the lowest energy3.The momentum range is still limited to ± 50% with the kinetic energy range from 32-250 MeV, so it would require additional RFQ and Linac (or one more FFAG).
Alessandro G. Ruggiero 29Erice – Sicily April 29, 2009
Alessandro G. Ruggiero 30Erice – Sicily April 29, 2009
1.3 m Diameter
1.5-GeV AGS – NS-FFAG
Side View
Diagnostic & Steering Boxes
D-Sector Magnet
F-Sector Magnets
Flanges & Bellows
Vacuum Pump
10 cm
Top View
D-Sector Magnet
F-Sector Magnets
Flanges & Bellows
Vacuum Pump
30 cm
Diagnostic & Steering Boxes
RF Cavity
Diagnostic & Steering Boxes
D-Sector Magnet
F-Sector Magnets
Vacuum Pump
100 k$
500 k$
0 m 2.0 m 4.0 m 6.0 m
Alessandro G. Ruggiero 31Erice – Sicily April 29, 2009
1.5-GeV AGS – NS-FFAG
B1
B2
C1 Foil C2
From DTL
Injection Orbit
Bump Orbit
Circulating Beam
Injected Beam
20 x 20 mm Foil
400 MeV 1.5 GeV
30 cm x 10 cm Vacuum Chamber
Kicker Septum
F D F F D F F D F
Alessandro G. Ruggiero 32Erice – Sicily April 29, 2009