FFAG stands for Fixed Field Alternating Gradient accelerator. It is a type of circular particle accelerator that uses alternating gradient focusing with fixed magnetic fields. Some key advantages of FFAGs include fast acceleration, flexibility of operation, and large acceptance allowing high beam intensities. The document discusses the 150 MeV FFAG proton accelerator project at KEK including its injection system using a baby cyclotron and tandem accelerator, RF cavity design using magnetic alloys, main magnet design using triplet sectors, and extraction system. It also briefly mentions medical FFAG design studies aiming for features like small footprint, variable extraction energy, high current output for applications like hadron therapy.

1. FFAG
Fixed Field Alternating Gradient Accelerator
Siavash zare
SHIRAZ PARAMEDICAL
UNIVERSITY-2015
1. What is an FFAG ?
2. 150 Mev FFAG
3. Designs for hadron therapy

3. horizontal vertical
What is an FFAG ?
A Fixed-Field Alternating Gradient accelerator (FFAG) is a circular particle
accelerator concept on which development was started in the early 50s.
 Alternating gradient is a focusing scheme with both sign of gradient magnets, focusing and
defocusing elements.
Development is stopped in late 1960s because:
• Magnet design was complicated. It was hard to get desired 3-D fields profile
in practice.
• No material for RF cavity. It requires high shunt impedance, high response
time, and wide aperture.
• Synchrotron was more compact and better choice for accelerator of high
energy frontier.

4. Revival in late 1990s
Technology becomes ready and enough reason to re-start development:
• 3-D calculation code such as TOSCA becomes
available. Static fields can be modeled precisely.
• RF cavity with Magnetic Alloy (FINEMET as an example)
has most suitable properties for FFAG.
• Growing demands for fast cycling, large acceptance, and
high intensity in medium energy accelerator regime.

6. World First Proton FFAG Accelerator
PoP(proof-of-principle) FFAG :KEK 2000

7. FFAG (Fixed Field Alternating
Gradient)
Advantages• Alternating gradient : Like synchrotron : strong focus accelerator
FFAGs rely on Alternating Gradient focusing so that the beam size can be much smaller.
• Fixed field: like cyclotron : Zero chromaticity , Higher repetition rate : so higher
average current
• Fast acceleration
You can accelerate very quickly (as fast as your RF allows…)
• flexibility, easy operation.

8. Classification of FFAG
• Scaling FFAG: (Non-linear , Radial sector magnet , constant
tune non-isochronous)
MURA (e-model)
PoP, 150 MeV (The project to construct the 150 MeV FFAG accelerator
is under going at KEK)
PRISM
Muon acceleration ( Nufact-J, low frequency RF)
• Non-Scaling FFAG: (Linear , spiral sector magnet , non-
constant tune non isochronous, smaller magnet)
 EMMA(U.K) (Electron Machine with Many Applications)
disadvantage
complex
advantage
advantage
Very complex

9. 150 MeV FFAG

11. injectors
Baby-cyclotron :
proton beam is extracted from the cyclotron to the FFAG.
After transportation line, with septum magnet, electrode and two bump magnet, beam will
be put in the acceleration orbit.

12. An injected beam is deflected by the magnetic septum and its angle is
adjusted by the electrostatic septum.
To observe beam position, two thin plates are installed near those septa.
injectors

13. Tandem Accelerator (*Van de Graaff Accelerator*)
The tandem accelerator employed as a heavy ions (10B 12C 16O 19F 35Cl 72BR …) injector to
the 150 MeV FFAG.
Beams from the tandem accelerator will also be used for AMS, nuclear physics experiment,
and so on.
injectors

14. injectors

15. Tandem Accelerator
Van de graaff
injectors

16. injectors

17. injectors

18. RF cavity
Requirements of RF cavity
• Broad band
Frequency sweep of a factor.
• High gradient
Make it fast acceleration possible.
• Large aperture
Especially in horizontal to
accommodate orbit excursion.
To achieve the rapid cycle acceleration in the proton FFAG, an RF cavity with high field gradient and
broadband impedance is necessary. These requirements have been satisfied by using a high-
permeability soft magnetic alloy (MA) core (Magnetic Alloy instead of Ferrite) and a high power
broadband amplifier.
voltage required to achieve the rapid acceleration
of 100 Hz with two RF cavities
The maximum shunt impedance is 200 Ω

19. RF cavity
the cooling system for MA cores had a technical difficulty in terms of the thermo mechanical
reliability. Since the efficiency of the heat cooling was low, the temperature on inner surface
of the core reached over 150°C. To resolve this problem, a new type of the RF cavity with a
high-efficiency cooling system has been developed.
Developed RF cavity for 150 MeV FFAG

20. RF cavity
The cavity consists of two MA cores, and the water-cooled plates are attached to one
side of the cores. A thin thermally conductive spacer is inserted between the core and
the cooling plate.
the water cooling plate for the RF cavity. The blue
area and arrows indicate the coolant passage and
the direction of water follow, respectively.

21. FFAG main magnet
F Sector
D Sector
Shunt
Magnet for 150MeV FFA
The design of the main magnet was carried out with
3-dimensional field calculation by a code TOSCA
Instead of using F (forces) and D (defocus) magnets separately, combine FDF together
(triplet).We make a triplet sector magnet, Defocus, Forces ,Defocus magnet.

22. (a) OriginalRadial Sector (b) Triplet Radial Sector
The triplet type of the magnet has many advantages. The fringing field between focusing
and defocusing fields can be easily cancelled. Long straight sections which gives sufficient
space for installing the injection and extraction devices, and the beam diagnostics
instruments, can be obtained. Another practical side benefit is the weight reduction.
Triplet type of the magnet
FFAG main magnet

23. Extraction
Extraction is the process of ejecting a particle beam from an accelerator and into a transfer line or a
beam dump.
The extraction scheme is fast extraction commonly used in synchrotrons while a kicker magnet and a
septum magnet should work at 100Hz. Proton beam bunch is accelerated with Rf voltage and extracted
every 10msec. The layout of extraction devices and calculated extraction orbit in FFAG ring are shown
below.
With the magnet, it is possible to extract beam
from the region of FFAG magnet. If the beam is
extracted from the region of straight section, the
extraction septum magnet should bend the beam
in large angle

24. Extraction
Kic k e r a n d s e p tu m
magnetkicker magnet provides time selection of beam to be injected/extracted. The field
produced by a kicker magnet must rise/fall within the time period between the beam
Bunches.
a septum is a device which separates two field regions. Important features of septa
are an ideally homogeneous (electric or magnetic) field in one region, for deflecting
beam, and a low fringe field (ideally zero magnetic and electric field) next to the
septum so as not to affect the circulating beam.

25. Medical FFAG Design Studies
Have been many and varied.
I’ve chosen a few to highlight… but it is a wide topic

26. Goals of FFAG designs for Medical Accelerators
•Ultimate design consistent with carbon therapy
• Preliminary lattices capable of 400 MeV for protons
• Small footprint: ~40m normal conducting, 20 m superconducting
(protons)
• Synchrotron-like features
• Variable extraction energy
• Multiple extraction points – multiple treatment areas
• Cyclotron-like features
• High current output
• Ease of operation