Development of Non-Scaling FFAG

Takeichiro YokoiJohn Adams Institute for Accelerator Science

Oxford University

RCNP 研究会「ミュオン科学と加速器研究」 20/10/2008

Particle physics -factory, muon source, proton driver

-factory-factory

FFAGMedical

Particle therapy, BNCT, X-ray source

Particle Particle therapytherapy

FFAG

Energy ADSR, Nucl. Transmutation

ADSRADSRFFAG

CONFORM CONFORM ((Construction of a Non-scaling FFAG for Oncology, Research and Medicine) aims to develop the Non-scaling FFAG as a versatile accelerator. (Project HP: www.conform.ac.uk)

EMMA

PAMELA

(PAMELA)

Introduction ...• FFAG(Fixed Field Alternating Gradient) Accelerator has an ability of

rapid particle acceleration with large beam acceptance. wide varieties of applications

CONFORM : Construction of a Non-scaling FFAG for Oncology, Research and Medicine

EMMA ( PM: R.Edgecock ) Rutherford Appleton Lab Daresbury Lab. Cockcroft Ins.

Manchester univ. John Adams Ins. BNL (US) FNAL (US) CERN LPNS (FR) TRIUMF (CA)

PAMELA (PM: K.Peach) Rutherford Appleton Lab Daresbury Lab. Cockcroft Ins.

Manchester univ. Oxford univ. John Adams Ins. Imperial college London Brunel univ. Gray Cancer Ins. Birmingham univ. FNAL (US) LPNS (FR) TRIUMF (CA)

Two main projects are going on ….. (1) EMMAEMMA: Construction of electron machine (prototype for muon accelerator)

(2) PAMELAPAMELA : Design study of NS-FFAG particle therapy facility ( Proton & Carbon )

What is NS-FFAG ? Fixed field ring accelerator with “small dispersion linear lattice”

Small dispersionSmall dispersion …① Orbit shift during acceleration is small Smal

l Magnet aperture, energy variable extraction

② Path length variation during acceleration is small fixed frequency rf can be employed for relativistic particle acceleration

Fixed field linear lattice …Fixed field linear lattice …

① Simple and flexible lattice configuration tunability of operating point

② Large acceptance

③ Large tune drift ( focusing power B/p ) Fast acceleration is required

~20mm ∆r/r<1%

Kinetic Energy(MeV)

TO

F/t

urn(

ns)

|df/f|~0.1%

€

B0 = Δx × B1

B0

x

10MeV

20MeV

/cell/c

ell

Daresbury labo.Daresbury labo.

EMMA: Electron Model for Many Applications

Electron NS-FFAG as a proof of principle is to be built as 3-year project.(host lab: Daresbury lab.)

It is also a scaled-down model of muon accelerator for neutrino factory. Research items are . . .

(1) Research of beam dynamics of NS-FFAG

(2) Demonstration of NS-FFAG as a practical accelerator

(3) Demonstration of fast acceleration with fixed frequency RF

3mm(normalized)Acceptance

1.3GHzRF

10~20MeV(variable)Extraction energy

10~20MeV(variable)Injection energy

16.57mCircumference

42 (doublet Q) Number of Cell

5m5m

Muon Acceleration

EMMA :Beam acceleration

Resonance is a coherent effect Fast acceleration can circumvent the problem

Resonant crossing accelerationResonant crossing acceleration

Small variation of path length makes it possible to adopt fixed frequency rf for relativistic particle

Fast asynchronous accelerationFast asynchronous acceleration

* In EMMA, Acceleration completes within 10turns(~500ns)

EMMA is a unique system to observe transient process of resonance precisely. Unique playground for nonlinear dynamics !!

Kinetic Energy(MeV)

TO

F/tu

rn(n

s)

10MeV

20MeV

/cell

/cell

|df/f|~0.1%

10MeV

20MeV

PAMELA:Particle Accelerator for MEdicaL Applications

Advantage of particle therapy : good dose concentration and better biological effectiveness Advantage of FFAG :

(1) Higher intensity (compared to ordinary synchrotron )

(2) Flexible machine operation ( compared to cyclotron )

(3) Simultaneous(multi-port) beam extraction

photonphoton protonproton

PAMELA : design study of particle therapy facility for proton and carbon using NS-FFAG ( prototype of slow accelerating NS-FFAG Many applications!!! Ex. ADSR )

Spot scanning

Difficulty is resonance crossing in slow acceleration

PAMELA:Clinical requirements Dose uniformity should be < ~2% To achieve the uniformity, precise intensity modulation is a must IMPT (Intensity Modulated Particle Therapy)

Beam of FFAG is quantized. At the moment, instead of modulating the intensity of injected beam, shooting a voxel with multiple bunches is to be employed.

SOBP is formed by superposing Bragg peak

time

Inte

gra

ted cu

rrent

Synchrotron & cyclotron

Gate width controls dose

time

Inte

gra

ted cu

rrent

FFAG

Step size controls dose

“Analog IM”

“Digital IM”PAMELA meets muon science !!

If 1kHz operation is achieved, more than 100 voxel/sec can be scanned even for the widest SOBP case. 1 kHz repetition is a present goal (For proton machine : 200kV/turn)

PAMELA : Beam Dynamics

Field imperfection severely affects beam blow up in the resonance

crossing

rf: 5kv/celldx: 100µm(RMS)

dx: 10µm(RMS)

dx: 1µm(RMS)

Beam blow-up rate can be estimated quantitatively

Integer resonance

Half integer resonance

Challenges: Understanding the Challenges: Understanding the

dynamics in resonance crossingdynamics in resonance crossing

Requirements for lattice

Linear NS-FFAG (200kV/turn, average B0;n,, w/o ∆B1,x=100m)

For slow acceleration case, (~200keV/turn) integer resonance crossing should be avoided.

Single half integer resonance crossing would be tolerable

Structure resonance also should be circumvented.

pos(m)

eV(M

eV/t

urn)

Integer resonance (=6,1mm mrad.norm)

Integer resonance blowup constant

210 210 260 260 320 320

70 70 7090 90 90

kV/turn

(m)

Theoretical value

~2m

PAMELA : Lattice

Integer resonance crossing must be circumvented. Tune-stabilization by introducing higher order multipole field is required

One option : Non-Linear NS-FFAG (simplified scaling FFAG) : B=B0 (R/R0)k B=B0 [1+k∆R/R0+k(k-1)/2 (∆R /R0 )

2 ····] * Eliminating higher order multipoles

(1) Long straight section (~2m)

(2) Small tune drift ( <1)

(3) Short beam excursion(<20cm)

(4) Limited multipoles (Up to decapole)

Challenges: Tune stabilized NS-FFAG latticeChallenges: Tune stabilized NS-FFAG lattice

by S. Machida(RAL)

PAMELA : Magnet

by H.Witte (JAI)

Superposition of helical field can form multipole field

Dipole Quadrupole

DecapoleOctapole

Sectapole

Applicable to superconducting magnet

~17cm

40cm

Feasible option for magnet !!

Challenges: Large aperture, short length, strong fieldChallenges: Large aperture, short length, strong field

Well-controlled field quality Present lattice parameters are within engineering limit

PAMELA : Magnet (cnt’d)Dipole Quadrupole

Sextapole Octapole

Acceleration Rate(1) Half integer resonance

(2) 3rd integer resonance Nominal blow-up margin : 5 (1mm mrad 5mm mrad)

With modest field gradient error (210-3), acceleration rate of 50kV/turn can suppress blow up rate less than factor of 5.

For the considered range, 3rd integer resonance will not cause serious beam blow-up

Required accelerating rate : >50kV/turn

1/0-1

eV/turn (MeV)

∆B2/B2

eV/turn (MeV)

1/0

∆B1/B1

∆B1/B1

1/0:50kV/turn

∆B1/B1

1/0 :200kV/turn

∆B1/B1

eV/t

urn(

MeV

)

PAMELA: Beam Acceleration

€

P =(ΣV )2

Rdt∫

€

(ΣV )2 ≡ (ΣVisin[ f i(t)])2

€

=Σi(Visin[ f i(t)])

2 + Σi≠ j

(Visin[ f i(t)]⋅V jsin[ f j (t)])

€

1

Tdt ⏐ → ⏐ 0∫

time

Energy

1ms

Option 1

time

Energy

1ms

Option 2

Option 1: P Nrep2

Option 2: P Nrep

Multi-bunch acceleration is preferable from the viewpoint of efficiency and upgradeability

Repetition rate: 1kHz min. acceleration rate : 50kV/turn (=250Hz)

How to bridge two requirements ??

Low Q cavity (ex MA) can mix wide range of frequencies

Multi-bunch acceleration

2-bunch acceleration using POP-FFAG : Mori et al. (PAC 01 proceedings p.588)

∆f 4 fsy

Multi-bunch acceleration has already been demonstrated

In the lattice considered, typical synchrotron tune <0.01 more than 20 bunches can be accelerated simultaneously (6D Tracking study is required)

“Hardware-wise, how many frequencies can be superposed ??”

Test of multi-bunch accelerationExtraction (5.5MHz) 50kV

Injection　(2.3MHz) 50kV

PRISM RF PRISM rf can provide 200kV/cavity

It covers similar frequency region

Brf-wise, MA can superpose more than 20 bunches

Now, experiment using PRISM cavity is under planning ( in this October)

Applications for ADS Accelerator Driven System

EADF parameters

ADS will be used for ADSR, nucl. transmutation.

ADS will employ high power low energy proton accelerator as proton driver (<1GeV, >1mA)

FFAG, cyclotron, LINAC are the candidates

Key issues are cost and reliability (how to realize redundancy ?)

From the view point of redundancy, FFAG is a competitive candidate.

Proton driver for ADS is one of main applications for PAMELA type FFAG.

Bkicker ∆x ~ aperture

Multi-turn extraction in NS-FFAG

Why? Circulating bunch = extracted bunch Low bunch intensity for spot scanning

For energy variable extraction, extraction system is required to be moves mechanically due to the radial orbit shift especially for HI ring (problems: response time, reliability)

Number of bunch accelerated simultaneously is limited by kicker aperture. ( For the kicker aperture of 2cm, minimum orbit separation is ~4cm. ) charge exchange injection is preferable from this point of view

( Life time of kicker ? : ex 106 msec = 1000 sec = 17min )

For the application of ADSR, pulsed beam structure might not be preferable from the viewpoint of ADS core damage

Multi-Turn Extraction in NS-FFAG (cnt’d)

∆v<0.5

~2% of F/D ratio can change the vertical tune more than 0.5 In a lattice with vertical tune drift, by changing the F/D ratio, resonance energy can be varied Half integer resonance can be used for the extraction : “ Energy variable multi-turn extraction in fixed field accelerator”

”With present design strategy, is it possible to develop a lattice with vertical tune drift of less than 0.5? ”

If it is realized, it will solve almost all the problems in PAMELA

Resonance point

H

v

a layout

Slow extraction (vertical)

HI ring

Proton ring

Fast extraction (horizontal)

p

HI

1turn injection (horizontal)

Charge exchange injection(horizontal)

Fast extraction (horizontal)

Summary

PAMELA is in a position of prototype machine of NS-FFAG for non-relativistic particle

It has wide range of application like medical machine and proton driver for ADS.

Intensive study is going on (dynamics, rf, magnet, clinical requirement etc.)

Lattice requirements is now getting clear.

For acceleration, multi-bunch acceleration provides efficient and upgradeable option but still needs investigation.

By the end of next year , hope an doable overall scenario is proposed .