Development of Non-Scaling FFAG Takeichiro Yokoi John Adams - - PowerPoint PPT Presentation

Development of Non-Scaling FFAG

Takeichiro Yokoi

John 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 ν-factory, muon source, proton driver FFAG Medical Particle therapy, BNCT, X-ray source FFAG Energy ADSR, Nucl. Transmutation FFAG 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)

What is NS-FFAG ?

⇒ Fixed field ring accelerator with “small dispersion linear lattice”

① Orbit shift during acceleration is small ⇒Small Magnet aperture, energy variable extraction ② Path length variation during acceleration is small ⇒ fixed frequency rf can be employed for relativistic particle acceleration 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) TOF/turn(ns)

|df/f|~0.1%

B0 = Δx × B

1

B0
 Δx


10MeV 20MeV

/cell /cell

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
 1.3GHz
 RF
 10~20MeV(variable)
 Extraction
energy
 10~20MeV(variable)
 Injection
energy
 16.57m
 Circumference
 42

(doublet

Q)

 Number
of
Cell


Muon Acceleration

EMMA :Beam 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)
 








TOF/turn(ns)


10MeV
 20MeV


/cell
 /cell


|df/f|~0.1% 10MeV 20MeV

PAMELA:Particle Accelerator for MEdicaL Applications


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


Synchrotron

 &
cyclotron


Gate width controls dose


time
 Integrated
current


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/cell dx: 100µm(RMS) dx: 10µm(RMS) dx: 1µm(RMS)

Beam blow-up rate can be estimated quantitatively Integer resonance Half integer resonance

Requirements for lattice

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

 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. σpos(m) eV(MeV/turn)

Integer resonance (ν=6,1πmm mrad.norm)

Integer resonance blowup constant

210 210 260 260 320 320 70 70 70 90 90 90 kV/turn

σ(µm)

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)

by S. Machida(RAL)

PAMELA : Magnet

by H.Witte (JAI)

Dipole Quadrupole Decapole Octapole Sectapole

 Applicable to superconducting magnet

~17cm

40cm

⇒ Feasible option for magnet !!

 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

(1πmm mrad → 5πmm mrad)

 With modest field gradient error (2×10-3),

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 ε1/ε0-1

eV/turn (MeV)

∆B2/B2

eV/turn (MeV)

ε1/ε0

∆B1/B1

1 

∆B1/B1 ε1/ε0 1:50kV/turn ∆B1/B1 ε1/ε0 :200kV/turn ∆B1/B1

eV/turn(MeV)

PAMELA: Beam Acceleration

P = (ΣV)2 R dt

∫

(ΣV)2 ≡ (ΣVisin[ fi(t)])2 = Σ

i (Visin[ fi(t)])2 + Σ i≠ j(Visin[ fi(t)]⋅V jsin[ f j(t)])

1 T dt  →  0

∫ time Energy 1ms

Option 1

time Energy 1ms

Option 2 Option 1: P∝ Nrep

2

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 acceleration

Extraction (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)

∆νv<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

νH νv

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 .