PAMELAan overview

Takeichiro Yokoi

JAI, Oxford University

Introduction

PAMELA(Particle Accelerator for MEdicaL Applications ) aims to design particle therapy accelerator facility for proton and carbon using NS-FFAG with spot scanning Prototype of non-relativistic NS-FFAG (Many applications !! Ex. proton driver, ADS) It also aims to design a smaller machine for biological study as a prototype.Difficulty is resonance crossing acceleration in slow acceleration rate As a practical machine, economy is an issue.

Collaboration

PAMELA (PM: K.Peach) Rutherford Appleton Lab Daresbury Lab. Cockcroft Inst. Manchester Univ. Oxford Univ. John Adams Inst. Imperial College London Brunel Univ. Gray Cancer Inst. Birmingham Univ. FNAL (US) LPNS (FR) TRIUMF (CA)

In this session ….

T.Yokoi … Overview

A.Kacperek … Medical requirement

H. Witte … Magnet option

C. Beard … RF option

S. Sheehy … Lattice

Clinical requirements (1) : Spot scanning

Spot scanning can fully exert the advantage of particle therapy and pulsed beam of FFAG matches well to the treatment

Typical voxel size : 4mm 4mm ~10mm 10mm Energy range : 70MeV~250MeV Typical @patient : ~1m

Extraction scheme : Fast extraction

Beam emittance : ~10 mm mrad (normalized)

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

Beam of FFAG is quantized. Good stability of injector and precise loss control are indispensable for medical applications

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

“How high is the intensity of a beam bunch?”

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”

Medical requirement (2): IMPT To investigate the requirement of injector, formation of SOBP in IMPT was studied using analytical model of Bragg peak

The study of beam intensity quantization tells intensity modulation of 1/100 is required to achieve the dose uniformity of 2%. (minimum pulse intensity:~106 proton/1Gy) Monitor is a crucial R&D item of PAMELA

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)

InjectorInjector can preferably cope with proton and heavy ion injection

(ICL group lead by J.Pozinsky investigating the scheme )

Two injectors are to be employed: cyclotron for proton, RFQ for HI

Typical beam emittance from injectors : 1 mm mrad (normalized)

Tracking study of RFQ line is undergoing. (transmission efficiency> 75% is achieved

Stability of intensity is typically less than 5%

Lattice

†

At present, two different types of lattice are proposed for NS-FFAG of non-relativistic particle

(1) Linear lattice (by E.Keil et al.) Small excursion, large tune drift, short drift space, ordinary combined function magnet

(2) Non-Linear Lattice (by C. Johnston et al.) * sextupole for chromaticity correction Large excursion, small tune drift, long drift space, wedged combined function magnet

Cells Tunes for 30-400 MeV Tune-stablized FFAG

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.2 0.4 0.6 0.8 1

Momentum (GeV/c)

nux/cell-modelnuy/cell-modelnux/cell-approxnuy/cell-approx

In lattice design study, we are now focusing on the understanding of dynamics of proton NS-FFAG : dynamics of slow resonance crossing acceleration, field quality, tolerance etc…

Test Lattice

Wedge shaped combined function magnet (quadrupole)

small number of cell (#cell:14), and long straight section(>1m)

Long excursion(>80cm) variable energy extraction, rf cavity

Relatively weaker field gradient(4.5T/m), Max dipole field:1.5T (on orbit)

As a test lattice, tune stabilized lattice proposed by C. Johnston was employed

Tune of test latticeCells Tunes for 30-400 MeV Tune-stablized FFAG

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.2 0.4 0.6 0.8 1

Momentum (GeV/c)

nux/cell-modelnuy/cell-modelnux/cell-approxnuy/cell-approx

Using ZOGUBI, lattice building was carried out.

Horizontal tune can be well reproduced. However, to reproduce vertical tune, wedge angle was needed to be tweaked. The source of discrepancy must be identified. One possible source is the fringing field model

The beam dynamics is basically subjected by the tune As long as tune is similar, the dynamics can be discussed in a similar way.

Original design

ZGOUBI result

Acceleration (perfect lattice)

Horizontal beam blows up slightly ( amplitude wise:~6% for 400MeV acceleration

It is caused by the transverse kick by rf acceleration due to the tilted orientation of accelerating field to the beam axis. Arrangement of rf cavity could affect the intrinsic horizontal beam blow up, But this effect is not important

210keV/turn

Acceleration (Vertical) The beam acceleration was carried out for vertically distributed beam with various positioning error and accelerating rate (horizontal beam size: 0)

Beam blow-up is clearly observed at integer resonance

V:260keV/turn

‘Microscopic’ study is required to understand the blow-up process

Integer resonance crossing (1)R. Baartman proposed a simple formula to evaluate the amplitude growth during resonance crossing

€

ΔA =π

Qτ

R

Q

Bn

B

Stronger focusing suppresses amplitude growth through smaller

Design parameter Intrinsic parameter of lattice

€

Δ(A2−m )

2 − m=

π

2m−1bn,m

m

Qτ

€

bn,m +1 =1

n

R

B

1

m!

∂mBn

∂xm

€

Qτ = ΔQ / turn

For integer resonance Q, (m=1, n=Q)

€

1

2

β

εΔε ⋅

Qτ

σ pos

= πR

Q

BU :N

B

€

Bn = BU :N ⋅σ pos

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ΔA =1

2

β

εΔε

(A ≈ βε )

Integer resonance crossing (2)

Tracking study was carried out around integer resonance(Q=4,3)

3 acceleration rate, 2 alignment error were examined

100 different lattice configurations

For single integer resonance crossing, Baartman’s formula can estimate the growth rate 210 210 260 260 320 320

70 70 7090 90 90

210 210 260 260 320 320

70 70 7090 90 90

kV/turn

(m)

kV/turn

(m)

Theoretical value

Half integer resonance crossing

€

logA f

Ai

=π

2

R

nB

∂Bn

∂x (=2Q)

€

logA f

Ai

=π

2

R

nB

∂Bn

∂x

1

Qτ (n=2Q)

€

R ≡ logA f

Ai

Qτ

σ fld

=π

2

R

nB

∂BU :N

∂xDesign parameter

.

By introducing focusing error to individual magnet, blow-up rate was estimated

100 different error settings were examined

Baartman’s formula can somehow evaluate the blow-up rate of half integer resonance

Lattice parameter

Structure resonance

Q=4 Q=3.5

Dynamic aperture

Q=3

Q=2.5

Dynamic aperture 20mm mradQ=3.5 Q=2.5

Ncel 14 4Q=14 (2Q=7) is structure resonance

Even with only positioning error, resonance is excited at Q=3.5 **Field gradient error caused by the positioning error

is<10-3

210kV/turn

Requirements for lattice

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

Up to half integer resonance, Baartman’s formula can somehow evaluate the blow-up rate.

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. ** Contribution of higher order components, ex fringing field, remains for future study

“Is there doable lattice option at the moment ??”

pos(m)

eV(M

eV/t

urn)

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

Lattice optionS.Machida proposed semi-scaling FFAG for proton therapy (up to decapole)

Tune drift ∆<1 (no integer crossing, no structure resonance crossing)

Orbit excursion ~30cm

Long straight section (>2m)

H.Witte (magnet), S.Sheehy (lattice)

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

)

Acceleration Scheme

€

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 (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 (possibly in this October)

Summary PAMELA intends to design particle therapy facility to deliver proton and carbon using FFAG.

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.

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

Accelerationrf: 5kv/celldx: 100µm(RMS)

dx: 10µm(RMS)

dx: 1µm(RMS)

Acceleration (Horizontal)

V:260keV/turn

The beam acceleration was carried out for horizontally distributed beam (Vertical beam size: 0)

For horizontal motion, beam blow up is controllable. (Half integer resonance affect slightly for the case of positioning error.)

The blow up should be checked with realistic distribution (finite beam size for both direction)