PAMELA an overview - J-PARC

Transcript PAMELA an overview - J-PARC

PAMELA an overview

Takeichiro Yokoi JAI, Oxford University

Introduction

 

PAMELA

 ( P article A ccelerator for ME dica L A 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)

pplications ) aims  It also aims to design a smaller machine for biological study as a prototype.



Difficulty is resonance crossing acceleration in slow acceleration rate

Collaboration

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. In this session ….

T.Yokoi … Overview A.Kacperek … Medical requirement H. Witte … Magnet option C. Beard … RF option FNAL (US) LPNS (FR) TRIUMF (CA) S. Sheehy … Lattice

Clinical requirements (1) : Spot scanning

Spot scanning pulsed beam can fully exert the advantage of particle therapy and of FFAG matches well to the treatment Typical voxel size : 4mm  4mm ~10mm  Energy range : 70MeV~250MeV Typical  @patient : ~1m 10mm Extraction scheme : Fast extraction Beam emittance : ~10  mm mrad (normalized)

Clinical requirements (2): IMPT

SOBP is formed by superposing Bragg peak Dose uniformity should be < ~2%  To achieve the uniformity, precise intensity modulation is a must

IMPT

(

ntensity

odulated

article

herapy) Synchrotron & cyclotron Beam of FFAG is quantized.  Good stability of injector and precise loss control are indispensable for medical applications FFAG New approach to medical accelerator control is required in PAMELA Gate width controls dose time

“Analog IM”

Step size controls dose time

“Digital IM”

Medical requirement (2): IMPT

 To investigate the requirement of injector, generation 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:~10 6 proton/1Gy

)  Monitor is a crucial R&D item of PAMELA  If 1kHz operation is achieved, more than 100 voxel/sec can be scanned in PAMELA for the widest SOBP case.



1 kHz repetition is a present goal (For proton machine : 200kV/turn)

Injector

Injector 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

Cells Tunes for 30-400 MeV Tune-stablized FFAG (2) Non-Linear Lattice (by C. Johnston et al.)

0.4

0.35

* sextupole for chromaticity correction 0.25

Large excursion, small tune drift, long drift 0.2

0.15

space, wedged combined function magnet 0.1

0.05

nux/cell-model nuy/cell-model nux/cell-approx nuy/cell-approx 0 0.2

0.4

0.6

Momentum (GeV/c)

0.8

1 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

As a test lattice, tune stabilized lattice proposed by C. Johnston was employed  Wedge shaped combined function magnet (quadrupole)  small number of cell (#cell:14), and long straight section(>1m)  Long excursion(>60cm)  variable energy extraction, rf cavity  Relatively weaker field gradient, Max dipole field:1.5T (on orbit)

Tune of test lattice

Cells Tunes for 30-400 MeV Tune-stablized FFAG

0.4

0.35

0.3

0.25

0.2

0.15

0.1

0.05

0 0.2

nux/cell-model nuy/cell-model nux/cell-approx nuy/cell-approx 0.4

0.6

Momentum (GeV/c)

0.8

Original design 1  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 ZGOUBI result  The beam dynamics is basically subjected by the tune  As long as tune is similar, the dynamics can be discussed in a similar way.

Acceleration (perfect lattice)

210keV/turn

Horizontal beam blows up slightly ( amplitude wise:~3% for 400MeV acceleration  It is possibly caused by the transverse kick by rf acceleration due to the tilted orientation of accelerating field to the beam axis. Potentially, arrangement of rf cavity could affect the intrinsic horizontal beam blow up, But this effect is not important

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

V:260keV/turn

Integer resonance crossing (1)

R. Baartman proposed a simple formula to evaluate the amplitude growth during resonance crossing  ( 2

 2 

m m

)  2 

 1

b n

m m Q



b n

 1

  1

n B m

 

turn



m B n



x m

  

 



R B n Q B

  Stronger focusing suppresses amplitude growth through smaller  1 2      



pos

 

R Q B U

N B

Design parameter

B n

 

 1 2

B U

    (

  )  

pos



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

kV/turn

210 210 260 260 320 320 

(



) 70 90 70 90 70 90

kV/turn

210 210 260 260 320 320 

(



) 70 90 70 90 70 90

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

Theoretical value

Half integer resonance crossing

A A f f A A i i

    2 2

R R

 



x n x n



 log

A A i f





fld

Design parameter   2

R nB



B U



Lattice parameter   By introducing focusing error to individual magnet, blow-up rate was estimated  .  Baartman’s formula can some how evaluate the blow-up rate of half integer resonance

Structure resonance

N cel 14



4Q=14 (2Q=7) is structure resonance Q=4 Q=3.5

Q=3

Dynamic aperture

Q=2.5

Dynamic aperture 20  mm mrad Q=3.5

Q=2.5

210kV/turn Even with only positioning error, resonance is excited at Q=3.5 **Field gradient error caused by the positioning error is<10 -3

Requirement for lattice

 pos (m) Linear NS-FFAG(average B n )  Up to half integer resonance, Baartman’s formula can some how evaluate the blow up rate.

 For slow acceleration case, (~200keV/turn) integer resonance crossing should be avoided.  Single half integer resonance would be tolerable  Structure resonance also should be circumvented. 

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

Lattice option

S.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   1 /  0  :50kV/turn  1 /  0  :200kV/turn ∆B 1  ∆B 1 (2) 3rd integer resonance  Nominal blow-up margin : 5 (1  mm mrad  5  mm mrad)  With modest field gradient error (2  10 -3 ), acceleration rate of 50kV/turn suppresses the blow up rate less than factor 5.  For the range, 3rd integer resonance will not arise serious beam blow-up 

Requirement of accelerating rate : >50kV/turn

Acceleration Scheme

Repetition rate: 1kHz   min. acceleration rate : 50kV/turn (=250Hz) How to bridge two requirements ??

Energy

Option 1

Energy

Option 2

  1ms time 1ms time

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

 ( 

) 2  ( 

) 2  (



V i dt sin

[

f i

(

)]) 2  

(

V i sin

[

f i

(

)]) 2  



(

V i sin

[

f i

(

)] 

V j sin

[

f j

(

)]) 

 0 Option 1: P  N rep 2 Option 2: P  N rep  Multi-bunch acceleration is preferable from the viewpoint of efficiency and upgradeability 

Multi-bunch acceleration

Multi-bunch acceleration has already been demonstrated ∆



4 f sy

2-bunch acceleration using POP-FFAG (PAC 01 proceedings p.588) Typical synchrotron tune <0.01  more than 20 bunches can be accelerated simultaneously

“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 feed 200kV/cavity  It covers similar frequency region  B rf -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 overall doable scenario is proposed .

Acceleration

dx: 100µm(RMS) rf: 5kv/cell dx: 10µm(RMS) dx: 1µm(RMS)

Acceleration (Horizontal)

 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)