PAMELA an 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

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. 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 : ~1m Extraction scheme : Fast extraction Beam emittance : ~10  mm mrad (normalized)

Clinical requirements (2): IMPT 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.  Good stability of injector and precise loss control are indispensable for medical applications New approach to medical accelerator control is required in PAMELA 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”

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 (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 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(>60cm)  variable energy extraction, rf cavity Relatively weaker field gradient, Max dipole field:1.5T (on orbit) As a test lattice, tune stabilized lattice proposed by C. Johnston was employed

Tune of test lattice 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:~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 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  Stronger focusing suppresses amplitude growth through smaller  Design parameter Intrinsic parameter of lattice For integer resonance Q, (m=1, n=Q)

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 kV/turn (m)(m) (m)(m) Theoretical value

Half integer resonance crossing (=2Q) (n=2Q) Design parameter. By introducing focusing error to individual magnet, blow-up rate was estimated 100 different error settings were examined  Baartman’s formula can some how 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 20  mm mrad Q=3.5 Q=2.5 N cel 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< kV/turn

Requirement for lattice  pos (m) eV(MeV/turn) 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   ∆B 1 1/01/0  :50kV/turn ∆B 1 1/01/0  :200kV/turn (1) Half integer resonance (2) 3rd integer resonance Nominal blow-up margin : 5 (1  mm mrad  5  mm mrad) With modest field gradient error (2  ), 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 time Energy 1ms Option 1 time Energy 1ms Option 2 Option 1: P  N rep 2 Option 2: P  N rep 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 f sy Multi-bunch acceleration has already been demonstrated 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 rf: 5kv/cell dx: 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)