Development of Non-Scaling FFAG

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

EMMA Particle physics Particle therapy -factory, muon source, proton driver PAMELA FFAG ADSR Medical FFAG Particle therapy, BNCT, X-ray source Energy (PAMELA) ADSR, Nucl. Transmutation FFAG -factory 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) Introduction ... • FFAG(Fixed Field Alternating Gradient) Accelerator has an ability of rapid particle acceleration with large beam acceptance.  wide varieties of applications

CONFORM : Constructionof aNon-scalingFFAGfor Oncology, Research andMedicine • Two main projects are going on ….. (1) EMMA: Construction of electron machine (prototype for muon accelerator) (2) PAMELA: Design study of NS-FFAG particle therapy facility ( Proton & Carbon ) 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) 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)

10MeV 20MeV ~20mm ∆r/r<1% |df/f|~0.1% /cell TOF/turn(ns) B0 x Kinetic Energy(MeV) /cell What is NS-FFAG ?  Fixed field ring accelerator with “small dispersion linear lattice” Small dispersion … Orbit shift during acceleration is small Small Magnet aperture, energy variable extraction Path length variation during acceleration is small  fixed frequency rf can be employed for relativistic particle acceleration Fixed field linear lattice … Simple and flexible lattice configuration  tunability of operating point Large acceptance Large tune drift ( focusing power B/p )  Fast acceleration is required

Number of Cell 42 (doublet Q) Circumference 16.57m 5m Injection energy 10~20MeV(variable) Extraction energy 10~20MeV(variable) RF 1.3GHz Acceptance 3mm(normalized) Daresbury labo. Muon Acceleration EMMA: Electron Modelfor 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

10MeV /cell 20MeV /cell |df/f|~0.1% 20MeV TOF/turn(ns) 10MeV Kinetic Energy(MeV) EMMA :Beam acceleration Resonance is a coherent effect Fast acceleration can circumvent the problem Resonant crossing acceleration Small variation of path length makes it possible to adopt fixed frequency rf for relativistic particle Fast 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 !!

Spot scanning photon proton PAMELA:Particle Acceleratorfor 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 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

SOBP is formed by superposing Bragg peak 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:Clinical requirements Dose uniformity should be < ~2% To achieve the uniformity, precise intensity modulation is a must IMPT (Intensity Modulated Particle Therapy) Synchrotron & cyclotron Gate width controls dose 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. Integrated current time “Analog IM” FFAG Integrated current Step size controls dose time “Digital IM” PAMELA meets muon science !!

dx: 100µm(RMS) rf: 5kv/cell dx: 10µm(RMS) dx: 1µm(RMS) PAMELA : Beam Dynamics Challenges: Understanding the dynamics in resonance crossing Integer resonance Half integer resonance Beam blow-up rate can be estimated quantitatively Field imperfection severely affects beam blow up in the resonance crossing

Theoretical value Integer resonance (=6,1mm mrad.norm) eV(MeV/turn) kV/turn (m) pos(m) 320 320 260 260 210 210 90 70 90 70 70 90 Requirements for lattice Integer resonance blowup constant • 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. Linear NS-FFAG (200kV/turn, average B0;n,, w/o ∆B1,x=100m)

~2m PAMELA : Lattice Challenges: Tune stabilized NS-FFAG 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 Long straight section (~2m) Small tune drift ( <1) Short beam excursion(<20cm) Limited multipoles (Up to decapole) by S. Machida(RAL)

40cm ~17cm Sectapole Quadrupole Dipole Octapole Decapole PAMELA : Magnet Challenges: Large aperture, short length, strong field Superposition of helical field can form multipole field • Applicable to superconducting magnet • Well-controlled field quality • Present lattice parameters are within engineering limit  Feasible option for magnet !! by H.Witte (JAI)

PAMELA : Magnet (cnt’d) Quadrupole Dipole Sextapole Octapole

1/0  1/0 :200kV/turn :50kV/turn 1/0 eV/turn(MeV) ∆B1/B1 ∆B1/B1  ∆B1/B1 ∆B1/B1 Acceleration Rate (1) Half integer resonance eV/turn (MeV) (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 can suppress blow up rate less than factor of 5. • For the considered range, 3rd integer resonance will not cause serious beam blow-up 1/0-1 eV/turn (MeV) ∆B2/B2  Required accelerating rate : >50kV/turn

Energy Option 1 1ms Option 1: P Nrep2 Option 2: P Nrep PAMELA: Beam Acceleration Repetition rate: 1kHz  min. acceleration rate : 50kV/turn (=250Hz)  How to bridge two requirements ?? Option 2 Energy time time 1ms Low Q cavity (ex MA) can mix wide range of frequencies Multi-bunch acceleration is preferable from the viewpoint of efficiency and upgradeability

Multi-bunch acceleration Multi-bunch acceleration has already been demonstrated ∆f  4 fsy 2-bunch acceleration using POP-FFAG : Mori et al. (PAC 01 proceedings p.588) 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 ??”

Extraction (5.5MHz) 50kV Injection(2.3MHz) 50kV Test of multi-bunch acceleration 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 • 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. EADF parameters

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

H Resonance point v ∆v<0.5 Multi-Turn Extraction in NS-FFAG (cnt’d) ~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

a layout Fast extraction (horizontal) Slow extraction (vertical) Charge exchange injection(horizontal) p HI Proton ring Fast extraction (horizontal) 1turn injection (horizontal) HI ring

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 .

Development of Non-Scaling FFAG