Proton acceleration using FFAGsJ. Pasternak, Imperial College, London / RAL

1. Introduction

2. Lattice studies for PAMELA

3. Tune stabilization

4. Towards high intensity FFAG proton driver.

Proton acceleration is very important:• Medical applications• neutrino factory• super beam • beta beam• neutron production• radioactive beam facility• muon collider• antiproton production• ADSR systems• etc.

RACCAM Project

• N 10• k 5.15• Spiral angle 53.5°• Rmax 3.46 m• Rmin 2.8 m• (Qx, Qy) (2.77, 1.64)• Bmax 1.7 T• pf 0.34• Injection energy 6-15 MeV• Extraction energy 75-180 MeV• h 1• RF frequency 1.9 – 7.5 MHz• Bunch intensity 3109 protons

Change of energy takes 0.1 s!

Nonlinear Nonscaling FFAGs (NNSFFAG -?) were proposed by G. Rees. They use nonlinear fields for various reasons, but off-momentum orbits do not scale.

Motivations for medical Nonlinear Nonscaling design:• Reduction of orbit excursion with respect to scaling designs – in order to achieve energy variability by kicker system and reduce the magnet cost

• Acceleration with (quasi)constant tunes in order to allow for low RF gradient. Acceleration based on MA cavities with modest gradient.

Nonliner fields are used to control tune variation.

Lattice studies for PAMELA

Basic assumptions for PAMELA

• Space needed for extraction sepum (1 T) defines length of long straight• Doublet to limit number of magnets and allow for long straight • Both magnets – rectangular of equal length• Short ss fixed to 0.1 m• Magnet packing factor fixed at 0.4• Lattice of non-scaling type (negative deflection in F)• Chromatic correction to limit tune excursion below 0.5 per ring by introducing multipoles – NONLINEAR NON-SCALING FFAG• Phase advance per cell > 90° for H and <90° for V• Free parameters: cell length, number of cells, negative deflection

Orbit excursion ~ External magnet radius (??)

Preliminary proton (carbon) lattice parameters

• N 24• Lcell 1.9 m• Lmagnet 0.38 m• Lstraigh 1.04 m• Orbit excursion 0.22 m• R 7.25 m• (Qx, Qy)/cell (0.26, 0.12)• Bmax 1.8 T (normal conducting)• pf 0.4• Injection energy 17 MeV (4.2 MeV/n)• Extraction energy 250 MeV (68.3 MeV/n)

Tune stabilization - example

Parameters:

Number of cells 12Lattice type DFD triplet(QH, QV) (3.8, 1.3)R 4.8 mDrift Length 1 mExtraction septum field 0.8 TProtons 15-200 MeV

D magnet – positive bending

F magnet – negative bending

Linear optics (2)

Betatron functions at 84.25 MeV Dispersion

Chromaticity correction

Magnetic field m

T

Chromaticity correction

Magnetic field m

T

Chromaticity correction (3)

Orbits without correction Orbits with correction

Beam Dynamics

x, m

py

y, m

px

Vertical unnormalized DA at 84.25 Mev 1900 m

Horizontal unnormalized DA at 84.25 Mev 780 m

Motivations for FFAG proton driver for Neutrino Factory

• Very high repetition rate – 100 Hz or more• Constant magnetic field• Simple operation• Cost effective• Magnet and RF technology known• FFAG can boost linac energy (by factor 3-4 in momentum)

Main parameters of neutrino factory proton driver:• 4 MW• 50 Hz• 5 – 10 GeV• 3-5 bunches at 2 ns (rms)

Current scenario – G. Rees:• limited to 50 Hz• 2 rings• low injection energy• complicated lattice cell (5 magnets)

RCS 50 Hz50 Hz, 3 GeV

200 MeV

H- Linac

NF Proton Driver (2)

FFAG – 10 GeV

NF Proton Driver (3)

Alternative 1)

300 MeV H- Linac

2.5 GeV, 5 MW FFAG, 100 Hz

Neutrino factorytarget, 4 MW, 50 Hz

Neutron production target, 2.5 MW, 50 Hz

RCS or FFAG, 10 GeV, 50 Hz

• Still 2 rings• 100 – 200 Hz for booster FFAG operation possible

800 MeV H- Linac Neutrino factorytarget, 4 MW, 50 Hz, 5GeV

5 GeV, 5 MW FFAG, 100 Hz

NF Proton Driver (4)

Neutron production target, 2.5 MW, 50 Hz,2.5 GeV

• Now 1 FFAG ring!• 100 – 200 Hz for booster FFAG operation possible• Operation as an accumulator ring possible

Alternative 2)

Scaling or Non-scaling ?

• High intensity operation requires chromaticity close to zero -> scaling!

• But …non-scaling designs allow for smaller orbit excursion and simpler magnets.

• Nonlinear non-scaling, tune stabilized lattices may be a solution.

Preliminary design parameters (alternative 1)

• N of cells 64• Lattice type dublet •R 34.6 m•(Qx, Qy)/cell (0.269, 0.19)•Bmax 1.7 T• Magnet packing factor 0.4•E 0.3 - 2.5 GeV•h 5• RF swing 4.5– 6.5 MHz• Drift length 1.9 m• T 37.6

Summary and future plans

• FFAGs are perfect machines for many applications!

• We need to compare a scaling designs with the non-scaling tune stabilized ones.

• Tune stabilization has to be studied in detail.

• Space charge simulations have to be performed.

• Possibility to introduce insertions has to be studied.