FFAG Accelerator Proton Driver for Neutrino Factory

1. FFAG AcceleratorProton Driverfor Neutrino Factory Alessandro G. Ruggiero Brookhaven National Laboratory

2. FFAG Accelerators There is recently a renewed interest in Fixed-Field Alternating-Gradient (FFAG) Accelerators for a varied of applications in Nuclear and High-Energy Physics, Energy Technology and Medical Therapy. FFAG Accelerators have the capability to accelerate charged particles over a large momentum range (±30-50%) and the feature of constant bending and focusing fields. Thus magnets do not need to be ramped and particles can be accelerated very fast at the rate given by the limitation of the accelerating field from RF cavities placed in proper location between magnets. The performance of FFAG accelerators is thus to be placed between Linear Accelerators, with which they share the fast acceleration rate, and Synchrotrons as they allow the beam to re-circulate over few revolutions. They are similar to Cyclotrons but also take advantage of alternating focusing and bending for a more radial compact geometry, and free themselves from a rigid RF frequency – Path Length relation. A.G. Ruggiero -- NuFact 05 - Frascati

3. Initiatives at Brookhaven Study of feasibility of FFAG Accelerators to accelerate intense beams of protons in the GeV energy range, for instance: • AGS Upgrade with a new FFAG injector spanning over the energy range of 400 MeV to 1.5 GeV corresponding to a momentum excursion of ±40%. The ring would be housed in the AGS tunnel and has henceforth a circumference of 807 m. The repetition rate is 2.5 or 5.0 Hz. (reference 1) • A site-independent 1.0-GeV Proton Driver capable to deliver as much as 10-MW of average beam power at the high repetition rate of 1 kHz. The injection energy is assumed at 200 MeV and the corresponding momentum excursion is then 45%. The circumference is 201 m. (reference 2) A.G. Ruggiero -- NuFact 05 - Frascati

4. Reference Material [1] A.G. Ruggiero, “1.5-GeV FFAG Proton Accelerator for the AGS Upgrade”, Invited Talk to EPAC-04, July 6-11, 2004, Lucerne, Switzerland. [2] A.G. Ruggiero, “A 1-GeV 10-MWatt Proton Driver”, Invited Talk to ICFA-HB2004 Workshop, October 18-22, 2004, Bensheim, Germany. [3] A.G. Ruggiero, “Design Criteria of a Proton FFAG Accelerator”, Proceedings of the FFAG’04 Workshop, October 13-16, 2004, KEK, Tsukuba, Japan. [4] A.G. Ruggiero, “Adjusted Field Profile for the Chromaticity Cancellation in a FFAG Accelerator”, Proceedings of ICFA-HB2004 Workshop, October 18-22, 2004, Bensheim, Germany. [5] A.G. Ruggiero, “Revised Adjusted Field Profile Estimate Criterion for FFAG Accelerators”, C-A/AP/208, BNL, March 25, 2005. A.G. Ruggiero -- NuFact 05 - Frascati

5. FFAG Lattices for Proton Beams Two lattice configurations and magnet arrangements have been proposed: Scaling Lattice that has the advantage of constant orbit parameters across the large momentum aperture but at cost of high bending fields, large magnet aperture and a limitation on available drift space. This lattice has been experimentally demonstrated at KEK with a pair of FFAG proton rings that have been commissioned. Non-Scaling Lattice where orbit parameters vary considerably across the momentum aperture but with the benefit of lower bending fields, smaller magnet aperture and allowance for more drift space. The engineering and construction of a FFAG Accelerator based on this principle are greatly simplified and also expected to be more economical. Yet there is the concern of the beam stability when crossing a large number of resonances, some linear and others not, some driven by errors, misalignment and magnet imperfections, and others that appear to be structural. A Non-Scaling FFAG Accelerator has never been practically demonstrated. Novel ideas have also recently been proposed, for instance to flatten the tune variation with an Adjusted Field Profile. In the case of proton beams, the concern of multiple resonance crossing is to be coupled to the longitudinal beam dynamics requiring a fast frequency-varying RF cavity system, and to the presence of space-charge forces at injection that, despite the fast rate by which the region of relevance is traversed, still may be significant. A.G. Ruggiero -- NuFact 05 - Frascati

6. FFAG Accelerators for Proton Drivers 3 FFAG Rings 0.4 - 1.5 GeV 1.5 - 4.45 GeV 4.45 - 11.6 GeV Single-turn Transfer 400-MeV Injector Multi-turn Injection Single-turn Extraction A.G. Ruggiero -- NuFact 05 - Frascati

7. Three - FFAG Accelerator Rings (1) A.G. Ruggiero -- NuFact 05 - Frascati

8. Three - FFAG Accelerator Rings (2) A.G. Ruggiero -- NuFact 05 - Frascati

9. Three - FFAG Accelerator Rings (3) A.G. Ruggiero -- NuFact 05 - Frascati

10. RF Frequency & Power Injector Ring Low-Energy Ring High-Energy Ring A.G. Ruggiero -- NuFact 05 - Frascati

11. Circulating Beam 20 x 20 mm Foil Injected Beam 1.5 GeV 400 MeV 12 cm x 25 cm Vacuum Chamber B1 Injection Orbit B2 Bump Orbit C1 Foil C2 From DTL Injector Ring and Injection A.G. Ruggiero -- NuFact 05 - Frascati

12. D F F S S g g Lattice Parameters Non-Scaling Lattice A.G. Ruggiero -- NuFact 05 - Frascati

13. Lattice Functions All Rings Linear Field Profile Injection Orbit A.G. Ruggiero -- NuFact 05 - Frascati

14. Tune Variation & RadialCompactnesssame result for all Rings A.G. Ruggiero -- NuFact 05 - Frascati

15. Linear Field Distribution Injector Ring Low-Energy Ring High-Energy Ring A.G. Ruggiero -- NuFact 05 - Frascati

16. Adjusted Field Profile (revised) High-Energy Ring Same for all Rings A.G. Ruggiero -- NuFact 05 - Frascati

17. Conclusions * FFAG Accelerators for Proton Driver up to 20 MW and 12 GeV are feasible * Cost Estimate of 1.5 GeV FFAG is about 50 M$ * Issues: Space Charge at Injection Injector Linac (400-MeV DTL or ????) Multi-turn Injection of H– Magnet Feasibility Adjusted Field Profile Fast RF sweep (ferrite, RF power) Numerical Tracking * Repetition Rate --> 100 Hz For Target one should raise it to > 1 kHz Or CW Mode of Operation (Harmonic Number Jump) A.G. Ruggiero -- NuFact 05 - Frascati