FFAG Accelerator Proton Driver for Neutrino Factory

FFAG AcceleratorProton Driver

for Neutrino Factory

FFAG AcceleratorProton Driver

for Neutrino Factory

Alessandro G. RuggieroBrookhaven National Laboratory

Alessandro G. RuggieroBrookhaven National Laboratory

June 23, 2005June 23, 2005 A.G. Ruggiero -- NuFact 05 - FrascatiA.G. Ruggiero -- NuFact 05 - Frascati 22

FFAG AcceleratorsFFAG 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.

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.


Initiatives at BrookhavenInitiatives 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)

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)


Reference MaterialReference 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.

[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.


FFAG Lattices for Proton BeamsFFAG 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.

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.


FFAG Accelerators for Proton DriversFFAG Accelerators for Proton Drivers

F F D

Extraction Trajectory

Injection Trajectory

Single-turn Extraction

Single-turn Transfer

400-MeV Injector

3 FFAG Rings0.4 - 1.5 GeV1.5 - 4.45 GeV4.45 - 11.6 GeV

Multi-turn Injection


Three - FFAG Accelerator Rings (1)Three - FFAG Accelerator Rings (1)

Injector Ring

Low-EnergyRing

High-EnergyRing

Kinetic Energy: Inj. Ext.

GeV 0.401.50

1.504.45

4.4511.6

Inj. Ext.

0.71310.9230

0.92300.9847

0.98470.9972

p/p ±% 40.45 40.43 40.41

Circumference m 807.091 818.960 830.829

No. of Periods 136 136 136

Period Length m 5.934 6.022 6.109

Harmonic Number 136 138 140

RF = 5.9345 m

MHz 36.0246.03

46.0349.75

49.7550.38



Injector Ring

Low-EnergyRing

High-EnergyRing

Energy Gain / Turn MeV 0.60 0.90 2.00

No. of Revolutions 1834 3278 3576

RF Peak Voltage MVolt 1.20 1.80 4.00

Acceleration Period

ms 6.137 9.398 10.001

Injection Period ms 1.144 -- --

Repetition Rate kHz 0.137 0.106 0.100

Gap Voltage kVolt 20 30 40

Gaps per Cavity 2 2 2

No. of Cavities 30 30 50



Injector Ring

Low-EnergyRing

High-EnergyRing

Protons / Cycle 1.0 x 1014 1.0 x 1014 1.0 x 1014

Average Current mA 1.60 1.60 1.60

Average Power MW 2.40 7.12 18.56

Nor. Emittance (full)

mm-mrad

100 100 100

Act. Inj. Emittance mm-mrad

98.32 41.69 17.68

Bunching Factor 4.0 4.0 4.0

Tune-Shift 0.343 0.188 0.085

Half Vert. Beam Size

cm 2.12 1.38 0.90

Half Hor. Beam Size

cm 3.41 2.22 1.46


RF Frequency & PowerRF Frequency & Power

Injector Ring

Low-Energy

Ring

High-Energy

Ring

MHz

# turns

MW

# turns

MHz

# turns

MW

# turns

MHz

# turns

MW

# turns


Injector Ring and InjectionInjector Ring and Injection

Injection Energy MeV 400

H– Source Current mA 35

RFQ Transmission % 80

Chopping Ratio % 50

Inject. Beam Current

mA 14

Inj. Protons / turn 3.3 x 1011

Injected Turns 303

Pulse Length ms 1.144

Duty Cycle 0.1144

B1B2

C1 Foil C2From DTL

Injection Orbit

Bump Orbit

20 x 20 mm Foil

Injected Beam400 MeV

1.5 GeV

Circulating Beam

12 cm x 25 cm Vacuum Chamber


Lattice ParametersLattice Parameters

D FFS S

gg

Non-Scaling Lattice

InjectorRing

Low-Energy Ring

High-EnergyRing

Drifts: S g

mm

1.267250.30

1.285880.3044

1.30450.3088

F-sector: Length Field min Field max Gradient

mkGkG

Kg/m

0.70-0.784093.7944526.5817

0.71029-1.849188.9487660.8858

0.72059-4.2351820.4415139.476

D-sector: Length Field min Field max Gradient

mkGkG

Kg/m

1.401.83450

-1.39962-23.2956

1.420584.32645

-3.30084-53.3590

1.441189.90888

-7.51787-122.236

x max, in F in D

cmcm

17.2213.88

17.4614.07

17.6914.26


Lattice FunctionsLattice Functions

Phase Adv. / Cell H V

105.234o

99.9395o

Betatron Tune, H V

39.75537.755

Nat. Chromaticity, H V

-0.9263-1.8052

Transition Energy, T

105.482 i

All Rings

Linear Field Profile

Injection Orbit


Tune Variation & Radial Compactnesssame result for all Rings

Tune Variation & Radial Compactnesssame result for all Rings

QH

QV

x in cm

s in m injection

extraction


Linear Field DistributionLinear Field Distribution

kG

x, m

F-sector

kG

x, m

D-sector

kG

x, m

D-sector

kG

x, m

F-sector

kG

x, m

D-sector

Injector Ring

Low-Energy

Ring

High-Energy

Ring

kG

x, m

F-sector


Adjusted Field Profile (revised)Adjusted Field Profile (revised)

kG

x, m

D-sector

kG

x, m

F-sector

x in cm

s in m injection

extraction

QH

High-Energy

Ring

Same for all

Rings


ConclusionsConclusions* 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 InjectionInjector Linac (400-MeV DTL or ????)

Multi-turn Injection of H–

Magnet FeasibilityAdjusted Field ProfileFast 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)

* 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 InjectionInjector Linac (400-MeV DTL or ????)

Multi-turn Injection of H–

Magnet FeasibilityAdjusted Field ProfileFast 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)

Documents

FFAG Accelerator Proton Driver for Neutrino Factory