Status and recent progress on muon IDS-FFAG

J. Pasternak, Imperial College, London / RAL STFC

Work in collaboration and with contributions from: M. Aslaninejad (IC), J. Scott Berg (BNL), D. Kelliher (ASTeC/STFC/RAL),

S. Machida (ASTeC/STFC/RAL), H. Witte (JAI)

Outline of the talk

• Current baseline IDS FFAG design and alternative (J. Scott Berg, S. Machida). • Studies of injection/extraction for IDS muon FFAG (D. Kelliher, J.P., M. Aslaninejad, H. Witte).

• Injection/extraction hardware design studies (M. Aslaninejad, H. Witte, J.P.).

• Summary and future plans.

Non-scaling FFAG is preferred for muon acceleration from 12.6 to the final 25 GeV at the Neutrino Factory. Advantages include: • Allows very fast acceleration (~8-16 turns). • Large dynamic aperture due to linear magnets + high degree of symmetry • More turns than in RLA – more efficient use of rf• Quasi-isochronous – allows fixed frequency rf• Orbit excursion and hence magnet aperture smaller than in the case of a scaling FFAG•Principles of NS-FFAG will be soon tested during EMMA commissioning.

Introduction

Current NS-FFAG baseline

Lattice choice triplet with long drift:• due to longest drift injection/extraction seems to be most feasible comparing to other lattices• allows for symmetric injection/extraction,• good performance• but less cost-effective than the short drift triplet,• lattice needs to be further studied and optimised.• chromaticity correction can be added in order to correct the final energy spread due to ToF

Number of cells 64

Circumference 546 m

RF voltage 1.119 GV

Max field in F magnet

3.6 T

Max field in D magnet

6.5 T

F magnet radius 15.3 cm

D magnet radius 11.5 cm

Muon decay 5.6 %

Injection energy 12.6 GeV

Extraction energy 25 GeV

Scott’s lattice parameters.

Alternative solution - Nonliner NS-FFAG, S. Machida

Layout of FFAG with insertions

Introduction to injection/extraction

Working assumptions:

• Try to distribute kickers to reduce their strengths.

• Apply mirror symmetric solution to reuse kickers for both signs of muons.

F D FFF DD

Septum

PositiveMuons Negative

Muons

Septum

Kickers

Injection/Extraction in the Long Drift Triplet, D. Kelliher

System Injection Extraction

Type horizontal vertical

Number of kickers 3 4

Magnetic field in kickers

0.085 T 0.078 T

Kicker/septum length

2.4 m 2.4 m

Septum field 2 T ~4 T

Total number of cells used

5 6

Injectiongeometry

Extractiongeometry

• Large beam excursion near the septum requires special magnets with large aperture.• Those magnets may introduce orbit and optics distortions (correction can be possible).

Orbit shift due to extended fringe fields, J. P.

GeV

m• There are 3 curves on the plot: -orbit with the hard edge model, - with the soft edge model, - with shifted magnets

Zoom to see the differencebetween hard edge and soft edgeresults with shifted magnets.

This study suggest, that just by shifting the magnets we can correct the effect of special magnetson orbit distortion in the injection/extraction regions.

Preliminary study of IDS kickers (H.W., J.P.)

PS

PFN

PFN

PFN

switch

switch

switch

Transmission line Kicker Termination

• Due to the proton beam time structure, at least 3 independent Pulse Forming Networks (PFNs) and switches are needed for every muon train.

• Termination is very important to avoid reflections back to magnet (for injection).• Current is most likely to high for a single thyratron, but we can connect them in paralell.

Kicker field ~0.1 T

Kicker aperture 0.3m x 0.3 m

Voltage 60 kV

Max current ~30 kA

Rise/fall time 1.5 us

Kicker inductance ~3 uH

System impedance 1 Ohm

Number of kicker subsections 12

Number of PFNs per kicker 12

Total length of the kicker 2.4 m

IDS Kicker• Geometry

– Aperture: 0.3x0.3 m2 – Yoke: 120 mm– Length: 2.4 m

• Field: 100 mT• Current: 29 kA• Magnetic energy: 500 J• Inductance (single

turn): 2.8 uH• Impedance matching

– Add 5 plate capacitors (40 mm available)

Kicker geometry

EM simulations, M. Aslaninejad.

0µs 30µs 60µs 90µs 120µs 150µs 180µs 210µs 240µs-3KA

0KA

3KA

6KA

9KA

12KA

15KA

18KA

21KA

24KA

27KA

30KAI(R3)

Pulses for 3 muon buch trains separated by 100 us.

Recent progress on kicker circuit, H. Witte

Rterm

Lmag

1 Ohm

PFN 1

PFN 2

PFN 3

PFN 4

PFN 5

PFN 6

PFN 7

PFN 8

PFN 9

3 Ohm

Tfire=0 us

Tfire=100 us

Tfire=200 us

The assumed impedance was changed:Each PFN: Z= 3 Ohms

Voltage: 60 kVPeak current: 30 kAPeak current thyratron: 10 kAKicker: subdivided into 3 smaller kickersEach kicker: Travelling wave, 20 sections

Average current in Kicker

0.0µs 0.5µs 1.0µs 1.5µs 2.0µs 2.5µs 3.0µs 3.5µs 4.0µs 4.5µs 5.0µs 5.5µs 6.0µs 6.5µs 7.0µs-3KA

0KA

3KA

6KA

9KA

12KA

15KA

18KA

21KA

24KA

27KA

30KA(I(x4:L1)+I(x4:L2)+I(x4:L3)+I(x4:L4)+I(x4:L5)+I(x4:L6)+I(x4:L7)+I(x4:L8)+I(x4:L9)+I(x4:L10)+I(x4:L11)+I(x4:L12)+I(x4:L13)+I(x4:L14)+I(x4:L15)+I(x4:L16)+I(x4:L17)+I(x4:L18)+I(x4:L19)+I(x4:L20))/20

1.5 us

2 us

2 us

• Injection/extraction schemes in the NS-FFAG lattices were evaluated. The triplet lattice with long drift was chosen as the baseline.

• Alternative Nonlinear NS lattice with insertions and partial chromaticity correction was proposed.

• More beam dynamics studies are needed (chromaticity correction, errors, insertion).

• Substantial progress on the injection/extraction kicker design was achieved!

• Work focuses on the design of the superconducting extraction septum!

Summary