International Design Study of aNeutrino Factory

J. Scott BergBrookhaven National Laboratory

IPAC 201027 May 2010

Neutrino Physics

❍ Neutrinos have mass❍ Mass and flavor eigenstates different❍ Mixing matrix angles θ12, θ23, θ13

❑ θ13 possibly zero, θ23 near 45◦

❍ CP-violating phase δ (irrelevant if θ13 zero)❍ Squared mass differences

❑ |∆m2

21| ≪ |∆m

2

31|

❑ Sign of ∆m2

31unknown

2

Neutrino Properties3

2

1

1

2

3

e µ τ

ma

ss

2

3

Long Baseline NeutrinoExperiments

❍ Accelerator: make neutrinos in flavor eigenstate❑ Mixture of mass eigenstates

❍ Neutrinos propagate to far detector❑ Each mass eigenstate has different phase

advance❑ Phase advance: square of mass

❍ Detector: detect flavor eigenstate❑ Detect corresponding lepton (e, µ)

4

Neutrino Factory Goals

❍ Create high-energy muon beam❍ Decay in ring, directed through earth to far

detector❍ Well-defined spectrum from muon decay

❑ µ− creates νµ and ν̄e❑ Distinguish by sign of detected leptons

✧ Need magnetized detector

5

Neutrino Factory vs.Superbeams

❍ Get results forsmallest θ13

❍ Better precisionfor mixingparameters

❑ Especiallyinteresting ifnearlysymmetric

10–5

10–4

10–3

10–2

10–1

True value of sin22θ13

0

0.2

0.4

0.6

0.8

1

Fra

ctio

no

fδ

CP

SPL

T2HK

WBB

NF

BB

GLoBES 2006

6

Neutrino Factory AcceleratorComplex

❍ High-power proton driver, protons hit❍ Target, producing pions decaying to muons❍ Front end, reshapes and intensifies beam❍ Acceleration, increase energy to 25 GeV❍ Decay ring, neutrinos produced decay toward

far detectors

7

Neutrino Factory AcceleratorComplex

12.6–25 GeV FFAG

3.6–12.6 GeV RLA

0.9–3.6 GeV

RLA

Linac to

0.9 GeV Muon Storage Ring

Muon Storage Ring

Linac optionFFAG/synchrotron option

Proton Driver

Neutrino Beam

Neutrino Beam

Hg Target

Buncher

Bunch Rotation

Cooling

1.5 km

755 m

1.1

km

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International Design Study

❍ Goal: reference design report by end 2012❑ Basis for request to start project❑ Costs at 30% level

❍ Interim design report by end 2010❑ Move from design to engineering❑ Designs for all systems❑ Cost estimates at 50% level

❍ Focus on baseline: one design!

9

Baseline Parameters

❍ 25 GeV muon beam, both signs❍ Detectors at two distances

❑ 3000–5000 km❑ 7000–8000 km

❍ 5× 1020 muon decays per year per baseline

❍ Muon beam divergence of 0.1/γ

10

High-Power Proton Driver

❍ Supply protons to target to produce pions❍ Basic specifications:

❑ 4 MW proton beam power❑ Proton kinetic energy 5-15 GeV❑ RMS bunch length 1–3 ns❑ 50 Hz repetition rate❑ Three bunches, extracted up to 80 µs apart

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Muon Capture vs.Proton Energy

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0 10 20 30 40 50 60 70 80 90 100

Mes

ons/

prot

ons/

GeV

Proton Kinetic Energy, GeV

12

Muon Capture vs.Proton Bunch Length

13

Proton Bunch Structure

1–3 ns

> 160 µs

20 ms

14

Proton Driver Plans

❍ Will be upgrade to existing facility❍ Important to understand contribution to cost of

neutrino factory❍ Individual laboratories will contribute

❑ Plan to upgrade to neutrino factoryrequirements

❑ Corresponding cost estimate

15

Target

❍ Baseline is liquid mercury jet❑ Avoid target damage

❍ Target in 20 T field: pion capture❍ Demonstrated in MERIT experiment

❑ Proton beam pulses comparable to neutrinofactory

❑ Two bunches in rapid succession: no loss inproduction for second with spacing 350 µs orless

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Mercury Jet Target Station

IronPlug

ProtonBeam

NozzleTube

SC-1

SC-2 SC-3 SC-4SC-5

Window

MercuryDrains

MercuryPool

Water-cooledTungsten ShieldMercury

Jet

ResistiveMagnets

SplashMitigator

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Target Plans

❍ Engineering of target station and components❍ Jet nozzle: improve jet quality❍ Ensure sufficient shielding of superconducting

magnets❍ Fluid dynamics/engineering of Hg pool

❑ Acts as beam dump❑ Return Hg to loop

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Mercury Pool Dynamics

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Front End

❍ Pions (thus muons) start with large energyspread: reduce

❑ “Neuffer” phase rotation✧ Uses high-frequency RF✧ Does both signs

❑ Create 200 MHz bunch train❍ Reduce transverse beam size

❑ Ionization cooling

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Pion Spectrum

0

50

100

150

200

250

300

0 0.2 0.4 0.6 0.8 1

Mes

ons/

10M

eV/G

eV

Kinetic Energy, GeV

10GeV+50GeV+100GeV Beam-Mesons(Positives+Negatives) at 50m

10GeV50GeV

100GeV

21

Phase Rotation

ct

∆E

Drift rf-Buncher rf-Rotation

22

RF in Magnetic Field

❍ RF cavities in magnetic field❑ Large angular and energy acceptances

❍ Experiments: gradient reduced in magnetic field❍ Don’t have complete picture yet❍ Ongoing experiments

❑ Change magnetic field orientation w.r.t.surface

❑ Gas-filled RF cavities❑ Test different surface materials

23

Ionization Cooling Lattice

24

Gradient vs. Magnetic Field

0 1 2 3 4Solenoid Magnetic Field (T)

0

5

10

15

20

25

30

35

40

45G

radi

ent (

MV

/m)

25

Mitigation Strategies

❍ Reduce fields on cavities❑ Increase distance to magnets❑ Add bucking coils❑ Add shielding to solenoids

❍ Magnetically insulated lattice: high-E fieldsurfaces parallel to B

❍ Make cavity from beryllium❍ Fill cavities with pressurized hydrogen gas

26

Front End Plan

❍ Mitigation often reduces performance❍ Operation limits of cavities still unknown❍ Baseline: choose technically optimal design

❑ Earlier “Study IIa” lattice❑ Improved Neuffer phase rotation

❍ One alternative to understand penalty/cost ofmitigation

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Acceleration

❍ Efficiency: maximize passes through RF❍ Four stages to get good efficiency

❑ Linac to 0.9 GeV❑ Two RLAs: to 3.6 GeV and 12.6 GeV (4.5

passes)❑ FFAG to 25 GeV (11 passes)

❍ Use 200 MHz SCRF

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Acceleration

12.6–25 GeV FFAG

3.6–12.6 GeV RLA

0.9–3.6 GeVRLA

Linac to0.9 GeV

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AccelerationLinac and RLAs

❍ Lattices completely defined❍ More detailed magnet designs❍ Tracking beginning with soft ends

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AccelerationFFAG

❍ Many passes (11): no switchyard❍ Injection/extraction challenging

❑ 15 cm radius, 0.09 T field, 7 needed, 546 mring circumference

❍ Selected triplet lattice with long drifts❑ Longer drifts ease injection/extraction❑ Double cavity in long drift: better gradient

✧ Reduce longitudinal distortion: largetransverse amplitude

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AccelerationFFAG

❍ Add some chromaticity correction❑ Modest amount: hurts dynamic aperture❑ Helps longitudinal distortion

❍ Design kicker systems (magnet, power supply)❍ Study lattice dynamics in EMMA experiment

32

Decay Ring

❍ Long straights to maximize decays to detector❍ High beta functions in straight: reduce

divergence❑ Less divergence, less flux uncertainty for

given divergence uncertainty❍ Excellent dynamic aperture

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Decay RingDynamic Aperture

34

Decay RingDiagnostics

❍ Reduce flux spectrum uncertainty❍ Polarimeter: measure decay electron spectrum

❑ Neutrino flux depends on polarization❑ Detector transverse to beam, in matching

section following weak bend❍ In-beam He gas Cerenkov: beam divergence

❑ Emittance growth: verify if acceptable

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Decay RingPolarimeter

36

Low-Energy Neutrino Factory

❍ Same as above but stopping accelerationearlier, different decay ring

❍ Competitive with high energy (and bestsuperbeams) if θ13 large

❍ Interesting as part of staging❑ Start with low energy❑ Upgrade to high energy or larger detector

depending on physics results❍ Will be described in design reports

37

Conclusions

❍ Neutrino factory: precision measurements ofneutrino mixing

❍ Well-defined scenario, lattices almost complete❍ Continuing important R&D

❑ RF cavities in magnetic fields❑ MICE cooling experiment❑ EMMA: FFAG dynamics

❍ Starting engineering of components

38