THE NEUTRINO FACTORY

• Introduction

• NuFact stories :

• EU - principles of a NuFact

• US Study II, Study IIa

• NuFactJ - FFAG acceleration

• Conclusions (if any)

F. Méot DAPNIA

IntroductionA BRIEF HISTORICAL OVERVIEW :

• late 60’s : idea of muon colliders proposed : leptons w/o SR highest energy circular colliders

• 1974 : concept of a neutrino factory based on muon collider front end & muon decay ring

• early 80’s : ionisation cooling methods make these envisageable (luminosity / intensity)

• 1992 : US launch muon collider design studies

• 1995 : MuColl formed (mostly BNL, LBNL, Fermi) - 1996 : issues Muon Collider FS report, 2TeVx2TeV collider, L = 1035/cm2/s, 4MW p-driver

• 1998 : neutrino factory confirmed as a possible first step towards a muon collider

In Europe, muon collider foreseen as possible post-LHC project, 1998 : CERN

launches a prospective group, with the participation of MuColl

• 1999 : a NuFact Feasibility Study is launched at Fermi, based on Fermilab upgrade (8-16 GeV

pDriver) ; 2000 : a first FS report of a NuFact

• 2000 : “Study II” launched at BNL, completed in 2001 ; goals : a follow-on of Study I, BNL site based,

pin cost drivers

• In Japan, NuFact based on JPARC as p-driver + FFAG for acceleration to 20GeV. 2001 :

FS study report issued

• 2002, CERN FS report issued ; NuFact based on SPL 2.2 GeV p-driver, and on RLA -acc

• 2004, “Study IIa”, an upgrade of Study II, with various cost effective variants, e.g. FFAGs, and ±

EU : CERN design

• Principle of the NuFactory : - afap, store a high energy, well collimated or bunch train in a ring with long straight sections pointing to distant detectors ; - goal intensity : 1021 /year

* For reference : highest neutrino flux, currently planned for MINOS, is 108 and 5 105 e /year ; super-beams will have similar rate, yet with ~1/E3 detector event rate (overall gain of NuFact ~100)

• Muon acceleration needs be fast, rest lifetime : 2.2s (c= 659 m), i.e. 1.1ms at 50 GeV (c= 330 km)

• Accelerator chain : p-driver (high power), pion production (target), muon collect (magnetism), phase rotation

(E/E reduction), transverse cooling (emittance reduction), acceleration (RLA), storage (decay ring).

• Detectors : at least 2 with different LBL for precision.

11-50GeV

3-11GeV

1016p/s, 1.6 1012p/b

1021 /Y50GeV

<4MW>

Accelerate fast !

muon yield versus final E

- Superconducting Proton Linac, 2.2 GeV / [up to 4GeV ?], 2mA H- linear accelerator- stripping injection into accumulator ring - could be used in improved injector chain for LHC, and for ISOL applications - NuFact pulse : 2.8ms duration ; rep.rate 50Hz

Kyes to parameters : - Choice of energy : optimize yield - the subject of HARP - urgently needed ! , of production/capture/acceleration optimization studies - 4 MW : will yield 1021 /year in storage ring - 50Hz : a/ batches spacing must be > 50GeV lifetime (1.1ms); b/ 4MW upper limit (targetry/-collector)

proton driver : SPL

IPHICEA / IN2P3

RF 352MHz

bunch : 0.13ns, 3.85 108 p/bdp/p=1.2 10-2, emitance 50 mm.mrad.

2.3 1014 ppp x 50Hz = 1.1 1016 pps2.7ms pulse, <12mA>

Bunch train time structure

44MHz accumulator

* “Linac 4”, doubles Q/bunch to PS Booster *

T= 2.2 GeVIDC = 13 mA (during the pulse)IBunch= 22 mA3.85 108 protons/bunchlb(total) = 44 ps*H,V=0.6 m r.m.s

(140 + 6 empty)per turn

845 turns( 5 140 845 bunches per pulse)

no beam

2.8 ms20 ms

140 bunches

20 ms

3.2 s

Charge exchangeinjection

845 turns

PROTON ACCUMULATORTREV = 3.316 s

(1168 periods @ 352.2 MHz)

1 ns rms(on target)

22.7 ns

TARGET

H+140 bunches1.62 1012 protons/bunchlb(rms) = 1 ns (on target)

Fast ejection

KICKER20 ms

3.3 slb(total) = 0.5 ns

DRIFT SPACE+

DEBUNCHER

H-

11.4 ns

22.7 ns

5bunches

Fast injection(1 turn)

BUNCH COMPRESSORTREV = 3.316 s

(1168 periods @ 352.2 MHz)

BUNCHROTATIONRF (h=146)

Fast ejection

RF (h=146)

3 emptybuckets

17.2 ms

Accumulator and compressor rings - Located in ISR tunnel- Convert the SPL 2.7ms pulse into a 140-bunch train, rep.rate 50Hz- Compress bunches from 12.4ns down to 1ns length

X 5b/b x 850 turns = 1.6 1012 p/b

44MHz

352MHz

train, bunch spacing 22.7.ns

C = 942m 7 turns

On target : ~1016 p/s, 1023 p/Y

There are other options for a 4MW

p-driver

An example :

double, 15 GeV Rapid Cycling Synchrotron in

the ISR tunnel

RCS versions of a p-driver

Important to NuFact R/D : Recent innovation (UK), FFAG versions of p-driver

pumplet cell :4 MW

rotating tantalum target ring

Flying target :

• Liquid mercury jet (L30cm, 20m/s, 1cm) - cf. SNS ; low-energy p -> high Z is suitable, choice for the CERN study. Allows better handling of thermal and activation issues. 10 tons Hg buffer.

• Rotating solid target

Stationary target : • Graphite (80cm), other low-Z material• Tantalum beads (2mm, high Z), alternative to liq.Hg ; reduced shock effect, flowing g.He cooling ~1MW limit multi-target+funneling

A complete, high level radioactivity installation

Specifications for target studies :

- Proton Beam impulse <3s, rep.rate 10-50 Hz

- Energy 2-30 GeV, <I> < 2mA

- Power ~4 MW (25% absorbed in target), reasonable lifetime

Issues : - thermal shock, mechanical break, cooling, lifetime

20 cm

2 cm

Target

B : 20T 15cm

1.25T 1/B: 30cm

Once pions are produced... capture option 1 : 20T SC solenoid

leaves space for targetry solenoid lifetime > 1 year

Issues : radiation hardness, replacement cost

Proton bunch

Inner horn : 300 kA, 100s pulse

To decay channel

Hg target 1.5T at waist

B=0I/2R

B = 0

pion capture, option 2 : double horn cf. CNGS, NuMI

• efficiency ~ that of 20T solenoid• horn lifetime estimated 6 months heat, radiation damage, magnetic stress

Outer horn : 600 kA pulse, B at waist 0.3T

• decay channel, about 30 meters downstream of target -> 85% decayed into -bunch

• main objective : minimize decay induced beam emittance increase

• length ~30m (~85% decay), diameter ~60cm (high transmission)

• solenoid, 1.8T

or, AG focusing, B ~ 2-3T at r=30cm

• -beam in : 3cm transverse emittance, E : ~0-2GeV

• transmission of ’s through r=40cm channel into ~3cm, 0.7eV.s : 4%

p-bunch at target ~1ns

(x,x') channel acceptance

next : muons pion decay channel / mu collect

(x,x') -beam at horn exit

energy (MeV) vs. time (nsec)

0

200

400

600

800

1000

-5 0 5 10 15 20 25 30 35

p bunch (~1ns)

muon bunch

muon bunch spectrum

Muon bunch phase-rotation These stages are necessary because of the small acceptance of

the RLA chain (1.5cm, 0.15eV.s)

(Their importance is questioned with most recent RLA

designs that pull their acceptance towards 3cm, 0.7eV.s )

Goals, means : • Reduce energy-spread in the muon bunch• necessary for entering following cooling stage with suitable conditions• uses 44MHz, 2MV/m RF + solenoid focusing • bunch-to-bucket principle : a 180° piece (11ns) of the muon bunch fits into the 44MHz bucket• 50% of incoming ’s are captured ; E 100-300MeV• channel length : 30m - 30 cavities• Still, transverse cooling is needed next

Beam in

Beam out

Earlier

-bu

nch

longitudinal

0.1eV.s (~RLA acceptance)

Typical assembly 88 Mhz cavity ->

44 Mhz has 226cm diam.!

Ionization cooling of the muon beam

H

2

Rf

Liquid H2 -> dE/dx

Beamsolenoid

solenoid

BEAM IN

BEAM OUT

• The 200m long cooling channel is a linear accelerator with liq.H2 absorbers

• Three sections : 11 ( 444MHz cav. + H2abs) + Accel 44MHz + 25 ( 888MHz cav. + H2abs) 1m,2MV/m,60cm 0.24m 200280 0.5m,4MV/m30 0.4m

50m 30m 110m

RF restores only P// , E kept constant

Acceleration

• Pre-acceleration Linac from ~300MeV at exit of cooling (including

section for longitudinal matching to 220MHz) up to 3GeV ;

• Two RLA’s, 4 pass each, from 3 to 11 and from 11 to 50 GeV.

- RLA 1 : 2 1GeV linac, F 220MHz, horizontal spreader/recombiners

- RLA 2 : 2 5GeV linac, otherwise design copied from ELFE@CERN, including LEP cavities 352MHz

- Acceptance : 1.5cm norm. transverse, 0.15 eV.s longitudinal, limited by cavities

- <E>~MV/m over typical ~4km distance, hence fair muon survival ~90%

• R&D 200 MHz cavity. Acceptance no more limited by cavity, rather

by arc/combiners design, and reaches 3cm / 0.7eV.s. Principles :

- high V hence reduced RLA length to limit decay - high V entails high RF freq. > 100 MHz- hence the Cornell-CERN collaboration

11-50GeV3-11GeV

ELFE@CERN

ALS2

Decay ring Where do you prefer to take shifts?

Possible BL from Geneva :

Hammerfest (N) - Gd Sasso 2883k - 739k

Las Palmas (E) - Gd Sasso

2768k - 739k

South Tunis (T) - Brest (F) 1094k - 840k

• Triangle, or bow-tie (higher rate, lower vertical depth of 150m, civil engineering issue at Xing) • “ring” decay straights are inclined • high- decay straigths -beam divergence < 0.2/

SC optics to shorten the arcs

US study-II

, 1MW

p-Driver : AGS upgrade

H-

1MW : 6 b/fill x 2.5fills /s x 1.5 1013 p/b

C=200m

SCRF 805 MHz

SCRF 1.61 GHz

US study-II

p-Driver : upgrade of AGS rep. Rate

• H- source 2.5Hz+chopper+0.75MeV RFQ

• to replace the present AGS booster

• one fill has 6 bunches spaced 20ms, cycle rep. rate 2.5Hz, 1.5 1013 p/bunch at 1MW (cf. CERN : 140 bunches per fill, 50Hz, 1.6 1012 p/b at 4MW)

• possible compressor ring : a 4MW upgrade, 5Hz, 2 1014ppp

US study-II

• 4-pass single RLA ; 200 MHz SCRF

• Choice of a factor of ~10 energy increase, from CEBAF experience. 2.8 injection energy allows inj~1.

• Acceptance : transverse norm. 1.5 cm (bunch diameter mm initial/final), longitudinal 0.7 eV.s (bunch length 197/46 deg initial/final). muon decay during RLA is 90%

-> yields the 0.17mu in decay ring / 24GeV p

• Time structure of beam : 6 pulses, 67 bunches per pulse (200MHz), pulses spaced 20ms, 2.5Hz rep.rate

SC solenoid (1m/2T) 15MV/m SCRF

=90deg, p/p= 21%

=23deg, p/p= 7.5%Mag. aperture 30cm

Horizontal spreaders/rec

Mag. aperture 30cm

17MV/m

Magnet aperture 20cm

=20deg, p/p= 2%

Acceleration

Conclusions of Study II• Study I and II -Factory have demonstrated feasibility

• Still,

– need to persue R&D, in many domains

– expensive, cf., acceleration in Study II is ~500M$/1700M$, cooling 300M$

• Introduce FFAGs

Study Iia (2004)- FFAGs are introduced- cost / GeV lower than RLA

NuFACT Japan

+ Seoul+Beijing

JHF construction 2001-2006

• 50GeV ring : 4 bunches accelerated, <I>=20A, 3 1014 ppp, 0.4Hz, 1MW

• 8 bunches, bunch length ~6ns rms, spacing 0.5s,

• -acceleration : FFAG rings. Weak <E> ~1MV/m, acceleration distance to 20GeV is ~20km => muon survival only ~50%.

• Advantage of FFAG :

• very large acceptance transverse 3cm norm., longitudinal 5eV.s. (no phase-rotation, no cooling). This ensures 0.3/p and 10^20 decay/MW-p/drift/year in SR

• should be simpler (less R&D), and cheaper than RLA (no cooling section, FFAG is easier technology/construction). Technological challenges: Injection and ejection

FFAG R&D- POP proton machine, 500keV, operated in 2000

- a 150MeV proton FFAG is under commissioning

- PRISM, 20MeV FFAG for muon phase rotation : 0.8MW super-beam for stopped- experiments at JHF, approved.

- Principles :

B=B0(r/r0)k,

DFD cells.

PRISM

• Pion capture section• Decay section• Injection R&D NuFact!• Phase rotation section• Xtraction R&D NuFact!

• 1011-12 muon/s

FFAG a ring instead of linac– reduced # of rf cavities– reduced rf power – compact

01

23

45

x3 dynamic per stage

xz

•Low-E FFAG : – design still to be demonstarted– in particular injection/Xtraction

MERCI POUR

VOTREATTENTION

-beam

• Single flavour

ebar source 6He, T½=0.81 s, Elab = 580 MeV, = 130 GeV, 5 x 1013/se source 18Ne, T½=1.67 s, Elab = 930 MeV, = 130 GeV, 1012/s

• Known intensity & energy spectrum (small 6D emittance ion beams)

• Focussed

• Low energy

• Complementary to superbeams

• Analyzed for CERN accelerators only

• R&D for ion sources

• Hadronic pollution