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

Introduction A 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) : issues Muon Collider FS report, 2TeVx2TeV collider, L = /cm 2 /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 : 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 :  /year * For reference : highest neutrino flux, currently planned for MINOS, is 10 8   and e /year ; super-beams will have similar rate, yet with ~1/E 3 detector event rate ( overall gain of NuFact ~100 ) Muon acceleration needs be fast, rest lifetime : 2.2  s (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 GeV 3-11GeV p/s, p/b  /Y 50GeV 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  /year in storage ring - 50Hz : a/ batches spacing must be > 50GeV  lifetime (1.1ms); b/ 4MW upper limit (targetry/  -collector) proton driver : SPL IPHI CEA / IN2P3 RF 352MHz  bunch : 0.13ns, p/  b dp/p= , emitance 50 mm.mrad ppp x 50Hz = pps 2.7ms pulse, Bunch train time structure  44MHz accumulator * “Linac 4”, doubles Q/bunch to PS Booster *

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 5  b/b x 850 turns = p/b 44MHz 352MHz train, bunch spacing 22.7.ns C = 942m 7 turns On target : ~10 16 p/s, 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 <3  s, rep.rate Hz - Energy 2-30 GeV, < 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, 100  s pulse To decay channel  Hg target 1.5T at waist  B=  0 I/2  R 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 : 3  cm transverse emittance, E : ~0-2GeV transmission of  ’s through r=40cm channel into ~3  cm, 0.7  eV.s : 4% p-bunch at target ~1ns (x,x') channel acceptance next : muons pion decay channel / mu collect (x,x')  -beam at horn exit 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 (1.5  cm, 0.15  eV.s) (Their importance is questioned with most recent RLA designs that pull their acceptance towards 3  cm, 0.7  eV.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 MeV channel length : 30m - 30 cavities Still, transverse cooling is needed next Beam in Beam out Earlier  -bunch longitudinal 0.1  eV.s (~RLA acceptance) Typical assembly 88 Mhz cavity -> 44 Mhz has 226cm diam.!

Ionization cooling of the muon beam H2H2 Rf Liquid H 2 -> dE/dx Beam solenoid BEAM IN BEAM OUT The 200m long cooling channel is a linear accelerator with liq.H 2 absorbers Three sections : 11  ( 4  44MHz cav. + H 2 abs) + Accel 44MHz + 25  ( 8  88MHz cav. + H 2 abs) 1m,2MV/m,  60cm 0.24m 200  m,4MV/m  m 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 including LEP cavities 352MHz - Acceptance : 1.5  cm norm. transverse, 0.15  eV.s longitudinal, limited by cavities - ~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 3  cm / 0.7  eV.s. Principles : - high V hence reduced RLA length to limit  decay - high V entails high RF freq. > 100 MHz - hence the Cornell-CERN collaboration 11-50GeV 3-11GeV 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 p/b C=200m SCRF 805 MHz SCRF 1.61 GHz US study-II p-Driver : upgrade of AGS rep. Ratep-Driver 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, p/bunch at 1MW (cf. CERN : 140 bunches per fill, 50Hz, p/b at 4MW) possible compressor ring : a 4MW upgrade, 5Hz, ppp

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  in j ~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 GeV ring : 4 bunches accelerated, =20  A, ppp, 0.4Hz, 1MW 8 bunches, bunch length ~6ns rms, spacing 0.5  s,  -acceleration : FFAG rings. Weak ~1MV/m, acceleration distance to 20GeV is ~20km => muon survival only ~50%. Advantage of FFAG : very large acceptance transverse 3  cm norm., longitudinal 5  eV.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 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! muon/s FFAG a ring instead of linac –reduced # of rf cavities –reduced rf power –compact

x3 dynamic per stage x z Low-E FFAG : – design still to be demonstarted – in particular injection/Xtraction

MERCI POUR VOTRE ATTENTION

 -beam Single flavour e  bar source 6 He, T ½ =0.81 s, E lab = 580 MeV,  = 130 GeV, 5 x /s e source  18 Ne, T ½ =1.67 s, E lab = 930 MeV,  = 130 GeV, /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