Transcript No Slide Title

Introduction to particle
accelerators
Walter Scandale
CERN - AT department
Roma, marzo 2006
Lecture VI - neutrino projects
topics

Superbeam & Neutrino Factory & Muon Collider

Target

Proton driver
Scenarios for Neutrino beams
The basic blocks
– Proton driver 1 to 4 MW
– Muon accelerator
- Muon storage ring (decay ring / m - m collider)
This suggests (at least) 3 stages towards a neutrino factory:
1. Neutrino superbeam from pion decay with uo to 4 MW proton driver. (Stages
1a, 1b, 1c might be 1, 2, 4 MW proton driver performance.)
2. Add a muon capture channel + a muon accelerator
3. Add a storage ring to produce muon decay neutrinos nF (3a) and a m - m
collision storage ring (3b)
Neutrino Beams:
– Superbeam neutrinos from π± -> m± + nm (anti nm) . (Pions from pA -> π±X.)
– Factory neutrinos from m± -> e± anti nm ne (nm anti me). (Muons from π± -> m± + nm (anti nm) )
– b-beam neutrinos from 6He -> 6Li e- anti ne, 18Ne -> 18Fe+ ne
Components of a Neutrino Factory
Driver
— primary beam on production target
 Target,
Capture, Decay
— create π, decay into µ
 Bunching, Phase Rotation
— reduce ∆E of bunch
 Cooling
— reduce transverse emittance
 Acceleration
— 130 MeV ==> 20 GeV
 Decay Ring
— store for ~500 turns; long straigth section
In > 1 x 1020 µ decays / year @ one s.s.
 Proton
Driving issues of a Neutrino Factory
Constructing a muon-based nF is challenging
— muons have short lifetime (2.2 µs at rest)
 puts premium on rapid beam manipulations
– requires high-gradient RF for longitudinal cooling (in B field)
– requires presently untested ionization cooling technique
– requires fast acceleration system
— muons are created as a tertiary beam (p==> p ==> µ)
 low production rate
– target that can handle multi-MW proton beam
 large
muon beam transverse phase space and large
energy spread
– high acceptance acceleration system and storage ring
— neutrinos themselves are a quaternary beam
 even less intensity and “a mind of their own”
— developing solutions requires substantial R&D effort
 R&D should aim to specify:
– expected performance, technical feasibility/risk, cost (matters!)
Examples of Neutrino Factories
KEK scheme
The UK scheme
FFAG I
(3-8GeV)
FFAG II
(8-20GeV)
FFAG III
(20-50GeV)
(
Near Detector
Neutrino
Factory
Far Detector 2
Far Detector 1
R109
Muon Decay Ring
The Super Beam
A brief history of the Neutrino Factory
Muon storage ring is an old idea:

Charpak et al. (g – 2) (1960), Tinlot & Green (1960), Melissinos (1960)

muon colliders suggested by Tikhonin (1968)


but no concept for achieving high luminosity until ionization cooling
suggested by O’Neill (1956), Lichtenberg et al. (1956),
muon ionization cooling proposed by Skrinsky & Parkhomchuk (1981) and
Neuffer(1979, 1983)
 Neuffer
and Palmer (1995) suggested that a high-luminosity muon
collider might be feasible
 Neutrino
Factory and Muon Collider Collaboration started in 1995 has
since grown to 47 institutions and >100 physicists
 Snowmass
 study
 First
Summer Study (1996)
of feasibility of a 2+2 TeV Muon Collider [Fermilab 1996]
neutrino Factory suggested by Geer (1997)
The piece of cake: the ionization cooling
Momentum recovery
though RF
- RF cavities between absorbers replace E –> Net effect:
reduction in p at constant p||, i.e., transverse cooling.
- Reduce heating by Coulomb scattering:
 Strong focusing (small ß along the channel)
 Large radiation length Xo (low-Z absorber)
 High field solenoid / lithium lens
RF cavity
Sm all em ittan c e
L a rg e
e m itta nc e
A b s o rb e r

dE m
Em  Em s
dN
1



ds
2
ds
b
  

rms along  s
M o m en tu m lo s s is
op po si te to m o ti on,
p, p x , p y , E d ec rea se
dE
ds
m
N
Em

b  0.0014 GeV

A c c e le ra to r
M o m en tu m gai n
is pur e ly lo n gitudi na l
2
2b E m m m LR
3
Figure of merit:M = LR  dEm/ds
Ionization cooling test experiment: MICE
Ionization cooling is a brilliantly simple idea!
• BUT:
 never observed experimentally
 delicate design and engineering problem
 a crucial ingredient in the cost and performance optimization
Goals of MICE:
design, engineer and build a section of cooling
channel giving the desired performance for a nF;
 use a m beam and measure the cooling performance.

Status of MICE





Muon storage rings and Neutrino Factories may be the best
way to study neutrino mixing and CPV
nF technical feasibility has been demonstrated “on paper”
We need the experimental demonstration of muon ionization
cooling feasibility & performance
MICE Proposal approved and Phase 1 funded
Scope and time-scale comparable to mid-sized HEP experiment
I guess
there’ll always
be a gap
between
science and
technology
Progress of MICE
Focusing solenoid
Decay channel
and its solenoid
Cavity prototype
Final spectrometer
Ionization cooling: B-flip of solenoid
To get low ß and hence to produce small emittance
use a big S/C solenoids & high fields! ==> expensive
envelop
Ionization cooling: alternative lattices
Lattice design questions
 Many alternative configurations
1. Alternating solenoid
2. FOFO
3. Super-FOFO
4. (+ RFOFO,
5. DFOFO,
6. Single-Flip,
7. Double-Flip)
—both with cooling and non-cooling
==> arrive at baseline specifications
 end-to-end simulations
— correlations in beam and details of
distributions have significant effect on
transmission at interfaces (muons have
“memory”)
— simulation effort will tie all aspects
together
Alternating gradient allows low b with much less superconductor
Longitudinal cooling ?
 Transverse
ionization cooling self-limiting due to longitudinal emittance
growth, leading to particle losses
 straggling plus finite E acceptance of cooling channel
 need of longitudinal cooling for muon collider; could also help for nF
 Possible in principle by ionization above ionization minimum, but inefficient
due to straggling and small slope d(dE/ds)/dE
Neutrino factory based on extreme cooling
“extreme cooling” via emittance exchange in helical focusing channel filled with
dense low-Z gas or liquid proposed by R. Johnson, Y. Derbenev, et al. (Muons, Inc.)
Ecm = 5 TeV
<L> ~ 5·1034 cm-2s-1
prototype helical solenoid+rotating-dipole
+quad magnet from AGS “Siberian Snake”
µ production
µ–: 6 – 11 GeV
µ+: 9 – 19 GeV
4-MW Proton Beam on target
 10-30 GeV p-beam appropriate for both Superbeam and Neutrino Factory.
⇒ 0.8-2.5 ×1015 pps; 0.8-2.5 ×1022 protons per year of 107 s.
 Rep rate 15-50 Hz at Neutrino Factory, as low as 2 Hz for Superbeam.
⇒ Protons per pulse from 1.6 ×1013 to 1.25 ×1015.
⇒ Energy per pulse from 80 kJ to 2 MJ.
 Small beam size preferred:
≈ 0.1 cm2 for Neutrino Factory, ≈ 0.2 cm2 for Superbeam.
⇒ Severe materials issues for target AND beam dump.
Target / capture / decay
Critical issues
 Radiation Damage - Melting - Cracking (due to single-pulse “thermal shock”).
 Optimum target material
— solid or liquid
— low, medium, or high Z

Intensity limitations

Superbeam vs. Neutrino Factory trade-offs
— from target
— from beam dump
— horn vs. solenoid capture
— can one solution serve both needs?
— is a single choice of target material adequate for both?
Is there hope for a 4 MW target ?
 Several “smart” materials or new composites should be considered:
— new graphite grades
— customized carbon-carbon composites
— Super-alloys (gum metal, albemet, super-invar, etc.)
While calculations based on non-irradiated material properties may show that it is
possible to achieve 2 or even 4 MW, irradiation effects may completely change
the outlook of a material candidate.
 ONLY way is to test the material to conditions similar to those expected during
its life time as target.

Horns
Carbon composite target with
He gas cooling (BNL study):
Mercury jet target (CERN SPL
study):
For secondary pions
 with Eπ <∼ 5 GeV (Neutrino Factory), a high-Z target is favored,
 but for Eπ >∼ 10 GeV (some Superbeams), low Z is preferred.
Solenoids
Palmer (1994) proposed a solenoidal capture system for a Neutrino Factory.
 Collects both signs of p’s and m’s,
 Solenoid coils can be at some distance from proton beam.
⇒ ≥ 4 year life against radiation damage at 4 MW.
⇒ Proton beam readily tilted with respect to magnetic axis.
⇒ Beam dump out of the way of secondary p’s and m’s.
Solenoidal capture magnet (≈ 20 T)
with adiabatic transition to
solenoidal decay channel (≈ 1 T).
Mercury jet target and proton beam
tilt downwards with respect to the
horizontal magnetic axis of the
capture system
 The mercury collects in a pool that
serves as the beam dump (nF) .

   BR 2  in var iant
2
 B
p

 in var iant  p  , final  p  ,initial

p
R

B


B
B min
B max
⇒ Point-to-parallel focusing for Pp 
eBd
2 p c 2 n  1
⇒ Narrowband neutrino beams (less background)
En 
1
2
Pp 
eBd
2 p c 2 n  1
Liquid / solid target
Liquid target/dump using mercury, or a Pb-Bi alloy. ⇒ nF
≈ 400 J/gm to vaporize Hg (from room temp),
⇒ Need flow of > 104 g/s ≈ 1 l/s in target/dump to avoid boiling in a 4-MW beam.
Energy deposited in the mercury target (and dump) will cause dispersal, but at benign
velocities (10-50 m/s).
1-cm-diameter Hg jet in 2e12 protons at t = 0, 0.75, 2, 7, 18 ms (BNL E-951, 2001).
Solid Targets (Superbeams)
alternative
A solid, radiation-cooled stationary
target in a 4-MW beam will equilibrate
at about 2500 C.
⇒ Carbon is only candidate
(in He atmosphere to suppress sublimation.)
A moving band target (tantalum) could be considered in a toroidal capture system
Muon production based on FFAG
FFAG Magnet
scaling
KEK
Osaka Univ.
Proton driver for a Neutrino Factory
Proton Driver Questions
 Optimum
beam energy
— depends on choice of target ==> consider C, Ta, Hg
 Hardware
options
— FFAG, linac, synchrotron ==> compare performance, cost
 Beam
dynamics
– beam current limitations (injection, acceleration, activation)
– bunch length limitations and schemes to provide 1-3 ns bunches,
approaches for bunch compression
– repetition rate limitations (power, vacuum chamber,…)
– tolerances (field errors, alignment, RF stability,…)
 Superbeam
 Factory
versus Neutrino Factory
requirements
- required emittance and focusing
- staging
Proton drivers
P  E  I  E  I peak  DF
Intensity history of multi-GeV proton
accelerators.
The numbers in parenthesis indicate the
typical repetition rate.
 High proton beam power machines
presently operating, under
construction, or planned
Existing and Proposed Proton Drivers
d rive r
powe r
type
ene rgy
frequ e ncy
ppp
Pulse
st ruc tu re
[M W ]
[GeV]
[Hz]
[10
13
]
tp
[m s]
Nb
tb
[ns ]
1
Synch
28
2 .5
9
720
24
3
4
Synch
28
5
18
720
24
3
4
Synch
40
5
12 .5
720
24
3
2
Synch 1
8
15
10
1.6
84
1
2
Linac 2
8
10
15
F N A L MI
2
Synch
120
0 .67
15
10
530
2
C ER N S P L
4
LAR
2 .2
50
23
3 .2
140
1
4
LAR
3 .5
50
14
1.7
68
1
J -PA RC
0 .75
Synch
50
0 .3
31
4 .6
8
6
RA L
4
Synch
5
50
10
1.4
4
1
4
Synch
6 –8
50
8 .3
1.6
6
1
4
FF A G
10
50
5
2 .3
5
1
4
Synch
15
25
6 .7
3 .2
6
1
RA L/C ERN
4
Synch
30
8 .33
10
3 .2
8
1
KEK /Kioto
1
FF A G
1
10 4
0 .06
0 .4
10
10
1
FF A G
3
31 0 3
0 .06
0 .5
10
10
BN L -A GS
F N AL
The pulse structure is given in terms of the pulse duration tp, the number of bunches
Nb making up each pulse, and the final compressed rms bunch length tb.
Driver I: 4 MW, 50 Hz, 5 GeV
Achromat for
momentum and
betatron collimation
Momentum
ramping
Two rings each, stacked vertically
180 MeV, 280 MHz H- Linac
Two 50 Hz Rapid Cycling
Synchrotrons, with two
bunches of 2.5 1013 protons in
each.
Energy 180 MeV to 1.2 GeV
Two 25 Hz Rapid Cycling Synchrotrons,
4 bunches in each.
Energy 1.2 GeV to 5 GeV.
Bunch compression to 1 ns rms at pion
target
Mean radius 65m
Driver II: 4 MW, 25 Hz, 15 GeV
Two 12.5 Hz Rapid Cycling Synchrotrons,
6 bunches in each. Energy 3 GeV to 15 GeV.
Bunch compression to 1 ns rms at pion target
Mean radius
150m
Achromatic arc for
collimation
180 MeV, 280 MHz, H- Linac
Two rings each,
stacked vertically
Momentum
ramping
Two 25 Hz Rapid Cycling Synchrotrons, with
three bunches of 1.11 1013 protons in each.
Energy 180 MeV to 3 GeV
Challenges of the RCS








Large aperture magnets and much higher RF voltages per turn due to a low
energy injection and a large and rapid swing of the magnetic field,
Field tracking between many magnet-families under slightly saturated
conditions,
RF trapping with fundamental and higher harmonic cavities,
H- charge stripping foil,
Large acceptance injection/dump/extraction section,
Ceramic chambers,
Beam instabilities,
Comparison with full-energy linac+storage ring approach from view point of the
radiation protection.
20 ÷ 25 kV/m cavity
Other applications of Proton Drivers
Type of accelerator
Energy
[GeV]
duty
factor DF
Neutron for material studies
• neutron yield proportional to beam power
0.5 ÷ 10
CW ÷ 10-4
Neutron spallation | nuclear waste transmutation | accelerator driven
supercritical reactors
• lower energy to limit the power deposition in the target window
• higher energy up to full absorption of beam power in the reactor vessel
0.5 ÷ 5
CW
Kaons and heavy flavor
• high DT to minimize the detector dead time
• high energy to stay beyond production threshold
> 20
0.5 ÷ 1
Neutrino
• low DF to minimize background from cosmic rays
• energy tailored on wanted neutrino energy
> 1 GeV
10-5
Muons for neutrino factory
• low DF to limit the up-time of muon cooling channel
• high E to minimize the peak current (eg for 5MW ==> Ipeak ~ 150 A)
> 3 GeV
10-5
Muons for muon colliders
• low DF to minimize the muon bunch length (hence maximize the luminosity)
• high E to minimize the peak current (eg for 5MW ==> Ipeak ~ 2kA
20 ÷ 30
10-7
The b-beam concept
b-beam Piero Zucchelli
• A novel concept for a neutrino factory: the beta-beam, Phys. Let. B, 532 (2002) 166-172.
CONVENTIONAL METHODS :
Neutrino beams are produced using the decay of pions and muons.
Lorentz boost
high
ADVANTAGES OF BETA-BEAMS :
Pure (
or
) beams.
Well known neutrino fluxes.
Strong collimation.
A NOVEL METHOD TO PRODUCE INTENSE,
COLLIMATED, PURE HIGH ENERGY ne BEAMS
FROM BOOSTED RADIOACTIVE IONS.
CERN: b-beam baseline scenario
SPL
Nuclear
Physics
Decay
ISOL
target &
Ion source
ECR
Cyclotrons,
linac or
FFAG
Rapid cycling
synchrotron
6
2
SPS
PS
-
He  Li e n
6
3
Average
18
10
E cms  1.937 MeV

Ne  Fe e n
18
9
Average
Ring
Br = 1500 Tm
B=5T
Lss = 2500 m
E cms  1.86 MeV
An annual integrated flux of n


2.9*1018 anti-neutrinos (from 6He at g=100)
1.1*1018 neutrinos (from 18Ne at g=100)
With an Ion production in the target to the ECR source:
 6He=

2*1013 atoms per second
18Ne= 8 1011 atoms per second
*
CERN: b-beam baseline limitations
 Isotope
production
 The
self-imposed requirement to re-use a maximum of existing CERN
infrastructure
– Cycling time, aperture limitations, collimation systems etc.
 The
high intensity ion bunches in the accelerator chain and decay ring
– Space charge
– Decay losses
6He
18Ne
Decay ring [ions stored]
9.7*1013
7.5*1013
SPS ej [ions/cycle]
9. 0*1012
4.3*1012
PS ej [ions/cycle]
9.5*1012
4.3*1012
2*1013
2*1013
Source rate [ions/s]
Typical intensities of 108-109 ions for LHC injector operation (PS and SPS)
Decay ring design aspects
The ions have to be concentrated in a few very short bunches
– Suppression of atmospheric background via time structure.
 There is an essential need for stacking in the decay ring

– Not enough flux from source and injector chain.
– Lifetime is an order of magnitude larger than injector cycling (120 s
compared with 8 s SPS cycle).
– Need to stack for at least 10 to 15 injector cycles.

Cooling is not an option for the stacking process
– Electron cooling is excluded because of the high electron beam energy
and, in any case, the cooling time is far too long.
– Stochastic cooling is excluded by the high bunch intensities.

Stacking without cooling “conflicts” with Liouville
Lecture VI - neutrino projects
reminder
Neutrino physics is very appealing
Neutrino beam devices are complex and expensive
Superbeam is the basic initial block os a modern neutrino facility, it relies
on the construction of a multimegawatt proton driver
 Muon accelerators are the next step and rely on a performing target
system capture channel and on the very challenging ion cooling
 Neutrino factories and muon muon colliders are the last step (cost is
matter
 Beta-beams are a clever shortcut


