Introduction to particle accelerators

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Introduction to particle accelerators Walter
Scandale CERN - AT department Roma, marzo 2006
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Lecture VI - neutrino projects

• topics
• Superbeam Neutrino Factory Muon Collider
• Target
• Proton driver

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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
• 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.)
• Add a muon capture channel a muon accelerator
• Add a storage ring to produce muon decay
  neutrinos nF (3a) and a m - m collision storage
  ring (3b)

Neutrino Beams Superbeam neutrinos from p -gt
m nm (anti nm) . (Pions from pA -gt pX.)
Factory neutrinos from m -gt e anti nm ne (nm
anti me). (Muons from p -gt m nm (anti nm) )
b-beam neutrinos from 6He -gt 6Li e- anti ne, 18Ne
-gt 18Fe ne
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Components of a Neutrino Factory

• Proton Driver
• primary beam on production target
• Target, Capture, Decay
• create p, decay into µ
• Bunching, Phase Rotation
• reduce ?E of bunch
• Cooling
• reduce transverse emittance
• Acceleration
• 130 MeV gt 20 GeV
• Decay Ring
• store for 500 turns long straigth section

I? gt 1 x 1020 µ decays / year _at_ one s.s.
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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 (pgt p
  gt 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 RD
  effort
• RD should aim to specify
• expected performance, technical
  feasibility/risk, cost (matters!)

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Examples of Neutrino Factories
KEK scheme
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The UK scheme
To Far Detector 2
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The Super Beam
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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 ONeill
  (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 gt100 physicists
• Snowmass Summer Study (1996)
• study of feasibility of a 22 TeV Muon Collider
  Fermilab 1996
• First neutrino Factory suggested by Geer (1997)

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The piece of cake the ionization cooling

• - RF cavities between absorbers replace ?E gt 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
Figure of meritM LR ? dE?/ds
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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.

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Status of MICE

• Muon storage rings and Neutrino Factories may be
  the best way to study neutrino mixing and CPV
• ?F 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

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Progress of MICE
Cavity prototype
Decay channel and its solenoid
Final spectrometer
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Ionization cooling B-flip of solenoid
To get low ß and hence to produce small
emittance use a big S/C solenoids high fields!
gt expensive
envelop
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Ionization cooling alternative lattices

• Lattice design questions
• Many alternative configurations
• Alternating solenoid
• FOFO
• Super-FOFO
• ( RFOFO,
• DFOFO,
• Single-Flip,
• Double-Flip)
• both with cooling and non-cooling
• gt 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
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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 ?F
• Possible in principle by ionization above
  ionization minimum, but inefficient due to
  straggling and small slope d(dE/ds)/dE

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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 ltLgt 51034 cm-2s-1
prototype helical solenoidrotating-dipole quad
magnet from AGS Siberian Snake
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µ production

• 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.

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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
• from target
• from beam dump
• Superbeam vs. Neutrino Factory trade-offs
• 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.

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Horns
Carbon composite target with He gas cooling (BNL
study)
Mercury jet target (CERN SPL study)

• For secondary pions
• with Ep lt 5 GeV (Neutrino Factory), a high-Z
  target is favored,
• but for Ep gt 10 GeV (some Superbeams), low Z is
  preferred.

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Solenoids

• Palmer (1994) proposed a solenoidal capture
  system for a Neutrino Factory.
• Collects both signs of ps and ms,
• 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 ps and
  ms.

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 (?F) .

• ? Point-to-parallel focusing for
• ? Narrowband neutrino beams (less background)

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Liquid / solid target
Liquid target/dump using mercury, or a Pb-Bi
alloy. ? ?F 400 J/gm to vaporize Hg (from room
temp), ? Need flow of gt 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
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Muon production based on FFAG
Osaka Univ.
FFAG Magnetscaling
KEK
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Proton driver for a Neutrino Factory

• Proton Driver Questions
• Optimum beam energy
• depends on choice of target gt consider C, Ta,
  Hg
• Hardware options
• FFAG, linac, synchrotron gt 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 versus Neutrino Factory
• Factory requirements
• - required emittance and focusing
• - staging

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Proton drivers
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
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Existing and Proposed Proton Drivers
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.
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Driver I 4 MW, 50 Hz, 5 GeV
180 MeV, 280 MHz H- Linac
Achromat for momentum and betatron collimation
Two 50 Hz Rapid Cycling Synchrotrons, with two
bunches of 2.5 1013 protons in each. Energy 180
MeV to 1.2 GeV
Momentum ramping
Two rings each, stacked vertically
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
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Driver II 4 MW, 25 Hz, 15 GeV
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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 linacstorage ring
  approach from view point of the radiation
  protection.

20 25 kV/m cavity
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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 gt 20 0.5 1
Neutrino low DF to minimize background from cosmic rays energy tailored on wanted neutrino energy gt 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 gt Ipeak 150 A) gt 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 gt Ipeak 2kA 20 30 10-7
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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.
A NOVEL METHOD TO PRODUCE INTENSE, COLLIMATED,
PURE HIGH ENERGY ne BEAMS FROM BOOSTED
RADIOACTIVE IONS.
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CERN b-beam baseline scenario
Nuclear Physics
Br 1500 Tm B 5 T Lss 2500 m

• An annual integrated flux of n
• 2.91018 anti-neutrinos (from 6He at g100)
• 1.11018 neutrinos (from 18Ne at g100)
• With an Ion production in the target to the ECR
  source
• 6He 21013 atoms per second
• 18Ne 81011 atoms per second

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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 9.71013 7.51013
SPS ej ions/cycle 9. 01012 4.31012
PS ej ions/cycle 9.51012 4.31012
Source rate ions/s 21013 21013
Typical intensities of 108-109 ions for LHC
injector operation (PS and SPS)
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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

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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