Radioactive Ion Beams, 1

1
Radioactive Ion Beams

• A. Fabich, CERN
• on behalf of the Beta-beam Study Group
• http//cern.ch/beta-beam
• NuFact06, UCIrvine

2
Outline

• Beta-beam concept
• EURISOL DS scenario
• Layout
• Main issues on acceleration scheme
• Physics reach
• Other scenarios
• High-energy Beta-beams
• Monochromatic beams with electron capture
• Summary

3
Beta-beam principle

• Aim production of (anti-)neutrino beams from the
  beta decay of radio-active ions circulating in a
  storage ring
• Similar concept to the neutrino factory, but
  parent particle is a beta-active isotope instead
  of a muon.
• Beta-decay at rest
• n-spectrum well known from electron spectrum
• Reaction energy Q typically of a few MeV
• Accelerated parent ion to relativistic gmax
• Boosted neutrino energy spectrum En?2gQ
• Forward focusing of neutrinos ???1/g
• Pure electron (anti-)neutrino beam!
• NB Depending on b- or b--decay we get a
  neutrino or anti-neutrino
• Two (or more) different parent ions for neutrino
  and anti-neutrino beams
• Physics applications of a beta-beam
• Primarily neutrino oscillation physics and
  CP-violation

4
Production chain

• n-factory uses beam of 4th generation.
• Beta-beam uses 3rd generation beam.
• Beta-beam is technically closer to existing/used
  accelerator technology.
• .

n-factory
and charge conjugated
beta-beam
Ion source
Acceleration
Storage
Neutrino beam
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Choice of ion species

• Beta-active isotopes
• Distance from stability
• Production rates
• Life time
• Reasonable lifetime at rest
• If too short decay during acceleration
• If too long low neutrino production
• Optimum life time given by acceleration scenario
  and neutrino rate optimization
• In the order of a second
• Low Z preferred
• Minimize ratio of accelerated mass/charges per
  neutrino produced
• One ion produces one neutrino.
• Reduce space charge problems

EURISOL DS
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Baseline and detector

• Neutrino physics similar as in n-factory, but at
  different n-energies.
• Baseline distance
• Relativistic gamma in the range of 100 400
• Q-value of MeV ?? En in the range of GeV
• Baselines in the range of 100-1500 km
• Only one detector ? one baseline
• Location available for detector underground area?
• E.g. Fermilab-Soudan 730 km
• Suitable for g6He350.
• Detector technology
• No magnetized detector necessary
• Water Cherenkov is the standard choice.
• Technically considerable in the Megaton class
• Energy resolution of 250 MeV

CERN-Frejus 130 km
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Guideline to n-beam scenarios based on
radio-active ions

• Low-energy beta-beam relativistic g lt 20
• Physics case neutrino scattering
• Medium energy beta-beam g 100
• E.g. EURISOL DS
• Today the only detailed study of a beta-beam
  accelerator complex
• High energy beta-beam g gt350
• Take advantage of increased interaction
  cross-section of neutrinos
• Monochromatic neutrino-beam
• Take advantage of electron-capture process
• Accelerator physicists together with neutrino
  physicists defined the accelerator case of
  g100/100 to be studied first (EURISOL DS).

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The EURISOL scenario

• Based on CERN boundaries
• Ion choice 6He and 18Ne
• Relativistic gamma100/100
• SPS allows maximum of 150 (6He) or 250 (18Ne)
• Gamma choice optimized for physics reach
• Based on existing technology and machines
• Ion production through ISOL technique
• Post acceleration ECR, linac
• Rapid cycling synchrotron
• Use of existing machines PS and SPS
• Achieve an annual neutrino rate of either
• 2.91018 anti-neutrinos from 6He
• Or 1.1 1018 neutrinos from 18Ne
• Once we have thoroughly studied the EURISOL
  scenario, we can easily extrapolate to other
  cases. EURISOL study could serve as a reference.

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Ion production ISOL method

• 6He production
• converter technology using spallation neutrons
• Nominal production rate 51013 ions/s can be
  achieved.

• 18Ne production
• Spallation of close-by target nuclides 18Ne from
  MgO
• 24Mg12 (p, p3 n4) 18Ne10
• Direct target the beam hits directly the oxide
  target
• Required production rate of 51013 ions/s
• (for 200 kW dc, few GeV proton beam)
• Estimated production rate more than one order of
  magnitude too low!
• Novel production scenarios required.

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Low-energy accumulation

• Optional scenario to overcome short-fall in
  production rate
• Target operated in DC mode
• Not 100 of production is used
• Dead time during acceleration
• Simultaneous accumulation in low-energy ring
• Design of a low-energy accumulation ring
  dedicated for isotope accumulation.
• Possible solution. Yet not all technical issues
  addressed and solved.

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Production with re-circulating ions

• Production of unstable isotopes
• Primary ions circulate in the beam until they
  undergo nuclear processes in the thin target
  foil.
• Injection
• Permanent accumulation of primary ions Single
  ionized ions are fully stripped by a thin foil.
• Compensating ionization losses
• Acceleration at each turn by an adequate
  RF-cavity
• Ion channel
• E.g. 7Li D ? 8Li p
• 8Li t1/20.8 s, ltEngt6.7MeV
• Rate gt 1014 ions/s
• C. Rubbia et al. (see talk this week)

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Use of existing accelerators

• Use of CERN PS and SPS
• Difficulties
• Not designed for high intensity operation of
  radioactive ions
• No collimation, non-baked vacuum system, ...
• Slow cycling
• Allows no optimization on machine design
• Large ion loss
• Considerable activation
• Vacuum degradation
• Space charge
• Advantages
• Possible cost reduction
• Maximize use of well-known machines

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Intensity evolution during acceleration
Bunch 20th 15th 10th 5th 1st
total

• Cycle optimized for neutrino rate towards the
  detector
• 30 of first 6He bunch injected are reaching
  decay ring
• Overall only 50 (6He) and 80 (18Ne) reach decay
  ring
• Normalization
• Single bunch intensity to maximum/bunch
• Total intensity to total number accumulated in RCS

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Power losses - Activation
Power loss per unit circumference of a machine
Ploss/l ions Beta-beam Beta-beam
CNGS 6He 18Ne
RCS - 0.17 0.14
PS 3.3 2.2 2.8
SPS 0.25 0.4 0.25

• Nucleon losses compared
• PS and SPS comparable for CNGS and bb operation
• PS exposed to highest power losses

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Dynamic vacuum

• Decay losses cause degradation of the vacuum due
  to desorption from the vacuum chamber
• The current study includes the PS, which does not
  have an optimized lattice for unstable ion
  transport and has no collimation system
• The dynamic vacuum degrades to 310-8 Pa in
  steady state (6He)
• An optimized lattice with collimation system
  would improve the situation by more than an order
  of magnitude.

C. Omet et al., GSI
P. Spiller et al., GSI
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Decay ring
A. Chance et al., CEA Saclay

• Geometrical considerations
• Maximize straight section
• Shortest arcs possible
• High magnetic field
• SC magnets
• For EURISOL scenario (g100)
• Circumference 6900 m
• Length of straight section 2500m
• Ratio straight section/circumference 0.36
• Geometric sizing for other gamma ranges just by
  linear scaling ? ratio always about 36
• Neutrino rate

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Stacking process

• Longitudinal merging
• Mandatory for success of the Beta-beam concept
• Lifetime of ions (minutes) is much longer than
  cycle time (seconds) of a beta-beam complex

1) Injection

1. Injection off-momentum
2. Rotation
3. Merging oldest particles pushed outside
   longitudinal acceptance ? momentum collimation

3a) Single merge
2) Rotation
3b) Repeated merging
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Particle turnover

• 1 MJ beam energy/cycle injected
• ? equivalent ion number to be removed
• 25 W/m average
• Momentum collimation 51012 6He ions to be
  collimated per cycle
• Decay 51012 6Li ions to be removed per cycle
  per meter

bb
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Collimation and absorption

• Merging
• increases longitudinal emittance
• Ions pushed outside longitudinal acceptance
• ? momentum collimation
• in straight section
• Decay product
• Daughter ion occurring continuously along decay
  ring
• To be avoided
• magnet quenching reduce particle deposition
  (average 10 W/m)
• Uncontrolled activation
• Arcs Lattice optimized for absorber system OR
  open mid-plane dipoles

s (m)
Straight section Ion extraction et each end
A. Chance et al., CEA Saclay
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Physics reach

• EURISOL scenario
• g100
• each 6He and 18Ne with a 5-year run
• 2.91018 6He decays/year or 1.11018 6Ne
  decays/year
• Physics reach
• Sensitivity on Q13 down to 1o

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Towards high-energy beta-beams

• Beta-beam operation at higher relativistic g
  reduces the annual rate Rn due to
• Extended acceleration time
• Simple analytical approximation
• Boosted life time
• Average neutrino rate R at decay ring
• at fixed ion rates from production.
• Physics reach on neutrino beam side PR ? R g

R ? 1/g
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Using existing HE hadron machines
Machine tramp (including injector chain) s Gmax(proton) gmax (6He2) gmax (18Ne10)
Tevatron 18 1045 349 581
RHIC 101 (41) 268 89 149
LHC 1200 7600 2500 3500

• Tevatron most realistic scenario
• Comparable fast acceleration in all energy
  regimes
• gtop350
• About 70 survival probability for 6He
• Compare with 45 in the EURISOL DS
• (2 seconds accumulation time considered)
• Reduced decay losses and activation during
  acceleration
• Several studies on the physics reach exist, but
  annual neutrino rates have to be reviewed.

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n-Spectra

• Wide spectra from super- and Beta-beams
• Requires energy reconstruction in detectors
• solution EC monochromatic beam
• Electron capture
• pe-?? nn
• Sharp energy spectrum of the neutrino beam

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Monochromatic n-beam
Decay t1/2 BRn EC/b En MeV DEn MeV
148Dy?148Tb 3.1m 1 0.96 2.1
150Dy?150Tb 7.2m 0.64 1 1.4
152Tm?152Er 8.0s 1 0.45 4.4 0.52
150Tm?1508Dy 72s 1 0.77 3.0 0.4

• Disentangle measurement of q13 and dCP running at
  two different g
• Ion species 150Dysprosium
• Physics reach for 1018 neutrinos/year at DR, each
  5-year run at two different g

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Special aspects of a EC n-beam

• Requires acceleration of partly stripped ions
• Vacuum lifetime comparable to half-life
• Particle losses due to charge state change
  negligible
• Most promising candidate 150Dysprosium
• Main characteristics
• Heavy and exotic isotope
• Long lifetime
• Production required gt1015 150Dy atoms/second
• Production achievable 1011 150Dy atoms/second
• 50 microAmps primary proton beam with existing
  technology (TRIUMF)
• Acceleration demanding
• Balance for charge state between high magnetic
  rigidity and space charge

Decay t1/2 BRn EC/b En MeV DEn MeV
150Dy?150Tb 7.2m 0.64 1 1.4
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Physics reach in comparison

• For q13gt1O a Beta-beam scenario is useful.
• Improved situation in combination with
• Super-beam
• Simultaneous analysis of atmospheric neutrinos

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Summary

• Beta-beam accelerator complex is a very high
  technical challenge due to high ion intensities
• Activation
• Space charge
• So far it looks technically feasible.
• The physics reach for technically achievable
  scenarios is competitive for q13gt1O.
• Usefulness depends on the short/mid-term findings
  by other neutrino search facilities.
• Acknowledgment of the input given by M. Benedikt,
  A. Jansson, M. Lindroos, M. Mezzetto, beta-beam
  task group and related EURISOL tasks