RadioactiveIonBeams NuFact06 AFabich

Radioactive Ion Beams: 

Radioactive Ion Beams A. Fabich, CERN on behalf of the Beta-beam Study Group http://cern.ch/beta-beam NuFact’06, UCIrvine

Outline: 

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

Beta-beam principle: 

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 Cross-sections of neutrino-nucleus interaction

Production chain: 

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. . and charge conjugated n-factory beta-beam Ion source Acceleration Storage Neutrino beam

Choice of ion species: 

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

Baseline and detector: 

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 g6He=350. Detector technology No magnetized detector necessary Water Cherenkov is the standard choice. Technically considerable in the Megaton class Energy resolution of ~250 MeV LAr as an alternative choice. Higher resolution (~50 MeV) Technological challenge CERN-Frejus: 130 km

Guideline to n-beam scenarios based on radio-active ions: 

Guideline to n-beam scenarios based on radio-active ions Low-energy beta-beam: relativistic g < 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 >350 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 g=100/100 to be studied first (EURISOL DS).

The EURISOL scenario: 

The EURISOL scenario Based on CERN boundaries Ion choice: 6He and 18Ne Relativistic gamma=100/100 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 2.9*1018 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.

Ion production – ISOL method: 

Ion production – ISOL method 6He production converter technology using spallation neutrons Nominal production rate 5*1013 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 5*1013 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.

Low-energy accumulation: 

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.

Production with re-circulating ions: 

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: t1/2~0.8 s, <En>~6.7MeV Rate: > 1014 ions/s C. Rubbia et al. (see talk this week)

Use of existing accelerators: 

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

Intensity evolution during acceleration: 

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

Power losses - Activation: 

Power losses - Activation Nucleon losses compared PS and SPS comparable for CNGS and bb operation PS exposed to highest power losses Power loss per unit circumference of a machine

Dynamic vacuum: 

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 3*10-8 Pa in steady state (6He) An optimized lattice with collimation system would improve the situation by more than an order of magnitude. P. Spiller et al., GSI C. Omet et al., GSI

Decay ring: 

Decay ring Geometrical considerations Maximize straight section Shortest arcs possible High magnetic field SC magnets For EURISOL scenario (g=100) 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: A. Chance et al., CEA Saclay

Stacking process: 

Stacking process 1) Injection 2) Rotation 3a) Single merge 3b) Repeated merging 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 Injection: off-momentum Rotation Merging: “oldest” particles pushed outside longitudinal acceptance  momentum collimation

Particle turnover: 

~1 MJ beam energy/cycle injected  equivalent ion number to be removed ~25 W/m average Momentum collimation: ~5*1012 6He ions to be collimated per cycle Decay: ~5*1012 6Li ions to be removed per cycle per meter Particle turnover bb

Collimation and absorption: 

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

Physics reach : 

Physics reach EURISOL scenario g=100 each 6He and 18Ne with a 5-year run 2.9*1018 6He decays/year or 1.1*1018 6Ne decays/year Physics reach Sensitivity on Q13 down to ~1o

Towards high-energy beta-beams: 

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

Using existing HE hadron machines: 

Using existing HE hadron machines Tevatron most realistic scenario Comparable fast acceleration in all energy regimes gtop=350 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.

n-Spectra: 

n-Spectra Wide spectra from super- and Beta-beams Requires energy reconstruction in detectors “solution”: EC monochromatic beam Electron capture: p++e- n+n Sharp energy spectrum of the neutrino beam

Monochromatic n-beam: 

Monochromatic n-beam 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

Special aspects of a EC n-beam: 

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: >1015 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

Physics reach in comparison: 

For q13>1O a Beta-beam scenario is useful. Improved situation in combination with Super-beam Simultaneous analysis of atmospheric neutrinos Physics reach in comparison

Summary: 

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 q13>1O. 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