Radioactive Ion Beams

A. Fabich, CERN on behalf of the Beta-beam Study Group http://cern.ch/beta-beam NuFact’06, UCIrvine NuFact'06, Aug. 2006 A. Fabich, CERN Radioactive Ion Beams, 1

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

NuFact'06, Aug. 2006 A. Fabich, CERN Radioactive Ion Beams, 2

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 g max   Boosted neutrino energy spectrum: E n  2 g Q 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 g =100 NuFact'06, Aug. 2006 A. Fabich, CERN Radioactive Ion Beams, 3

Production chain

n -factory proton target p + + ...

m + + n m (super-beam) e + + n m + n e and charge conjugated    beta-beam proton target isotope isotope* + e + + n e n -factory uses beam of 4 th Beta-beam uses 3 rd generation.

generation beam.

Beta-beam is technically closer to existing/used accelerator technology.

Storage Neutrino beam .

Ion source NuFact'06, Aug. 2006 Acceleration A. Fabich, CERN Radioactive Ion Beams, 4

Choice of ion species

 Beta-active isotopes  Distance from stability  Production rates  Life time t 1/2 at rest (ground state) 1ms – 1s 1 – 60 s  b + or b 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 NuBase NuFact'06, Aug. 2006 A. Fabich, CERN Radioactive Ion Beams, 5

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  E n 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 g 6He =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 NuFact'06, Aug. 2006 A. Fabich, CERN CERN-Frejus: 130 km Radioactive Ion Beams, 6

Guideline to

n

-beam scenarios based on radio-active ions

 Low-energy beta-beam: relativistic g  Physics case: neutrino scattering < 20  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). NuFact'06, Aug. 2006 A. Fabich, CERN Radioactive Ion Beams, 7

The EURISOL scenario

  Based on CERN boundaries Ion choice: 6 He and 18 Ne  Relativistic gamma=100/100  SPS allows maximum of 150 ( 6 He) or 250 ( 18 Ne)  Gamma choice optimized for physics reach EURISOL scenario  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*10 18 anti-neutrinos from 6 He Or 1.1 10 18 neutrinos from 18 Ne  Once we have thoroughly studied the EURISOL scenario, we can “easily” extrapolate to other cases. EURISOL study could serve as a reference.

NuFact'06, Aug. 2006 A. Fabich, CERN Radioactive Ion Beams, 8

Ion production – ISOL method

6 He production

 converter technology using spallation neutrons

18 Ne production

  Spallation of close-by target nuclides 18 Ne from MgO:  24 Mg 12 (p, p 3 n 4 ) 18 Ne 10 Direct target: the beam hits directly the oxide target  Required production rate of 5*10 13 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.

Nominal production rate 5*10 13 can be achieved.

ions/s NuFact'06, Aug. 2006 A. Fabich, CERN Radioactive Ion Beams, 9

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.

EURISOL design  Possible solution. Yet not all technical issues addressed and solved.

NuFact'06, Aug. 2006 A. Fabich, CERN Radioactive Ion Beams, 10

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.: 7 Li + D   8 Li + p  8 Li: t 1/2 ~0.8 s, ~6.7MeV

Rate: > 10 14 ions/s C. Rubbia et al. (see talk this week) NuFact'06, Aug. 2006 A. Fabich, CERN Radioactive Ion Beams, 11

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 NuFact'06, Aug. 2006 A. Fabich, CERN Radioactive Ion Beams, 12

Intensity evolution during acceleration

Bunch 20 th 15 th total 10 th 5th 1st

Cycle optimized for neutrino rate towards the detector    30% of first 6 He bunch injected are reaching decay ring Overall only 50% ( 6 He) and 80% ( 18 Ne) reach decay ring Normalization  Single bunch intensity to maximum/bunch  Total intensity to total number accumulated in RCS NuFact'06, Aug. 2006 A. Fabich, CERN Radioactive Ion Beams, 13

Power losses - Activation Power loss per unit circumference of a machine

P

loss

/

l



E

loss

/

cycle t

cycle

*

circumfere nce

machine P loss /l [ions]

RCS PS SPS CNGS 3.3

0.25

6 Beta-beam He 18 Ne 0.17

2.2

0.4

0.14

2.8

0.25

Nucleon losses compared



PS and SPS comparable for CNGS and bb operation



PS exposed to highest power losses

NuFact'06, Aug. 2006 A. Fabich, CERN Radioactive Ion Beams, 14



Dynamic vacuum

Decay losses cause degradation of the vacuum due to desorption from the vacuum chamber 1.00E+10 1.00E+09 C. Omet et al., GSI  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 in steady state ( 6 He) Pa  An optimized lattice with collimation system would improve the situation by more than an order of magnitude.

NuFact'06, Aug. 2006 A. Fabich, CERN 1.00E+08 0 5 10 15

s [m]

20 25 30 35 P. Spiller et al., GSI Radioactive Ion Beams, 15

Decay ring

   20 b 1/2 (m) 15 b x 1/2 A. Chance et al., CEA Saclay Geometrical considerations   Maximize straight section Shortest arcs possible   High magnetic field SC magnets 10 b y 1/2 n x = 18.23

n y = 10.16

5 For EURISOL scenario ( g =100)    Circumference: 6900 m Length of straight section: 2500m Ratio straight section/circumference = 0.36

0 -5 0 D x 1000 2000 3000 Geometric sizing for other gamma ranges just by linear scaling  about 36%; ratio always  Neutrino rate:

R

 1 -

e

-

merges

ln( 2 )

t cycle t

1 / 2 g

I

sps

/

cycle

*

merges

*

f

straight

sec

tion

/

t

cycle

NuFact'06, Aug. 2006 A. Fabich, CERN Radioactive Ion Beams, 16

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 2) Rotation 1.

2.

3.

Injection: off momentum Rotation Merging: “oldest” particles pushed outside longitudinal acceptance  momentum collimation 3a) Single merge 3b) Repeated merging NuFact'06, Aug. 2006 A. Fabich, CERN Radioactive Ion Beams, 17

Particle turnover

 ~1 MJ beam energy/cycle injected  equivalent ion number to be removed ~25 W/m average LHC project report 773 bb p-collimation Momentum collimation Arc Arc   Momentum collimation: ~5*10 12 6 He ions to be collimated per cycle Straight section Decay: ~5*10 12 6 Li ions to be removed per cycle per meter NuFact'06, Aug. 2006 A. Fabich, CERN Radioactive Ion Beams, 18



Collimation and absorption

Merging:  increases longitudinal emittance  Ions pushed outside longitudinal acceptance  momentum collimation in straight section b

y

b primary collimator

x

 Decay product   Daughter ion occurring continuously along decay ring To be avoided:   magnet quenching: reduce particle deposition (average 10 W/m) Uncontrolled activation s (m) Straight section: Ion extraction et each end  Arcs: Lattice optimized for absorber system OR open mid-plane dipoles  NuFact'06, Aug. 2006 s (m) A. Fabich, CERN A. Chance et al., CEA Saclay Radioactive Ion Beams, 19

Physics reach

 EURISOL scenario  g =100   each 6 He and 18 Ne with a 5-year run 2.9*10 18 6 He decays/year or 1.1*10 18 6 Ne decays/year  Physics reach  Sensitivity on Q 13 down to ~1 o NuFact'06, Aug. 2006 A. Fabich, CERN Sin 2 (2  13 ) Radioactive Ion Beams, 20

Towards high-energy beta-beams

Beta-beam operation at higher relativistic g reduces the annual rate R n due to  Extended acceleration time

N ion

_

top

-

gamma



e

log( 2 )

t

1 / 2

N ion

_

produced

 g 

t

(

t

)

Lo wAcceler a tio n

+ g 

t a ccu m

/ 2 + g

t

(

t

) Simple analytical approximation R  1/ g  Boosted life time Average neutrino rate R at decay ring

Rate

  1  -

e

log( 2 )

N merg es t cycle

g

to p t

1 / 2   

N ion

_

top

-

gamma t cycle f straight

sec

tion

at fixed ion rates from production.

[n /s] Physics reach on neutrino beam side: PR  R g NuFact'06, Aug. 2006 A. Fabich, CERN Radioactive Ion Beams, 21

Using existing HE hadron machines

Machine Tevatron RHIC LHC t ramp (including injector chain) [s] 18 101 (41) ~1200 G max (proton) 1045 268 7600 g max ( 6 He 2+ ) 349 89 2500 g max ( 18 Ne 10+ ) 581 149 3500  Tevatron most realistic scenario   Comparable fast acceleration in all energy regimes g top =350  About 70% survival probability for 6 He  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.

NuFact'06, Aug. 2006 A. Fabich, CERN Radioactive Ion Beams, 22

n

-Spectra

 Wide spectra from super- and Beta-beams  Requires energy reconstruction in detectors D.A. Harris, FERMILAB-Conf-03/328-E  “solution”: EC monochromatic beam   Electron capture: p + +e  n+ n Sharp energy spectrum of the neutrino beam NuFact'06, Aug. 2006 A. Fabich, CERN Radioactive Ion Beams, 23

Monochromatic

n

-beam

 Decay 148 Dy  148 Tb 150 Dy  150 Tb 152 Tm  152 Er 150 Tm  1508 Dy t 1/2 3.1m

7.2m

8.0s

72s 1 1 BR n 1 0.64

EC/ b + 0.96

1 0.45

0.77

E n [MeV] 2.1

1.4

4.4

3.0

Disentangle measurement of  13 and d CP running at two different g  E n [MeV] 0.52

0.4

   13 [deg] Ion species: 150 Dysprosium Physics reach for 10 18 neutrinos/year at DR, each 5-year run at two different g NuFact'06, Aug. 2006 A. Fabich, CERN Radioactive Ion Beams, 24

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: 150 Dysprosium Decay 150 Dy  150 Tb t 1/2 7.2m

BR n 0.64

EC/ b + 1 E n [MeV] 1.4

Main characteristics:  Heavy and exotic isotope  Long lifetime  E n [MeV]   Production required: >10 15 150 Dy atoms/second Production achievable: 10 11 150 Dy atoms/second  50 microAmps primary proton beam with existing technology (TRIUMF)  Acceleration demanding  Balance for charge state between high magnetic rigidity and space charge NuFact'06, Aug. 2006 A. Fabich, CERN Radioactive Ion Beams, 25

Physics reach in comparison

  For  13 >1 O a Beta-beam scenario is useful.

Improved situation in combination with   Super-beam Simultaneous analysis of atmospheric neutrinos NuFact'06, Aug. 2006 A. Fabich, CERN Radioactive Ion Beams, 26

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  13 >1 O .

 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 NuFact'06, Aug. 2006 A. Fabich, CERN Radioactive Ion Beams, 27