1. A.Lachaize CNRS/IN2P3 IPN Orsay
The Rapid Cycling Synchrotron of the
EURISOL/Beta-Beam facility
A.Lachaize CNRS/IN2P3 IPN Orsay

2. Programme
The Beta-Beam complex
The Beta-Beam RCS : general parameters, optics, closed-orbit correction,
acceleration, beam losses, fast extraction,
chromaticity correction, main magnet design.
Additional studies
Conclusion

3. The Beta-Beam complex Subject of the talk
Production of neutrinos beam by beta decay of radioactive ion beams (Helium 6 and Neon 18) after
acceleration to high energy (γ = 100).
Based on existing CERN machines (PS-SPS)
The IPNO is in charge of the design of the new low energy ring required for bunching and acceleration
of ion beams before injection in the CERN PS.
Subject of the talk
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4. Quadrupole maximum gradient
The Beta-Beam RCS (General parameters)
Required for bunching and acceleration on the first harmonic of 20 pulses for accumulation in the CERN PS.
3-fold symmetry ring based on FODO cells with missing magnets to provide 3 achromatics arcs and 3 straights
sections for injection, acceleration and extraction. It is composed of 60 dipoles and 48 quadrupoles.
Schematic layout of the ring
Injection energy
100 MeV/u
Extraction energy
3.5 GeV eq. Proton
Maximum rigidity
14.47 T.m
Ring circumference m
Repetition rate
10 Hz
Dipole length
1.4 m
Bending radius m
Dipole field
0.2/1.08 T
Quadrupole length
0.4 m
Quadrupole maximum gradient
10.85 T/m
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5. The Beta-Beam RCS (Optics)
Tunes (H, V)
Maximum beta functions (H,V)
19m m
Natural chromaticities (H,V)
Momentum compaction
0.0349
Transtion gamma
5.35
RMS emittances at injection (H,V)
18.11 pi.mm.mrad
9.69 pi.mm.mrad
Beta functions
Tune diagram
Beam envelopes at injection
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6. Closed orbit prognosis and correction system
Assuming standard field and alignment errors, distortions of the closed orbit have been evaluated (5 mm rms in QF) with the code BETA.
A correction system based on 7H + 6V dipole steerers coupled to 14 BPM per period has been defined and correctors parameters have been specified.
Closed-orbit before correction
Closed-orbit after correction
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7. The Beta-Beam RCS (Multiturn injection)
Pulse length (50μs) longer than revolution time at injection (1.95μs). A closed orbit bump is needed to inject 26 turns of beam.
The injection scheme has been optimized to maximize the number of injected ions within the specified transverse emittances
(WinAgile code). The optimum filling is achieved when ions are injected with position and slope which minimize their Courant and
Snyder invariant about a variable closed orbit.
Septum wall position and pulsed kicker parameters have been specified and a preliminary sketch of the injection line has been studied.
Phase space distribution of the multiturn injected beam
Efficiency of 80%
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8. The Beta-Beam RCS (RF acceleration)
Fast acceleration (repetition rate of 10hz) requires a poweful RF system and a sophisticated voltage program.
At the beginning of the cycle the trapping process must be optimized to avoid particles losses.
Then, in order to maintain the central trajectory on the reference orbit, the acceleration must be linked to the magnetic field time
variation and the voltage must provide a sufficient bucket area to enclose the longitudinal emittance.
These different phases of the cycle have been simulated and optimized with the code ACCSIM and another code developed at IPNO
for this purpose.
Synchronous phase and
voltage program
Longitudinal emittances at extraction : 0.64 eV.s for Helium
1.4 eV.s for Neon
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9. The Beta-Beam RCS (Beam losses)
Beam losses occuring during injection, trapping and acceleration have been investigated with ACCSIM. Beam losses location and
intensity have been determined.
Injection losses : 20% of the beam lost on the electrostatic deflector.
Decay losses : 3.7% lost for Helium ions, 1.55% lost for Neon ions during the cycle
Capture and acceleration losses : 9% for Helium, 13.5% for Neon
Total transmission of the ring : ~70% for both ions
Losses location and intensity in the ring for Helium ions
Losses location and intensity during the cycle for Helium ions
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10. The Beta-Beam RCS (Fast extraction system)
Extraction system consists of 2 fast kickers and 3
septum magnets. The fast kickers are composed of 2 modules
for the first one (numbers 1 and 2) and 3 modules for the second
one (numbers 3 to 5).
The kicker layout is designed to produce sufficient separation
between the circulating and the extracted beams.
Then septum magnets produce the needed deviation angle
to eject the beam from the ring (numbers 6 to 8)
Realistic kicker and septum magnet parameters have been proposed. Their technology is based on existing designs made at
GSI for SIS18 and for the J-parc project in Japan.
Rise time
700 ns
Pulse length
200 ns
Horizontal aperture– Gap
10.0 cm
Vertical aperture- Gap
8.0 cm
Field for deflecting the beam
104 mT
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11. The Beta-Beam RCS (Chromaticity correction)
2 components for the ring chromaticity :
-Natural chromaticity
-Eddy currents induced chromaticity
Time varying fields in RCS magnets induce eddy currents in metallic vacuum chambers which in turn produce various multipole
fields acting on the beam.
In bending magnets vacuum chamber, one important component is a sextupolar component which modifies the ring chromaticity.
The contribution of this component to the ring chromaticity has been calculated and a chromaticity correction scheme providing a
large dynamic aperture has been defined .
It is composed of 9 sextupoles per super-period (3 for horizontal plane and 6 for the vertical plane).
Total chromaticity during cycle for Helium ions
Sextupolar normalized strength to correct this chromatcity
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12. The Beta-Beam RCS (Dynamic aperture)
A good chromaticity correction scheme must provide a sufficient dynamic aperture to obtain a stable motion everywhere in the
vacuum chamber.
Dynamic aperture for He at 10 Hz
Dynamic aperture for Ne at 10 Hz
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13. Biased sinusoidal ramp
The Beta-Beam RCS (Main magnet design) 1
A preliminary design of main dipoles and quadrupoles has been studied and proposed.
2D calculation of the transverse cross section have been made with the code POISSON.
Number of dipoles 60
Magnetic length
1.4 m
Good field region
± 5 cm (H) ± 5 cm (V)
Bending radius m
Magnetic field (He)
0.199 – 1.08 T
Magnetic field (Ne)
0.332 – 1.08 T
Gap height
10 cm
Maximum Ampere-turn
85940 A.t
Magnet cycle
Biased sinusoidal ramp
Dipole cross-section
C-type magnets have been selected for dipoles in order to afford easy extraction of Ne decay products.
Coil configuration and technology together with water cooling and power supply parameters have to be defined
more precisely, according to the CERN standards..
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14. Maximum Ampere-turn/ coil
The Beta-Beam RCS (Main magnet design) 2
Number of quadrupoles 48
Length
0.4 m
Bore radius
0.06 m
Maximum gradient
T/m
Maximum Ampere-turn/ coil
15545 A.t
Quadrupole cross-section
Coil configuration and technology together with water cooling and power supply parameters have to be defined
more precisely, according to the CERN standards..
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15. Additional studies and further work to be done
Beam loss distribution and associated dynamic vacuum effects have been estimated by GSI. No problems to obtain a pressure of 10-7 mbar.
Intra-beam scattering has been studied at CERN, it is not an issue in the RCS.
Shielding design and calculations have been done at CERN, the RCS radiation protection system is under study
The cost estimate of a RCS similar to the Beta-Beam RCS has been made by CERN.
The accelerator hardware (magnets, septa, collimators, vacuum system and beam monitoring system) is not technically defined in details.
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16. Conclusion
A complete design of the Beta-Beam RCS including a review of main dynamics issues has been done.
The Beta Beam RCS parameters are well inside typical RCS specifications and do not pose critical technical issues.
Further work is needed if we want to define the ring hardware in details.
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