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Loss problems associated with the acceleration of radioactive beams and what we can do about it

Loss problems associated with the acceleration of radioactive beams and what we can do about it. Loss issues (and ideas for solutions) in the CERN beta-beam baseline scenario. A.Jansson. f. fermilab. Loss issues. Activation of machine Hands-on maintenance possible?

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Loss problems associated with the acceleration of radioactive beams and what we can do about it

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  1. Loss problems associated with the acceleration of radioactive beams and what we can do about it Loss issues (and ideas for solutions) in the CERN beta-beam baseline scenario. A.Jansson f fermilab

  2. Loss issues • Activation of machine • Hands-on maintenance possible? • Heat load for super-conducting magnets? • Size of decay ring. A. Jansson, Rencontres de Moriond 2003

  3. Decay losses • The daughter nucleus will carry most of the initial kinetic energy. • Because of the change in magnetic rigidity (p/q), it will be lost somewhere in the machine. e- 6Li3+ 6He2+ e A. Jansson, Rencontres de Moriond 2003

  4. Activation limit US limit for hands-on maintenance • 1 W/m generally accepted limit from spallation sources ( ~1 GeV protons) • Large spread in experimental values (red circles). [ R. Hardekopf, in Fermilab-Conf-00/185] A. Jansson, Rencontres de Moriond 2003

  5. Decay losses / power dissipation Decay rate: (lab decreases with energy) Power dissipation: W independent of energy! Average power per unit length: (f is duty factor) A. Jansson, Rencontres de Moriond 2003

  6. CERN baseline scenario A. Jansson, Rencontres de Moriond 2003

  7. limit Estimated losses–CERN scenario 6He (lost on inside) 18Ne (lost on outside) These numbers assumes 8s rep rate and only include decay losses from the beta beam! * denotes equilibrium intensity in decay ring A. Jansson, Rencontres de Moriond 2003

  8. How bad is 9 W/m? • For comparison, a 50 GeV muon storage ring proposed for FNAL would dissipate 48 W/m in the 6T superconducting magnets. Using a tungsten liner to • reduce peak heat load for magnet to 9 W/m. • reduce peak power density in superconductor (to below 1mW/g) • Reduce activation to acceptable levels • Heat load may be OK for superconductor. • What about activation? [ N.V.Mokhov / C.J. Johnstone, Fermilab-Conf-00/207] A. Jansson, Rencontres de Moriond 2003

  9. Machine activation • Scaling of spallation source limits to higher energies? • Effect of material thickness/range (what gets activated)? • Simulations needed! [ R. Hardekopf, in Fermilab-Conf-00/185] A. Jansson, Rencontres de Moriond 2003

  10. How reduce energy deposition? • Decay losses can not be avoided, only redistributed (to some degree). • The energy deposited in the injectors is minimized by accelerating as fast as possible (reduced duty cycle). • New machines (e.g. decay ring) should be built with loss containment in mind. A. Jansson, Rencontres de Moriond 2003

  11. Decay ring Return straight (with injection, RF etc) FODO lattice Dispersion suppressor Dispersion suppressor Arc (FODO lattice) Arc (FODO lattice) neutrinos Dispersion suppressor Dispersion suppressor Matching section Matching section High beta (small divergence) production straight. FODO lattice (or drift) A. Jansson, Rencontres de Moriond 2003

  12. Decay in FODO lattice Example lattice for 6He2+ (top traces) and 6Li3+ (bottom traces). When beam decays, it will be mismatched relative to its periodic lattice, causing beta beating to occur (right) A. Jansson, Rencontres de Moriond 2003

  13. Stable motion limits 6He phase advance Minimal aperture at ~40 degrees per cell Ne is not a problem (focussing is reduced for decay product) FODO stability 6He Beta (arb units) 18Ne Beta (arb units) Phase advance per cell Max lattice beta Max propagated beta of secondary beam A. Jansson, Rencontres de Moriond 2003

  14. Options for straight sections • Add absorbers at quadrupole locations • Design straight sections to contain both primary and secondary beam. • Stability of motion • Sufficient aperture/low beta beating • “Clean” separation scheme needed in the end of straight sections (56 kW secondary beam power produced in each straight) small phase advance A. Jansson, Rencontres de Moriond 2003

  15. Matching section aperture • The matching section following the production straight usually feature a high beta location • Should have sufficient extra aperture to allow for beta beating of secondary beam, in order not to become an aperture restriction! A. Jansson, Rencontres de Moriond 2003

  16. Dispersion suppressor • Zero dispersion required in straights • The dispersion suppressor will naturally act as a separator at the end of the straight • Secondary beam appears to have large energy offset. • Place septum where beams are sufficiently separated. • Dispose of secondary beam cleanly. A. Jansson, Rencontres de Moriond 2003

  17. Beam separation in the arcs • For efficient and clean separation of decay products, need short magnets separated by drifts. • Contradicts keeping the arcs short relative to straight sections. • Absorb most of the energy in magnets? A. Jansson, Rencontres de Moriond 2003

  18. Custom SC magnet • Dipoles can be built with no coils in the path of the decay particles to minimise peak power density in superconductor (quench stability). [ S. Russenschuck, CERN] A. Jansson, Rencontres de Moriond 2003

  19. Conventional magnet alternative • Longer machine, lower losses/length, higher cost • C-magnet open to the inside. • Minimal thickness for ions to traverse. • But, decay products bend inwards! • Decay ring the size of LHC! Need more study!!!! 6He2+ 6Li3+ A. Jansson, Rencontres de Moriond 2003 Use VLHC magnet???

  20. Larger ring SC alternative • Increasing machine size reduces local losses (for constant intensity). • Arc drifts may allow some degree of separation • Inward bend! • Absorbers in front of magnets? • Cost! Need more study!!!! A. Jansson, Rencontres de Moriond 2003 Use VLHC magnet???

  21. Non-decay losses in decay ring • All injected beam is lost in the machine! • Most losses not linked to decay will be due to the stacking scheme (limited by longitudinal acceptance). • At equilibrium, particles are continuously being pushed out of the bucket. • Remove DC beam/satellites (using a kicker)? • Momentum collimation? A. Jansson, Rencontres de Moriond 2003

  22. Conclusions • 6He is the problematic ion species • Decay products from straights could be collected and disposed of rather cleanly. • Arc decay losses more difficult to control (activation likely to be a serious issue) • Dissipated energy in arcs is rather high, but not worse than for muon-based scenarios (seems possible to use SC magnets) A. Jansson, Rencontres de Moriond 2003

  23. Open questions… • Will SC magnets actually take the heat? • Detailed loss distribution • Translate losses into activation levels • Will SC survive? • Maintenance possible? • Detailed simulations needed! • Requires machine design (iterative process). A. Jansson, Rencontres de Moriond 2003

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