1. FFAG Concepts and Studies David Neuffer Fermilab

2. 2 Outline  Introduction  Feasibility studies use Linacs and recirculating linacs  Need to develop “cheaper” acceleration  FFAG Acceleration ??  Fixed-field permits fast-acceleration  ~10 turns possible ….  FFAG Lattice styles (DIMAD simulations):  “scaling” FFAG – Machida & Mori  “non-scaling” FFAG – Johnstone  FMC-like –Dejan Trbojevic  Longitudinal Motion Constraints  simulations

3. 3 Study 2 Costs ….  Study I, II -Factory – feasible but too expensive  Biggest cost item: acceleration (~600M$)

4. 4 FFAG Acceleration?  Linacs/RLA’s require a lot of rf  RLA multiple-pass transports + spreader/recombiners complicated and expensive  Muons decay too quickly for fast-cycling magnets  Need: Fixed-field lattice that can accept beam over large energy spread (6  20 GeV ?) for multipass return transports: FFAG lattice ?  With same transport for all turns can accelerate over more turns: less rf.  FFAG lattice can have large momentum acceptance; large transverse acceptance; need less cooling

5. 5 POP-first Proton FFAG  First Proton FFAG built and operated  All systems verified (magnet, rf, injection)

6. 6 FFAG magnet- 150 MeV FFAG  Figure shows yoke-free FFAG triplet used for 150 MeV proton FFAG  150 MeV FFAG is under construction (magnets done)

7. 7 PRISM – low-energy muon ring  Low-energy muon source  e experiments …

8. 8 Japan Neutrino Factory Scenario

9. 9 JNF Scenario  Use 50 GeV p-bunch to produce pions  Capture beam in 20-T  5-T transport channel  Short decay line; inject beam directly into low-energy FFAG  Capture beam in low-frequency rf bucket  Accelerate up chain of FFAGs to 20GeV  Inject into 20GeV storage ring

10. 10 “Scaling” FFAGS  Lattice Advantages: Naturally Zero chromaticity Disadvantages: Large negative bends (large circumference …) Nonlinear fields (from r k expansion) Not isochronous

11. 11 JNF- FFAGs lattice design  Lattices are “scaling” radial- sector FFAGs  Triplet focusing with reverse- bend D-quads  Low to high energy orbit width is ~0.5m  0.3  1.0 GeV,  1  3.0 GeV  3.0  10 GeV  10  20 GeV FFAGs  Lattices have been generated using SAD, DIMAD

12. 12 Parameters for JNF FFAG lattices

13. 13 Acceleration and Decay  Acceleration must avoid muon decay  Need ~1MV/m to avoid decay (2 MV/m gradient in cavities)

14. 14 Acceleration Parameters  For acceleration, use superconducting (smaller-radius) FFAGs  At 1MV/m, ~ 10 turns acceleration / FFAG  Assume harmonic h = 1 on lowest-energy FFAG; keep frequency constant  h = 1  4.75 MHz rf (???)  Initial beam from decay  300  150MeV/c;  10ns 

15. 15 Scenario requires ~2MV/m rf  Harmonic=1 (for lowest energy FFAG) implies 4.75 MHz;  Harmonic=2 implies 9.5 MHz; works OK in 1-D simulation  Experience indicates 26MHz cavity is more realistic (Iwashita)  Use 26 MHz + 3 rd harmonic ?

16. 16 Longitudinal Motion in FFAG  Equations of motion:  Motion is not very isochronous  h = 1 and h = 2 accelerations are OK;

17. 17 Injection and Extraction  Requires fast, large-aperture kickers; particularly for low- energy FFAGs  Risetime for 1GeV FFAG must be less than 200ns; 20 GeV FFAG can be > 1  s  Example: 150MeV FFAG will need 500g, 0.6m, 150ns  1GeV FFAG needs ~0.53 T-m

18. 18 “Non-scaling” FFAG (Johnstone)  6  20 GeV lattice; C=2100m  Basic lattice unit is FODO cell ~7m long;  Primary bending magnet is “D”;  Lattice is more isochronous  (transition at ~13 GeV)  B = constant (tune varies with energy)  Good linear behavior … (but large chromaticity …) FD

19. 19 Dejan Trbojevic Lattice  10  20 GeV  270m circumference  Strong focusing to very small dispersion:  6cm  No negative bends at central energy  Chromaticity corrected: Tune (E) more nearly constant (but does cross integers)

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21. 21 Summary  FFAG accelerators have been built and operated at KEK  POP FFAG  150 MeV FFAG (under construction)  PRISM (proposed)  RIKEN radioactive ion FFAG  FFAG accelerators could be used in neutrino factory  Need magnet, rf, injection/extraction R&D  Muon production and cooling options to be explored  Comparisons with other design approaches are not completed  FFAG or RLA or linac or ???  Cost estimates ???  Integration into complete neutrino factory scenario is also required