Acceleration Schemes for PAMELA Carl Beard ASTeC, Daresbury Laboratory

1. Acceleration Schemes for PAMELA Carl Beard ASTeC, Daresbury Laboratory FFAG08 Carl Beard

2. Pamela • Conceptual design study of a combined proton and light-ion Charged Particle Therapy (CPT) facility • PAMELA must accelerate both carbon and protons • From 50 to 250 MeV extraction energy Protons • 70 MeV/u to 450 MeV/u for Carbon • Energy range (beta) 0.2 – 0.7 • 2 or 3 rings concentric rings FFAG08 Carl Beard

3. Practical Considerations • Facility • Cyclotron footprint • Services • Power Supplies (magnets & RF) • RF • Diagnostics • Vacuum • Control system • Complex acceleration scheme!!! • Cryogenics \ Cooling • RF system • Large energy range (velocity factors) • Conversely – Achieve the design parameters, and then consider the practical aspect… FFAG08 Carl Beard

4. Design Constraints • Longitudinal Space (0.6 – 1m) • Aperture (10 – 15cm) • Energy range (beta) 0.1 (Carbon) – (0.7 Proton) • Energy gain/range per ring, undefined • Energy gain per turn \ cavity • 50 KV – 5MV • Voltage change • Frequency range?? • Low frequency (up to 40 MHz) • Medium Frequency (200 MHz say…) • High Frequency (800 MHz up to 1.3 GHz) • Rate of change of Frequency • Phase and Amplitude stability – this will depend on the acceleration regime • System has to be simple to operate • No in-house RF engineers planned to supervise the system FFAG08 Carl Beard

5. Options for consideration • Cavity type • Normal Conducting \ Superconducting • Single Cell (Fixed Frequency) • Ferrite Loaded Cavity • Travelling Wave Structure • Scheme • Broadband - NCRF • Modulated RF Cavity – NCRF • Harmonic Jumping Scheme • Fixed Frequency – SRF/NCRF • Power Sources • Tetrodes – low frequency <300 MHz • IOTs/Klystrons High Frequency >300 MHz • LLRF Control System FFAG08 Carl Beard

6. Examples of Cavity Types N.B. Bespoke systems recommended FFAG08 Carl Beard

7. Single Cell Broadband Cavities • Compact • Ferrite loaded cavity to increase bandwidth • Low Q • Low – high Frequency • Can maintain High R/Q even considering an aperture 10-15cm (Low f) • Tetrodes have can have ~200MHz Bandwidth • Higher frequency sources limited bandwidth • Exception; TWT • If acceleration scheme allows, SRF Cavity could be used. FFAG08 Carl Beard

8. High Gradient RF Cavity “Finemet” Magnetic Alloy Cores Low Q Superimposed Frequency (Coupled cavity) PoP FFAG RF Structure 0.7m 0.64m 1.1m ? FFAG08 Carl Beard

9. Muons, Inc. 5/24/2008 Compact, Tunable RF Cavities 9 Compact, Tunable RF Cavities New developments in the design of fixed-field alternating gradient (FFAG) synchrotrons have sparked interest in their use as rapid-cycling, high intensity accelerators of ions, protons, muons, and electrons. Potential applications include proton drivers for neutron or muon production, rapid muon accelerators, electron accelerators for synchrotron light sources, and medical accelerators of protons and light ions for cancer therapy. Compact RF cavities that tune rapidly over various frequency ranges are needed to provide the acceleration in FFAG lattices. An innovative design of a compact RF cavity that uses orthogonally biased ferrite or garnet for fast frequency tuning and liquid dielectric to adjust the frequency range and cool the cores is being developed using physical prototypes and computer models. The first example will be to provide 2nd Harmonic RF for the Fermilab Booster Synchrotron. FFAG08 Carl Beard

10. Test Cavity m Muons, Inc. Fig. 1: Conceptual design of a compact, tunable RF cavity for FFAG and other applications. Ferrite cores (black) and liquid dielectric (yellow) surround a ceramic beam pipe (green) with an RF iris as shown. Coils (red) outside of the cavity generate a solenoidal magnetic field that is transverse to the RF magnetic field. A laminated iron return yoke (black) localizes the field. 5/24/2008 Compact, Tunable RF Cavities 10 FFAG08 Carl Beard

11. Test Cavity m Muons, Inc. 5/24/2008 Compact, Tunable RF Cavities 11 FFAG08 Carl Beard

12. m Muons, Inc. Test Cavity-Ferrite-Liquid 5/24/2008 Compact, Tunable RF Cavities 12 FFAG08 Carl Beard

13. Li, Rimmer, 805 MHz Cavity 36cm 16cm 16cm • Power coupler is very large • SRF strucfture would be much larger FFAG08 Carl Beard

14. 805 MHz Cavity Parameters • Normal conducting – still high Q • High gradient FFAG08 Carl Beard

15. Travelling Wave Structure - Transmission line Particle velocity < c, Guide velocity = c Guide velocity slowed to match particle • Typically broadband (linear dispersion) • Efficiency reduced over large spread in beta • Small apertures for low velocities FFAG08 Carl Beard

16. Travelling Wave Structures 1) TWS can have more cells as for SWS (No trapped HOMs) 2) TWS require lots more drive power power exits through the output coupler. 3) When a cavity has a breakdown a TWS will absorb RF power causing extra damage 4) In NC cavities SWS should get higher fields in theory but field enhancement around the coupler prevents this. SLAC are still working on it. 5) TWS can sometimes have lower surface fields. 6) Beam loading is much higher in TWS meaning for an acc gradient of 50 MV/m in the NLC you need an unloaded gradient of 70 MV/m for example. 7) Damping wakfields in long TWS has been demonstrated. SWS should be just as good but it hasn't been proven. 8)By nature travelling wave structures require small irises to maintain a relatively modest R/Q. Spacing critical for low beta structures 9) TWS is more compact because it has less couplers and is also cheaper. It is also less sensitive to mechanical errors as it has a continuous dispersion. Broad bandwidth FFAG08 Carl Beard

17. Energy \ Frequency Requirements • Limitations -Energy gain per turn increases • Ramps from very low power to 5kW in a few microseconds… Frequency FFAG08 Carl Beard

18. Harmonic (Number) Jumping FFAG08 Carl Beard

19. Harmonic Number Jumping • Acceleration Schemes so far require frequency modulation • Scheme for fixed frequency highly desirable • Pre-programmed Phase and voltage • To ensure arrival at each RF station an integer number of wavelength later • Energy Increases • Velocity increases • Number of Harmonic jumps decrease FFAG08 Carl Beard

20. Harmonic Jumping • Fixed RF frequency • High frequency option possible • Stability may be an issue – LLRF Control • As velocity increases TTF changes • Acceleration per cavity will change • Could be advantageous – starting further off phase • Superconducting RF is a possible solution • Larger beam apertures by default • Stray (High) fields • heating flanges etc. • Local BPMs FFAG08 Carl Beard

21. Constant Harmonic Jump • Fixed RF Frequency • Harmonic Jump of 1 Demonstration Purposes FFAG08 Carl Beard

22. Fixed Harmonic Number Jump Demonstration Purposes Frequency Energy HN FFAG08 Carl Beard

23. HNJ & Frequency sweeping • Frequency sweep of multiple octaves required • Could limit the energy gain possible • Simplified Control System • Finite frequency shift • Smaller Harmonic jumps • Improved stability • Large energy range. FFAG08 Carl Beard

24. Controlled HNJ Demonstration Purposes Frequency Energy HN FFAG08 Carl Beard

25. Frequency & HNJ Modulation • Reduction in operating bandwidth • Achievable for Ferrite loaded and broadband cavity • Increased efficiency • Frequency returns back to initial frequency to allow continuous operation • Constant energy gain. • Fixed Power per cavity • Stepped “controlled” ramping of the Harmonic number FFAG08 Carl Beard

26. Summary • Standard acceleration scheme • Modulated RF • Broadband • Ramping of RF power limits the use • Bandwidth could be a number of octaves • Harmonic Number Jump • Large advantages • Reduce the required bandwidth • Fixed frequency • Low Level RF Control looks possible, but difficult • Hybrid of HNJ + Cavity (Modulated or Broadband) • Looks promising • Could this system work independently and reliably? • More comprehensive study required FFAG08 Carl Beard