1. PPM Focusing in Klystrons Michael Read Calabazas Creek Research Presented at CERN Aug 30, 2013 mike@calcreek.com

2. PPM Focusing Eliminates large magnet power supplies – Reduces operating and capital costs Conventional klystron magnet power supplies can consume more than 4% of average power of klystron Fields larger than Brillouin can be used – CCR designs have RMS fields ~ 1.5 x Brillouin – Requires careful shaping of field in electron gun Defocusing near output cavity can be avoided using “quasi-solenoidal” magnets CCR approach with pillbox magnets – Simple access for cavity cooling – Variability in magnet strength is averaged out

3. CCR PPM Focused Klystron

4. PPM Structure Variation in field around beam circumference < 0.05%

6. CCR PPM Klystrons 10 kW S-Band (in fabrication) – 1 A, 20 kV, 55%, 0.35 µpervs – Efficiency limited by beam interception 572 kW, 1.3 G – 11A @ 80 kV, 65%, 0.5 micro µpervs 75 MW L-Band (in initial design phase) – 379 A, 440 kV, 48.5%, perv 1.3 µ 5 MW S-Band (beginning fabrication) – 90.5 A, 127 kV, 48.3%, 2 µpervs

7. Design Codes RF Structure – SuperFish (LANL code for 2D RF structures) – KLSC (in house klystron code) – TESLA (NRL klystron code) – HFSS (commercial code for 3D elements) PPM Structure – Pandira (2D) (LANL magnetics code) – Maxwell 2D/3D (ANSYS magnetics code) Electron gun/beam – EGUN, TRAK (commercial 2D beam trajectory codes – BOA (CCR 3D trajectory/magnetics/thermal code) – TESLA (2D beam in klystron fields)

8. EGUN Simulation of PPM Klystron Beam 2D Simulation

9. BOA Simulation of PPM Klystron Beam 3D Simulation

10. TESLA Modeling of PPM Klystron

11. Off-Axis Focusing Off axis beam focusing requires only symmetry around beam axis Initial modeling shows very good symmetry

12. Geometry with off axis beams (single period)

13. Mag B On Axis (standard PPM focusing) Off Axis

14. Bz On Axis Off Axis

15. Bx (Br) On Axis Off Axis

16. Initial Simulation of Off-Axis Beam BOA simulation 20 kV, 1 A

17. Summary PPM focusing can be used in high efficiency klystrons Off axis focusing for multiple beam focusing should be as effective as in single beam devices

18. CCR MBK’s DOE 100 kW X-Band (fabricated) – 15 beams – perveance 4.5 micropervs (17.6 A @ 25 kV) 150 kW wide band C-Band (in design) – 18 beams – Perveance 5.5 micropervs (21.6 A @ 25 kV)

19. Mag scale factor 0.7 0.8 0.6