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DTL, S(F)DTL & CCL

DTL, S(F)DTL & CCL. C avity fundamental & technology of J-PARC linac. KEK Fujio Naito. Contents. I. Introduction to the RF cavity. II. Short story of beam motion III. DTL & SDTL for J-PARC. IV. ACS. Block diagram of the linac for J-PARC. Requirements for the linac of J-PARC.

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DTL, S(F)DTL & CCL

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  1. DTL, S(F)DTL & CCL Cavity fundamental & technology of J-PARC linac • KEK Fujio Naito

  2. Contents • I. Introduction to the RF cavity. • II. Short story of beam motion • III. DTL & SDTL for J-PARC. • IV. ACS

  3. Block diagram of the linac for J-PARC

  4. Requirements for the linac of J-PARC Current Average 675 μA Peak 50 mA Pulse Pulse width 500 μsec Repetition 50 Hz Chopping ratio 56 % RF duty (600μsec) 3 % Beam Energy 400 MeV Momentum width Δp/p = ±0.1 % (100 %) Emittance 3~5 πmm-mrad (99 %)

  5. I. RF field in the cavity • Microwave in the cylindrical waveguide • Microwave in the pill box cavity • Multi cell cavity

  6. Wave equations for Ez & Hz. Cylindrical coordinates (r,θ,z)

  7. Mode of the traveling wavefor z-direction Ez＝0, Hz＝0 (TEM) Ez＝0, Hz≠0 (TE) Ez≠0, Hz＝0 (TM) TM mode: Standard mode for RF accelerating cavity since Ez≠0.

  8. Solution for Ez ( TM mode )

  9. Solution for R • Boundary conditions: • R is finite at r=0. • Ez, Eθ is zero at r=a. ( a: cylinder radius ) A2=0, Jm(kca)=0, n-th root:Pmn=kca then kc=Pmn/a

  10. Bessel functions

  11. Electric field pattern of the TM 01 mode ( P01=2.405, λc=2πa/P01=2.61a )

  12. Dispersion curve (Tilt of the line) = vp/c (Tangent of the dispersion curve)= vg/c

  13. Boundaries for z-direction (cavity) (Forward wave) + (Backward wave) = (Standing wave) TM010 TM011 TM012

  14. TM modes in the cylindrical cavity

  15. Principle of the DTL

  16. TE modes in the cylindrical cavity

  17. Inter-digital H (IH) structure linac TE111 *Advantages High Q High Z *Disadvantages Et≠0 Ez: non-uniform ( EPAC2000, Kesler, et al. )

  18. Dispersion curve for the cylindrical cavity

  19. DTL-1 for J-PARC

  20. Ez distribution for DTL-1

  21. Boundaries for z-direction (cavity) (Forward wave) + (Backward wave) = (Standing wave) TM010 TM011 TM012

  22. Ez distribution for DTL-1

  23. Energy gain & Transit time factor Transit time factor Pill box cavity (TM010) If E(z,0)=constant,

  24. Other mportant parameters Z: shunt impedance ZTT: effective shunt impedance Q-value

  25. ZTT

  26. Measured Ez of the first 3 cells of DTL-1

  27. Ez distribution of SDTL-3

  28. Multi-cells cavity Example) 2 cells case Freq( 0-mode) < Freq.( π-mode )

  29. EM field in the magnetically coupled 2 cell cvity f(0) > f(π)

  30. Infinitely long cavity-chain structure Vg=0 Vg=(max) Vg=0 Dispersion curve (Brillouin zone)

  31. π/2 mode cavities SCS ACS APS

  32. EM field in SCC π/2 0 π f(0) < f(π/2) < f(π) Et≠0

  33. Bridge coupler

  34. Bridge coupler for ACS TM010 mode ( +TM014 ) TM012 mode ( +TM010 ) TM010 π/2 mode

  35. II. Beam motion in the DTL • Longitudinal oscillation • rf defocusing • ( Transverse oscillation )

  36. Velocity of particles

  37. Phase stability principle

  38. Phase acceptance ~ 3 |øs| øs ≠ 0 〜 30

  39. RF defocusing

  40. III. DTL & SDTL for J-PARC. Requirements for DTL & SDTL: • RF power source: Klystron • Tunable & compact quadrupole magnet in the DT • Precise alignment of DTs in the tank. • Higher Q-value of the tank • Uniform & stable accelerating field

  41. R&D subjects • Periodic Reverse (PR) Cu electro-forming method • Thick Cu plating on the tank inside • Compact quadrupole electro-magnet in the DT • Shield of ceramic vacuum chamber (by Vac. Gr. ) • DT alignment ( Results ) • Post-coupler tuning • ( Input coupler )

  42. Layout of the DTL for J-PARC

  43. Inside view of the DTL-1

  44. Periodic Revers ( Test cavity : (-) 20 sec (+) 4 sec ) A smooth deposit is obtained by periodically reversed current using a low copper-content acid copper sulfate bath containing no organic additives. Advantages of the PR process; (1) It produces thick deposit with smooth surface. (2) Deposit by this process has high electrical conductivity, low outgassing and sufficient thermal stability. (3) Mechanical properties of deposit is controllable.

  45. e (PR) Electroforming without brightning agent ~ OFC

  46. Standard fabrication process of PR elctroforming of Cu for the cavity: (1) pre-processing on the inner surface of the iron cylinder for the followed electroforming; (2) first PR copper electroforming (+0.5 mm); (3) lathing the copper surface (-0.2 mm); (4) 2nd electroforming(+0.5mm); (5) lathing(-0.2mm); (6) finishing by the electropolishing (-50μm), of which the depth has been chosen in order to get the better surface condition.

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