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Damping ring

Damping ring. K. Ohmi LC 説明会 @KEKB. Layout. Single tunnel Circumference 6.7 km Energy 5 GeV. 2 km. 35 km. Parameters. 5 GeV, 400 mA storage ring. Role of the damping ring. ge : 0.045 m  8x10 -6 , 2x10 -8 m at E=5 GeV e x =0.5 nm, e y =2 pm, s z =9 mm, dp/p=1.28x10 -3 .

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Damping ring

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  1. Damping ring K. Ohmi LC説明会@KEKB

  2. Layout • Single tunnel • Circumference 6.7 km • Energy 5 GeV 2 km 35 km

  3. Parameters • 5 GeV, 400 mA storage ring

  4. Role of the damping ring • ge: 0.045 m  8x10-6 , 2x10-8 m at E=5 GeV • ex=0.5 nm, ey=2 pm, sz =9 mm, dp/p=1.28x10-3. • Storage bunches every 3~6 ns spacing, where H=14,516 ( frf=650MHz, 1.5 ns). • tx=25 ms. • Fast injection and extraction kicker, ~3 ns. • LINAC Repetition: 5 Hz, storage time<200 ms. • Main Linac pulse : 2625-5534 every 370 ns. • Linac pulse length=1 ms, Rev. freq. frev=22 ms.

  5. Injection beam • Ne=2x1010 -1x1010. • Initial distribution of the beam • Initial emittance • Energy deviation <0.5%

  6. Damping ring shape • L=6695 m. 6角形 • Radiation damping time, tx=25 ms.Strage time <200 ms. Storage 8 damping time in maximum.

  7. Ring lattice • Arc: TME cell • Straight, wiggler, RF, injection and extraction: FODO cell. Arc cell

  8. Whole ring lattice wig wig inj wig wig

  9. Dynamic aperture • Injection beam, 2(Jx+Jy)=0.09, energy deviation 0.05% TESLA org. MCH 赤：error有 青：error無 PPA OCS

  10. Injection and extraction • Bunch spacings are 6 ns and 370 ns in the ring and the main linac, respectively. • Each bunch has to be injected and extracted individually. • Measurement with 33 cm stripline and 5 kV 3MHz pulser.

  11. Kicker and septum • 30 cm stripline operating at 22 kV. • 20 modules are required. • The kickers pulse every 300 (150) ns during 1ms. • Kicker amplitude jitter tolerance 10-3. • Septum should have 1ms plateau flat to 10-4 with a half-sin pulse of 10ms.

  12. Magnets • Super conducting damping wiggler with B=1.6T. Common cryogenic infra. with RF-cavity.

  13. Magnet field error

  14. Vertical emittance and misalignment • Design gey=20 nm

  15. RF system (superconducting) VRF=24 MV ns=0.067 a=4.2x10-4

  16. Cryogenic Plant

  17. Fast feedback system • The pickups are 4-button monitor • 16 bit signal processor • Bunches in all bucket can be controlled, H=14,516 input channel. >50 taps • Damping time <30 turn (resistive wall inst.).

  18. Vacuum system • Ante-chamber in arc • Wiggler chamber • NEG coated grooved aluminum chamber. Clearing electrodes are equipped. • 0.5 nTorr CO

  19. Intrabeam scattering

  20. Bunch filling • Ne=0.97x1010-2.02x1010 • Several bunch filling patterns are prepared. • The filling pattern

  21. Ion instability • Instability growth for P=0.3 nTorr (CO). • Number of bunches in a train<40 • Train gap>28x1.5ns • Feedback noise was not essential. No noise 1% feedback noise Ne=2.02x1010, Lsp=6 ns

  22. Ion instability for various filling patterns • Ne=0.99x1010 Lsp=3 ns Nb=49, Lgap=25x1.5 ns • Ne=1.29x1010 Lsp=3 ns Nb=53, Lgap=71x1.5 ns • Ne=1.54x1010 Lsp=4.5 ns Nb=25, Lgap=25x1.5 ns

  23. Electron cloud build-up Table 1. Electron cloud density near beam (m-3) before bunch passage, compared with threshold density for secondary electron yield d2,max=1.2.

  24. Electron cloud instabilityThreshold of the strong head-tail instability • Stability condition for wesz/c>1 • Since re=le/2psxsy, • Q=min(Qnl, wesz/c) Qnl=5-10? Depending on the nonlinear interaction • K~3 Cloud size effect. • wesz/c~12-15 for damping rings. • KQ=60-70 for analytical estimation. KEKB KQ~15

  25. Above or below the threshold? rth=1.2x1011 m-3 The density is above the threshold due to the multipactoring in bending magnets. OCSx2 was proposed at the first stage (BCD).

  26. Electron cloud instabilityClearing electrode • Electrode with 100V suppress the electron cloud build up

  27. Electron cloud instabilityGrowth rate of the coupled bunch instability • Slow growth rate (t~1000 turn), if the conditions (average density =10m down stream) are kept. • At injection, growth rate increases 10-20 times, (t~50-100 turn) OTW OCS

  28. Resistive wall impedance • Resistive wall wake integrated along the ring with considering chamber radius and beta function. • The resistive wall instability is serous for large circumference rings, because low frequency component of the resistive wake is the source, impedance of the slowest fractional tune, Z(1-Dn).

  29. Broad band impedance • Longitudinal • Transverse

  30. Single bunch instability • Longitudinal unstable, bunch lengthing • Transverse stable

  31. Coupled bunch instability • There is no reason that OCS is so bad. Tune should be chosen better. Growth time >30 turn. Transverse feedback system to suppress is required. • Longitudinal, no problem (KEKB type SC cav.).

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