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Damping ring K. Ohmi LC Layout Single tunnel Circumference 6.7 km Energy 5 GeV 2 km 35 km.

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Presentation on theme: "Damping ring K. Ohmi LC Layout Single tunnel Circumference 6.7 km Energy 5 GeV 2 km 35 km."— Presentation transcript:

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  : 0.045 m  8x10 -6, 2x10 -8 m at E=5 GeV  x =0.5 nm,  y =2 pm,  z =9 mm, dp/p=1.28x10 -3. Storage bunches every 3~6 ns spacing, where H=14,516 ( f rf =650MHz, 1.5 ns).  x =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. f rev =22  s.

5 Injection beam N e =2x10 10 -1x10 10. Initial distribution of the beam Initial emittance Energy deviation <0.5%

6 Damping ring shape L=6695 m. 6 角形 Radiation damping time,  x =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(J x +J y )=0.09, energy deviation 0.05% 赤: error 有 青: error 無 OCS TESLA org. PPA MCH

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  y =20 nm

15 RF system (superconducting) V RF =24 MV s =0.067  =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 N e =0.97x10 10 -2.02x10 10 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. N e =2.02x10 10, L sp =6 ns No noise 1% feedback noise

22 Ion instability for various filling patterns N e =0.99x10 10 L sp =3 ns N b =49, L gap =25x1.5 ns N e =1.29x10 10 L sp =3 ns N b =53, L gap =71x1.5 ns N e =1.54x10 10 L sp =4.5 ns N b =25, L gap =25x1.5 ns

23 Table 1. Electron cloud density near beam (m -3 ) before bunch passage, compared with threshold density for secondary electron yield  2,max =1.2. Electron cloud build-up

24 Electron cloud instability Threshold of the strong head-tail instability Stability condition for  e  z /c>1 Since  e = e /2  x  y, Q=min(Q nl,  e  z /c) Q nl =5-10? Depending on the nonlinear interaction K~3 Cloud size effect.  e  z /c~12-15 for damping rings. KQ=60-70 for analytical estimation. KEKB KQ~15

25 Above or below the threshold?  th =1.2x10 11 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 instability Clearing electrode Electrode with 100V suppress the electron cloud build up

27 Electron cloud instability Growth rate of the coupled bunch instability Slow growth rate (  ~1000 turn), if the conditions (average density =10m down stream) are kept. At injection, growth rate increases 10-20 times, (  ~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-  ).

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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