1. 20003.11.28SKEKB Mini Work Shop @KEK1 SKEKB Vacuum System – Arc Section – Contents Y.Suetsugu KEKB Vacuum Group 1.Beam Chambers 2.Pumps: Pump, Pressure, Vacuum Scrubbing 3.Connections: Flange, Bellows 4.Special Components: Movable Masks, HOM Dampers 5.Loss Factors 6.R&D Status 7.Remained Issues

2. 20003.11.28SKEKB Mini Work Shop @KEK2 1. Beam Chamber _1 Beam chamber Ante-chamber scheme

3. 20003.11.28SKEKB Mini Work Shop @KEK3 1. Beam Chamber _2 Merits of Ante-Chamber (1) Low power density of SR For LER, 134 W mm -2 (ha = 47 mm) [475  C] 39 W mm -2 (ha = 112 mm) [156  C] (2) Low Impedance For LER, 1 pumping port of KEKB: k = 6  10 7 V C -1 k = 9  10 5 V C -1 per 1 m Photon stop at SR channel: KEKB: k = ~5  10 9 V C -1 k = 1  10 5 V C -1 per 1 m

4. 20003.11.28SKEKB Mini Work Shop @KEK4 1. Beam Chamber _3 Merits of Ante-Chamber (3) Less photoelectrons in beam channel Simple Simulation (no 2nd electrons)  94 mm, no magnetic filed, 5000 photoelectrons Not perfect about 1/10

5. 20003.11.28SKEKB Mini Work Shop @KEK5 1. Beam Chamber _4 Cross Sections - LER  90 mm (now  94 mm) B, normal Q, Sx NEG Feed-through Ion Pump Half height = 7 mm

6. 20003.11.28SKEKB Mini Work Shop @KEK6 1. Beam Chamber _5 Cross Sections - HER 98  50 mm (now 104  50 mm) B, normal Q, Sx NEG Feed-through Ion Pump Half height = 7 mm

7. 20003.11.28SKEKB Mini Work Shop @KEK7 1. Beam Chamber _6 Cross Section at SX magnet –Most sever part Dig a groove with a depth of about 3 mm to make a space for Sx mover At present, No Solenoid in Q,Sx

8. 20003.11.28SKEKB Mini Work Shop @KEK8 1. Beam Chamber _7 Solenoid in Q –One turn Coil (an idea)

9. 20003.11.28SKEKB Mini Work Shop @KEK9 2. Pump _1 Goal Pressure : 5  10 -7 Pa in average –Pumping speed = 0.1 m 3 s -1 m -1 (@  = 1  10 -6 mol./photon) Pumps : Distributed Pumping Scheme –NEG strip (+ lumped ion pump) ST 707 NEG Strip (30 mm in width) Feed-trough for NEG activation (max. 50 A, 50 V)

10. 20003.11.28SKEKB Mini Work Shop @KEK10 2. Pump _2 Estimation of Pumping Speed –NEG: 2.0 (1.25) m 3 s -1 m -2 (after some saturation) –Lumped pumps between adjacent Q and Sx (0.1 m 3 s -1 ) HER LER

11. 20003.11.28SKEKB Mini Work Shop @KEK11 2. Pump _3 For more pumping speed –Double NEG strip as in chambers for Wiggler section –Put more lumped pumps near Q and Sx –Enlarge bore size of magnets and put pumps in magnets Assumption of  = 5  10 -7 molecules photon -1 may be reasonable Wiggler section

12. 20003.11.28SKEKB Mini Work Shop @KEK12 2. Pump _4 Vacuum Scrubbing (simulation) –  : Based on KEKB – I : Increases by 18.8 mA step when  > 5 hours (  : Brems., CO) – NEG : Activate when S < 0.02 m -3 s -1 LER Assumption

13. 20003.11.28SKEKB Mini Work Shop @KEK13 3. Connection _1 Use flange + bellows –One side of bellows is welded to beam chamber. –Make quite easy to handle beam chambers Combine?

14. 20003.11.28SKEKB Mini Work Shop @KEK14 3. Connection _2 Flange (1) Use special RF-bridge and Helico-flex (2) Use MO Flange* (Special gasket) Cu Gasket *K.Kakihara et al., Proc.LAM03

15. 20003.11.28SKEKB Mini Work Shop @KEK15 3. Connection _3 Bellows –New or improved RF-shield –No position feed back system for BPM Bellows-less design –Severe problems How to absorb alignment and manufacturing errors of chamber How to fix exactly welding plane in situ

16. 20003.11.28SKEKB Mini Work Shop @KEK16 3. Connection _4 General Layout HER LER

17. 20003.11.28SKEKB Mini Work Shop @KEK17 4. Special Components _1 Movable Mask –Basically the same structure with present type –Material of head : C or Be ? Beam Bellows Chamber Mask Chamber Bellows Chamber Mask Head

18. 20003.11.28SKEKB Mini Work Shop @KEK18 4. Special Components _2 Movable Mask –Problem : Impedance –k = 1 V pC -1 @  z = 3 mm ~200 kW !! –Reduce number? –Powerful HOM absorber ? @5000bunches and 9.4 A

19. 20003.11.28SKEKB Mini Work Shop @KEK19 4. Special Components _3 HOM absorbers for various components Slot Beam Chamber SiC Wing More powerful absorber is required for masks. Need help from RF specialists.

20. 20003.11.28SKEKB Mini Work Shop @KEK20 4. Special Components _4 Gate Valves –With RF shield (new or improved) –Tapers at both side

21. 20003.11.28SKEKB Mini Work Shop @KEK21 5. Impedances (Loss Factors) Summary of Loss Factors (  z = 3 mm) 30~40 V pC -1

22. 20003.11.28SKEKB Mini Work Shop @KEK22 6. R&D Status _1 Ante-Chamber –Without photon stops –Test model will be installed this year.

23. 20003.11.28SKEKB Mini Work Shop @KEK23 6. R&D Status _2 Ante-Chamber_Type-1 –Under manufacturing in BINP –Material : Copper (OFC) –Forming : Stamp –Welding : EBW

24. 20003.11.28SKEKB Mini Work Shop @KEK24 6. R&D Status _3 Ante-Chamber_Type-2 –Under manufacturing in MHI –Material : Copper (OFC) –Forming : Drawing –Welding : EBW

25. 20003.11.28SKEKB Mini Work Shop @KEK25 6. R&D Status _3 Bellows (RF Shield) –Comb-type RF Shield High thermal strength, Low impedance Inside view a = 10 mm, b = 15 mm, c = 2 mm

26. 20003.11.28SKEKB Mini Work Shop @KEK26 6. R&D Status _4 Bellows (RF Shield) –Heating test transmitting 508 microwaves gave a promising result. –Trial models are being tested in this run. Trial model for LER 1284 bunches Good up to 1500mA

27. 20003.11.28SKEKB Mini Work Shop @KEK27 7. Remained Other Issues How to suppress electron cloud (e + ring) –Solenoid Inside of Q, Sx? –Surface treatment? Design of straight sections –Wiggler Region –Local Correction Region –etc….. IR

28. 20003.11.28SKEKB Mini Work Shop @KEK28 Ref. New Movable Mask Structure Ver.4 – Large impedance even for long taper Intrinsically disturb fields around bunch Beam Mask Chamber Mask Head ~200 kW !!

29. 20003.11.28SKEKB Mini Work Shop @KEK29 Ref. New Movable Mask Structure Proposal of New Structure (Only an Idea now) Ceramics (Fixed) Metal

30. 20003.11.28SKEKB Mini Work Shop @KEK30 Ref. New Movable Mask Structure Electric Fields Metal SupportsCeramics Supports

31. 20003.11.28SKEKB Mini Work Shop @KEK31 Ref. New Movable Mask Structure Issues to be studied –Trapped Mode (TEM like mode) Grooved duct to couple with TE11 mode Or Small diameter to rise cut off Use Winged-type HOM damper –Heating No heat conduction by ceramics By radiation Need estimation of input power 100W ⇒ 1000 °C –Charge up Thin coating of low conductivity metal Thin narrow strip of metal? –Need help of RF specialists and R&D by a trial model!!.