Overview of Super KEKB M Tawada KEK Super

Overview of Super. KEKB M. Tawada (KEK) Super B Factory Workshop in Hawaii April 20, 2005

Contents • • • • Strategy Machine Parameters Beam-beam simulations Lattice design Interaction region Magnet system Impedance and collective effects RF system Vacuum system Beam instrumentation Injector & damping ring Construction scenario Summary

Strategy Beam-beam parameter Lorentz factor Beam current Ratio of luminosity & tune shift reduction factors: 0. 8 ~ 1 (short bunch) Classical electron radius Beam size ratio@IP 1 ~ 2 % (flat beam) Vertical beta function@IP Increase beam currents • 1. 7 A (LER) / 1. 3 A (HER) → 9. 4 A (LER) / 4. 1 A (HER) Smaller by*/ Shorter z • 6 mm→ 3 mm / 5 mm → 3 mm Increase xy • 0. 05→ 0. 187

Lattice Parameters and Beam-Beam Effect bare lattice with beam-beam unit Beam current (LER/HER) I 9. 4/4. 1 A Beam energy (LER/HER) E 3. 5/8. 0 Ge. V Emittance ex 24 128 nm Horizontal beta at IP bx* 20 2. 3 cm Vertical beta at IP by* 3 2. 4 mm Horizontal beam size x * 69 54 mm Vertical beam size y * 0. 73 1. 23 mm r = y*/ x* 1. 1 2. 3 % Crossing angle (30 mrad crab crossing) qx 0 0 mrad Luminosity reduction RL 0. 86 0. 82 xx reduction Rxx 0. 99 0. 97 xy reduction Rxy 1. 11 1. 16 RL/Rxy 0. 78 0. 72 Horizontal beam-beam (estimated with S-S simulation) xx 0. 152 0. 041 Vertical beam-beam (estimated with S-S simulation) xy 0. 215 0. 187 Luminosity L Beam size ratio Reduction ratio 4. 0 x 1035 cm-2 s-1

8 Ge. V Positron beam 4. 1 A 3. 5 Ge. V Electron beam 9. 6 A

Beam-beam limit • Beam-beam parameter of 0. 05 has been already achieved with a finite crossing angle at KEKB. • Beam-beam simulation say: – Head-on collision improve the beam-beam parameter.

Crab crossing scheme Head-on Crab-crossing Crab crossing scheme restores the full luminosity of head-on collision. Crab cavity will be tested at the current KEKB machine in 2006.

Beam-beam simulation Tune Survey in Super. KEKB without parasitic collision effect. Lpeak=4. 0 x 1035 cm-2 s-1 (L/bunch=8. 0 X 1031, Nb=5000) Talk by Ohmi

Lattice Design: the arc section The beam-optical parameters can be adjusted to Super. KEKB without changing the lattice in the arc section. KEKB lattice: 2. 5 pi cell and non-interleaved chromaticity correction scheme. ®Wide tunability of horizontal emittance, momentum compaction factor. ®Principle nonlinearities in sextupole pairs cancelled out to give large dynamic aperture Talk by Koiso

Dynamic aperture issue • • Dynamic aperture of Super. LER with beam-beam effects. Tracking simulation is "Weak. Strong". Small difference between no beam-beam and xy=0. 07. Case xy=0. 14, dynamic aperture slightly shrinks. Touschek lifetime: – 50 min (no beam-beam) – 45 min (xy= 0. 14) 2 Jy/2 Jx=1% g 2 Jx (m) • nx/ny=45. 51/43. 545 No beam-beam xy=0. 07 xy=0. 14 Dp/p 0 (%) * no damping / 1000 turns * no machine error

IR design layout QC 2 RE QC 2 LP HER beam QCSLQCSR QC 1 LE QC 2 LE • • QC 1 RE QC 2 RP LER beam Issues for IR design • QC 1 magnet - Normal or Superconducting • Strong synchrotron light from QCS • Dynamic aperture with high beam parameter • Background to Belle Since we change working point near the half integer tune, IR need to be redesigned. Move QCSs, QC 1 s, QC 2 s closer to IP. QCS and compensation solenoid magnets overlap in Super. KEKB. Full crossing angle 30 mrad. Rotate LER beam 8 mrad. IR magnet design issue -> Talk by Ohuchi

IR Vacuum design issues • Strong SR from QCS magnets. – SR power: 194 k. W in HER & 78 k. W in LER – Large aperture is needed at QC 2 magnets in order to avoid SR since two beams and the SR don’t lie in the same plane. – Should provide sufficient cooling to every SR irradiation. • Intense HOM power – Extrapolation from KEKB gives a heat by HOM about 100 k. W*(bunch length factor). – The cooling of HOM will be a big problem. – Compact HOM absorber will be needed. • Denser Distribution of vacuum pumps to need to reduce the beam background. – The space for the pump must be reserved in the magnet.

Beam duct layout Left hand side (1) • Flange connection in the bore of QCS-L (magic flange). • The ducts of LER from QCSL to QC 2 LP escape SR. • LER downstream ducts avoid SR down to 5 m from IP. LER ducts avoid SR. LER SR: 65 k. W IP Beam ducts Separate z=1. 5 m from IP. BM: Beam Position Monitor, BL: Bellows Magic flange

Beam duct layout Right hand side (1) • In HER , all ducts are expected to avoid SR. • The BPM at the end of the QCS chamber is possible only if the electrodes clear the inner bore of QCSR. • HER downstream ducts avoid SR down to 8 m from IP(? ). HER ducts avoid SR IP HER SR: 179 k. W LER Beam ducts Separate z=1. 5 m from IP. BM: Beam Position Monitor, BL: Bellows Manageable in installation ?

Magnet System • Outside of the IR, most of the present KEKB magnets will be reused. • Some magnets for Nikko RF section and ante-chamber section will have to be newly designed and fabricated. Magnet Number Location Big bore radius HER Quad 20 Nikko LER-Quad 2 Oho Sextupole 49 Arc Wide gap steering 450 Arc & Tsukuba • Half of the wiggler magnets will be removed due to add RF cavities to Oho straight section. Damping time in LER will be 1. 5 times larger.

Impedance and Collective Effects • • • Resistive Wall Instability – Growth rates (800 -1000 s-1) <damping rate of feedback system (5000 s-1). Closed Orbit Instability due to long-range resistive wake (Danilov) – Thresholds (12. 3/12. 2 A for LER/HER) > design currents Electron Cloud Instability (Positron Ring) – With ante-chambers and positrons in the HER, simulations show that 60 G solenoid field should clear the electrons. Uncertainties: • Distribution on walls and amounts of electrons. • Behavior of electrons inside lattice magnets. • • Ion Instability (Electron Ring) – Currently suppressed by feedback. – With electrons in LER, simulated initial growth rate faster than feedback damping rate, leading to dipole oscillation with amplitude of order of vertical beam size →possible loss of luminosity. Coherent Synchrotron Radiation – Investigations under way.

Coherent synchrotron radiation • CSR cause the energy spread and instability because of (1) shorter bunch length, (2) higher bunch current and (3) small bending radius. • Dr. Agoh has developed new method to estimate CSR with shielding effect by vacuum chamber. • Simulation shows – CSR affects Super. LER seriously. – CSR can be suppressed by smaller vacuum chamber. • Investigation with the other impedances is in progress. Talk by Agoh

Vacuum system • High beam current and shorter bunch length causes: – Heating due to intense synchrotron radiation. • 28 k. W/m in LER, twice as high as in KEKB • 22 k. W/m in HER, 4 times as high as in KEKB – High gas load • Need higher pumping speed. – High photoelectron yield • -> Ante-chamber • -> Surface coating with low SEY materials • -> Solenoid field – Heating due to intense HOM power • Minimize loss factor for each vacuum components • HOM absorbers to be installed near large impedance sources. – High wall current • peak: 250 A ( z=3 mm) Talk by Suetsugu

Ante-chamber R&D Smaller SR Power Density Lower Impedance Lower photoelectron production Electrons in the beam channel [Electron Monitor] Prototype ducts were installed in the LER (Jan. 2004) Photoelectrons decreased by factors at high current (Ib >1 000 m. A). The reduction was by orders at low current (Ib <100 m. A). Multipactoring seems to become important at higher current. Combination with solenoid field, and an inner surface with a low SEY will be required at higher current.

Bellows chamber with comb type RF-shield High thermal strength l Low impedance l No sliding contact on the surface facing the beam l Two circular bellows chamber was installed in LER two years ago. Good results were obtained. Temperature decreased to <1/6 Temperature of comb ~ 50 C at 1. 6 A No damage after 1. 5 year operation

Vacuum parameters (HOM related) for Super. KEKB Loss factor k (V/C) Length or # of components Total k (V/C) HOM power(k. W) Resistive wall 4. 1´ 109 2200 m 8. 9´ 1012 1780 Pumping holes 8. 8´ 105 2200 m 1. 9´ 109 0. 38 Flanges 1´ 108 800 8´ 1010 16 Bellows 4´ 109 800 3. 2´ 1012 640 Photon mask 1´ 104 800 8´ 106 0. 0016 Gate Valve 3´ 109 16 4. 8´ 1010 9. 6 Movable mask 1´ 1012 16 1. 6´ 1013 3200 Taper 3´ 109 72 2. 2´ 1011 44 HOM dampers to be installed.

RF system upgrade • To handle a much higher current and shorter bunch length, upgrade of RF system will be needed. • Adopt the same RF frequency of 508 MHz as KEKB. – Save the construction cost and time. – Technical uncertainties would be relatively small. • Use ARES+SCC for HER and ARES for LER. • The number of RF unit will be doubled. – ARES(LER) : 10 → 28 – ARES(HER) : 6 → 16 – SCC(HER) : 8 → 12

ARES upgrade • Increase stored energy – By enlarging the coupling hole between the A-C cavities, increase energy ratio Us/Ua = 9 → 15. – One klystron feed RF power to one ARES cavity. • HOM load issues – Upgrade of HOM damper: 26 → 80 k. W/cavity. • Input coupler – 400 k. W/cavity → 800 k. W/cavity. – Ti. N coated coupler have been completed and being tested in the new test-stand up to 800 k. W (CW). • Longitudinal coupled bunch instability due to the ARES cavities must be cured by bunch-by-bunch feedback system. Talk by Kageyama

Superconducting Cavity • • Add 4 cavities for HER In Super. KEKB, HOM power of 60 k. W/cavity at 4. 1 A has to be absorbed. – c. f. In KEKB, the current HOM power is only 15 k. W/cavity at 1. 2 A. • HOM damper upgrade is needed. Talk by Mitsunobu

Crab Cavity for Super. KEKB • A new type crab cavity will be needed, which can be used at 10 A. Two different types based on different methods to damp the accelerating mode (Lower Frequency Mode). Coaxial coupler Notch filter Additional waveguide damper (1) Coaxial couplers Type (2) Waveguide damper Type Additional waveguide damper Waveguide damper for the LFM

Beam Position Monitors SMA connector with male contact pin • Front-end electronics – Use same 1 GHz detector for normal chamber. – Need to develop the 508 MHz detector and up-converter for antechamber to avoid HOM contamination of pick-up signals. • New button electrodes – Developing the new button electrodes. – 12 mm -> 6 mm diameter • Signal power same as at present, at higher beam currents, to match dynamic range of existing front-end electronics. – Use low permittivity ceramic to reduce HOM. Talk by Flanagan Flange mounted Small diameter electrode

Synchrotron radiation monitors • Current extraction chamber (copper) may need increased cooling. • HOM leakage power will be 500 W. • May need HOM absorbers • Direct mirror heating from SR irradiation should be minimized. • Increase bend radius of weak bends • Lowers total incident power. • Also increases visible light flux – desirable to help see effect of single crab cavity Talk by Flanagan

Bunch-by-Bunch Feedback • Transverse feedback similar to the present design – Detection frequency 2. 0 -> 2. 5 GHz. – Transverse kicker needs work to handle higher currents – Improved cooling, supports for kicker plates. • Longitudinal feedback to cure ARES HOM and 0/Pi mode instability – Use DAf. NE-type (low-Q cavity) kicker. • Digital FIR and memory board to be replaced by new GBoard under development at/with SLAC. – Low noise, high speed (1. 5 GHz), with custom filtering functions possible. – Extensive beam diagnostics. Talk by Flanagan

Injector upgrade Intensity upgrade e-: increase bunch current. e+: improve capture efficiency by improving pulse coil. l Energy upgrade for e+ • Boosted by the C-band accelerator modules. • Field gradient 21 42 MV/m l Smaller e+ emittance for IR & C-band module aperture. • e+ damping ring l Faster e+ / e- switching for continuous injection • switched by the kicker before the target. • e+ and e- go through independent beam lines. l Talk by Furukawa

C-band modulator & klystron - Some problems of DC PS were fixed. - No trouble since Sep. 2004. RF compressor - SLED type (TE 038). - 200 MW output power is achieved at Test Stand. - Multiplication factor: 4. 7 times at peak. Inverter DC PS 1. 8ｍ Prototype of C-band - Field gradient 42 MV/m with RF compressor. Mix-mode RF window - TE 11 +TM 11 - 300 MW transmission power is achieved. S-band section C-band section

Damping ring • Positron emittance needs to be damped to pass reduced aperture of C-band section and to meet IR dynamic aperture restrictions. – Electron DR may be considered later to reduce injection backgrounds in physics, but for now only DR considered. • To reduce beam background to Belle – Injected beam charge is doubled – Needed damped beam for smaller energy-tail and emittance tail. • Damping ring located downstream of positron target, before Cband accelerating section. 1 -Ge. V Damping Ring 0 RTL-line (BCS) Sector-2 Positron target 50 m LTR-line (ECS) Sector-3 C-band acc. section

Damping ring parameters RF: Use KEKB ARES cavity (509 MHZ)

Damping Ring Lattice FODO cell w/alternating bends Dynamic aperture Green = injected beam, red = 4000 turns max deviation (thick = ideal machine, thin = machine errors included) • FODO cell has large dynamic aperture, but large momentum compaction factor increases required accelerating voltage. • Reversing one of the bends reduces the momentum compaction factor. • Adopt reverse/forward ratio of ~1/3 Large dynamic aperture Wide operational tune space

Facility KEKB(design) Super. KEKB Unit Magnet PS 3. 84 MW Magnet 6. 35 MW SR 8 26 MW HOM 0. 43 9 MW RF system 16 38 MW Total 34. 6 83. 2 MW Total site consumption power : 120 MW

Construction schedule “Minor” upgrade Belle “Major” upgrade Crab cavity KEKB 1000 fb-1 construction J-PARC 1 construction Budget 2004 05 06 07 shutdown 08 09 Calendar year 10 S-KEKB ILC construction 11 12

Budget

Summary • Super. KEKB is a quite challenging. • Target luminosity is 4. 0 x 1035 cm-2 s-1, a new luminosity frontier. • There are many issues due to the very high beam current and short bunch length. • Further simulation and hardware R&D work toward Super. KEKB are on-going.

Beam-beam simulation Parasitic collision effect for KEKB positrons electrons x w/o parasitic (KEKB) Parasitic collision Crossing angle 22 mrad s Parasitic collision - Long range beam-beam force - Beam-beam separation: 6. 6 mm(KEKB, 22 mrad) 9. 0 mm (Super. KEKB, 30 mrad) - Luminosity degradation is negligible if good working point are chosen. simulation study is in progress w/ parasitic (KEKB) 4 backet spacing

Crab cavity positrons electrons x Crossing angle 30 mrad s w/o Crab cavity effectively creates head-on collision. It can improve the luminosity. Crab cavity for KEKB will be installed in Nikko straight section in Jan. 2006. w/ Crab cavity Because of high HOM power to dampers, another type of crab cavity in Super KEKB will be necessarily.

IR Vacuum design issues QC 2 design should be checked against the fact that the two beams and the SR don’t lie in the same plane. SR fans from QCSR