Overview of SuperKEKB 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

Beam size 1 ~ 2 % (flat beam) Beam current Beam-beam parameter Vertical beta Ratio of luminosity & tune shift reduction factors: 0.8 ~ 1 (short bunch) Lorentz factor Classical electron radius Strategy Increase beam currents 1.7 A (LER) / 1.3 A (HER) → 9.4 A (LER) / 4.1 A (HER) Smaller  y * / Shorter  z 6 mm→3 mm / 5mm →3 mm Increase  y 0.05→0.187

Lattice Parameters and Beam-Beam Effect bare latticewith beam-beamunit Beam current (LER/HER)I 9.4/4.1 A Beam energy (LER/HER)E 3.5/8.0 GeV Emittance xx nm Horizontal beta at IP x*x* cm Vertical beta at IP y*y* 32.4 mm Horizontal beam size x*x* 6954 mm Vertical beam size y*y* mm Beam size ratio r =  y * /  x * % Crossing angle (30 mrad crab crossing) xx 00 mrad Luminosity reductionRLRL  x reduction RxRx  y reduction RyRy Reduction ratioR L /R  y Horizontal beam-beam (estimated with S-S simulation) xx Vertical beam-beam (estimated with S-S simulation) yy LuminosityL 4.0 x cm -2 s -1

8GeV Positron beam 4.1 A 3.5GeV 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 SuperKEKB without parasitic collision effect. Lpeak=4.0x10 35 cm -2 s -1 (L/bunch=8.0X10 31, Nb=5000) Talk by Ohmi

Lattice Design: the arc section The beam-optical parameters can be adjusted to SuperKEKB without changing the lattice in the arc section. KEKB lattice: 2.5pi 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 SuperLER with beam-beam effects. Tracking simulation is "Weak- Strong". Small difference between no beam-beam and  y =0.07. Case  y =0.14, dynamic aperture slightly shrinks. Touschek lifetime: –50 min (no beam-beam) –45 min (  y = 0.14)  p/p 0 (%)  2J x (m) 2J y /2J x =1% x / y =45.51/ No beam-beam  y =0.07  y =0.14 * no damping / 1000 turns * no machine error

IR design layout QCSR QCSL QC2RP QC2LP QC2LE QC2RE QC1RE QC1LE LER beam HER beam Move QCSs, QC1s, QC2s closer to IP. QCS and compensation solenoid magnets overlap in SuperKEKB. Full crossing angle 30 mrad. Rotate LER beam 8 mrad. IR magnet design issue -> Talk by Ohuchi Issues for IR design QC1 magnet - Normal or Superconducting Strong synchrotron light from QCS Dynamic aperture with high beam- beam parameter Background to Belle Since we change working point near the half integer tune, IR need to be re- designed.

IR Vacuum design issues Strong SR from QCS magnets. –SR power: 194 kW in HER & 78 kW in LER –Large aperture is needed at QC2 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 100kW*(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) SR:65kW Flange connection in the bore of QCS-L (magic flange). The ducts of LER from QCSL to QC2LP escape SR. LER downstream ducts avoid SR down to 5m from IP. BM:Beam Position Monitor, BL:Bellows Beam ducts Separate z=1.5m from IP. LER LER ducts avoid SR. Magic flange IP

Beam duct layout Right hand side (1) SR:179 kW 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 8m from IP(?). HER LER BM:Beam Position Monitor, BL:Bellows Beam ducts Separate z=1.5m from IP. Manageable in installation ? HER ducts avoid SR IP

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. 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. MagnetNumberLocation Big bore radius HER Quad20Nikko LER-Quad2Oho Sextupole49Arc Wide gap steering450Arc & Tsukuba

Impedance and Collective Effects Resistive Wall Instability –Growth rates ( 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 60G 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 SuperLER 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 kW/m in LER, twice as high as in KEKB 22 kW/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: 250A (  z =3mm) Talk by Suetsugu

Ante-chamber R&D Electrons in the beam channel Photoelectrons decreased by factors at high current (I b >1 000 mA). The reduction was by orders at low current (I b <100mA). 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. Prototype ducts were installed in the LER (Jan.2004) [Electron Monitor] Smaller SR Power Density Lower Impedance Lower photoelectron production

Bellows chamber with comb type RF-shield 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 High thermal strength Low impedance No sliding contact on the surface facing the beam

Vacuum parameters (HOM related) for SuperKEKB Loss factor  (V/C) Length or # of components Total  (V/C) HOM power(kW) Resistive wall 4.1  m 8.9  Pumping holes 8.8  m 1.9  Flanges 1   Bellows 4   Photon mask 1   Gate Valve 3   Movable mask 1   Taper 3   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 508MHz 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 kW/cavity. Input coupler –400 kW/cavity → 800 kW/cavity. –TiN coated coupler have been completed and being tested in the new test-stand up to 800 kW (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 SuperKEKB, HOM power of 60kW/cavity at 4.1 A has to be absorbed. –c.f. In KEKB, the current HOM power is only 15 kW/cavity at 1.2A. HOM damper upgrade is needed. Talk by Mitsunobu

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

Beam Position Monitors Front-end electronics –Use same 1GHz detector for normal chamber. –Need to develop the 508MHz detector and up-converter for ante- chamber 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. SMA connector with male contact pin Flange mounted Small diameter electrode Talk by Flanagan

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 DAfNE-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. Energy upgrade for e + Boosted by the C-band accelerator modules. Field gradient 21  42 MV/m Smaller e + emittance for IR & C-band module aperture. e + damping ring Faster e + / e - switching for continuous injection switched by the kicker before the target. e + and e - go through independent beam lines. Talk by Furukawa

C-band 1.8 ｍ Inverter DC PS C-band section S-band section RF compressor - SLED type (TE038) MW output power is achieved at Test Stand. - Multiplication factor: 4.7 times at peak. C-band modulator & klystron - Some problems of DC PS were fixed. - No trouble since Sep Mix-mode RF window - TE11 +TM MW transmission power is achieved. Prototype of C-band - Field gradient 42MV/m with RF compressor.

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 C- band accelerating section. 050 m Positron target Sector-2Sector-3 LTR-line (ECS) RTL-line (BCS) 1-GeV Damping Ring C-band acc. section

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

Damping Ring Lattice 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 Dynamic aperture Green = injected beam, red = 4000 turns max deviation (thick = ideal machine, thin = machine errors included) FODO cell w/alternating bends Large dynamic aperture Wide operational tune space

Facility KEKB(design)SuperKEKBUnit Magnet PS3.84 MW Magnet6.35 MW SR826MW HOM0.439MW RF system1638MW Total MW Total site consumption power : 120MW

Construction schedule KEKBS-KEKBshutdown construction J-PARC 1 constructionILC construction 1000fb -1 Calendar year Crab cavity “Minor” upgrade “Major” upgrade Belle KEKB Budget

Summary SuperKEKB is a quite challenging. Target luminosity is 4.0x10 35 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 SuperKEKB are on-going.

Beam-beam simulation Parasitic collision effect for KEKB s x electronspositrons Crossing angle 22mrad w/o parasitic (KEKB) w/ parasitic (KEKB) 4 backet spacing Parasitic collision - Long range beam-beam force - Beam-beam separation: 6.6 mm(KEKB, 22mrad) 9.0 mm (SuperKEKB, 30mrad) - Luminosity degradation is negligible if good working point are chosen. simulation study is in progress Parasitic collision

Crab cavity s x electronspositrons Crossing angle 30mrad w/o Crab cavity w/ Crab cavity 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 Because of high HOM power to dampers, another type of crab cavity in Super KEKB will be necessarily.

IR Vacuum design issues QC2 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