1 SuperKEKB Upgrade project of KEKB KEK Yukiyoshi Ohnishi

Y. Ohnishi (KEK) 2 Target of SuperKEKB Extremely high luminosity B factory –Luminosity = ~ cm -2 s -1 –Int. L > 1000 /fb/year at SuperKEKB (Int. L = 100 /fb/year at present machine) Strategy : 1.Unique –Asymmetric energy, double ring collider, finite x-angle, high beam current, extremely low beta & short bunch, crab crossing 2.Upgrade –Scrap & Build –Application of existing components Major upgrade in

Y. Ohnishi (KEK) 3 History of peak luminosity in last 25 years SuperKEKB cm -2 s year ~ ? is good prediction for the future !

Y. Ohnishi (KEK) 4 Motivation KEKB will loose its competitiveness in Competitors in 5 years –LHC-B, BTeV, (SuperPEP-II) –Luminosity of LHC-B/BTeV corresponds to cm -2 s -1 e + e - collider. Physics motivation 1. PRECISION TEST of Kobayashi-Maskawa scheme 2.Search for NEW SOURCE of Flavor Mixing and CP Violation 3. Study of the FLAVOR STRUCTURE of SUSY, identification of SUSY breaking mechanism KEKB is R&D machine for SuperKEKB.

Y. Ohnishi (KEK) 5 Machine parameters of SuperKEKB Luminosity formula : Beam-beam tune shift parameters : Assumed that the "transparency" conditions : Alternative expression of luminosity : “ Optimal coupling ”

Y. Ohnishi (KEK) 6 Machine parameters of SuperKEKB (cont'd) Luminosity is proportional to : Brute Force Concept : –Higher beam current –Smaller beta function at I.P (as well as short bunch length) –Larger beam-beam parameters x Luminosity reductions

Y. Ohnishi (KEK) 7 Luminosity reductions Half crossing angle:  x = 15 mrad Horizontal beta at I.P:  x * = 30 cm Vertical beta at I.P:  y * = 3 mm Emittance : 33 nm (6.4 % coupling) R L : Luminosity reduction due to geometrical R  : Tune shift reduction R L /R  y is a function of crossing angle, beta, emittance, bunch length. R L /R  y = 0.8 (KEKB : ~1)  x * = 15 cm  x * = 30 cm  x = 15 mrad

Y. Ohnishi (KEK) 8 Strategy of SuperKEKB Primary target of luminosity is cm -2 s -1. –Beam-beam parameter : ~ 0.05 (experience at KEKB) –Vertical beta at I.P : 3 mm (bunch length : 3 mm) –Beam current : 9.4 A (LER) x 4.1 A (HER) –Half crossing angle : 15 mrad Brute force concept cm -2 s -1 is also considered. –Extensibility in the future is important. Political issue should NOT KILL cm -2 s -1 machine.

Y. Ohnishi (KEK) 9 Machine parameters of SuperKEKB (detail) Head-on collision (effective) Need crab cavity S-S, S-W simulation Energy : 3.1/9 GeV Options April 2002 from SBF Luminosity

Y. Ohnishi (KEK) 10 High beam current RF system Vacuum system Photoelectron cloud effect Fast ion instability (FII) Bunch by bunch feedback system Higher order mode (HOM) Injector linac

Y. Ohnishi (KEK) 11 RF system Requirements : –Large amount of RF power –Very large HOM loss at cavities –Heavy beam-loading Strategy : Existing RF system is used as much as possible. RF frequency : 509 MHz (same as KEKB) Cavity : ARES (LER) / ARES+SCC (HER) –Improvements and modifications are needed. –ARES (NC cavity) / SCC (SC cavity) K. Akai et al.

Y. Ohnishi (KEK) 12 Accelerator Resonant coupled with Energy Storage

Y. Ohnishi (KEK) 13

Y. Ohnishi (KEK) 14 Modification of RF system Total beam power is higher than KEKB by factor 4. Need high power fed to each cavity. Increase number of RF stations. ~ Double RF. –Half of wigglers in LER is replaced to RF cavities.

Y. Ohnishi (KEK) 15 RF system parameters 30/ KEKB

Y. Ohnishi (KEK) 16 (Each building for 4 〜 6 RF units.) D8D7 D4 D10 D11 new D1D2 D5 LER-RF (ARES) HER-RF (ARES) HER-RF (SCC) 5 buildings should be added. Layout of RF stations

Y. Ohnishi (KEK) 17 Heavy beam-loading on the accelerating mode Longitudinal instability Growth rate of the -1 mode caused by large detuning is very high (~10 4 ), even with ARES and / or SCC. –Strong damping by feedback with comb filter is inevitable. –Zero-mode stabilization should also be improved. Beam phase modulation due to abort gap Abort gap of KEKB has been reduced (1  s → 0.5  s). –Further reduction to 0.2  s is required. Δφ = 5.2° (LER  s gap)

Y. Ohnishi (KEK) 18 R&D issues for RF HOM dampers –as well as Input couplers and Damper at C-cavity Impedance estimation RF control –Feedback for zero mode and -1, -2 modes Klystron and high-power system –Reduce crowbar trips –Improve reliability of dummy loads Beam test of improved system

Y. Ohnishi (KEK) 19 Vacuum system Ante-chamber –Reduce power density of synchrotron radiation at Wall. –Reduce effect of photoelectron cloud. –Low impedance / no pumping port in beam chamber –High linear pumping speed (Target : 100 l/s/m) –Solenoid winding before installation (e + ring) Bellows –No heating or discharge problem due to HOM –Need low impedance Movable masks –No damage of mask head due to beam hitting –No HOM heating –Need low impedance HOM absorber chamber Y. Suetsugu et al.

Y. Ohnishi (KEK) 20 Design of Ante-chamber Ante-chamber Beam SR Cooling water Pump LER arc section LER [Ion pump section] IP, NEG feed through Cooling water NEG strip

Y. Ohnishi (KEK) 21 Design of Ante-chamber (cont'd) Very large SR power No photon stop Ante-chamber for LER –Max. SR power line density : 29 kW/m(14.8 kW/m) –Power density : 40 W/mm 2 (37 W/mm 2 ) Ante-chamber for HER –Max. SR power line density : 25 kW/m(5.8 kW/m) –Power density : 40 W/mm 2 (14.5 W/mm 2 ) (KEKB)

Y. Ohnishi (KEK) 22 Ante-chamber R&D Ante-chamber with photon stop (Prototype 2001) Bending [B2P.73] Quadrupole [QF2P.33] positron beam Photoelectron Monitor Photon Stop

Y. Ohnishi (KEK) 23 Ante-chamber R&D (cont'd) Prototype has been tested in LER at KEKB. Photoelectrons in beam chamber are measured. Number of electrons measured by a photoelectron monitor reduced to about 1/7 compared to the usual single chamber. Solenoid is still effective to reduce number of electrons by 1/2.

Y. Ohnishi (KEK) 24 Ante-chamber R&D (cont'd) R&D for production procedure (BINP, Russia) No photon stops (special material : GlidCop etc.) New prototype will be installed during this summer. Confirm reduction of photoelectrons in beam chamber. Prototype 2003

Y. Ohnishi (KEK) 25 New Bellows with RF-shield (Comb structure) Low HOM leakage High thermal strength Loss factor : 1/4 of present bellows No multipactering Less flexibility : –expansion < ± 3 mm –offset < ~ 0.2 mm –bending angle < ± 2 deg. RF-shield 2 mm 1 mm 10 mm Reduction of impedance sources

Y. Ohnishi (KEK) 26 New Bellows with RF-shield (cont'd) Machining is available. Application to ante-chamber

Y. Ohnishi (KEK) 27 Movable mask R&D Heating of components near mask: – Chamber type (Version 4) as KEKB is better. But, Heating of bellows is a problem. –Beam steering scheme solves the troubles of bellows. –Long tapers will reduce TE mode HOM power. How does the mask head harmonize the ante-chamber structure ? Version 4 HOM absorbers near the mask head is needed. Plunger type (Version 5) is another option.

Y. Ohnishi (KEK) 28 HOM absorber chamber (slot type) SiC rod Effective for TE mode HOM that causes heating of bellows. Tested at KEKB

Y. Ohnishi (KEK) 29 Small beta function at I.P Optics –flat beam –beta functions :  x * /  y * = 30 cm / 3 mm Interaction region (IR) design –QCS, special magnets (QC1, QC2) Dynamic aperture

Y. Ohnishi (KEK) 30 Optics at IR beta function at I.P :  x * /  y * = 30 cm / 3 mm LER HER H. Koiso et al.

Y. Ohnishi (KEK) 31 Layout of beam lines at IR Half crossing angle : 15 mrad Final focusing quadrupoles (QCS) locate at the position as close to the IP as possible. Pos. from the IPSuper-KEKBKEKB QCS-R mm1920 mm QCS-L969.4 mm1600 mm The QCS magnets are overlaid with the compensation solenoids (ES). compact & short in z N. Ohuchi et al.

Y. Ohnishi (KEK) 32 QCS (Left) QCS (Right) QC1 (Left) QC1 (Right) Option 1: Superconducting magnet Option 2: Normal-conducting magnet ESR QCS

Y. Ohnishi (KEK) 33 Bz (central field), T L (coil length), m ESRESL Super-KEKBKEKB ESR: N (4.3 tons)ESR: N (0.7 tons) ESL: N (13.8 tons)ESL: N (2.4 tons) Electro-magnetic force acting on ESR and ESL from the Belle (in z- direction) Field distortion in Belle detector

Y. Ohnishi (KEK) 34 Dynamic aperture Field distributions of the detector, compensation solenoids, QCSs along longitudinal direction are given by slices of 4 cm thickness with const. field. Multipole components not included. Natural chromaticity : –-87.9 (horizontal) – (vertical) LER 6-D tracking simulation with SAD No lattice errors Dynamic aperture of LER lattice satisfies the requirement for the injection and lifetime (Touschek ~230 min). injection

Y. Ohnishi (KEK) 35 Short bunch length Higher order mode (HOM) –Impedance estimation Coherent synchrotron radiation (CSR) Optics design –Momentum compaction factor (  ) : -2 ~ +4x10 -4 –Negative  lattice may help to reduce bunch length.

Y. Ohnishi (KEK) 36 Beam lifetime at cm -2 s -1 Luminosity lifetime –dN/dt = -  L –Cross section of radiative Bhabha: 2.14x cm 2 –Loss rate : 0.34 mA/s –LER/HER : 460/200 min Vacuum lifetime –~10 hours (? depends on vacuum system) Touschek lifetime –LER/HER : 230/1650 min (estimated from dynamic aperture) Overall lifetime of LER/HER : > ~150 min (inc. beam-beam) –Loss rate : 1 mA/s (LER)/ 0.46 mA/s (HER) Continuous injection –Need 5Hz ~ 10 Hz repetition (70% injection efficiency)

Y. Ohnishi (KEK) 37 Requirements to linac injector at SuperKEKB 1. e+ beam energy 3.5 → 8.0 GeV Energy switch : 8.0 GeV e - / 3.5 GeV e + → 8.0 GeV e + / 3.5 GeV e - (a) This helps to reduce beam blowup due to photoelectron effects. (b) e- charge > e+ charge 2. Injection charge 1.0 → 5.0 nC (e - ) 0.6 → 1.2 nC (e + ) For larger stored current : 1.1A e - / 2.6 A e + → 9.4 A e - / 4.1 A e + 3. Simultaneous Injection (both e + /e - ) 4. Smaller e+ emittance T. Kamitani et al.

Y. Ohnishi (KEK) 38 Higher acceleration field scheme for 8 GeV e+ (Beam recirculation scheme is also under consideration, but skipped here.) 2-Bunches for Simultaneous Injection 1-st bunch -> e - Injection 2-nd bunch -> e + production S-band accl. units are replaced with C-band units. Accl. Field 21 -> 41 MV/m e + Damping Ring for lower emittance

Y. Ohnishi (KEK) 39 KEKB injector linac accelerator unit New C-band accelerator unit Present S-band accelerator unit Wave guide C-band SLED Pulse Modul- ator C-band Kly- stron Wave guide C-band SLED Pulse Modul- ator C-band Kly- stron Wave guide S-band SLED Pulse Modulator S-band Kly- stron C-band accelerating structuresS-band accelerating structures S-Band to C-Band

Y. Ohnishi (KEK) 40 C-band components R&D status Klystron (Toshiba 50 MW C-band Klystron ) Pulse Modulator (Compact type) Sub-booster klystron (satellite 40 kW Klystron is modified to 5712 MHz) Already Fabricated Accelerating structure #1 (2pi/3-mode, scaled down from S-band) Under Engineering design (parameter tuning) Wave guides, RF Window, Flange Under fabrication 3-dB Hybrid, Dummy load Under Engineering design (parameter tuning) Toward 2003 Summer beam test at KEKB Linac (1 Pulse Modulator + 1 Klystron + 1 Accel. structure 1m-long) Toward 2004 Spring beam test at KEKB Linac (1 Pulse Modulator + 1 Klystron + 1 RF compressor + 2 Accel. structures 1m-long) Accelerating structure #2 (New power coupler design) Under basic design RF pulse compressor (LIPS-type TE038-mode) Under basic design

Y. Ohnishi (KEK) 41 C-band Klystron Compact pulse modulator Test accel. cavity RF measurement

Y. Ohnishi (KEK) 42 Toward higher luminosity Crab crossing –Beam-beam simulations –Design of crab cavity for 1-2 A (KEKB) –Design of crab cavity for 10 A Four beams (neutralization) –Analytic calculation –Beam-beam simulations Round beam –Not considered yet.

Y. Ohnishi (KEK) 43 Beam-beam simulation Target luminosity : ~ cm -2 s -1 Number of bunches : 5000 Energy : 3.5 GeV (LER) / 8 GeV (HER) Beam current : I(HER) = (3.5/8) x I(LER) Weak-strong simulation  x = 0 mrad  x = 15 mrad x = x = x = x = x = K. Ohmi et al.

Y. Ohnishi (KEK) 44 Crab cavity Squashed cell operating in TM2-1-0 (x-y-z) Coaxial beam pipe + HOM dampers Designed for 1 〜 2A beam Squashed cell operating in TM2-1-0 HOM damping using wave guides without coaxial beam pipe damper –Heavy damping of all HOM’s except TM –Smaller loss factor –More power to damper is allowed than the present scheme. Cure high-Q TM1-1-0 –Frequency control, Feedback w/ parallel comb filter K. Hosoyama and K. Akai et al. New design for SuperKEKB Present design for KEKB

Y. Ohnishi (KEK) 45 Crab crossing Crab crossing is powerful scheme to achieve high luminosity. It is hard to develop crab cavity for extremely high beam current. Test of crab crossing at KEKB in 2005 –1 crab : 11 mrad / HER  x = 200 m Crab cavity Nikko straight section Need magnet reconfiguration A. Morita et al. KEKB HER

Y. Ohnishi (KEK) 46 Crab crossing (cont’d) Dynamic aperture can be kept as same as the case w/o crab cavity at KEKB. w/o crab cavity w/ crab cavity KEKB (operation)

Y. Ohnishi (KEK) 47 Summary R&D of SuperKEKB is going on. Long-term plan of KEKB includes SuperKEKB. –KEKB has already achieved L = 9.5 x cm -2 s -1. (design:10 34 ) New components and schemes to achieve higher luminosity have been or will be tested at KEKB. Expression of Interest was written in Jan Workshops on higher luminosity B-Factory were held. –Aug. 2001, Jan. 2002, Aug. 2002, Feb Letter of Intent will be written this year. Thanks to a lot of efforts of volunteers working on KEKB.