2 Design strategy Natural extension of present KEKB the same boundary between KEKB and Belleconventional flat beam schemeround beamA baseline design of SuperKEKB IR has been completed.Details are described in LoI (2004).
4 Issues of IR Design Issues Causes Measures Dynamic aperture Lower beta’s at IP.Place QCS magnets. closer to IP.Damping ring.Physical apertureLarger crossing angle.(22mrad -> 30mrad)Heating of IR componentsHigher beam currents.Higher power of SR from QCS magnets.Shorter bunch length (HOM).Under study.Detector beam backgroundHigher power and critical energy of SR from QCS magnets.QCS closer to the IP.Higher Luminosity.Under study by Belle Group.
5 Place QCS magnets closer to IP SuperKEKBKEKBThe boundary between KEKB and Belle is the same.ESL and ESR will be divided into two parts (to reduce E.M. force).QCSL (QCSR) will be overlaid with (the one part of ) ESL(ESR).
6 IR magnet layout QC2RE QC2LP QC1RE HER beam QCSR QCSL LER beam QC1LE QC2RPQC2LE
7 HER dynamic aperture bare lattice BX/BY=20/.3 cm H. KoisoHER dynamic aperture bare lattice BX/BY=20/.3 cminjectionbeamRequired: H/V 4.5/0.52 ×10-6m
8 Local correction scheme also in HER? HER local chromaticity correction scheme is not compatible with installation of crab cavities in Tsukuba section.If we want to install crab cavities in Tsukuba, we can not adopt the local correction scheme in HER.We need to wait for the results of the experiment with the crab cavities in Nikko section next year.
9 New issues Horizontal tune very close to half-integer SR fanPhysical aperture in IRIdea of waist controlTraveling focusCrab waist
10 } Beam-beam simulation Head-on y ~0.33 (.503, .550) Tune Survey in SuperKEKBwithout parasitic collision effect.Lpeak=8.3x1035cm-2s-1(L/bunch=1.66X1032, Nb=5000)Head-on}y ~0.33(.503, .550)Simulation by K. Ohmi
11 Estimation of dynamic effects Input parametersx0 = 0.152x = variable(0.503)x = 24 nmx* = 20 cmx~ 2.0cmx=0.15mx[cm]x[m]x’[mrad]SAD2.00.1252.5B-B1x, x’2.300.1282.493x , x’4.189 x 0.2093 x 2.23x’~ 2.5mrad
12 Fan of SR with dynamic effects 9ex (3 sx, 3sx’) is taken into account.xx0 = 0.1, nx = .510nx = > x’~1.4mradnx = > x’~2.5mrad
13 Power of SR from QCS Magnets QCSRQCSLMagnet length [m]0.330.42Dx [mm]34.529.1G [T/m]37.235.4B [T]1.281.03Eb [GeV]8.03.5I [A]4.19.4P [kW]179 (27)64.6 (10)( ): present KEKB Design
14 x in IR with dynamic effects LER IRx*= 4.78cm, x = 98.7nm (x*0= 40cm, x0 = 12nm )(red)x*= 4.45cm, x = 217nm (x*0= 20cm, x0 = 24nm )(blue)
16 Parameters of IR quad (LoI) bx (mm)82110221216b x22.214.171.124.16.72.5
17 Waist control To avoid effects of “Hourglass” effect Traveling focus Sextupole magnets + crab cavitiesRF quadrupleEnergy difference (RF cavity) + chromatic effectCrab waistSextuple magnets + crossing angle + small x sizeKick by sextuplevertical focus depending on xharmful or not?
19 Crab waist (SuperB workshop @ LNF) Smaller area of interaction > effectively short bunch > smaller beam is needed to keep yhighSmaller beam-beam tuneshift (Hor.)Cancellation of main and long range forceStill crab waist is needed.Shift of waist pointsHarmful effect of crossing angle is partially canceled.Basic schemecrossing anglesmall x sizecrab waiste-e+original waistcrabbed waistx2ss = x/tan(2) ~ x/(2)
23 SX strength and phase advance (hor.) Traveling focus with crabCrab waistzssamesame
24 IssuesEffectiveness of the traveling focus and crab waist schemes at KEKB or SuperKEKBBeam-Beam simulationGeometrical luminosity with traveling focusLattice designStudies under wayEffects of the other nonlinear terms of SX (Sx3)To be studiedHow to localize SX nonlinearity in the presence of the beam-beam kick
25 Effectiveness of waist control on KEKB or SuperKEKB performance Results of beam-beam simulationsTraveling focusNo remarkable improvement in the luminosity (K. Ohmi, Y. Ohnishi)The beam lifetime may be improved.Crab waistWith the present KEKB parameters, a remarkable improvement is expected.At SuperKEKB, a higher luminosity would be obtained, if very small x* and y* are realized.
26 Effect of crab waist at KEKB H=25 x py2.present KEKBK. OhmiWithout crab cavities, a similar luminosity improvement is expected with the crab waist.
27 Super KEKB (K. Ohmi, F. Tawada) Crab waistex9.00E-096.00E-09ey4.50E-116.00E-11bx (mm)20010050by (mm)310.5sz (mm)64ns0.0250.01ne5.50E+103.50E+10np1.26E+111.27E+118.00E+10f/2 (mrad)15xx0.3970.04180.0220.05470.0298xy0.794->0.330.19850.1790.1780.154Lum (W.S.)8E+356.70E+351.00E+363.95E+354.80E+35Lum (S.S.)8.25E354.77E359E35(n)3.94E354.27E35SuperKEKB designSuperKEKB alternative
28 Study of crab waist optics Estimation of sextupole strengthOptics design (under way)Optics requirementsPhase advance S1 -> IPN (horizontal)(2N+1)/2 (vertical)High y and x at S1S1->S2: connected with I or -I transformerDynamic aperture with crab waistTo be studied
35 Summary A baseline design of SuperKEKB IR has been completed (LoI). Dynamic aperture of HER is still marginal and more studies are needed.The present design luminosity of 8.3 x 1035 is obtained with a combination of head-on collision and horizontal tune of .503.With this tune, the physical aperture around IP and SR fan of QCS are serious and without solving these problem, the design luminosity would not be realized.
36 Summary [cont’d]As new ideas, we have considered two schemes of “traveling focus” and “crab waist”.The beam-beam simulation showed that a luminosity gain by the traveling focus is small, although the beam lifetime may be improved.On the other hand, the luminosity gain from the crab waist seems big even with the present KEKB parameters.We are studying the optics of the crab waist and are considering a beam test of this scheme.
37 Comments on crab waist with very small beta’s and emittance K. Ohmi’s simulation showed that a higher luminosity is obtained by using the crab waist with very small beta’s and conventional tunes.However, I haven’t considered this possibility seriously, since the dynamic (physical) aperture problem seemed serious.M. Biagini’s talk showed that the dynamic aperture issue is within a range of study if combined with very small emittance.More studies on dynamics aperture issue are needed.Optimization of various parametersInjection schemeEffects of machine errors (and beam-beam)We will consider the crab waist scheme as an alternative option of SuperKEKB.
38 Dynamic aperture for “ideal” lattice with FF (3 Km, 7 GeV) A. Wolski3 sigmaCoupling resonanceCoordinate spaceTune spaceFrequency map analysis, sextupoles tuned for 0 chromaticity
39 Total Wall Power (60% transfer eff.): 32 MW SBF 4 GeVSBF 7 GeVC (m)3251.Bw (T)1.4Lbend(m)5.610.6N. bends96Bbend (T)0.1550.144Uo (MeV/turn)4.46.4N. wigg. cells84tx (ms)19.824.ts (ms)10.12.ex (nm)0.380.565sE1.1x10-31.32x10-3Ibeam (A)2.5Pbeam(MW)11.9.M. Biaginicm sE=0.85x10-3Total Wall Power (60% transfer eff.): 32 MW
42 Fan of SRConsideration of the particle distribution in the phase spaceEffects of dynamic-b and dynamic-emittanceThese effects are very large with the horizontal tune very close to the half integer.We took 9ex (3 sx, 3sx’) into consideration.
43 Enlargement of SR fan due to dynamic effects without dynamic effectswith dynamic effectsSource pointQCSRE(Arc side)HERQCSLE(Arc side)LERObservation pointExit of QC1REExit of QC1LEex[nm]2458gx* (1/bx*) [/m]522.5Distance from a source point [m]2.871.94Dx[mm]COD5.25.53 sx, 3sx’5.15.417.718.3Total10.310.922.923.8xx = 0.1, nx = .510
44 IP x, x’ from beam-beam simulation (Ohmi, Ohnishi) 6.64mrad295mx’~6.7mradx~280mx=(x)/(x’) ~ 4.18cmx=x/x’ ~ 2.30cmx=x*x’~ 0.128mx’~ 7.46mx=(x)*(x’) ~ 1.88m
45 Rad. Bhabha BG sim. for Super-KEKB BarrelBWDEndCapFWDEndCapRealistic designbased on discussionwith QCS groupExpected BGfrom other sourceswith heavy metaltotal ~ 1.5 tonL=25x1034 /cm2/s~4 % oftotal BGL=1034 /cm2/sO. Tajima
46 Super-KEKB (current) design Average Vacuum 5x10-7 Pa1st layer
47 (sim. for particle shower) Average Vacuum 2.5x10-7 PaSuppressed byNeutron shieldBeampipe radius 1.51cm1st layerBGx33 (several MRad/yr)!?(sim. for particle shower)
48 SummaryBackscattering of QCS-SR is not serious, but strongly depends on IR chamber configurationVacuum level is very importantOriginal design (5x10-7 Pa) is serious BGx25w/ further effort (2.5x10-7 Pa) BGx18Increasing of Touschek origin BGSmaller bunch size & higher bunch currents are reasonMight be reduced by further studyRadiative Bhabha origin BG can be suppressedBeampipe radius 1.5cm 1cmFurther simulation study of shower particles into SVD is important-30%
49 From KEKB to SuperKEKB Synchrotron Radiation (SR) (2) The exact path of the SR from QCS and its spread were not strictly taken into account in the first design.This caused a high temperature at unexpected portions of a vacuum chamber.Deformation of vacuum chamberMotion of magnets.SuperKEKBThe design of QC magnets in the LoI looks trying to give a sufficient clearance for the SR down to QC2.The design of the beam duct layout also tried to avoid the SR.However, the design should be checked against the fact that the two beams and the SR don’t lie in the same plane.
50 From KEKB to SuperKEKB Detector Background Back scattering of the SR from QCS by a HER Al beam duct became a noise source. (Cu has a smaller cross section of the back scattering than that of Al.)Shields against the detector background should have been incorporated from the first design.SuperKEKBChamber material: Cu (cooling, shielding, small back scatter of SR)Beam ducts avoid the SR down to 8m (HER downstream) and 5m (LER downstream) from IP.Shield should be taken into consideration from the first design.
51 From KEKB to SuperKEKB Higher Order Mode (HOM) (1) The HOM power turned into heat in IR is, in the unit of the loss factor, around 474 V/nC. (Estimated from the temperature rise of cooling water)Heat up of the bellows will be unacceptable level in Super KEKBSuperKEKBExtrapolation from KEKB gives as a heat by HOM about 100kW (bunch length factor).Is the compact HOM absorber possible?The cooling for HOM will be a big problem.The comb type bellows is expected to be durable.