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January 13, 2004D. Rubin - Cornell1 CESR-c BESIII/CLEO-c Workshop, IHEP January 13, 2004 D.Rubin for the CESR operations group

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January 13, 2004D. Rubin - Cornell2 CESR-c Energy reach 1.5-6GeV/beam Electrostatically separated electron-positron orbits accomodate counterrotating trains Electrons and positrons collide with ±~3.5 mrad horizontal crossing angle 9 5-bunch trains in each beam (768m circumference)

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January 13, 2004D. Rubin - Cornell3 CESR-c IR Summer 2000, replace 1.5m REC permanent magnet final focus quadrupole with hybrid of pm and superconducting quads Intended for 5.3GeV operation but perfect for 1.5GeV as well

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January 13, 2004D. Rubin - Cornell4 CESR-c IR * ~ 10mm H and V superconducting quads share same cryostat 20cm pm vertically focusing nose piece Quads are rotated 4.5 0 inside cryostat to compensate effect of CLEO solenoid Superimposed skew quads permit fine tuning of compensation At 1.9GeV, very low peak => Little chromaticity, big aperture

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January 13, 2004D. Rubin - Cornell5 CLEO solenoid 1T( )-1.5T( ) Good luminosity requires zero transverse coupling at IP (flat beams) Solenoid readily compensated even at lowest energy *(V)=10mm E=1.89GeV *(H)=1m B(CLEO)=1T

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January 13, 2004D. Rubin - Cornell6 CESR-c Energy dependence Beam-beam effect In collision, beam-beam tune shift parameter ~ I b /E Long range beam-beam interaction at 89 parasitic crossings ~ I b /E ( for fixed emittance ) (and this is the current limit at 5.3GeV) Single beam collective effects, instabilities Impedance is independent of energy Effect of impedance ~I/E

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January 13, 2004D. Rubin - Cornell7 CESR-c Energy dependence (scaling from 5.3GeV/beam to 1.9GeV/beam) Radiation damping and emittance Damping Circulating particles have some momentum transverse to design orbit (P t /P) In bending magnets, synchrotron photons radiated parallel to particle momentum P t /P t = P/P RF accelerating cavities restore energy only along design orbit, P-> P+ P so that transverse momentum is radiated away and motion is damped Damping time ~ time to radiate away all momentum

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January 13, 2004D. Rubin - Cornell8 CESR-c Energy dependence Radiation damping In CESR at 5.3 GeV, an electron radiates ~1MeV/turn ~> ~ 5300 turns (or about 25ms) SR Power ~ E 2 B 2 = E 4 / 2 at fixed bending radius 1/ ~ P/E ~ E 3 so at 1.9GeV, ~ 500ms Longer damping time Reduced beam-beam limit Less tolerance to long range beam-beam effects Multibunch effects, etc. Lower injection rate

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January 13, 2004D. Rubin - Cornell9 CESR-c Energy dependence Emittance L ~ I B 2 / x y = I B 2 / ( x y x y ) 1/2 x ~ y (coupling) I B / x limiting charge density Then I B and therefore L ~ x CESR (5.3GeV), x = 200 nm-rad CESR (1.9GeV), x = 30 nm-rad

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January 13, 2004D. Rubin - Cornell10 CESR-c Energy dependence Damping and emittance control with wigglers

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January 13, 2004D. Rubin - Cornell11 CESR-c Energy dependence In a wiggler dominated ring 1/ ~ B w 2 L w ~ B w L w E /E ~ (B w ) 1/2 nearly independent of length (B w limited by tolerable energy spread) Then 18m of 2.1T wiggler -> ~ 50ms -> 100nm-rad < <300nm-rad

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January 13, 2004D. Rubin - Cornell12 Optics effects - Ideal Wiggler B z = -B 0 sinh k w y sin k w z Vertical kick ~ B z

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January 13, 2004D. Rubin - Cornell13 Optics effects - Ideal Wiggler Vertical focusing effect is big, Q ~ 0.1/wiggler But is readily compensated by adjustment of nearby quadrupoles Cubic nonlinearity ~ (1/ ) 2 We choose the relatively long period -> = 40cm Finite width of poles leads to horizontal nonlinearity

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January 13, 2004D. Rubin - Cornell14 7-pole, 1.3m 40cm period, 161A, B=2.1T Superconducting wiggler prototype installed fall 2002

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January 13, 2004D. Rubin - Cornell15 Wiggler Beam Measurements -Measurement of betatron tune vs displacement consistent with modeled field profile and transfer functon

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January 13, 2004D. Rubin - Cornell20 6 wigglers installed spring 2003

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January 13, 2004D. Rubin - Cornell21 6 Wiggler Linear Optics Lattice parameters Beam energy[GeV]1.89 * v [mm] * h [m] Crossing angle[mrad] Q v Q h Number of trains Bunches/train Bunch spacing[ns] Accelerating Voltage[MV] Bunch length[mm] Wiggler Peak Field[T] Wiggler length[m] Number of wigglers x [mm-mrad] E /E[%] 12 0.56 3.8 9.59 10.53 9 4 14 10 9 2.1 1.3 6 0.15 0.08

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January 13, 2004D. Rubin - Cornell22 Machine Status Commissioning with 6 wigglers beginning in August 2003 -Measure and correct linear optics -Characterize - wiggler nonlinearity -Injection -Single beam stability -Measure and correct “pretzel” dependent /sextupole differential optics

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January 13, 2004D. Rubin - Cornell23 Wiggler Beam Measurements Beam energy = 1.89GeV -Optical parameters in IR match CESR-c design -Measure and correct betatron phase and transverse coupling - Measurement of lattice parameters (including emittance) in good agreement with design

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January 13, 2004D. Rubin - Cornell24 Wiggler Beam Measurements -Injection 1 sc wiggler (and 2 pm CHESS wigglers) -> 8mA/min 6 sc wiggler -> 50mA/min 1/ = 4.5 s -1 1/ = 10.9s -1

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January 13, 2004D. Rubin - Cornell25 Wiggler Beam Measurements 6 wiggler lattice -Injection 30 Hz 68mA/80sec60 Hz 67ma/50sec

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January 13, 2004D. Rubin - Cornell26 Wiggler Beam Measurements -Single beam stability 1/ = 4.5 s -1 1/ = 10.9s -1 2pm + 1 sc wigglers 6 sc wigglers

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January 13, 2004D. Rubin - Cornell27 Measurement and correction of linear lattice Measured - modeled Betatron phase and transverse coupling

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January 13, 2004D. Rubin - Cornell28 Sextupole optics Modeled pretzel dependence of betatron phase due to sextupole feeddown Difference between measured and modelled phase with pretzel after correction of sextupoles

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January 13, 2004D. Rubin - Cornell29 Beam profiles due to horizontal excitation Best luminosity Solenoid compensation Coupling parameters in the interaction region

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January 13, 2004D. Rubin - Cornell30 CESR-c Peak Luminosity

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January 13, 2004D. Rubin - Cornell31 CESR-c integrated luminosity

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January 13, 2004D. Rubin - Cornell32 1-jan-2004

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January 13, 2004D. Rubin - Cornell33 2.5pb -1 /day 28-Dec-2003

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January 13, 2004D. Rubin - Cornell34 CESR-c parameters ParameterMeasured (Design) Beam energy[GeV]1.88 (1.88) Luminosity[10 30 /cm 2 /s ] 45 (300) I b [ma/bunch]1.7 (4) I beam [ma/beam]55 (180) vv 0.025 (0.04) hh 0.036 Wigglers6 (12) E /E[10 -4 ] 0.8 (0.81) [ms] 110 (55) B w [T]2.1(2.1) * v [mm] 13 (10) h [nm]160 (220)

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January 13, 2004D. Rubin - Cornell35 CESR-c Status Remaining 6 (of 12) wigglers will be installed is spring 2004 Double damping decrement -> Faster injection -> Higher single beam current -> Reduced sensitivitiy to current limiting parasitic crossings -> Higher beambeam current limit -> Increased tune shift parameter Machine studies/beam instrumentation in progress -> Improved correction of linear and nonlinear optical errors -> More precise and reliable correction of coupling errors -> Improved tuning “knobs” and algorithms

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January 13, 2004D. Rubin - Cornell36 CESR-c design parameters

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January 13, 2004D. Rubin - Cornell37 Machine modeling -Wiggler transfer map -Compute field table with finite element code -Tracking through field table -> transfer maps

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January 13, 2004D. Rubin - Cornell38 Machine modeling - Fit analytic form to field table

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January 13, 2004D. Rubin - Cornell39 Machine modeling -Wiggler map Fit parameters of series to field table Analytic form of Hamiltonian -> symplectic integration -> taylor map

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January 13, 2004D. Rubin - Cornell40 Simulation -Machine model includes: -Wiggler nonlinearities -Beam beam interactions (parasitic and at IP) -Synchrotron motion -Radiation excitation and damping -Weak beam -200 particles - initial distribution is gaussian in x,y,z - track ~ 10000 turns

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