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January 13, 2004 D. Rubin - Cornell 1
CESR-c
BESIII/CLEO-c Workshop, IHEP
January 13, 2004
D.Rubin
for the CESR operations group
January 13, 2004 D. Rubin - Cornell 2
CESR-cEnergy 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)
January 13, 2004 D. Rubin - Cornell 3
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
January 13, 2004 D. Rubin - Cornell 4
CESR-c IR* ~ 10mm
H and V superconducting quads share same cryostat
20cm pm vertically focusing nose piece
Quads are rotated 4.50 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
January 13, 2004 D. Rubin - Cornell 5
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
January 13, 2004 D. Rubin - Cornell 6
CESR-c Energy dependence
Beam-beam effect• In collision, beam-beam tune shift parameter ~ Ib/E• Long range beam-beam interaction at 89 parasitic
crossings ~ Ib/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
January 13, 2004 D. Rubin - Cornell 7
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 (Pt/P) In bending magnets, synchrotron photons radiated parallel to particle momentum Pt/Pt = 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
January 13, 2004 D. Rubin - Cornell 8
CESR-c Energy dependence Radiation damping
In CESR at 5.3 GeV, an electron radiates ~1MeV/turn ~> ~ 5300 turns (or about 25ms)
SR Power ~ E2B2 = E4/2 at fixed bending radius 1/ ~ P/E ~ E3 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
January 13, 2004 D. Rubin - Cornell 9
CESR-c Energy dependence
Emittance• L ~ IB2/ xy
= IB2/ (xyxy)1/2
• x~ y (coupling)
• IB/ x limiting charge density • Then IB and therefore L ~ x
CESR (5.3GeV), x = 200 nm-radCESR (1.9GeV), x = 30 nm-rad
January 13, 2004 D. Rubin - Cornell 10
CESR-c Energy dependence
Damping and emittance control with wigglers
January 13, 2004 D. Rubin - Cornell 11
CESR-c Energy dependence In a wiggler dominated ring
• 1/ ~ Bw2Lw
~ Bw Lw
E/E ~ (Bw)1/2 nearly independent of length (Bw limited by tolerable energy spread)Then 18m of 2.1T wiggler -> ~ 50ms -> 100nm-rad < <300nm-rad
January 13, 2004 D. Rubin - Cornell 12
Optics effects - Ideal Wiggler
πλϑ20
0 w
E
ceB=
Bz = -B0 sinh kwy sin kwz
Vertical kick ~ Bz
€
′ y = −B0
2L
2(E0 /ce)2y +
2
3
2π
λ
⎛
⎝ ⎜
⎞
⎠ ⎟2
y 3 + ... ⎛
⎝ ⎜ ⎜
⎞
⎠ ⎟ ⎟
January 13, 2004 D. Rubin - Cornell 13
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/ λ)2
We choose the relatively long period -> λ = 40cm
Finite width of poles leads to horizontal nonlinearity
January 13, 2004 D. Rubin - Cornell 14
7-pole, 1.3m 40cm period, 161A, B=2.1T
Superconducting wiggler prototype installed fall 2002
January 13, 2004 D. Rubin - Cornell 15
Wiggler Beam Measurements-Measurement of betatron tune vs displacement consistent with modeled field profile and transfer functon
January 13, 2004 D. Rubin - Cornell 16
January 13, 2004 D. Rubin - Cornell 17
January 13, 2004 D. Rubin - Cornell 18
January 13, 2004 D. Rubin - Cornell 19
January 13, 2004 D. Rubin - Cornell 20
6 wigglers installed spring 2003
January 13, 2004 D. Rubin - Cornell 21
6 Wiggler Linear Optics
Lattice parameters
Beam energy[GeV] 1.89*
v[mm]
*h[m]
Crossing angle[mrad]
Qv
Qh
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
January 13, 2004 D. Rubin - Cornell 22
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
January 13, 2004 D. Rubin - Cornell 23
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
January 13, 2004 D. Rubin - Cornell 24
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
January 13, 2004 D. Rubin - Cornell 25
Wiggler Beam Measurements 6 wiggler lattice
-Injection
30 Hz 68mA/80sec 60 Hz 67ma/50sec
January 13, 2004 D. Rubin - Cornell 26
Wiggler Beam Measurements
-Single beam stability
1/ = 4.5 s-1 1/ = 10.9s-1
2pm + 1 sc wigglers 6 sc wigglers
January 13, 2004 D. Rubin - Cornell 27
Measurement and correction of linear lattice
Measured - modeled
Betatron phase
and transverse coupling
January 13, 2004 D. Rubin - Cornell 28
Sextupole optics
Modeled pretzel dependence of betatron phase due to sextupole feeddown
Difference between measured and modelled phase with pretzel after correction of sextupoles
January 13, 2004 D. Rubin - Cornell 29
Beam profiles due to horizontal excitation Best luminosity
Solenoid compensation Coupling parameters in the interaction region
January 13, 2004 D. Rubin - Cornell 30
CESR-c Peak Luminosity
January 13, 2004 D. Rubin - Cornell 31
CESR-c integrated luminosity
January 13, 2004 D. Rubin - Cornell 32
1-jan-2004
January 13, 2004 D. Rubin - Cornell 33
2.5pb-1/day28-Dec-2003
January 13, 2004 D. Rubin - Cornell 34
CESR-c parameters
Parameter Measured (Design)
Beam energy[GeV] 1.88 (1.88)
Luminosity[1030/cm2/s] 45 (300)
Ib[ma/bunch] 1.7 (4)
Ibeam[ma/beam] 55 (180)
v 0.025 (0.04)
h 0.036
Wigglers 6 (12)
E/E[10-4] 0.8 (0.81)
[ms] 110 (55)
Bw[T] 2.1(2.1)
*v[mm] 13 (10)
h[nm] 160 (220)
January 13, 2004 D. Rubin - Cornell 35
CESR-c StatusRemaining 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
January 13, 2004 D. Rubin - Cornell 36
CESR-c design parameters
January 13, 2004 D. Rubin - Cornell 37
Machine modeling-Wiggler transfer map
-Compute field table with finite element code
-Tracking through field table -> transfer maps
January 13, 2004 D. Rubin - Cornell 38
Machine modeling
- Fit analytic form to field table
January 13, 2004 D. Rubin - Cornell 39
Machine modeling-Wiggler map
Fit parameters of series to field table
Analytic form ofHamiltonian -> symplectic integration -> taylor map
January 13, 2004 D. Rubin - Cornell 40
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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