CESR-c
BESIII/CLEO-c Workshop, IHEP
January 13, 2004
D.Rubin
for the CESR operations group
January 13, 2004 D. Rubin - Cornell 1
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)
January 13, 2004 D. Rubin - Cornell 2
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 3
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 4
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 5
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 6
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 7
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 8
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-rad
CESR (1.9GeV), x = 30 nm-rad
January 13, 2004 D. Rubin - Cornell 9
CESR-c Energy dependence
Damping and emittance control with wigglers
January 13, 2004 D. Rubin - Cornell 10
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 = 40cm
Finite width of poles leads to horizontal nonlinearity
January 13, 2004 D. Rubin - Cornell 13
Superconducting wiggler 7-pole, 1.3m
40cm period,
prototype installed fall 2002
161A, B=2.1T
January 13, 2004 D. Rubin - Cornell 14
Wiggler Beam Measurements
-Measurement of betatron tune vs displacement consistent with
modeled field profile and transfer functon
January 13, 2004 D. Rubin - Cornell 15
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
6 wigglers installed
spring 2003
January 13, 2004 D. Rubin - Cornell 20
6 Wiggler Linear Optics
Lattice parameters
Beam energy[GeV] 1.89
*v[mm] 12
*h[m] 0.56
Crossing angle[mrad] 3.8
Qv 9.59
Qh 10.53
Number of trains 9
Bunches/train 4
Bunch spacing[ns] 14
Accelerating Voltage[MV] 10
Bunch length[mm] 9
Wiggler Peak Field[T] 2.1
Wiggler length[m] 1.3
Number of wigglers 6
x[mm-mrad] 0.15
E/E[%] 0.08
January 13, 2004 D. Rubin - Cornell 21
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 22
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 23
Wiggler Beam Measurements
-Injection
1 sc wiggler (and 2 pm
CHESS wigglers) -> 8mA/min
1/ = 4.5 s-1
6 sc wiggler -> 50mA/min
1/ = 10.9s-1
January 13, 2004 D. Rubin - Cornell 24
Wiggler Beam Measurements
6 wiggler lattice
-Injection
30 Hz 68mA/80sec 60 Hz 67ma/50sec
January 13, 2004 D. Rubin - Cornell 25
Wiggler Beam Measurements
-Single beam stability
2pm + 1 sc wigglers 6 sc wigglers
1/ = 4.5 s-1 1/ = 10.9s-1
January 13, 2004 D. Rubin - Cornell 26
Measurement and correction of linear lattice
Measured - modeled
Betatron phase
and transverse coupling
January 13, 2004 D. Rubin - Cornell 27
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 28
Solenoid compensation
Coupling parameters in the interaction region
Beam profiles due to horizontal excitation
Best luminosity
January 13, 2004 D. Rubin - Cornell 29
CESR-c Peak Luminosity
January 13, 2004 D. Rubin - Cornell 30
CESR-c integrated luminosity
January 13, 2004 D. Rubin - Cornell 31
1-jan-2004
January 13, 2004 D. Rubin - Cornell 32
28-Dec-2003 2.5pb-1/day
January 13, 2004 D. Rubin - Cornell 33
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 34
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
January 13, 2004 D. Rubin - Cornell 35
CESR-c design parameters
January 13, 2004 D. Rubin - Cornell 36
Machine modeling
-Wiggler transfer map
-Compute field table
with finite element code
-Tracking through field
table -> transfer maps
January 13, 2004 D. Rubin - Cornell 37
Machine modeling
- Fit analytic form to field table
January 13, 2004 D. Rubin - Cornell 38
Machine modeling
-Wiggler map
Fit parameters of
series to field table
Analytic form of
Hamiltonian
-> symplectic integration
-> taylor map
January 13, 2004 D. Rubin - Cornell 39
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
January 13, 2004 D. Rubin - Cornell 40