Operational Status of CESRc

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Operational Status of CESR-c

• James A. Crittenden
• Accelerator Physics Seminar
• Wilson Lab
• 28 July 2006

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CESR Storage Ring and Injectors
CESR-c Operation since 2003 12 s.c. wigglers
since mid-2004 1.5-6 GeV beam energy Presently
2.085 GeV 768 m circumference 24
bunches/beam 60 mA/beam The electron and
positron beams are separated by means of
electrostatic separators. The optical
distortions introduced by this pretzel orbit
are corrected using the lattice design
flexibility afforded by 180 quadrupole and
sextupole magnets.
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CESR as a Charm Factory
CLEO-c and CESR-c A New Frontier in Weak and
Strong Interactions CLNS 01/1742 October 2001
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From 5.3 GeV ???4s)) to 1.9 GeV ????s))
?
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8-pole Superconducting Wiggler Magnets
Production and Testing Considerations for CESR-c
Wiggler Magnets, D.H.Rice et al, PAC2003
Beam-based characterization of wiggler
nonlinearities accurately modeled for
three-wiggler cluster in-situ. Analytic wiggler
field model uses Taylor mapping for fast tracking
simulation.
Tune Shift (kHz)
Field Modeling for the CESR-c Wiggler Magnets,
J.A.Crittenden et al., PAC2005
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Commissioning Milestones
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Luminosity History
CESR-c Performance of a Wiggler-Dominated
Storage Ring, A. Temnykh, PAC2005

• Developments since PAC 2005
• New IR Optics
• Electron Injection into collision
• BBI included in lattice design
• Constraint on ee- symmetry
• New diagnostic tools

Diagnostics of Interaction Point Properties and
Bunch-by-Bunch Tune Measurements in
CESR, G.W.Codner et al, Beam Instrumentation
Workshop 2006
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CESR-c Operating Parameters
Design report 2001 4/2005 4/2006 L (1030 cm-2
s-1) 300 65 70 Ibeam (mA) 180 75 65 Nr
Bunches 45 40 24 ?H (nm-rad) 220 135 120 ?V
0.04 0.024 0.029 ?? V (cm) 1.0 1.2 1.2 ?E/E
(10-4) 0.81 0.85 0.81 ?H,V (ms) 55 50 55
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Improved Solenoid Compensation
New IR Compensation Scheme 2006 Skew-quadrupole
compensation of CLEO detector solenoid was
implemented in 2001 and used for 5.3 GeV
operation. Full CESR luminosity modeling in
early 2005 indicated that the energy-dependence
of compensation is more important at CESR-c
energy due to larger energy spread Two-solenoid
solution was DA?NE-inspired, but optics design
was complicated by existing permanent and s.c.
quadrupoles
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Improved Tune Plane Footprint
Vertical Tune (kHz)
Horizontal Tune (kHz)
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Topping Off Reliability Duty Cycle
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Modelling the CESR-c BBI
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Empirical Test of the BBI Model
Studies of the Beam-Beam Interaction at CESR,
M.G.Billing and J.A.Crittenden, MUOPLS043, EPAC06
BBI-Induced Orbit Distortion Last August, we
measured the horizontal electron orbit (t1.b1) in
the presence of the positron beam (t2-6.b1-5).
The plot shows the electron orbit with the
undistorted orbit subtracted. The green dots
show the measurements made by eleven gated beam
position monitors in a region free of parasitic
crossings. The red line shows the results of the
model. The BBI-induced distortion reaches 0.4
mm in this region and these orbit deformations
are modelled to an accuracy of about 0.05 mm.
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Present Operational Limit
Present stored-current limit 2.5 mA in 8x3
operation in collision, but higher if the beams
are separated at the IP . Limit on a single
electron bunch into 8x3 positrons is 8 mA. As a
result, much effort has been put into modeling
the beam-beam interaction both at the IP and at
the parasitic crossings. Some improvement has
been obtained already by including consideration
of the long-range BBI in the lattice design.
Nonetheless, the distortion of the beta function
is substantial, even when the tunes are held
constant during filling.
Present current limit
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Near-term Improvement Plans
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Completion of CLEO-c Physics Program
The primary operational tool for compensating the
beam-beam interaction at CESR has been global
tune adjustment employing all quads to compensate
the beam-beam interactions. At points of
horizontal (vertical) separation, these have a
defocusing effect in the horizontal (vertical)
plane and a focusing effect in the vertical
(horizontal) plane, while focusing in both planes
at the main interaction point. The tune shift at
the interaction point is typically five time
greater than that from all the parasitic
crossings, so the primary operational adjustment
is to reduce tune globally as the colliding
current increases. Such a global adjustment
necessarily results in local distortions of the
phase function. We are presently developing a
compensation method based on local phase
distortion correction using the 8 quadrupoles
surrounding each of the sets of three parasitic
crossings. Six quantities are compensated
horizontal and vertical phase advance, and the
sine and cosine components of the beta function.
We have demonstrated during machine studies
experiments that the correction coefficients for
the near-IP crossings are effective in
compensating the distortions arising from the IP
itself. Modelling results of both the beta
function distortion and the dynamic aperture
indicate that the operational current limit may
be raised by 50.