1. The Proposed Conversion of CESR to an ILC Damping Ring Test Facility
M. Palmer, R. Helms, D. Rubin, D. Sagan, J. Urban, M. Ehrlichman
Abstract: In 2008 the Cornell Electron Storage Ring (CESR) will end nearly three decades of providing electron-positron collisions for the CLEO experiment. At that time it will be possible to reconfigure CESR as a damping ring test facility, CesrTF, for the International Linear Collider project. With its 12 damping wigglers, CesrTF will offer horizontal emittance in the few nanometer range and, ideally, vertical emittances approaching those specified for the ILC damping rings. An important feature of the CesrTF concept is the ability to operate with positrons or electrons. Positron operation will allow detailed testing of electron cloud issues critical for the operation of the ILC positron damping rings. Other key features include operation with wigglers that meet or exceed all ILC damping ring requirements, the ability to operate from 1.5 to 5.5 GeV beam energies, and the provision of a large insertion region for testing damping ring hardware. We discuss the CesrTF machine parameters, critical conversion issues, and experimental reach for damping ring studies.
CesrTF Baseline Lattice
CesrTF Conversion
Dynamic Aperture bx
North IR with Wigglers (Top View)
Lattice design carried
out with 6 wigglers in
North IR and 6 wigglers
in the CESR arcs. Zero
dispersion regions created
for all wigglers. by
~18 m
Frequency Map Analysis
Color Scale:
Points plotted at ½ damping time
Tunes calculated for 1st half and
2nd half of damping time
South IR with RF Cavities for Short Bunch Operation (Top View)
Wiggler
Locations hx
Move 6 wigglers to North IR
Add cryogenic support
Add electron cloud diagnostics
Space for insertion devices in South IR
Ample cryogenics support
SCRF cavities for short bunch length operation
Instrumentation (eg, possible laserwire installation)
Could support an extraction line
Upgrade feedback system for 4 ns spaced bunches
Upgrade beam instrumentation
Ultra-low emittance measurement
CLEO
North IR
South IR
14W
15W
14E
15E
19E
19W
Wiggler Moves
Target ey~ 5 – 10 pm
Parameter
Value E
2.0 GeV
Nwiggler 12
Bmax
2.1 T ex
2.25 nm Qx
14.59 Qy
9.63 Qz
0.098
sE/E
8.6 x 10-4
tx,y
47 ms sz
6.8 mm ap
6.4 x 10-3
Tune Scans to Determine Working Point
Intrabeam Scattering (Preliminary)
Low Emittance Operation
Nominal CESR Magnet Alignment Resolutions
Equilibrium Emittance with IBS for Baseline Lattice
Calculation assumes vertical emittance is dominantly due to emittance coupling.
ex grows by factor of ~3 from zero current to ILC bunch current
Nominal Values
Misalignment
Nominal Value
Quadrupole, Bend and Wiggler Offsets
150 mm
Sextupole Offsets
300 mm
Quadrupole, Bend, Wiggler and Sextupole Rotations
100 mrad
Example Vertical Emittance Sensitivities
IBS growth rates scale as 1/g4 a increase energy
Increases zero current emittance
Decreases sensitivity to IBS
Can also lengthen bunch
Explore 2.5 GeV lattice with 9 mm bunch as potential configuration for low
emittance studies at the ILC bunch current (eg, electron cloud studies)
Dominant Sensitivity
Correction Algorithm
Randomly misalign elements using multiple seeds
Orbit correction followed by dispersion correction
using steering and skew quadrupole correctors
Include effects of BPM errors
Equilibrium Emittance for 2.5 GeV Lattice and 9mm Bunch Length
ex grows by a factor of < 1.6 from zero current to ILC bunch current.
Zero current ex ~2.85 nm. .
Correction Type
Average Value
95% Limit
Orbit Only
10.2 pm
21.4 pm
Orbit+Dispersion
3.9 pm
8.2 pm
CESR-c/CLEO-c program ends on March 31, 2008
7-9 month conversion followed by commissioning
Available for ILC DR R&D in early 2009
Operating Schedule
Approximately 110 running days/year in 2 periods
Interleaved with CHESS X-ray running
Significant downtime at each transition for installation of prototypes and other hardware
Minimum of 3 years of operation as a test facility
Conclusion: Simulations indicate that CesrTF can be operated in a regime that is useful for a range of damping ring studies. In particular, CesrTF will have the ability to study physics issues associated with the damping ring wigglers and validate the final design of the ILC wigglers and vacuum chamber. The machine will be able to directly explore the impact of the electron cloud on the emittance. Due to the modest scope of the conversion, CesrTF offers an efficient route towards exploring key areas of ILC damping ring physics and technology on a timescale consistent with the start of ILC construction.
Conversion and Operations Plan