1. A U.S. Department of Energy Office of Science Laboratory Operated by The University of Chicago Argonne National Laboratory Office of Science U.S. Department of Energy Overview of 6 km Damping Ring Study Kwang-Je Kim for ANL-FNAL-UIUC Collaboration ILC-Americas Work Shop SLAC, Stanford, CA October 14-16, 2004

2. Pioneering Science and Technology Office of Science U.S. Department of Energy KJK, ILC-Americas WS, SLAC, 10/14-16/04 2 6-km Damping Ring Study The 17-km Tesla dog-bone design assumed 20 ns rise- & fall-time kickers. If kickers with shorter rise & longer fall time are available, damping rings can be “small” using a injection scheme by Joe Rogers. Fast kickers were discussed by Frisch and Gollin. This is an overview of work on a 6-km small damping ring by ANL- FNAL-UIUC collaboration and J. Rogers & A. Wolski. Content: -Current status: linear lattice, instability estimates, & alignment sensitivities -Plan for a next level study using tools developed for higher brightness light sources

3. Pioneering Science and Technology Office of Science U.S. Department of Energy KJK, ILC-Americas WS, SLAC, 10/14-16/04 3 APS, a 1 km, 7 GeV Ring at Work

4. Pioneering Science and Technology Office of Science U.S. Department of Energy KJK, ILC-Americas WS, SLAC, 10/14-16/04 4 Damping Ring Lattice Development Initial work started at Fermilab (Amin Xiao’s talk) A 6-km, 5 GeV ring with TME lattice using the procedure discussed in P. Emma and T. Raubenheimer, PRSTAB,4, 021001 (2001) -77 m of wigglers compared to 400 m in TESLA. -Higher current in smaller ring than TESLA. -Performance similar to the TESLA design.

5. Pioneering Science and Technology Office of Science U.S. Department of Energy KJK, ILC-Americas WS, SLAC, 10/14-16/04 5 6 km 17-km Dogbone Emery’s thesis (1990) APS Energy (GeV)5.0 4.07.0 Circumference (m)61141700022291104 L w (m)77468360 F w =I 2w /I 2A 8.517.332 Injected  (m-rad)1.0  10 -2 n/a 1.3  10 -3 Equilibrium  (m-rad)5.5  10 -6 8  10 -6 2.0  10 -7 3.5  10 -5 Extracted  (m-rad)8  10 -6 n/a Damping time,  x (ms) 272813.59.6 rms Bunch Length (mm)66~65.8 rms Energy Spread (10 -3 )1.3 0.9 (2.4 with impedance) 0.96 Particles/Bunch (10 10 )2.0 1.412.0 Average Current (mA)4431590.3100-300 Major Parameters of DRs and APS

6. Pioneering Science and Technology Office of Science U.S. Department of Energy KJK, ILC-Americas WS, SLAC, 10/14-16/04 6 Instability Estimates (Bill Ng) Incoherent space charge tune shift =0.026 << 0.31 for TESLA -Smaller circumference, larger beam size (larger disp.) Instabilities -Longitudinal: Single- & multi-bunch thresholds;safe -Transverse: Single bunch threshold; safe multi-bunch threshold; safe with damper -Electron cloud: Growth time about 1s with solenoids -Fast ion: Growth less than 20% with feedback (@ 10 -10 )

7. Pioneering Science and Technology Office of Science U.S. Department of Energy KJK, ILC-Americas WS, SLAC, 10/14-16/04 7 Quadrupole and Sextupole Alignment Sensitivities (A. Wolski) 6-km DR less sensitive than Tesla dogbone Both 6-km DR and Tesla dogbone more sensitive than ATF ATF TESLA Dogbone ILC Small Quadrupole Jitter [nm]24180.7198 Quadrupole Rotation [  rad] 82540.558.3 Sextupole Alignment [  m] 45.611.340.4

8. Pioneering Science and Technology Office of Science U.S. Department of Energy KJK, ILC-Americas WS, SLAC, 10/14-16/04 8 The “Small” DR Looks Doable. Next Step? Further optimization of parameters - Energy (3.7GeV), lattice, Next-level study with tools and technology developed for high-brightness light sources: -Impedance modelling and minimization -Beam monitoring and feedback -Wiggler development -Photon absorbers

9. Pioneering Science and Technology Office of Science U.S. Department of Energy KJK, ILC-Americas WS, SLAC, 10/14-16/04 9 Tools for Nonlinear Beam Dynamics (Louis Emery’s Talk) Toolkit approach combined with comprehensive tracking code elegant developed by M. Borland Parallel simplex optimizer being developed by H. Shang An example of future investigation -Trade-off in non-linearities between weaker focusing arc cell design and longer wiggler to maximize dynamic aperture

10. Pioneering Science and Technology Office of Science U.S. Department of Energy KJK, ILC-Americas WS, SLAC, 10/14-16/04 10 RF BPM Diagnostics & Feedback Orbit motion is characterized by a PSD spectrum in range 0 to f rev /2 RMS orbit jitter at extraction is equal the integral of PSD spectrum Orbit feedback reduces beam motion only in a certain band, say, 0-60 Hz (APS) -> Orbit jitter is reduced somewhat depending on the PSD details For damping ring, higher-bandwidth feedback may be needed to reduce jitter sufficiently

11. Pioneering Science and Technology Office of Science U.S. Department of Energy KJK, ILC-Americas WS, SLAC, 10/14-16/04 11 Vacuum Chamber Issues Minimizing Impedances: -Make use “impedance database” obtained by modeling and measuring local impedance (e.g., by orbit response matrix) Suppress electron cloud effects: -Employ solenoids, slots, low-secondary-yield- coefficient coatings, and/or corrugation -Based on experimental and modelling experiences at APS (K. Harkay, R. Rosenberg, L. Loiacono)

12. Pioneering Science and Technology Office of Science U.S. Department of Energy KJK, ILC-Americas WS, SLAC, 10/14-16/04 12 Wiggler Development Radiation damage of PM undulator( M. Petra) Superconducting wiggler (S.H. Kim); Useful for damping wiggler? The LCLS undulator under construction at APS is similar to that used for positron production scheme.

13. Pioneering Science and Technology Office of Science U.S. Department of Energy KJK, ILC-Americas WS, SLAC, 10/14-16/04 13 Photon Absorbers APS dipole fan and undulator photon beam absorbers sustain high intensities ( S. Sharma) -Upto 600 mA for dipole fan, 300mA for undulator Damping ring absorbers can be scaled from APS designs

14. Pioneering Science and Technology Office of Science U.S. Department of Energy KJK, ILC-Americas WS, SLAC, 10/14-16/04 14 Summary With the development of fast kickers “small” damping rings are a serious option for ILC. Preliminary study of a 6 km, 5 Gev DR look promising. Further optimization and next level study are planned using tools for light source improvement. More information: Studies Pertaining to a Small Damping Ring for the International Linear Collider, FERMILAB-TM-2272-AD-TDFERMILAB-TM-2272-AD-TD ILC Damping Rings web site: http://awolski.lbl.gov/ILCDR/http://awolski.lbl.gov/ILCDR/