A U.S. Department of EnergyOffice of Science LaboratoryOperated by The University of Chicago

Argonne National Laboratory

Office of ScienceU.S. Department of Energy

Overview of 6 km Damping Ring Study

Kwang-Je Kimfor ANL-FNAL-UIUC Collaboration

ILC-Americas Work Shop

SLAC, Stanford, CAOctober 14-16, 2004

2Pioneering Science andTechnology

Office of Science U.S. Department

of EnergyKJK, ILC-Americas WS, SLAC, 10/14-16/04

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

3Pioneering Science andTechnology

Office of Science U.S. Department

of EnergyKJK, ILC-Americas WS, SLAC, 10/14-16/04

APS, a 1 km, 7 GeV Ring at Work

4Pioneering Science andTechnology

Office of Science U.S. Department

of EnergyKJK, ILC-Americas WS, SLAC, 10/14-16/04

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.

5Pioneering Science andTechnology

Office of Science U.S. Department

of EnergyKJK, ILC-Americas WS, SLAC, 10/14-16/04

6 km17-km

DogboneEmery’s thesis

(1990) APS

Energy (GeV) 5.0 5.0 4.0 7.0

Circumference (m) 6114 17000 2229 1104

Lw (m) 77 468 360

Fw=I2w/I2A 8.5 17.3 32

Injected (m-rad) 1.010-2 1.010-2 n/a 1.310-3

Equilibrium (m-rad) 5.510-6 810-6 2.010-7 3.510-5

Extracted (m-rad) 810-6 810-6 n/a n/a

Damping time,x (ms) 27 28 13.5 9.6

rms Bunch Length (mm) 6 6 ~6 5.8

rms Energy Spread (10-3) 1.3 1.3 0.9 (2.4 with impedance)

0.96

Particles/Bunch (1010) 2.0 2.0 1.4 12.0

Average Current (mA) 443 159 0.3 100-300

Major Parameters of DRs and APS

6Pioneering Science andTechnology

Office of Science U.S. Department

of EnergyKJK, ILC-Americas WS, SLAC, 10/14-16/04

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)

7Pioneering Science andTechnology

Office of Science U.S. Department

of EnergyKJK, ILC-Americas WS, SLAC, 10/14-16/04

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] 241 80.7 198

Quadrupole Rotation [rad] 825 40.5 58.3

Sextupole Alignment [m] 45.6 11.3 40.4

8Pioneering Science andTechnology

Office of Science U.S. Department

of EnergyKJK, ILC-Americas WS, SLAC, 10/14-16/04

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

9Pioneering Science andTechnology

Office of Science U.S. Department

of EnergyKJK, ILC-Americas WS, SLAC, 10/14-16/04

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

10Pioneering Science andTechnology

Office of Science U.S. Department

of EnergyKJK, ILC-Americas WS, SLAC, 10/14-16/04

RF BPM Diagnostics & Feedback

• Orbit motion is characterized by a PSD spectrum in range 0 to frev/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

11Pioneering Science andTechnology

Office of Science U.S. Department

of EnergyKJK, ILC-Americas WS, SLAC, 10/14-16/04

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)

12Pioneering Science andTechnology

Office of Science U.S. Department

of EnergyKJK, ILC-Americas WS, SLAC, 10/14-16/04

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.

13Pioneering Science andTechnology

Office of Science U.S. Department

of EnergyKJK, ILC-Americas WS, SLAC, 10/14-16/04

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

14Pioneering Science andTechnology

Office of Science U.S. Department

of EnergyKJK, ILC-Americas WS, SLAC, 10/14-16/04

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-TD

• ILC Damping Rings web site: http://awolski.lbl.gov/ILCDR/