overview of 6 km damping ring study

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

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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

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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.

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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

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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)

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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

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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

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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

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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)

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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.

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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/