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Optical Stochastic Cooling. Fuhua Wang MIT-Bates Linear Accelerator Center. Outline. Introduction: history, concept Experiment with electron beams: proposal & research at MIT & MIT/Bates OSC for RHIC, Tevatron … Summary . History. A. Zholents,….

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slide1
Optical Stochastic Cooling

Fuhua Wang

MIT-Bates Linear Accelerator Center

4Th Electron-Ion collider Workshop

Hampton University

outline
Outline
  • Introduction: history, concept
  • Experiment with electron beams:

proposal & research at MIT & MIT/Bates

  • OSC for RHIC, Tevatron …
  • Summary

4Th Electron-Ion collider Workshop

Hampton University

slide3
History

A. Zholents,…

1968 - Stochastic Cooling proposed by S. van der Meer. It was proved to be a remarkably successful over next several decades. (For a detailed historic account see CERN report 87-03, 1987, by D. Möhl.)

1993 - Optical Stochastic Cooling (OSC) proposed by Mikhalichenko and Zolotorev

1994 - Transient time method of OSC proposed by Zolotorev and Zholents

1998 - Proposal for proof-of-principle experiment in the Duke Electron Storage Ring (potential application for Tevatron was in mind)

2000 - OSC of muons by Wan, Zholents, Zolotorev

2001 - Proposal for proof-of-principle experiment in the storage ring of the Indiana University

2001 - Quantum theory of OSC, by Charman and also by Heifets, Zolotorev

2004 - Babzien, Ben-Zvi, Pavlishin, Pogorelsky, Yakimenko, Zholents, Zolotorev, Optical Stochastic Cooling for RHIC Using Optical Parametric Amplification

2007 - Proposals for Optical amplifier development and OSC experiment at MIT-Bates.

4Th Electron-Ion collider Workshop

Hampton University

slide4
“bad” mixing

“good” mixing

kicker

DL ~1/bandwidth=1/B

g

amplifier

p

pick-up

number of particles in the sample

Lb

Stochastic Cooling

S. van der Meer, 1968

D. Möhl, “Stochastic Cooling for Beginners”, CERN

4Th Electron-Ion collider Workshop

Hampton University

slide5
optical “slicing”

microwave “slicing”

sample length ~10 mm

sample length ~10 cm

OSC also allows transverse slicing

Diffraction limited size of the radiation source

resulting in further decrease of Ns:

Towards Optical Stochastic Cooling

OSC explores a superior bandwidth of optical amplifiers, BOSC~ 1014 Hz

4Th Electron-Ion collider Workshop

Hampton University

slide6
M. Zolotorev & A. Zholents, 1994

N S N S N

Particle delayed

Light pulse delayed and amplified

Particle emits light pulse of length Nl

Particle receives longitudinal kick from amplified light pulse

  • Particles in the second undulator see light emitted by themselves and neighboring particles within “coherent slice” Nul
  • Bypass delay Dℓ for particles on central orbit set such that it is on the zero crossing of the electric field in the 2nd undulator
  • “Off axis” particles receive a momentum kick
  • Notice: for =2m, /2 phase shift corresponding 1.7 fs : system stability ?

Transit-time method of OSC

4Th Electron-Ion collider Workshop

Hampton University

slide7
OSC Formalism

Phase between electron and light at U2:

Light from U1 is amplified and provides momentum kick at U2:

Sum of momentum kicks by amplified light from all Ns coherently radiating electrons produces a change of d2 for an individual electron:

Average over all Ns electrons assumed to be normally distributed (Gaussian) in x, ,  with rms widths , <>, <> to find:

4Th Electron-Ion collider Workshop

Hampton University

slide8
OSC Formalism, con’t

Cooling rates per orbit:

Find:

4Th Electron-Ion collider Workshop

Hampton University

experiment with electron beams
Experiment with electron beams

Significance:

  • OSC in low energy e-beam ring is ideal for demonstration & test experiment in high-energy hadron beam collider rings.
  • OSC cooling can be observed in seconds: short experiment time scale.
  • Optical amplifier is available.
  • Low cost beam bypass, undulators and ring interface, low experiment cost.

OSC experiment at MIT-Bates SHR ring : 2007(BNL CAD review)-

Motivation:

  • Proof-of-principle & OSC system study for high-energy colliders.
  • Concept developments: Cooling mechanism, OSC and ring lattice interface.
  • Technical system: optical amplifier, diagnostics & control.

4Th Electron-Ion collider Workshop

Hampton University

slide10
Collaboration List

W. Barletta, K. Dow, W. Franklin, J. Hays-Wehle, E. Ihloff, J. van der Laan, J. Kelsey, R. Milner, R. Redwine, S. Steadman, C. Tschalär, E. Tsentalovich, D. Wang and F. Wang,

MIT Laboratory for Nuclear Science, Cambridge, MA 02139 & MIT-Bates Accelerator Center, Middleton, MA 01949

F. Kärtner, J. Moses, O.D. Mücke and A. Siddiqui

MIT Research Laboratory of Electronics, Cambridge, MA 02139

T.Y. Fan, Lincoln Laboratory, Lexington, MA 02420

M. Babzien, M. Blaskiewicz, M. Brennan, W. Fischer, V. Litvinenko, T. Roser and V. Yakimenko, Brookhaven National Laboratory, Upton, NY 11973

S.Y. Lee

Indiana University Cyclotron Facility, Bloomington, IN 47405

W. Wan, A. Zholents and M. Zolotorev

Lawrence Berkeley National Laboratory, Berkeley, CA 94720

V. Lebedev,V. Shiltsev

Fermilab, Batavia, IL 60510

4Th Electron-Ion collider Workshop

Hampton University

slide11
Small-angle bypass: Concept

Based on Optical parametric amplifier: total signal delay ~20ps only! Then we can choose small-angle chicane with path length increase of 20 ps ~ 6 mm.

4 parallel-edge benders and one (split) weak field lens. Choose =65 mrad, L=6mm.

First order optics:

4Th Electron-Ion collider Workshop

Hampton University

slide12
Small-angle bypass:Tolerances

C. Tschalär, J. van der Laan

Tolerances to conserve coherence are much relaxed for small-angle bypass.

Absolute setting demands:

R51, R52, R56 setting within ~±5%

  • magnet current setting ± 2 %
  • field lens current setting ± 5 %
  • magnet longitudinal positioning ± 10 mm
  • field lens transverse positioning ± 100 mm

Stability (~1 hour) demands:

Variation for central orbit length in chicane ≤ 0.1 m = 20°phase

  • magnet current 10-5
  • lens current 3 * 10-3
  • magnet longitudinal position 50 m
  • lens transverse position 250 m

4Th Electron-Ion collider Workshop

Hampton University

slide13
Bypass optics and ring lattice requirementsC. Tschalär

Choose bypass (Rij) and ring(Twiss, dispersion) parameters to have a proper range of <2>(,<2>,..) for cooling.

4Th Electron-Ion collider Workshop

Hampton University

slide14
Bates Experiment Parameters

Growth (damping) rates at equilibrium state:

4Th Electron-Ion collider Workshop

Hampton University

slide15
OSC Insertion

SHR Lattice for OSC Experiment

4Th Electron-Ion collider Workshop

Hampton University

slide16
SHR OSC Simulation: x and <2>

<2> decreases with x.

Optimal cooling achieved by adjusting G.

4Th Electron-Ion collider Workshop

Hampton University

slide17
Particle Distribution with OSC: Gaussian

C. Tschalär

OSC tracking: 104 particles, 106 turns. Bates SHR, Nb=108.

4Th Electron-Ion collider Workshop

Hampton University

slide18
OSC tracking: 104 particles, 106 turns. Bates SHR, Nb=108.

Particle Distribution with OSC: “BOX”

4Th Electron-Ion collider Workshop

Hampton University

slide19
OSC Tuning Diagnostics

J. Hays-Wehle, W. Franklin

  • Interference signal maximal when light amplitudes same (low gain alignment)
  • E2 is maximal for f=0 (f=/2 for OSC) use in feedback system
  • Perform phase feedback in high gain operation ? (work on analysis and bench test, J Hays-Wehle)
  • Correlate with beam size measurements (sync. Light monitors, streak camera)

4Th Electron-Ion collider Workshop

Hampton University

slide20
10 µJ, or 20 W

2nJ, or 40mW

bunch length: 20 ps, 1 nsrepetition rate: 20 MHz, ~2 MHz

Tevatron: 1 pJ

Bates: 0.2 pJ

Dispersion free

40-70 dB

Amplification

  • High broadband amplification: G~104 (107), 10% bandwidth (undulator)
  • Dispersion free: group delay variation less than 0.1 optical cycles
  • Short overall delay to enable short chicane bypass to maintain
  • interferometric stability and reduce cost
  •  Broadband Optical Parametric Amplification (OPA) with low conversion
  • Ultra-broadband optical amplifiers suitable for OSC at Bates can be built using commercial picosecond lasers, PPLN based OPA at 2 microns

Optical amplifier requirements for OSC:

Bates & TevatronF. Kärtner, A. Siddiqui

4Th Electron-Ion collider Workshop

Hampton University

20

slide21
50 ps, 1030 nm Laser

20 MHz, 20 W, 1 mJ

2 nJ

40 mW

Undulator

Radiation

BaF2 wedges

1mm

Beam radius:

f = 12 cm

w = 0.5 mm

2 mm

PPLN

n=2

0.2 pJ

4 µW

f = 380 cm

f = 380 cm

24cm

103cm

270cm

103cm

270cm

Lenses and wedges, 1mm, n=1.5

Total optical delay is only 5.5 mm ~ 20 ps

Amplifier layout for Bates OSC

F. Kärtner, A. Siddiqui

PPLN: Periodically Poled Lithium Niobate

4Th Electron-Ion collider Workshop

Hampton University

21

slide22
OSC for RHIC

4Th Electron-Ion collider Workshop

Hampton University

slide23
Integrated luminosity gain (slow down emittance growth) estimates for proton beams: 60% to 100%. MIT/Bates proposal review 2/12/2007W. Fischer

4Th Electron-Ion collider Workshop

Hampton University

slide24
OSC for Tevatron: Layout

OSC location

4Th Electron-Ion collider Workshop

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numerical example for tevatron osc c tschal r
Tevatron: protons

Undulators:10 periods of 2.7m = 27 m long

B=8Tesla; K=1.1;=0.38; =2; k=•106/m

Amplifier:

OSC Chicane: choose

Cooling time :

Current luminosity lifetime ~ 10 hours

Numerical Example for Tevatron OSCC. Tschalär

4Th Electron-Ion collider Workshop

Hampton University

slide26
Original Long Straight

32.5 mrad

72m

OSC Insertion

19.7 mrad

Optical line

89.4m

Dipole 4.4T, 25.6m

Bending angle and drift space set to have:

Path delay : L=10mm=30 ps

x=55.7cm

Eased magnet tolerances

Dipole 8.0T

Undulator 8T, 27m

Dipole 8.2 T, 8m

Quadrupole 2m , g 400T/m, aperture 2cm.

Small-Angle Magnetic Bypass Chicane (conceptual design)

4Th Electron-Ion collider Workshop

Hampton University

slide27
High-Power Optical Amplifier for Tevatron: Development Plan

J. Gopinath et al., MIT-LL, A. Siddiqui et al.,MIT-RLE

  • OSC at the Tevatron needs >20 W output power and linear gain => 1 kW pump power with 2% conversion. OPA needs “perfect” beam (M2<1.2)
  • High-Power pump Laser:
  • Cryogenically cooled Yb:YAG lasers (Demo: 500-W, 2007)
  • T. Y. Fan, MIT Lincoln Laboratory
  • MIT-LL ATILL Program (5kW laser)
  • High-power OPA design and demonstration:
    • Trade study to evaluate NLO crystal candidates for average-power performance and designs for high-power OPA
    • Measure key engineering parameters needed for high-power OPA (thermal conductivity, optical absorption, dn/dT)
    • Demonstration of 20-W OPA with phase control
  • Successful OSC at the Tevatron needs forward looking development now if it needs to be available in 2 years.

4Th Electron-Ion collider Workshop

Hampton University

27

slide28
Summary
  • OSC concept, based mostly on current technology, is a viable solution to high-energy hadron beam cooling.
  • Important development tasks include: high average output power optical amplifier (including pump laser), OSC interface with collider rings and cooling diagnostics & control.
  • Experiment with electron beam can advance OSC concepts and technical systems in a short time period and with minimal funding support. It is an essential step prior to a full-scale implementation of OSC systems in high-energy hadron beam colliders.

4Th Electron-Ion collider Workshop

Hampton University

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