Transcript osc
Optical Stochastic Cooling Fuhua Wang MIT-Bates Linear Accelerator Center 5/20/2008 4Th Electron-Ion collider Workshop Hampton University 1 Outline • Introduction: history, concept • Experiment with electron beams: proposal & research at MIT & MIT/Bates • OSC for RHIC, Tevatron … • Summary 5/20/2008 4Th Electron-Ion collider Workshop Hampton University 2 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 8703, 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. 5/20/2008 4Th Electron-Ion collider Workshop Hampton University 3 Stochastic Cooling S. van der Meer, 1968 D. Möhl, “Stochastic Cooling for Beginners”, CERN L ~1/bandwidth=1/B kicker “bad” mixing g amplifier “good” mixing Lb p L number of particles in the sample Ns N Lb pick-up i n 1 x g x Ns i n decrement Ns k x n k x2 2 xrms 2g g 2 Ns 1 Max. decrement at g 1 Ns 5/20/2008 4Th Electron-Ion collider Workshop Hampton University 4 Towards Optical Stochastic Cooling microwave “slicing” Ns N sample length ~10 cm b optical “slicing” sample length ~10 mm OSC also allows transverse slicing x d resulting in further decrease of Ns: N s N Diffraction limited size of the radiation source d b x 2 OSC explores a superior bandwidth of optical amplifiers, BOSC~ 1014 Hz 5/20/2008 4Th Electron-Ion collider Workshop Hampton University 5 Transit-time method of OSC M. Zolotorev & A. Zholents, 1994 N S N S Particle emits light pulse of length N N Particle delayed Light pulse delayed and amplified Particle receives longitudinal kick from amplified light pulse • Particles in the second undulator see light emitted by themselves and neighboring particles within “coherent slice” Nu • Bypass delay ℓ 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 =2mm, /2 phase shift corresponding 1.7 fs : system stability ? 5/20/2008 4Th Electron-Ion collider Workshop Hampton University 6 OSC Formalism Phase between electron and light at U2: R51 x R52 hd , =k , h R51 R52 ' R56 Light from U1 is amplified and provides momentum kick at U2: eE0 N u u K d 2 d1 G sin Gg g : optical amplication factor 2c p Sum of momentum kicks by amplified light from all Ns coherently radiating electrons produces a change of d2 for an individual electron: d 22 d12 2Gd1 sin G 2 N s / 2 Average over all Ns electrons assumed to be normally distributed (Gaussian) in x, , d with rms widths <x>, <>, <d> to find: 1 Ns Ns (d n 1 2 2k d12k ) d 2 2 d1 2 d 2 2Gkh d 2 e 2 2 G2 Ns / 2 where 2 =k 2 R512 x 2 R52 2 2 h 2 d 2 5/20/2008 4Th Electron-Ion collider Workshop Hampton University 7 OSC Formalism, con’t Cooling rates per orbit: Find: 1 x 2 2 T 2 2 2 x d 2 L d 2 T Gk h R56 e L 2Gkhe 2 / 2 2 / 2 G 2 N s 2 / 2 d 2 G 2 N s / 2 d 2 where 2 2 / x 2 2 / 2 d 2 / 2 5/20/2008 4Th Electron-Ion collider Workshop Hampton University 8 Experiment with electron beams Significance: • • • • OSC in low energy e-beam ring is ideal for demonstration & test experiment in highenergy 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. 5/20/2008 4Th Electron-Ion collider Workshop Hampton University 9 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 5/20/2008 4Th Electron-Ion collider Workshop Hampton University 10 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. Q B1 0 B2 1 Optical Amplifier Q1 Q2 B3 B4 2m 4 parallel-edge benders and one (split) weak field lens. Choose =65 mrad, L=6mm. First order optics: R56 2 2 (1 / 2 f q ) R51 2 R52 / L, R51 2m / f q 2 / f q , f q ~ 230m L 2 5/20/2008 4Th Electron-Ion collider Workshop Hampton University 11 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 • field lens current setting • magnet longitudinal positioning • field lens transverse positioning ±2 % ±5 % ± 10 mm ± 100 mm Stability (~1 hour) demands: Variation for central orbit length in chicane ≤ 0.1 mm = 20°phase • magnet current 10-5 • lens current 3 * 10-3 • magnet longitudinal position 50 mm • lens transverse position 250 mm 5/20/2008 4Th Electron-Ion collider Workshop Hampton University 12 Bypass optics and ring lattice requirements C. Tschalär 2 2 A D A D 2 2 2 2 k 2 A R56 d B E B E A R51 ' R52 / 2; D R51 ' R52 / 2; B 2 / '2 / 2; E 2 / '2 / 2; Optimize D and E for maximal cooling rates : 2 R52 2 ' R51 2 2 A2 2 2 2 R56 k 2 A R56 d k 2B B 2 2 Optimal 2 1 Choose bypass (Rij) and ring(Twiss, dispersion) parameters to have a proper range of <2>(,<d2>,..) for cooling. 5/20/2008 4Th Electron-Ion collider Workshop Hampton University 13 Bates Experiment Parameters SHR Natural Beam energy (MeV) , RF: f(GHz)/ V (kV) 300, 2.856/14 Electrons/bunch, bunch number, average current 1108 , 12, 0.3mA Chicane: L(m), bending angle (mrad)/ radius(m) 5.55, 65 / 3.85 Inverse chicane matrix elements: R51, R52, R56 8.610-4, 2.52mm, -12mm Undulator: L, period, 2m, 20cm, 2mm Lattice parameters at second undulator =3m, =6m , =2 SR damping time x (sec.) 4.83 Beam emittance, x (nm), 10% coupling 47 96 Energy spread, rms bunch length 8.5e-5, 5.1 mm 1.67e-4, 9.8mm Growth (damping) rates at equilibrium state: 5/20/2008 IBS effect g IBS x g x , syn x 0 1 f 0 x OSC 0 x d 02 f g IBS d gl , syn 2 1 0 d OSC 0 2 d 4Th Electron-Ion collider Workshop Hampton University 14 SHR Lattice for OSC Experiment OSC Insertion 5/20/2008 4Th Electron-Ion collider Workshop Hampton University 15 SHR OSC Simulation: x and <2> <2> decreases with x. Optimal cooling achieved by adjusting G. 5/20/2008 4Th Electron-Ion collider Workshop Hampton University 16 Particle Distribution with OSC: Gaussian C. Tschalär OSC tracking: 104 particles, 106 turns. Bates SHR, Nb=108. Initial 2 1, decreasing Initial 2 2 , decreasing Distribution remained Gaussian. Tails developed, Gaussian centeral part. r x 2 ( ) 2 : radius in normalized x- phase space. 5/20/2008 4Th Electron-Ion collider Workshop Hampton University 17 Particle Distribution with OSC: “BOX” OSC tracking: 104 particles, 106 turns. Bates SHR, Nb=108. Initial 2 1, decreasing Distribution converted to Gaussian. Initial 2 2 , decreasing Tails developed, Gaussian centeral part. Cooling slows down as 2 becomes smaller. Implications for hadron beams ? 5/20/2008 4Th Electron-Ion collider Workshop Hampton University 18 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) 5/20/2008 4Th Electron-Ion collider Workshop Hampton University 19 Optical amplifier requirements for OSC: Bates & Tevatron F. Kärtner, A. Siddiqui Tevatron: 1 pJ Bates: 0.2 pJ bunch length: 20 ps, 1 ns repetition rate: 20 MHz, ~2 MHz 10 µJ, or 20 W 2nJ, or 40mW 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 5/20/2008 4Th Electron-Ion collider Workshop Hampton20University 20 Amplifier layout for Bates OSC F. Kärtner, A. Siddiqui 50 ps, 1030 nm Laser 20 MHz, 20 W, 1 mJ Undulator Radiation Beam radius: w = 0.5 mm 0.2 pJ 4 µW f = 12 cm f = 380 cm 270cm 2 nJ 40 mW BaF2 wedges 1mm 2 mm PPLN n=2 f = 380 cm 24cm 103cm 103cm Lenses and wedges, 1mm, n=1.5 Total optical delay is only 5.5 mm ~ 20 ps 270cm PPLN: Periodically Poled Lithium Niobate 5/20/2008 4Th Electron-Ion collider Workshop Hampton21University 21 OSC for RHIC 5/20/2008 4Th Electron-Ion collider Workshop Hampton University 22 Integrated luminosity gain (slow down emittance growth) estimates for proton beams: 60% to 100%. MIT/Bates proposal review 2/12/2007 W. Fischer 5/20/2008 4Th Electron-Ion collider Workshop Hampton University 23 OSC for Tevatron: Layout OSC location 5/20/2008 4Th Electron-Ion collider Workshop Hampton University 24 Numerical Example for Tevatron OSC C. Tschalär Tevatron: protons 1045; T 21m s; nb 36; N b 2.4 1011 d 0 1.4 10-4 ; 4.3 10 -9 m Undulators: 10 periods of 2.7m = 27 m long B=8 Tesla; K=1.1; =0.38; =2m; k=•106/m Amplifier: P 20W AL 4.8 1017 J ; G 0.83 1012 , OSC Chicane: choose G P 1; 2 / 2 2 / 0.22m; A 0.93mm; R56 3.7mm for 18m; 2m; .11: Cooling time : T / T d R51 4.7 104 ; R52 8.4mm e 1 1/ 2 2 / G 2 hours Current luminosity lifetime ~ 10 hours 5/20/2008 4Th Electron-Ion collider Workshop Hampton University 25 Small-Angle Magnetic Bypass Chicane (conceptual design) 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: Dipole 8.0T Path delay : L=10mm=30 ps Undulator 8T, 27m x=55.7cm Dipole 8.2 T, 8m Quadrupole 2m , g 400T/m, aperture 2cm. 5/20/2008 Eased magnet tolerances 4Th Electron-Ion collider Workshop Hampton University 26 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. 5/20/2008 4Th Electron-Ion collider Workshop Hampton27University 27 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. 5/20/2008 4Th Electron-Ion collider Workshop Hampton University 28