e + e - Linear Collider Disclaimer This talk was lifted from an earlier version of a lecture by N.Walker Eckhard Elsen DESY DESY Summer Student Lecture 3 rd August 2006 1
Disclaimer II Talk is largely based on TESLA design which meanwhile evolved into the design of the International Linear Collider (ILC) some reference will be made to the specifics of the ILC (The TESLA numbers are only indicative of the foreseen ILC performance). 2
The TESLA Linear Collider Technical Design Report (TDR) published in March 2001 500 GeV LC based on SCRF technology Chosen as the basis for the International Linear Collider 3
Energy Frontier + ee Colliders ILC LEP at CERN, CH Ecm = 180 GeV PRF = 30 MW 4
Why a Linear Collider? Synchrotron Radiation from an electron in a magnetic field: Energy loss per turn of a machine with an average bending radius ρ: Energy loss must be replaced by RF system 5
Cost Scaling $$ Linear Costs: (tunnel, magnets etc) $ lin ρ RF costs: $ RF ΔE E 4 /ρ Optimum at $ lin = $ RF Thus optimised cost ($ lin +$ RF ) scales as E 2 6
The Bottom Line $$$ 7
The Bottom Line $$$ 8
The Bottom Line $$$ 9
Solution: Linear Collider No Bends, but lots of RF! bang! e + e - 15 km For a E cm = 1 TeV machine: Effective gradient G = 500 GV / 15 km = 34 MV/m Note: for LC, $ tot E 10
The TESLA linear collider Now a separate project 11
A Little History A Possible Apparatus for Electron-Clashing Experiments (*). M. Tigner Laboratory of Nuclear Studies. Cornell University - Ithaca, N.Y. M. Tigner, Nuovo Cimento 37 (1965) 1228 While the storage ring concept for providing clashingbeam experiments ( 1 ) is very elegant in concept it seems worth-while at the present juncture to investigate other methods which, while less elegant and superficially more complex may prove more tractable. 12
A Little History (1988-2006) SLC (SLAC, 1988-98) NLCTA (SLAC, 1991-) TTF (DESY, 1994-2006) ATF (KEK, 1991-) FFTB (SLAC, 1992-1995) SBTF (DESY, 1994-1998) CLIC CTF1,2,3 (CERN, 1994-) FLASH (DESY, 2006-) Over 18 Years of Linear Collider R&D 13
The Luminosity Issue particles per repetition bunch rate No. bunches in bunch train Beam-beam enhancement factor (pinch effect) LEP f rep = 40 khz beam cross-section at Interaction Point (IP) LC LEP: f rep 130 6 = 5-200 µm 2 Hz! LC: 550 5 nm 2 14
The Luminosity Issue Requirements for Next Generation LC: L 10 34 cm 2 s 1 E cm = 0.5-1 TeV 15
The Luminosity Issue P beam L = 1 4πE cm (E cm f rep n b N) N σ x 1 σ y H D Requirements for Next Generation LC: L 10 34 cm 2 s 1 E cm = 0.5-1 TeV 16
The Luminosity Issue Efficiency L = 1 4π ηp RF E cm N σ x 1 σ y H D Beamstrahlung (energy loss δe/e) Requirements for Next Generation LC: L 10 34 cm 2 s 1 E cm = 0.5-1 TeV 17
Beamstrahlung e + RMS Energy Loss for a flat beam (σ x» σ y ) 18
Beamstrahlung e γγ e + γ hard γs radiated by intense electric field of approaching beam = Beamstrahlung RMS Energy Loss for a flat beam (σ x» σ y ) δ BS E cm σ z ( N σ x ) 2 19
Luminosity re-visited IP focusing & Emittance L ηp RF E 3/2 cm ( δ BS σ z ) 1/2 1 σ y H D Requirements for Next Generation LC: L 10 34 cm 2 s 1 E cm = 0.5-1 TeV 20
Emittance and Strong Focusing σ y * ε y β y * = 5 nm = 3 10-8 m = 0.4 mm 21
Limit on β* σ z y β* = depth of focus reasonable lower limit for β* is bunch length σ z Thus set β* = σ z s IP (s = 0) 22
Final Luminosity Scaling Law High Beam Power Superconducting RF Small IP vertical Technology beam size High current (n b N) High efficiency (P RF P beam ) L ηp L ηp RF ( δ RF ( δ BS ) 1/2 BS E E ɛ ) 1/2 cm y ɛ y Small emittance ε y Strong focusing (small β* y ) 23
TESLA superconducting 9-cell Niobium cavity operated at 2 K 24
The Superconducting Advantage Low RF losses in resonator walls (Q 0 10 10 compared to Cu 10 4 ) high efficiency η AC beam long beam pulses (many bunches) low RF peak power large bunch spacing allowing feedback correction within bunch train. 25
The Superconducting Advantage Low-frequency accelerating structures 1.3 GHz (for Cu 6-30 GHz) very small wakefields relaxed alignment tolerances high beam stability 26
Wakefields Just Ohm s Law: The TESLA concept: Put a large current through a low impedance 27
Wakefields (alignment tolerances) Misplaced cavity Banana 28
Wakefields (alignment tolerances) Transverse Wakefield Kick f 3 10 3 Ratio of deflecting wakefield to accelerating field for 1mm offset 10 4 10 5 10 6 TESLA C-band X-band CLIC 29
The TESLA Test Facility (TTF) Cavity strings are prepared and assembled in ultra-clean room environment at TTF 30
The TESLA Test Facility (TTF) TTF Test Linac constructed from completed Cryomodules now user facility: FLASH 31
The TESLA Linac Damping Ring Cryomodule B M A E Cavities 32
The TESLA Linac ~1m 1 9-cell 1.3GHz Niobium Cavity 33
The TESLA Linac ~16m 12 9-cell 1.3GHz Niobium Cavity 1 Cryomodule 34
The TESLA Linac K 36 9-cell 1.3GHz Niobium Cavity 3 Cryomodule 1 10MW Multi-Beam Klystron 35
The TESLA Linac Per Linac (Ecm = 500 GeV): 10,296 Cavities 858 Cryomodules 286 Klystrons Gradient: 23.4 MV/m (inc. 2% overhead) LENGTH 14.4km (fill factor: 74%) 36
Cryoplants Each linac divided into 6 Cryo-units (~140 cryomodules) 7 refrigeration (liquid He) plants housed in 7 surface halls (~5km) 37
Cryohalls Refrigerators LINAC tunnel 38
10MW Multibeam Klystron Design power and pulse length (1.5ms) at 65% efficiency reached at TTF The Thomson TH1801 multibeam klystron 39
10MW Multibeam Klystron Design power and pulse length (1.5ms) at 65% efficiency reached at TTF The Thomson TH1801 cathode 40
The LINAC is only one part of a linear collider! The SC linac can: Efficiently accelerate a high charge to high energies (high RF beam power transfer efficiency) Preserve the required small bunch volumes (small emittance) because of low wakefields Has relatively relaxed tolerances 41
The LINAC is only one part of a linear collider! BUT how do we: Produce the electron charge? Produce the positron charge? Make small emittance beams? Focus the beam down to 5nm at the IP? 42
The LINAC is only one part of a linear collider! 43
The LINAC is only one part of a linear collider! 44
The LINAC is only one part of a linear collider! 45
The LINAC is only one part of a linear collider! 46
The LINAC is only one part of a linear collider! 47
The LINAC is only one part of a linear collider! 48
The LINAC is only one part of a linear collider! 49
Machine Overview (TESLA) 50
Electron Sources Laser-driven photo-injectors 51
Positron Source Replacing planar undulator with HELICAL undulator gives possibility of POLARISED POSITRONS 52
Small Emittances Require normalised emittances of γε x = 10-5 m γε y = 3 10-8 m Thermionic guns (ε~10-5 ) and state-of-theart RF guns (ε~10-6 ) not good enough Emittance Damping Ring required 53
Damping Rings ring in which the bunch train is stored for T ~200 ms ε x,y is damped down due to synchrotron radiation effects: initial emittance (~0.01m for e + ) final emittance equilibrium emittance damping time ~ 28 ms 54
How β-damping works y not changed by photon δp replaced by RF such that Δp z = δp. since y = dy/ds = p y /p z, we have a reduction in amplitude: δy = δp y Must take average over all β-phases: where and hence LEP: E ~ 135 GeV, P γ ~ 70 GeV/s, τ D ~ 4 s 55
How β-damping works y not changed by photon δp replaced by RF such that Δp z = δp. since y = dy/ds = p y /p z, we have a reduction in amplitude: δy = δp y Must take average over all β-phases: where and hence LEP: E cm ~ 135 GeV, P γ ~ 4.7 10 3 GeV/s, τ D ~ 28 ms 56
Damping Rings for LC Typically E 3-5 GeV B bend = 0.2 T ρ 50-80 m <P γ > = 240 GeV/s [330 kv/turn] hence τ D 28 ms Note: ε eq E 2 /ρ 57
TESLA Damping Rings Long pulse: 950ms c = 285km!! Compress bunch train into 18km ring Minimum circumference set by speed of ejection/injection kicker (~20ns) Unique dog-bone design: 90% of circumference in linac tunnel. 58
Limits on ε eq Horizontal emittance defined by lattice (presence of dispersion in x-plane leads to so-called anti-damping): theoretical vertical emittance limited by space charge intra-beam scattering (IBS) In practice, ε y limited by magnet alignment errors [cross plane coupling] typical vertical alignment tolerance: Δy 30 µm requires beam-based alignment techniques! 59
Damping Rings Dogbone Straight Sections Dogbone Arc Tunnel 60
Cryohall and dogbone tunnel 61
longitudinal phase space Bunch Compression bunch length from ring ~ few mm required at IP 100-300 µm dispersive section 62
Bunch Compression Damping ring Bunch length After compression (300 µm) 6 mm 63
Bunch Compression 2.8% ΔE/E Damping ring (~ppm) After compression 5 GeV: 2.8% 250 GeV: 0.6 64
Final Focus System for small β* Optical telescope required to strongly demagnify the beam (M x 1/100, M y 1/500) Strong focusing leads to unacceptable chromatic aberrations [non-linear optics] Require 2nd-order optical correction uses non-linear elements (sextupoles) 65
Beam Delivery System Positron Production System 66
Beam Delivery System Collimation System 67
Beam Delivery System Final Focus System 68
Beam Delivery System σ y = 3 µm Demagnification: 636 σ y = 5 nm 69
Stability Tiny (emittance) beams Tight component tolerances Field quality Alignment Vibration and Ground Motion issues Active stabilisation Feedback systems Linear Collider will be Fly By Wire 70
Stability: some numbers Cavity alignment (RMS): 500 µm Linac magnets: 100 nm BDS magnets: 10-100 nm Final lens : ~ nm!!! Parallel-to- Point focusing 71
IP Fast (orbit) Feedback Long bunch train: 2820 bunches t b = 337 ns Beam-beam kick 72
IP Fast (orbit) Feedback Systems successfully tested at TTF 73
Banana Effect : Beam-Beam Simulation Instability driven by vertical beam profile distortion Strong for high disruption Distortion caused by transverse wakefields and quad offset only a few percent emittance growth Tuning can remove static part Nominal TESLA Beam Parameters + y-z correlation (equivalent to few % projected emittance growth) Beam centroids head on 74
Long Term Stability -0 0 0 0 0 0 1 1 1 1 1 0.4999999950079738 1 1.499999105253642 2.000000019968105 2.49999995007974 2.999998240459424 3.499999642579026 4.00000007987242 4.500005038084225 4.99999995007974 5.500003932313996 5.999996540823126 6.499994662198795 6.999999355046412 7.499995451387862 8.000000239617259 8.500001453918005 9.000010166025021 9.500008634136071 10 14.9999565138204 20.00000019968105 24.9999995007974 29.99991332716149 35.00015760710146 40.0000007987242 44.99973953258034 49.99999950079741 54.99965939764022 59.9998272533644 64.99949761981438 70.00031591308971 74.9997818203002 80.00000239617258 85.00021025917172 89.99947996372016 94.99921136225953 100 149.999565138204 200.0000019968105 249.999995007974 299.9991332716151 350.0015760710147 400.0000079872421 449.9973953258035 499.9999950079744 549.9965939764023 599.9982725336441 649.9949761981438 700.0031591308972 749.9978182030022 800.0000239617267 850.0021025917174 899.9947996372017 949.9921136225963 1000 1499.99565138204 2000.000019968105 2499.999950079741 2999.991332716155 3500.015760710145 4000.000079872422 4499.973953258032 4999.99995007974 5499.96593976402 5999.982725336443 6499.949761981435 7000.031591308973 7499.978182030024 8000.000239617269 8500.021025917184 8999.94799637202 9499.921136225967 10000 14999.95651382041 20000.00019968108 24999.99950079741 29999.91332716152 35000.15760710142 40000.00079872419 44999.73953258029 49999.99950079746 54999.65939764026 59999.82725336449 64999.4976198143 70000.31591308981 74999.78182030033 80000.00239617263 85000.21025917193 89999.4799637203 94999.21136225959 100000 149999.5651382042 200000.0019968106 249999.9950079744 299999.1332716156 350001.5760710146 400000.0079872424 449997.3953258034 499999.9950079743 549996.5939764022 599998.2725336445 649994.9761981437 700003.1591308989 749997.8182030041 800000.0239617258 850002.1025917188 899994.7996372039 949992.1136225953 1 hour 1 day 1 minute 10 days No Feedback IP Feedback IP Feedback & slow orbit feedback 75
Damping ring to IP Simulations bunch compressor linac BDS Gaussian bunch from DR Ideal machine Change of bunch compressor phase by ±2.5 deg (powerful knob at the SLC) This is just an example what we intend to study 76
Timeline 1995 SLAC produced X-Band design report (ZDR) 2001 TESLA TDR Published US Snowmass HEP Workshop: World-Wide Consensus 2003 KEK (Japan) X-Band GLC TDR Published 2004 International Technology Recommendation Panel Decision (X-Band or TESLA?) SCRF 1 st ILC Workshop, KEK Japan, November 2004 2005 Formation of Global Design Initiative and Regional Design Teams, Baseline defined 2 nd ILC Workshop, Snowmass Colorado, USA, August 2005 2006 Reference Design Report 2007-2008 International TDR with full costs 2008+ Site selection, start of construction 2015++ Begin e + e - physics 77
more on the ILC go to www.linearcollider.org or subscribe to www.linearcollider.org/newsline 78