FACET-II Design, Parameters and Capabilities

Transcription

1 FACET-II Design, Parameters and Capabilities 217 FACET-II Science Workshop, October 17-2, 217 Glen White

2 Overview Machine design overview Electron systems Injector, Linac & Bunch compressors, Sector 2 Positron systems Source, return lines, damping ring, Linac injection Operation modes Single-bunch, multi-bunch, e-, e+, e- & e+, collimated Independent witness bunch injector Achievable beam parameters KPP s Transverse emittance, peak current and charge range and tradeoffs Extreme I pk and other exotic options Design capabilities discussed here -> see later talk for stability analysis 2

3 Machine Design

4 FACET-II Electron Systems (Stage-I) Injector Bunch compressors in Sector 11 (BC11) and Sector 14 (BC14) Beam diagnostics Sector 2 initially untouched, ideas for improvements later RF Gun Collimation BC2 L1 BC11 L2 BC14 L3 Final Focus & Experimental Area SLAC Linac Tunnel (Sectors 1 19) 8

5 Electron Injector 4 MeV 63 MeV 135 MeV YAG screen BPMs Vault shield wall OTR screens Gun L-A L-B TCAV Phase cavity Toroid Laser heater Diagnostics section Dump screen/fc RF Gun, E =9-12MV/m L accelerates to 135 MeV LH chicane off project, space reserved 35 bend into main linac Sector 11 Q < 5 nc, <3 A peak current Design: γε x = 3 2 nc, 24 A Emittance compensation design using IMPACT-T Beam distribution from IMPACT-T simulation used to assess FACET-II performance in tracking model Design of the Injector Complex up to BC11 based on LCLS Sector 2 injector 5

6 Electron Injector Optimization & Simulation Parameter Peak current at injector exit Peak current at Sector 2 IP Bunch length after injector (rms) Bunch length at Sector 2 IP (core rms) Transverse emittance after injector (9%) Transverse emittance into Sector 19 (9%) Tranverse beam size at Sector 2 IP (core rms) LH = laser heater Symb ol Unit Req. Tracking Simulation Results Orion Orion + LH LCLS LCLS + LH I pk ka I pk ka > σ z μm σ z μm < γε x,y γε x,y μmrad μmrad σ x,σ y μm < < , , , , All options meet KPP requirements Increased longitudinal brightness possible with LCLS gun 9.9 ε-compensation optimization & tracking with IMPACT-T & Lucretia Optimize: Gun Sol Gun RF phase Cathode-La drift 2 nd solenoid 6

7 Main Linac Layout & Bunch Compressors Standard station (klys & ~12m RF) Feedback station (klys & ~12m RF) Spare station (klys & ~12m RF) L1 E 1 =335 MeV L2 E 2 =4.5 GeV 11-1/2 BC > > > >14-6 BC14 L1X (upgrade) L3 E 3 =1. GeV TCAV 15-1-> > > > >19-8 Sector 2 Sector 2 operations GeV possible (1 GeV design) Feedback and TCAV diagnostics stations included in design Beyond-baseline parameters shown may include x-band 4 th harmonic linearizing structure (L1X) to improve linearity of chirp 7

8 FACET-II Positron Systems (Stage-II) Existing target in S19 & return lines, truncated in S1 New return-line booster for 2->335 MeV in S14 New horizontal & vertical return-line doglegs for DR injection DR & DR extraction and pre-compression in S1 RF Gun 4 nc Collimation BC11 BC14 e + DR LP L1 L2 L3 Final Focus & Experimental Area BC1 Positron Production & Return Line Sector 14 Return Line Acceleration BC2 SLAC Linac Tunnel (Sectors 1 19) 12

9 Positron Damping Ring in Sector m diameter ring Vertical injection & extraction SLC septa, kickers & RF New combined-function arc magnet designs 9

10 Positron Damping Ring Design Overview 1 5 Hz σ z = 3.9 mm, σ δ =.62 % γε t = 5.5 μm-rad (fully coupled, defined by IBS) Parameter DR designed, incuding collective effects Value Energy, E [MeV] 335. Bunch Charge, Q [nc] 1. Beam Current, I [ma] 14. Circumference, C [m] Arc Bend Radius, ρ [m -1 ].78 RF Energy Acceptance, A [%] Tune, ν a, ν b 4.588, 2.57 Emittance, γε a,b [µm-rad] Bunch length, σ z [mm] Energy spread, σ δ [%] Mom. compaction, α p.525 Damping partition, J x, J y, J z 2.15,1.,.85 Damping time, τ a, τ b, τ c [ms] 16.9, 36.4, 43. Natural Chromaticity, ξ a, ξ b -6.5, -4.4 Chromaticity, ξ a, ξ b +1, +1 Syn. Energy loss / turn, U [kev] RF voltage, V RF [MV] RF frequency, f RF [MHz] 714. Harmonic Number [n] 51 Synchrotron Tune.37 (521.9 khz, 26.8 turns) 1

11 Positron Transport Lines: Ring to Linac Positron Extraction and Compression Sector MeV e+ from PDR à Vertical bend Diagnostic waist e+ Bunch compressor Bunch length monitor L-P E spread screen New Beamline Designed to Extract Positrons from DR, Diagnose & Condition for Linac

12 PARAMETERS & CAPABILITIES

13 Operating Modes Single Bunch [Baseline] e - e + (parameters of single bunch tracked to IP) Collimated Single Bunch [Baseline] e - e + (as above, using collimator jaws to optimize I pk / Q / ε) Notched Beam [Baseline] e - e + (FACET-like operations) Shaped Injector Pulse [Upgrade] e - (controlled, shaped laser pulse from e - injector laser) 2 Bunch [Upgrade] e - + e + ( Stage III option simultaneous IP) Max I pk [Upgrade] e - (Re-imagined BC2 and FFS layout for max compression)

14 FACET-II Key Performance Parameters Description of Scope Units Threshold KPP Objective KPP Beam Energy [GeV] 9 1 Bunch Charge (e-/e+) [nc].1/.1 2/1 Normalized Emittance in S19 (e-/e+) [µm-rad] 5/5 2/2 Bunch Length (e-/e+) [µm] 1/1 2/2 Threshold KPPs Minimum parameters against which the project s performance is measured when complete Objective KPPs Desired operating parameters which may be achieved during steady operation Baseline design allows for objective key performance parameters specified by science program 14

15 Baseline FACET-II Electron Single-Bunch Design Parameters 4.3 MeV σ z =.85 mm σ δ = 4 kev Q=2nC rf gun Linac- L=6m 135 MeV σ z =.85 mm σ δ =.1 % γε x/y = 3 μm-rad BC11 L=6m R 56 = -48 mm 335 MeV σ z = 4-5 µm σ δ = % BC14 L=22m R 56 = -36 mm 4.5 GeV σ z = 8-1 µm σ δ = % φ rf ~ -18:-21 φ rf ~ -37:-39. φ rf = γε x/y < 4.4/3.3 μm-rad BC2 R 56 = 5 mm L=39m 1 GeV σ z = µm σ x,y = 1-2 µm σ δ = % I pk = 3-7 ka DL1 R 56 = 6.3 mm L=12m L1 Linac-1 L=18m L2 Linac-2 L=322m L3 Linac-3 L=471m Final Focus (β x, y =.1-1 m) SLAC Linac Tunnel (Sectors 1 19) W-chicane & Final Focus (S2) Compression scheme : verified with tracking simulations 15

16 Baseline FACET-II Positron Parameters BC1 Compression scheme designed to satisfy objective KPP, verified with tracking simulations 16

17 Particle Design and Tracking Simulation 6D start-end particle tracking using IMPACT-T and Lucretia IMPACT-T used for injector tracking, including 3-D space charge Tool used for LCLS/LCLS-II Lucretia: Matlab-based toolbox for electron beam design and beam dynamics modeling of single-pass beamlines Benchmarked against other tracking engines in context of Linear Collider design and FACET Elegant, PLACET, MADX/PTC, Liar, BMAD, LiTrack Tracking includes effects of ISR, CSR, longitudinal and transverse wakes in structures, longitudinal space charge Treatment of error sources Magnetic fields, element offsets, RF errors Design and simulation of FACET-II using well tested simulation tools 17

18 Example FACET-II Longitudinal Compression Profile

19 Start-End Tracking Longitudinal Phase Space at IP Electron Positron Design core bunch length <2um for both electrons and positrons achieved 19

20 Start-End Tracking Transverse Dimensions at IP Electron Positron Meets typical E2 requirements for σ x,y < 2 μm 2

21 Manipulation of Electron IP Using Linac Phasing Spread out longitudinal profile with current peaks at head & tail Somewhat suitable configuration for 2-bunch notch profiles for plasma experiments Difficult to fine-tune drive/witness bunch parameters Need additional parameters: manipulation of injector profiles

22 Shaped Injector Pulse to Deliver 2-Bunch Notched Beam in S2 IP S2 Notch Collimator

23 Example Compression with Collimation (2nC e+ source, e- x- band linearizer & LH) 2-bunch BC1END'(e+'insertion) e2 &'e+'z/δ phase'space e " : σ z (um)+/+i pk (ka) 287+/ / / / /+76 δ E (%)'/'Q'(nC).3'/'1.2.9'/'1.2.5'/'.7.4'/'.7.4'/'.7 e + : σ z (um)/+i pk (ka) 35+/ / / / /+12.1 δ E (%)'/'Q'(nC).5'/' '/'1.2.6'/'.6.5'/'.6.5'/'.6 Tracked longitudinal phase space from BC11, simultaneously for electrons and positrons 23

24 Configuration Options with Collimation - Electrons Electron compression configuration tailored for high peak current 1x7 β * =.1m Compression settings: BC11, BC14, BC2 collimators L1S phase L1X amplitude BC2 R 56 Requires x-band linearizer Trade-offs Final charge Final transverse emittance Stability of delivered beam nc 24

25 Configuration Options with Collimation - Positrons Positron compression configuration tailored for high peak current 1-35 x 7 β * =.1m Compression settings: BC1, BC14, BC2 collimators LP amplitude BC2 R 56 Trade-offs Final charge nc Final transverse emittance Stability of delivered beam 25

26 BC2 Re-design Current BC2E ( W-chicane ) Many magnets, large beta functions : difficult beam alignment with large energy spread Experience difficulties with alignment and aberrations / optics control BC2E is known from simulations to be limiting factor for max peak current performance due to CSR Re-design BC2E with fewer bend magnets and fewer quads For future simultaneous e-, e+ ops: need positron arm (BC2P) Make use of magnets recovered from W-chicane

27 BC2 Requirements Deliver KPP electron and positron beams Simultaneous solution for e- and e+ (e+ arm with 5.25 cm path length difference) R 56 adjustable in range -5 mm Relative e-, e+ spacing adjustability Small β in chicanes (FACET experience) Minimized chromaticity, 2 nd order dispersion at IP Maximize peak current throughput (minimize CSR emittance growth) 5.25 cm 2856 e- MHz e+ In Linac-3 BC2-5 µm At IP Sector 2 system provides: final bunch compression, transverse focusing at experimental IP, Inversion of e+ / e- time ordering 27

28 BC2E Re-Design Reduced magnet count Few bends, simpler design -> less CSR emittance degradation Shorter by 3.5 m : allows to move TCAV after B1 -.1 X / m Z / m BC2E Re-designed for simpler operation and better performance

29 New BC2 Layout (Stage-III) BC2P e + X / m e BC2E Z / m BC2P similar to previous design, shortened in z, re-matched to maintain correct path difference

30 New BC2E/P Optics (R 56 = 5mm) BC2E BC2P x,y [m] S [m] x y x Dispersion [m] x,y [m] S [m] x y x Dispersion [m] Optics design meeting BC2 requirements

31 Improved Electron Beam Quality with New BC2E dp (%) Q (nc) rms dp/p = % rms Z = um dp/p (%) I (ka) Mean Energy = 1. GeV =.7 um I(pk) = ka z z ( m) z ( m) Original W-chicane : I pk (max) = 7 ka, γε = 13 μm-rad Re-designed BC2E: I pk (max) = 176 ka, γε = 7 μm-rad y ( m) = 6.3 um y y ( m) Q (nc) rms X = um rms Y = um Q = 2 nc Q (nc) x ( m) = 6. um x -2 2 x ( m) Particle tracking demonstrates improved longitudinal and transverse beam S2 IP with increased peak current capability

32 Further Performance Improvements - Upgraded FFS Injector laser heater + L1X δ E 5 3 kev rms Collimation (2 -> 1.2 nc) in BC11 & BC14 Simplified FFS, β * > 5 cm Spoilers to symmetrize transverse IP σ x = 4 1 μm γε x = 7 22 μm-rad I pk = 7 3 ka

33 Beam Tracking with Upgraded FFS 5 = 9.6 um y 5 Mean Energy = 1. GeV 1 1 y ( m) y ( m) dp (%) dp/p (%) LH = 3 kev +FFS Spoilers Q (nc) y ( m) 1-1 rms X = um rms Y = um Q = nc = 2.5 um y Q (nc) y ( m) x ( m) = 1.7 um x -5 5 x ( m) Q (nc) rms dp/p = % rms Z = um dp (%) I (ka) -1 = 1.9 um I(pk) = ka z dp/p (%) Mean Energy = GeV z ( m) z ( m) LH = 5 kev.2.4 Q (nc) x ( m) = 6.4 um x Q (nc) z ( m) =.4 um I(pk) = 3.65 ka z 4 rms X = um rms Y = um Q = nc Q (nc).3.2 rms dp/p = % rms Z =.7443 um I (ka) x ( m) z ( m)

34 Beam Quality Small correlations still present in beam even with spoiler option x-z correlations due to CSR Improvement requires zig-zag chicane design with active CSR compensation Tracked Macro Particle Distribution in x-z plane CSR Wake Potential

35 Path-Length Adjustability Coarse and fine adjustment controls: Δz - 5 μm Infrequently used- re-tuning required after adjustment B3 Δθ = 18.6 mrad (for 5 μm) Move Q5, S3E/L to orbit (54 mm) Correct angle with Q5 Δx=-21 mm Δz +/- 1 μm Continuously adjustable with minimal impact on other delivered beam parameters 2 X 4-bend chicanes θ = 6.45 mrad ( ) = +/- 1 μm X / m Z / m Path length adjustability within BC2P meets requirements

36 Independent Electron Witness Bunch S2 Source Parameters Parameter Symbol Value Initial Bunch Charge Q i 35 pc Normalized γε x / γε y 1 / 1 um.rad Transverse emittance FWHM Bunch Length Δt b 1. ps Peak Bunch Current I pk 3 A Injector Parameters Parameter Symbol Value Drive Beam Energy E d 1. GeV Witness Bunch Final Energy E w 1 MeV rms Transverse Final Spot Size σ x / σ y < 1 / 1 um rms Longitudinal Final Bunch Length σ z < 1 um Final Bunch Charge Q f 1 pc Final Peak Current I pk 3, A Final Beta Functions β x / β y 5 x 5 mm System Length s 18 m Injection Bend Angle Φ degrees

37 Simulated Witness Injector Bunch

38 Parameter Summary Summary of high peak current for various configuration options summarized below Configuration I * pk [ka] σ * z [μm] σ * x [μm] γε * x [μm-rad] Q [nc] e- e+ e- e+ e- e+ e- e+ e- e+ Baseline (single or 2- bunch) 2-bunch (2nC posi+lh+l1x+coll) Notched (Drive, Witness) +LH , , , , GeV BC2 Upgrade BC2+FFS Upgrade +L1X+COLL Witness Bunch Injector MeV *LH = needs laser heater in injector, L1X = needs x-band harmonic cavity in L1, COLL = utilizes collimation in BC11 & BC14

39 Backup Slides

40 BC2E Compression Performance 2D CSR ε => A γ I r D N F L H ρ K > O > σ N I ε 4 A π β@ A γ Λr D N F L F ρσ N I Λ = ln ρσ N I I > I σ A 1 + σ A σ N [Y. Cai: PR-AB 2, 6442 (217)] 1 2 (s) (analytic) 1 2 Emittance growth [ m-rad] (x) (analytic) Tracking with 1d CSR Tracking with 2d CSR rms Bunch Length z [ m] Emittance growth [ m-rad] (s) (analytic) (x) (analytic) Tracking with 1d CSR Tracking with 2d CSR Peak Current [ka] Transverse component of CSR wake important for high I pk Newly added feature in Lucretia to perform 2D CSR calculation: only included for Upgraded parameters Fractional impact on results smaller for high-compression cases