FACET-II Design, Parameters and Capabilities 217 FACET-II Science Workshop, October 17-2, 217 Glen White
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
Machine Design
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
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 L1 @ Sector 11 Q < 5 nc, <3 A peak current Design: γε x = 3 μm-rad @ 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
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 -.24.24.36.33 I pk ka >1 7 36 95 56 σ z μm - 838 839 617 618 σ z μm <2 1.8 4.3 1.5 2.8 γε x,y γε x,y μmrad μmrad σ x,σ y μm <2-2.9 2.9 3. 3. <2 3.9 3.3 4. 3.5 17.7, 12.2 16.1, 11.9 17.5, 9.8 16.5, 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
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 BC11 11-4->11-8 12-1->12-8 13-1->13-8 14-1->14-6 BC14 L1X (upgrade) L3 E 3 =1. GeV TCAV 15-1->15-8 16-1->16-8 17-1->17-8 18-1->18-8 19-1->19-8 Sector 2 Sector 2 operations 4.-13.5 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
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
Positron Damping Ring in Sector 1 2.9 m diameter ring Vertical injection & extraction SLC septa, kickers & RF New combined-function arc magnet designs 9
Positron Damping Ring Design Overview 1 nc @ 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] 21.41 Arc Bend Radius, ρ [m -1 ].78 RF Energy Acceptance, A [%] 2.9-4.1 Tune, ν a, ν b 4.588, 2.57 Emittance, γε a,b [µm-rad] 5.5-5.8 Bunch length, σ z [mm] 3.-3.9 Energy spread, σ δ [%].48-.62 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] 1.362 RF voltage, V RF [MV] 1.1-2.2 RF frequency, f RF [MHz] 714. Harmonic Number [n] 51 Synchrotron Tune.37 (521.9 khz, 26.8 turns) 1
Positron Transport Lines: Ring to Linac Positron Extraction and Compression Sector 1-11 335 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
PARAMETERS & CAPABILITIES
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 delivery @ IP) Max I pk [Upgrade] e - (Re-imagined BC2 and FFS layout for max compression)
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
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 = 1-1.5 % BC14 L=22m R 56 = -36 mm 4.5 GeV σ z = 8-1 µm σ δ = 1-1.5 % 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 = 1.5-2 µm σ x,y = 1-2 µm σ δ = 1-1.5 % 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
Baseline FACET-II Positron Parameters BC1 Compression scheme designed to satisfy objective KPP, verified with tracking simulations 16
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
Example FACET-II Longitudinal Compression Profile
Start-End Tracking Longitudinal Phase Space at IP Electron Positron Design core bunch length <2um for both electrons and positrons achieved 19
Start-End Tracking Transverse Dimensions at IP Electron Positron Meets typical E2 requirements for σ x,y < 2 μm 2
Manipulation of Electron Bunch @ 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
Shaped Injector Pulse to Deliver 2-Bunch Notched Beam in S2 @ Injector @ S2 IP S2 Notch Collimator
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+/+.4 287+/+.4 24 /+3.4 24+/+3.8 1+/+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+/+.4 35+/+.4 29 /+3.1 29+/+3.1 7.4+/+12.1 δ E (%)'/'Q'(nC).5'/'1.2 1.2'/'1.2.6'/'.6.5'/'.6.5'/'.6 Tracked longitudinal phase space from BC11, simultaneously for electrons and positrons 23
Configuration Options with Collimation - Electrons Electron compression configuration tailored for high peak current 1x7 um @ 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 13 ka @ 1.5 nc 24
Configuration Options with Collimation - Positrons Positron compression configuration tailored for high peak current 1-35 x 7 um @ β * =.1m Compression settings: BC1, BC14, BC2 collimators LP amplitude BC2 R 56 Trade-offs Final charge 16 ka @ 1.7 nc Final transverse emittance Stability of delivered beam 25
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
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
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 -.2 -.3 -.4 -.5 193 1935 194 1945 195 1955 196 1965 197 Z / m BC2E Re-designed for simpler operation and better performance
New BC2 Layout (Stage-III) BC2P 1.8.6.4 e + X / m.2 -.2 -.4 e - -.6 -.8 BC2E 193 1935 194 1945 195 1955 196 1965 197 197 Z / m BC2P similar to previous design, shortened in z, re-matched to maintain correct path difference
New BC2E/P Optics (R 56 = 5mm) BC2E BC2P 12.15 6 x,y [m] 1 8 6 4 2 5 1 15 2 25 3 35 4 45 S [m] x y x.1.5 -.5 -.1 -.15 -.2 -.25 Dispersion [m] x,y [m] 5 4 3 2 1 1 2 3 4 S [m] x y x.2.1 -.1 -.2 Dispersion [m] Optics design meeting BC2 requirements
Improved Electron Beam Quality with New BC2E dp (%) 1.5 -.5-1 -1.5.1.2 Q (nc) rms dp/p = 1.3472 % rms Z = 1.2352 um dp/p (%) I (ka) Mean Energy = 1. GeV 1.5 -.5-1 -1.5 =.7 um I(pk) = 176.22 ka z 2 15 1 5 4 6 8 z ( m) 4 6 8 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) 4 2-2 = 6.3 um y y ( m) 4 2-2 -4.5.1 Q (nc) rms X = 7.1141 um rms Y = 16.1216 um Q = 2 nc Q (nc) -4.8.6.4.2-2 2 x ( m) = 6. um x -2 2 x ( m) Particle tracking demonstrates improved longitudinal and transverse beam quality @ S2 IP with increased peak current capability
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 profile @ IP σ x = 4 1 μm γε x = 7 22 μm-rad I pk = 7 3 ka
Beam Tracking with Upgraded FFS 5 = 9.6 um y 5 Mean Energy = 1. GeV 1 1 y ( m) y ( m) dp (%).5 -.5 dp/p (%).5 -.5 LH = 3 kev +FFS Spoilers -5.1.2.3 Q (nc) y ( m) 1-1 rms X = 1.9448 um rms Y = 9.94291 um Q = 1.1572 nc = 2.5 um y Q (nc) y ( m) -5.5.4.3.2.1 1-1 -5 5 x ( m) = 1.7 um x -5 5 x ( m) -1.1.2.3 Q (nc) rms dp/p =.723398 % rms Z = 2.1219 um dp (%) 2 1-1 I (ka) -1 = 1.9 um I(pk) = 72.39 ka z 8 6 4 2 dp/p (%) Mean Energy = 9.998 GeV 2 1-1 -5 5 1 15 z ( m) -5 5 1 15 z ( m) LH = 5 kev.2.4 Q (nc).4-4 -2 2 x ( m) = 6.4 um x.2.4.6 Q (nc) -2 2 4 z ( m) =.4 um I(pk) = 3.65 ka z 4 rms X = 9.76639 um rms Y = 3.2115 um Q = 1.15646 nc Q (nc).3.2 rms dp/p =.84943 % rms Z =.7443 um I (ka) 3 2.1 1-4 -2 2 x ( m) -2 2 4 z ( m)
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
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 ( - 9.14) = +/- 1 μm X / m 1.8.6.4.2 -.2 -.4 -.6 -.8 193 1935 194 1945 195 1955 196 1965 197 197 Z / m Path length adjustability within BC2P meets requirements
Independent Electron Witness Bunch Injector @ 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 25.78 degrees
Simulated Witness Injector Bunch
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 7 6 2 17 18 16 13 1 2 1 13 12 1.8 8 11 1 2 2 1.7.7 32,16 -- 5 -- 1, 1 -- 6, 8 -- 1.5,.5 -- 1 GeV BC2 Upgrade 176 --.8 -- 6 -- 7 -- 2 -- BC2+FFS Upgrade +L1X+COLL Witness Bunch Injector 3 --.4 -- 8 -- 22 -- 1.2 -- 3 -- 5 -- 7 -- 1.9 --.1 -- 1 MeV *LH = needs laser heater in injector, L1X = needs x-band harmonic cavity in L1, COLL = utilizes collimation in BC11 & BC14
Backup Slides
BC2E Compression Performance 2D CSR ε 4 5 7.5 1 => β @ A γ I r D N F L H ρ K > O > σ N I ε 4 A 3 + 2 3 24π 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] 1 1 1 1-1 1-2 (x) (analytic) Tracking with 1d CSR Tracking with 2d CSR 1-3 1 2 3 4 5 rms Bunch Length z [ m] Emittance growth [ m-rad] 1 1 1 1-1 1-2 (s) (analytic) (x) (analytic) Tracking with 1d CSR Tracking with 2d CSR 1-3 5 1 15 2 25 Peak Current [ka] Transverse component of CSR wake important for FACET-II @ 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