#### Transcript bunch-com

A bunch compressor design and several X-band FELs Yipeng Sun, ARD/SLAC 2011-04-13, LCLS-II meeting Design of two bunch compressors Presentation Title Page 2 Magnetic bunch compression Bunch L phase space e- source 3-Dip. Chicane RF Energy modulation (correlation): RF structure, laser, wake field etc. Bunch compression Page 3 Dispersive region: chicane, wiggler arc, dogleg etc. Different bunch compressors 3(4) dipole chicane, R56 <0, T566 >0 achromatic to any order Wiggler, R56 <0, T566 >0 achromatic to any order? Arc, R56 >0, T566 >0 2-Dip. Dogleg w/ quad+sextupole, R56 >0, T566 tunable Chicane w/ quadrupole+sextupole, R56 tunable, T566 tunable NLCTA chicane shape Dispersion relations Bunch compression Page 5 Bunch compressor with dipoles and drifts Bunch compression Page 6 General chicane (1) Bunch compression Page 7 General chicane (1) Bunch compression Page 8 General chicane (2) Bunch compression Page 9 General chicane (2) Bunch compression Page 10 An FEL with LCLS injector (S-band+X-band harmonic) Plus X-band Linac2 and Linac3 Presentation Title Page 11 Scaling 250-10pC Total length of accelerator Assume 70% RF in linac Final bunch length versus bunch charge Presentation Title Page 12 Longitudinal wake potential 'long' range Presentation Title Page 13 Linac3 length needed for de-chirp after BC2 Presentation Title Page 14 Accelerator shape (LCLS injector + X-band) Presentation Title Page 15 LiTrack, LCLS, 250pC, 3kA Presentation Title Page 16 LiTrack, LCLS injector+X-band, 250pC, 3kA Presentation Title Page 17 Optics LCLS LCLS-Injector + X-band Presentation Title Page 18 Elegant simulation, 250 pC, 3 kA (w/ and w/o CSR) LCLS LCLS w/o CSR Presentation Title Page 19 Elegant simulation, 250 pC, 3 kA LCLS LCLS-Injector + X-band (½ R56 in BC2, 0.7 bending angle Presentation Title Page 20 Elegant simulation, 250 pC, 5 kA LCLS (L3, 30degree) LCLS-Injector + X-band (½ R56 in BC2, 0.7 bending angle) Presentation Title Page 21 Elegant simulation, 250 pC, 5 kA, Projected emittance LCLS (L3, 30degree) LCLS-Injector + X-band (½ R56 in BC2, 0.7 bending angle) Presentation Title Page 22 Elegant simulation, 250 pC, 5 kA, Trajectory LCLS (L3, 30degree) LCLS-Injector + X-band (½ R56 in BC2, 0.7 bending angle) Presentation Title Page 23 LCLS-Injector + X-band (0.5 R56 in BC2, 0.7 bending angle), 250 pC, 5 kA BC1 end BC2 entrance BC2 end Presentation Title Page 24 Linac3 end Potential X-band advantage over S-band •Maintain a flat energy profile when pushing for shorter bunch length and higher peak current (i.e. 6kA at 250pC), due to stronger X-band longitudinal wake in Linac3, to remove energy correlation (chirp); plus possible cancellation of nonlinear chirp between RF, wake and CSR effects. •Similar or smaller CSR emittance growth in BC2, benefiting from a weaker dipole and a larger energy correlation generated in Linac2 (previous argument) •Compact (300m vs 1000m, at 14GeV) •For LCLS, increasing current from 3kA to 6kA requires a smaller L1 phase to generate a longer bunch in ~400m Linac2, so that the L wake chirp is much smaller, and the bunch is compressed more in BC2 with same L2 phase; if keeping similar L1 phase and increasing L2 phase (i.e. from 36d to 37.5), the final energy profile will be very nonlinear. Presentation Title Page 25 Elegant simulation, 250 pC, 5 kA LCLS (L1, 19degree; L2, 36degree; L3, 30degree) LCLS (L1, 22degree; L2, 37.5degree; L3, 0degree) Presentation Title Page 26 An X-band RF based FEL with optics linearization 250 pC Presentation Title Page 27 Bunch length after compression Final coordinate (square) Minimum length Neglect small initial un-correlated energy spread 1st order optimal compression: 2nd order optimal compression: 3rd order optimal compression: Bunch compression Page 28 Full compression using optics linearization 1st order dispersion 2nd order dispersion 3rd order dispersion Bunch compression Page 29 Minimize CSR (1) short interaction time Bunch compression Page 30 New design BC1 (1) first order B1 0.2m 7 degree B2 0.2m 3 degree QF QD R56 = 17 mm B3 0.2m -3 degree B4 0.2m -7 degree New design BC1 (2) second order SF1&2 SD1&2 T166 = T266 = 0; symmetric K3(SF1) = -K3(SD2) K3(SF2) = -K3(SD1) T566 = 170 mm Minimize CSR (2) phase space matching general X’ X’ CSR CSR X’ specific CSR Large β x Small β x Optimal β and α x Optimized to minimize CSR impact on emittance Bunch compression Page 33 X-band based 2 stage FEL (1) 250pc, 300micron Bunch compression Page 34 Final profile at 7GeV (collimation in middle of BC1) Presentation Title Page 35 Slice emittance evolution, 250 pC, 6 kA BC1 entrance BC1 end BC2 entrance Presentation Title Page 36 Linac3 end An X-band RF based FEL with normal chicane BC 10 pC Presentation Title Page 37 Max bunch length w/o harmonic RF Bunch compression Page 38 Bunch compressor and linac design BC1 BC2 Bunch compression Page 39 Linac cell X-band based 2 stage FEL (3) 10pc, 40micron 54 MeV (C. Limborg) 6 GeV FEL simulation Setup • FEL at 2 keV , 6 Å (FEL at 8 keV, 1.5 Å) • Electron Charge 10 pC, Centroid Energy 6 GeV, peak current 3 kA with profile as shown in previous slides – S2E file down to undulator entrance • LCLS Undulator with larger gap lw = 3 cm (1.5 cm); beta-function ~ 15 m Juhao Wu FEL performance 1.5 angstrom 6 angstrom Juhao Wu Presentation Title Page 42 BC parameters summary Bunch compression Page 43 Possible test at NLCTA Presentation Title Page 44 Motivation and simulation condition Motivation oDemonstrate effective bunch compression (5 to 10 times) with x-band RF Scheme 1: use normal chicane + positive RF chirp (current NLCTA) Scheme 2: use optics w/ higher order dispersion + positive/negative RF chirp (need to install 4/6 sextupoles in the big chicane) oInvestigate tolerances on timing jitter, misalignment etc.; emittance growth Simulation condition: In Elegant, including transverse and longitudinal wake, coherent synchrotron radiation (CSR), longitudinal space charge (LSC) and velocity bunching 0.5 million macro-particles For scheme 1, current operating optics For scheme 2, new optics 20 pC beam at 5MeV, 0.5ps RMS bunch length, 5e-3 RMS energy spread, 1 m.mrad transverse emittance Beam energy: 60 MeV at BC1, 120 MeV at BC2 Bunch compression Page 45 NLCTA optics (current operation) R56 =-73mm T566 = 111mm R56 =-10mm T566 = 15mm Bunch compression Page 46 Scheme 1 (1) L phase, current and bunch length Initial Linac1 BC1 Linac2 Bunch compression Page 47 BC2 Scheme 1 (2) no compression, on crest Initial Linac1 BC1 Linac2 Bunch compression Page 48 BC2 Scheme 1 (3) 2 stage compress 20 times, end Bunch compression Page 49 Scheme 1 (4) effect of timing jitter, near full compression Timing jitter between laser and RF (assumed same for two RF sections) On phase + 115 fs (0.5 degree) Bunch compression Page 50 - 115 fs Scheme 1 (5) effect of timing jitter, under compression Timing jitter between laser and RF (assumed same for two RF sections) On phase + 115 fs (0.5 degree) Bunch compression Page 51 - 115 fs Scheme 2 (1) optics Install 4/6 sextupoles in the big chicane 6 meters long Chicane w/ quadrupole+sextupole, R56 tunable, T566 tunable Bunch compression Page 52 Scheme 2 (2) L phase and current Bunch compression Page 53 Scheme 2 (3) 1 stage compress 10 times, end Bunch compression Page 54 Scheme 2 (4) Sensitivity to timing jitter Deviation between analytical formulae and simulation due to: Small difference of beam(RF) parameters being employed Collective effects in simulation Bunch compression Page 55 Thank you for your patience! I would like to thank the following people for their great help and useful discussions: C. Adolphsen , K. Bane, A. Chao, Y. Cai, Y. Ding, J. England, P. Emma, Z. Huang, C. Limborg, Y. Jiao, Y. Nosochkov, T. Raubenheimer, M. Woodley, W. Wan, J. Wu Bunch compression Page 56 Current less sensitive to RF phase jitter 20pC, 80 micron Bunch compression Page 57 LCLS 150 MeV z 0.83 mm 0.10 % 6 MeV z 0.83 mm 0.1 % rf gun Lh L =0.6 m rf=-160 250 MeV z 0.19 mm 1.8 % ...existing linac L1 DL-1 L =12 m R56 0 13.6 GeV z 0.022 mm 0.01 % Paul Emma L =9 m rf = -25° L =6 m 4.3 GeV z 0.022 mm 0.76 % X L =330 m rf = -41° L =550 m rf = -10° L2 L3 BC-1 L =6 m R56= -36 mm BC-2 L =22 m R56= -25 mm undulator L =120 m DL-2 L =66 m R56 = 0 TESLA-XFEL 6 MeV z 2.0 mm 0.1 % 120 MeV z 0.5 mm Lh 2.0 % L =1.4 m rf= -191 L=8m rf -22° rf gun L0 C L = 16 m rf = -40° L1 375 MeV z 0.1 mm 1.4 % 1.64 GeV z 0.020 mm 0.5 % 20.5 GeV z 0.020 mm 0.01 % L = 72 m rf = -40° L 850 m rf = 0° L2 L3 BC-1 BC-2 L4m L 14 m R56= -76 mm R56= -36 mm undulator L =? m BC-3 L 18 m R56= -11 mm (2003 parameters) Energy change + optics (dispersion) (2) Emittance & trajectory (slice) For sufficiently large slice number, one can assume same energy change in one slice Change slice trajectory Other terms Change slice emittance CSR energy change + phase rotation (smear) Emittance & trajectory (slice) For over-compress, CSR-process can be treated as an integral process, with continuing bunch compression (lengthening). Change slice trajectory & emittance Negligible