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LCLS-IISC Undulator Options Present Status 08/24/2013

LCLS-IISC Undulator Options Present Status 08/24/2013. Heinz-Dieter Nuhn, Tor Raubenheimer , Juhao Wu. Outline. Assumed beam parameters and undulator requirements Baseline undulator parameters LCLS performance with HXR Short gain length options for SXR SCU options and benefits

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LCLS-IISC Undulator Options Present Status 08/24/2013

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  1. LCLS-IISC Undulator OptionsPresent Status 08/24/2013 • Heinz-Dieter Nuhn, Tor Raubenheimer, Juhao Wu

  2. Outline Insert Presentation Title in Slide Master Assumed beam parameters and undulator requirements Baseline undulator parameters LCLS performance with HXR Short gain length options for SXR SCU options and benefits Genesis simulations Caveats: not all simulation/calculations are done for exactly the same period devices and parameters but they are similar and can be scaled to understand parameter the space

  3. Assumed FEL Configuration Insert Presentation Title in Slide Master • High rep rate beam could be directed to either of two undulators HXR or SXR bunch-by-bunch • 120 Hz beam could be directed to the HXR at separate times • The SC linac would be located in Sectors 0-10 and would be transported to BSY in the 2km long Bypass Line. It would use a dual stage bunch compressor. • A dechirper might be used to further cancel energy spread for greater flexibility in beam parameters • The high rep rate beam energy would be 4 GeV and the HXR would fill the LCLS hall with ~144 m while the SXR would be <75 m so that it could be fit into ESA • Both undulators would need to support self-seeding as well as other seeding upgrades

  4. Assumed Beam Parameters Insert Presentation Title in Slide Master The assumed emittance of 0.43 at 100 pC is roughly 25% larger than the LCLS-II baseline. It is more conservative than the NLS or the scaled NGLS values (the latter are consistent with the LCLS-II baseline) however a gun has not yet been demonstrated that achieves the desired emittances. Reduced emittances will decrease gain lengths. Peak current is consistent with higher energy beams and BC’s

  5. High Level Parameters from David Schultz Table Insert Presentation Title in Slide Master

  6. Undulator Requirements Insert Presentation Title in Slide Master Requirements: SXR self-seeding operation between 0.2 and 1.3 keV in ESA tunnel (<75 meters) with 2.5 to 4 GeV beam HXR self-seeding operation between 1.3 and 4 keV in LCLS tunnel (~144 meters) with 4 GeV beam HXR SASE operation up to 5 keV with 4 GeV beam Primary operation of SXR and TXR at constant beam energy  large K variation HXR operation comparable to present LCLS with 2 to 15 GeV beam

  7. Undulator Parameters Insert Presentation Title in Slide Master • To cover the range of 0.2 to 1.3 keV using SASE in less than 50 meters (to allow for seeding)  lw ~ 40 mm • A conventional hybrid undulator with 40 mm and a 7.2 mm minimum gap would have Kmax ~ 6.0 which easily covers the desired wavelength range at 4 GeV • To achieve 5 keV using SASE with less than 144 meters at 4 GeV  TXR lw <= 26 mm • A conventional hybrid undulator with 26 mm and a 7.2 mm minimum gap would have Kmax ~ 2.4 which covers desired wavelength range at 4 GeV • Provides reasonable performance with LCLS beam

  8. Baseline Tuning Range for 4 GeV Kmin = 0.55 SASE HXR: lw = 26 mm, L = 144 m SXR: lw = 41 mm, L = 75 m Self-Seeding Kmin = 0.91 Ephoton[keV] Kmin = 1.6 Self-Seeding Kmax = 2.44 Kmax = 6.0 Ebeam [GeV] Kmin is chosen to saturate within given length for SASE or Self-seeding Kmaxis set to the maximum value for a 7.2 mm gap variable gap undulator

  9. X-ray pulse energy at High Rate More than enough FEL poweralthough results assume fullbeam and are ~2x optimistic Insert Presentation Title in Slide Master

  10. Comparison of HXR with LCLS performance at 120 Hz (1) 26 mm HXR covers 2 keV at ~4 GeV to 30+ keV at 14 GeV – beam energy might be reduced futher ifdesired Insert Presentation Title in Slide Master

  11. Comparison of HXR with LCLS performance at 120 Hz (2) 26 mm HXR provideslower pulse energy than 30 mm LCLS Insert Presentation Title in Slide Master

  12. Options for HXR: SCU, IV, or 30 mm period (1) Insert Presentation Title in Slide Master To recover the LCLS performance, we need to increase K. Can (1) increase the period, (2) adopt an in-vacuum design, or (3) consider a planar or helical SCU. Example of ahelical SCU below howeverhave not incuded poorerSCU fill factor results areoptimistic

  13. Options for HXR: SCU, IV, or 30 mm period (2) Insert Presentation Title in Slide Master Example of a 30 mm period hybrid undulator below. Nearly recovers LCLS performance (reduction due to slightlylarger gap with VG undulator) however the maximum photon energy at highrate, i.e, 4 GeVis now 4.3 keV not5 keV as with 26 mm period

  14. Short Gain Length Options for SXR Insert Presentation Title in Slide Master The full length of 75 m will be tight in ESA at the maximum photon energy of 1.3 keV and provides little margin. There are three options: (1) lower the beam emittance through either a better injector (LCLS comparable – see slide 4), (2) decrease the SXR period and increase K, or (3) decrease the beam energy and the SXR period. Example 1: decrease to 26 mm with K=2.4  gain length roughly ½ but almost all tuning is done with energy Example 2: decrease to 30 mm with K=2.0  self-seeding at 1.6 keV and 4 GeV requires ~65 meters Problem: a shorter period conventional hybrid SXR will not cover the full wavelength range at constant energy  SCU

  15. SCU options Insert Presentation Title in Slide Master • An SCU has a number of benefits: • Would attain comparable performance as LCLS even while achieving 5 keV at 4 GeV at high rate by operating with high K • Would reduce allow shorter SXR period to reduce SXR beam energy and gain length to ensure space in ESA while still covering full wavelength range at constant energy.

  16. GENESIS SIMULATION Electron parameters Good Bad Good Barely Good OK J. Wu (SLAC), jhwu@slac.stanford.edu, 08/05/2013 • Centroid energy 4 GeV; 100 pC compressed to 1 kA; normailizedemittance: 0.45 mrad; slice energy spread: sE = 300 keV except for LCLS case with 15 GeV • 6 cases – details in following pages • Case 1: HXR Kmin = 0.91; lw = 26 mm; Lw = 144 m (study SS 4keV) • Case 2: SXR Kmin = 1.6; lw = 41 mm; Lw = 75 m (study 1.6 keV) • Case 3: SXR Kmax= 6.0; lw = 41 mm; Lw = 75 m (study 200 eV) • Case 4: SXR K = 1.9; lw = 41 mm; Lw = 75 m (study 1.3 keV) • Case 5: SXR K = 2.0; lw = 30 mm; Lw = 75 m (short gain len.) • Case 6: HXR in LCLS TW parameters but K too high for hybrid undulator

  17. Summary Insert Presentation Title in Slide Master Present parameters based on: HXR: 26 mm, 144 meters hybrid VG SXR: ~40 mm, 75 meters hybrid VG (simulations for 41 and 39 mm – either work). Both choices have limitations: SXR gain length is too long to guarentee self-seeded operation at 1.6 keV in ESA (barely works at 1.3 keV) HXR does not reproduce LCLS performance Shorter period SXR and longer period HXR fix some issues but introduce others. SCU solves many limitations.

  18. Case 1: HXR shortest seeding wavelength J. Wu (SLAC), jhwu@slac.stanford.edu, 08/05/2013 • Case 2: HXR Kmin = 0.91; lw = 26 mm; Lw = 144 m • SASE: saturates around 70 m

  19. Case 1: Self-seeding OK at 4 keV Monochromator J. Wu (SLAC), jhwu@slac.stanford.edu, 08/05/2013 • Case 1: HXR Kmin = 0.91; lw = 26 mm; Lw = 144 m • Self-seeding: will saturates

  20. Case 2: SXR 1.6 keV J. Wu (SLAC), jhwu@slac.stanford.edu, 08/05/2013 • Case 2: SXR Kmin = 1.6; lw = 41 mm; Lw = 75 m • SASE: saturates around 60 m

  21. Case 2: SXR self-seeding not OK at 1.6 keV Monochromator J. Wu (SLAC), jhwu@slac.stanford.edu, 08/05/2013 • Case 2: SXR Kmin = 1.6; lw = 41 mm; Lw = 75 m • Self-seeding: won’t saturates

  22. Case 3: SXR at 200 eV – short gain length J. Wu (SLAC), jhwu@slac.stanford.edu, 08/05/2013 • Case 3: SXR Kmax = 6.0; lw = 41 mm; Lw = 75 m • SASE: saturates around 35 m

  23. Case 3: 200eV self-seeding fine Monochromator J. Wu (SLAC), jhwu@slac.stanford.edu, 08/05/2013 • Case 3: SXR Kmax = 6.0; lw = 41 mm; Lw = 75 m • Self-seeding: will saturates

  24. Case 4: SXR at 1.3 keV J. Wu (SLAC), jhwu@slac.stanford.edu, 08/05/2013 • Case 5: SXR Kmin = 1.9; lw = 41 mm; Lw = 75 m • SASE: saturates around 55 m

  25. Case 4: SXR at 1.3 kev barely OK for self-seeding Monochromator J. Wu (SLAC), jhwu@slac.stanford.edu, 08/05/2013 • Case 5: SXR Kmin = 1.9; lw = 41 mm; Lw = 75 m • Self-seeding: barely saturates

  26. Case 5: alternate SXR for shorter gain length J. Wu (SLAC), jhwu@slac.stanford.edu, 08/05/2013 • Case 4: SXR Kmax = 2.0; lw = 30 mm; Lw = 75 m • SASE: saturates around 45 m

  27. Case 5: alternate sxr for shorter gain length Monochromator J. Wu (SLAC), jhwu@slac.stanford.edu, 08/05/2013 • Case 4: SXR Kmax = 2.0; lw = 30 mm; Lw = 75 m • Self-seeding: will saturates

  28. Case 6: HXR with 15 GeV beam – K not realistic Centroid energy 15 GeV; 150 pC compressed to 3 kA; normailized emittance: 0.4 mrad; slice energy spread: sE = 1.3 MeV J. Wu (SLAC), jhwu@slac.stanford.edu, 08/05/2013 • Case 1: HXR K = 4.2; lw = 26 mm; Lw = 144 m • SASE: saturates around 50 m

  29. Case 6: HXR at 15 GeV but K not realistic Monochromator J. Wu (SLAC), jhwu@slac.stanford.edu, 08/05/2013 • Case 1: HXR K = 4.2; lw = 26 mm; Lw = 144 m • Self-seeding: reaching about 500 GW

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