1. SCUs for the LCLS-II HXR FEL SCUs for the LCLS-II HXR FEL P. Emma, et. al. July 9, 2014 Hard X-Ray (HXR) FEL for LCLS-II must cover 1-5 keV (4-GeV) SASE to 5 keV is just possible (with no margin) Self-seeding with PMU not possible beyond 4 keV Radiation dose at 1 MHz threatens PMU fields (  K/K ~ 0.01%) SCU can extend photon range toward 8 keV (1 MHz), and beyond, can allow TW peak-power levels (120 Hz), and with much less sensitivity to radiation dose L2-Linac L3-Linac HXU SXU Sec. 21-30 LHBC1 BC2 BC3 D2 D10  -wall 0.65 m 0.93 m 2.50 m L1 “kicker” LTUH LTUS LCLS-I Linac P e  120 kW P e  250 kW L u  145 m

2. PMU NbTi Nb 3 Sn g = 5 mm g = 4 mm E = 4.0 GeV (nominal) 145 m  x,y = 0.40  m I pk = 1 kA  E = 500 keV  = 16 m 20% L u margin 3.4-m seg’s 1.0-m breaks 1 und. missing 1.5 keV low-lim.  x,y = 0.40  m I pk = 1 kA  E = 500 keV  = 16 m 20% L u margin 3.4-m seg’s 1.0-m breaks 1 und. missing 1.5 keV low-lim. magnetic gap is 2.3 mm larger than vac. gap, g 7.6 keV SASE 4.8 keV SASE 6.8 keV SASE u = 25.6 mm, 18.4 mm, 16.8 mm K = 0.6-2.4, 1.1-3.0, 1.3-3.2 B = 0.2-1.0 T, 0.6-1.8 T, 0.8-2.0 T

3. PMU NbTi Nb 3 Sn g = 5 mm g = 4 mm E = 4.2 GeV (stretch) 8.2 keV SASE 145 m u = 25.6 mm, 18.4 mm, 16.8 mm ~7 keV HXRSS limit  x,y = 0.40  m I pk = 1 kA  E = 500 keV  = 16 m 20% L u margin 3.4-m seg’s 1.0-m breaks 1 und. missing  x,y = 0.40  m I pk = 1 kA  E = 500 keV  = 16 m 20% L u margin 3.4-m seg’s 1.0-m breaks 1 und. missing magnetic gap is 2.3 mm larger than vac. gap, g

4. E = 4.8 GeV (20% upgrade) 10 keV SASE PMU NbTi Nb 3 Sn g = 5 mm g = 4 mm 145 m u = 25.6 mm, 18.4 mm, 16.8 mm 8.3 keV HXRSS limit magnetic gap is 2.3 mm larger than vac. gap, g

5. P (TW) z (m) Add field taper to SCU TeraWatt Peak Power Possible C. Emma, C. Pellegrini, Z. Huang  1.2 TW Nb3Sn g m = 7.2 mm  = 0.4 um E = 7.8 GeV f = 120 Hz I pk = 4 kA

6. Possible SCU Layout in LCLS-II (HXR) Joel Fuerst, ANL

7. Joining Three 1.5-m Magnets into a Single 4.5-m Device Magnets conduction cooled through gap separation extrusion Gap separation ensures “seamless” core-to-core joint Core center channels may be omitted

14. End corrector Phase shifter dipole Alignment verification quads and B x correction LbLbLbLb LbLb Second Field Integral with phase shifter +k+k +k+k -2k Compact phase shifter uses one end corrector from each undulator and one extra dipole magnet in between Distance between the undulator cores ~13 cm for this layout (could be reduced if alignment quadrupoles are not necessary) Joint sections for Nb 3 Sn undulator are 4 cm long for each core Joining Two 1.5-m Segments (13 cm extra)

15. Cold Break (quadrupole magnet) Conceptual design of a compact quadrupole magnet at breaks – Directly attached to undulator cold mass – Integrated quadrupole strength of 4 T (LCLS-II) can be obtained – Independently powered coils can be used for x-field correction End corrector Quadrupole Magnet

16. Vertical Alignment with Alignment Quadrupoles Use reference quads at each end of ~3-m structure – Tuning and calibration based on line between magnetic center of two quads – Fiducialization performed with stretched wire measurement and referenced to fiducials on outside of cryostat – Allows for beam based alignment by moving cryostat to find center of quads with electron beam Small Alignment Quad Full Length Quadrupole

17. DC Resistive-Wall Wakefield (cold bore & warm) cold bore warm bore Cu Al Cu Al

18. Undulator Parameters (4 GeV)

19. SCU Advantages Dramatically improved HXR-FEL performance (~7 keV with SC- Linac & 1-TW with Cu-Linac) Orders of magnitude less radiation dose sensitivity (1 MW!) No mechanical motion (DC power supply drives each segment) Less tunnel space required – looks like LCLS-I und. (?) Can easily be arranged as vertical polarizer (hor. fields) Cryo-plant (4.5K, 280 W) might serve as injector stand-in at 2K (7.5M$) – cryo-dist. system not incl. Might drop 5 linac CM’s (3.4 GeV) and still get 5 keV (Ti or Sn)? Or drop 10 linac CM’s (2.8 GeV) and still get 4 keV (Sn only)?

20. 1.What decision criterion should be used to make this technology decision in 2015. 2.What is the impact on the LCLS-II project schedule and what additional resources are needed to develop production SCUs and install them by the same April 2018 date presently planned for the PMUs? 3.What other subsystems would have to be developed / designed / specified and become part of the baseline? How would they fit into the facility / tunnel? 4.What other reviews would we have to organize before this could become baseline? 5.What other assurance would you want as the project director before you can support the change? Questions