1. LCLS-II-HE FEL Facility Overview
Tor Raubenheimer
LCLS-II-HE “1st Experiments” meeting, October 30-31, 2017

2. LCLS and LCLS-II Overview LCLS-II-HE Concept
Outline
LCLS and LCLS-II Overview
LCLS-II-HE Concept
Performance and Operating Modes
LCLS-II-HE 1st Exp. Meeting, October 30-31, 2017

3. Introduction LCLS-II starts from the LCLS X-ray FEL
The LCLS is the world’s 1st x-ray Free Electron Laser (FEL)
LCLS electron source is the SLAC Cu linac
Includes one fixed gap undulator
Six experimental stations
Before discussing the LCLS-II, I should note that the LCLS-II will build on the LCLS which started operation in 2009 and formally completed in The LCLS uses the last 1/3 of the SLAC copper linac to generate a beam energy as high as 15 GeV and can cover the X-ray wavelengtths from 250 to 11k eV. It uses a single fixed gap undulator that is roughly 130 meters long and supplies x-rays to 6 experimental stations.
X-ray Range
250 to 12,600 eV
FEL Pulse Length
< fs
FEL Pulse Energy
~3 mJ (2 * 10 keV)
Repetition Rate
120 Hz

4. Linac Coherent Light Source Facility
New SCRF linac and injector in 1st km of SLAC linac tunnel
and LCLS-II Upgrade
(1st light 2020)
Injector at 2-km point
Existing Linac (1 km)
(with modifications)
Electron Transfer Line (340 m)
Undulators (130 m)
Near Experiment Hall
The LCLS-II upgrade project was formally initiated with a CD0 in 2010 as the LCLS constyruction was finishing. The initial implementation of the LCLS-II involved re-using the middle 1/3 of the SLAC linac and supplying x-rays to another experimental hall. In the summer of 2013, BESAC suggested that greater scientific impact could be made with high rate x-rays with an energy as high as 5 keV and the project was redirected. The present design is illustrated here.
X-ray Transport Line (200 m)
LCLS-II-HE 1st Exp. Meeting, October 30-31, 2017
Far Experiment Hall

5. LCLS-II X-ray Coverage Using SASE and Self-Seeding
2-15 GeV Electron Beam
LCLS-I
Cu Linac
LCLS-II SASE
LCLS-II Self-Seeding
SASE
SC Linac
High Rep Rate
4.0 GeV Electron Beam
Self-Seeding 5 10 15 20 25
Photon Energy (keV)
Future expansion options
External seeding below 1 keV
Self seeding between keV
X-rays beyond 5 keV from the SCRF linac with >4 GeV beam energy
Additional FEL’s using 1.2 MW e-
Legend
Cu SASE
Cu Self Seeded
High Rep Rate SASE
Self Seeded (Grating)
LCLS-II-HE 1st Exp. Meeting, October 30-31, 2017

6. LCLS-II Accelerator Layout New Superconducting Linac  LCLS Undulator Hall
Two sources: MHz rate SCRF linac and 120 Hz Cu LCLS-I linac
Hard and Soft X-ray undulators can operate simultaneously in any mode
SCRF beam destination controlled with fast (ms) magnetic deflector
Undulator
SC Linac (up to 1 MHz)
Cu Linac (up to 120Hz)
Soft X-ray
keV
with >> 20 Watts
Hard X-ray
keV
with > 20 Watts
keV
with mJ-class X-ray pulses
HXU
SXU
Sec
Sec
keV (1 MHz)
SCRF
4 GeV
1-25 keV (120 Hz)
1-5 keV (1 MHz)
LCLS-I Linac
GeV
proposed
FACET-II
LCLS-II Linac
1 km
2 km
1 km
LCLS-II-HE 1st Exp. Meeting, October 30-31, 2017

7. LCLS-II Cryomodule 35 new 1
LCLS-II Cryomodule 35 new 1.3 GHz Crymodules to be installed in SLAC linac tunnel
Cryomodule components will be from industry and will be assembled at Fermilab and JLAB
12 meters
CM to be fabricated at FNAL and JLab; Prototypes are being assembled and tested through Installation 2018.
LCLS-II-HE 1st Exp. Meeting, October 30-31, 2017

8. Variable Gap Hybrid Undulators Will install two new undulators in Hall
Variable gap undulators used in LCLS-II to provide greater wavelength tuning flexibility: standard vertical gap for SXR and a horizontal gap Vertically Polarized Undulator for HXR.
LCLS-II-HE 1st Exp. Meeting, October 30-31, 2017

9. LCLS-II Undulator Layout Replace Existing LCLS Undulator with HXR and add SXR
21 SXU Segments
32 HXU Segments
Space for polarization upgrade
Space for future upgrades
Existing Diamond Crystal Self-Seeding System
New SXR Self-Seeding System for High Power Loads
LCLS-II-HE 1st Exp. Meeting, October 30-31, 2017

10. LCLS-II High Energy Upgrade Possible LCLS-II extension to go from 5 keV  12.8 keV or more
Left space in the LCLS-II for additional cryomodules  Add 20 additional cryomodules and 2nd bypass Three independent sources: CuRF 2-15 GeV, 120 Hz; LCLS-II: 3-4 GeV, 31 mA; LCLS-II-HE: 3-8 GeV, 31 mA
LCLS-II-HE 1st Exp. Meeting, October 30-31, 2017

11. LCLS-II-HE Goals Build on LCLS-II Performance Goals
Hard X-rays at 1 – 13 keV with the possibility of approaching 20 keV
Soft X-rays at 0.2 – 1.3 keV or 1 – 5 keV at the same time as the production of hard X- rays
Hard X-ray (as well as soft X-ray) self-seeding at MHz-rates
The hard X-ray beamlines and instruments will be upgraded to maximize the science from the MHz-rate high energy FEL beams
Hard X-ray experimental hall (FEH) will be modified to incorporate an additional experimental instrument
The performance of LCLS and LCLS-II operational modes and techniques will not be negatively impacted by the LCLS-II-HE upgrade
LCLS-II-HE 1st Exp. Meeting, October 30-31, 2017

12. LCLS-II-HE X-ray Performance
LCLS-II-HE will extend the performance from the SCRF linac substantially (total power limited <200W)
SCRF Linac with ~1 MHz rate
CuRF Linac with 120 Hz rate
̶ SXR
̶ HXR
Undulators will also produce %-level 3rd harmonic radiation out to ~30 keV
LCLS-II-HE 1st Exp. Meeting, October 30-31, 2017
LCLS-II-HE 1st Exp. Meeting, October 30-31, 2017

13. Analytic Estimate of Power at the 3rd Harmonic Without post-saturation taper
Expect result is robust through ~30 keV but degrades faster above
LCLS-II-HE 1st Exp. Meeting, October 30-31, 2017

14. Start-2-End Simulation Results
Examples at 8 and 13 keV
Fundamental Energy
8 keV
13 keV
Unit s
Maximum Repetition Rate
929 (300)
kHz
FW Pulse Duration
30 (105)
30 (102) fs
Total energy/pulse
235 (625)
108 (57) mJ
Source point relative to end of undulator
25 (19)
24 (21) m
First Harmonic
Photons per FEL pulse
0.18 (0.49)
(0.028)
1012
Relative FWHM Bandwidth
0.05 (0.09)
0.06(0.1) %
FWHM Source Size
36 (37)
26 (22) 𝜇m
FWHM Source Divergence
2.4 (2.0)
1.8 (1.8)
𝜇rad
Third Harmonic
0.15 (0.29)
(0.005)
1010
0.06 (0.1)
<36 (<37)
<26 (<22)
<2.4 (<2.0)
<1.8 (<1.8)
20 pC, 13 keV
100 pC, 8 keV
LCLS-II-HE 1st Exp. Meeting, October 30-31, 2017

15. LCLS-II / LCLS-II-HE X-ray Configurations
Photon Energy ( keV & 1-25 keV)
1% is fast using e- energy (10 ms)
Full range uses gap control (5 min.)
Cu-Linac is slow if Dl/l > 10% (15-30 min)
Use energy or gap for Cu-Linac (3-15 GeV)
Pulse Duration
fs (slow changes: 1-2 hrs)
Use of slotted-foil may limit beam rate
Cu-Linac as existing (1-min., fs)
< 10 fs with reduced bunch charge
Beam Rate (< 1 MHz & 120 Hz)
Trigger fast kickers (sec)
May be set from ‘one-shot’ to 1 MHz
Total beam power < 240 kW/FEL (rate limit)
FEL Pulse Energy
Up to 8 mJ (250-fs pulse, 800 W, 250 eV)
Up to 6 mJ (3-6 keV is best), 3-4 mJ typical
Fast kickers allow quick switching
1 s
LCLS-II-HE 1st Exp. Meeting, October 30-31, 2017

16. LCLS-II-HE Operating Modes
Spreader kickers allow flexible bunch patterns to SXR and HXR
SXR choices
HXR SC-Linac options or
HXR Cu-Linac options
3.8 GeV
< 31 mA e-
SC-Linac (< 1 MHz)
keV with >> 20 W
3-8 GeV
1-13 keV with >20 W
3-15 GeV (3-10 GeV if CuRFSXR)
( 120Hz)
1-25 keV with mJ pulses
0.2-5 keV with >> 20 W
3-10 GeV
Cu-Linac ( 120Hz)
keV with mJ pulses
LCLS-II-HE 1st Exp. Meeting, October 30-31, 2017

17. Photon Energy Upgrade Options
Reduced emittance, higher peak current, and/or higher energy can enable 17 ~ 18 keV. Shorter undulator period can do similar.
LCLS-II-HE 1st Exp. Meeting, October 30-31, 2017

18. LCLS-II-HE X-ray Pulse Energy
Expected performance, including post-saturation taper, with improved injector is illustrated in green
LCLS-II-HE 1st Exp. Meeting, October 30-31, 2017

19. LCLS-II-HE Brightness
Brightness of LCLS-II-HE will exceed 1025 at 12.8 keV and extend out to >20 keV with additional injector improvements
LCLS-II-HE 1st Exp. Meeting, October 30-31, 2017

20. LCLS-II-HE Conceptual Design Report
Chapter
Title
Preface
Introduction 1
Project Summary, Background, & Mission Need 2
Scientific Opportunities 3
Project Overview 4
Accelerator Parameters & FEL Performance 5
LCLS-II-HE FEL Layout 6
SRF Linac Systems 7
Electron Transport 8
Photon Transport and Diagnostics 9
Experimental Instruments 10
Controls and Safety Systems 11
Data Systems 12
Infrastructure and Facilities 13
Radialogical Considerations 14
Environment, Safety, Health 15
Upgrade Opportunities
App. A
LCLS-II-HE Key Parameters
>30 SLAC staff members contributed to the CDR.
LCLS-II-HE 1st Exp. Meeting, October 30-31, 2017
CDR Sept 24.pdf

21. External CDR Review – Oct. 27, 2017

22. Summary
LCLS-II on track to deliver MHz-rate FEL X-ray’s from 0.2 to 5 keV with commissioning in 2020
LCLS-II-HE uses capacity designed into LCLS-II to double electron beam energy and increase spectral reach >12.8 keV
R&D program to electron beam brightness will further increase spectral range to ~20 keV
Capabilities developed at LCLS should be available at LCLS-II and LCLS-II-HE
LCLS-II-HE 1st Exp. Meeting, October 30-31, 2017