1. LCLS-II Delta Undulator Study for SXR Polarization Control
James MacArthur for the Delta Team 6/3/15
James MacArthur for the Delta Team 6/3/15

2. Why Circular Light Magnetism Probing Chirality
Magnetic materials exhibit circular dichroism at L edges (XMCD)
Thalidomide – was used for morning sickness, handedness critical
Thalidomide: one handed verison of the molecule cured morning sickness, the other caused fetus deformities. Affected 10,000 babies in the late 50s.
Drug industry spends billions trying to make sure this doesn’t happen.
Amino acids are left handed, sugars right handed, we don’t know why
Very fast magnetic phenomena may be tested with the circular dichroism technique.

3. LCLS Solution: Delta Undulator
Axial View
4 magnet rows
4 magnets per period
Arbitrary polarization
3.2 m, 100 periods
Installed Sept 2014
Girder 33

4. Delta Undulator: Changing K
39 mm Magnetostatic simulation in radia, producing a K_eq of 5.5, matching the LCLS-II max K.
2 period simulation

5. Delta Undulator: Polarization Control

6. Basic Afterburner Layout
Planar Undulators:
Delta Undulators:
Seed radiation is decomposed into RCP and LCP
RCP interacts in Delta, LCP goes through
Degree of Circular Polarization:

7. Example Simulation Planar Undulators: Delta Undulators:
higher power contrast = better s3/s0

8. Simulation Conditions
Genesis 1.3 time dependent simulations
Ideal beam
4 GeV
0.4 MeV energy spread
0.4 um emittance
1 kA peak current (no horns)

9. Simulation Results 1 nm, no Taper 1 x DELTA 2 x DELTA 3 x DELTA
7 Planar
0.02 GW/ 0.80
0.12 GW/ 0.96
0.58 GW/ 0.99
8 Planar
0.09 GW/ 0.81
0.46 GW/ 0.96
1.55 GW/ 0.99
9 Planar
0.38 GW/ 0.80
1.46 GW/ 0.95
2.92 GW/ 0.97
10 Planar
1.24 GW/ 0.76
3.00 GW/ 0.90
3.60 GW/ 0.92
2 nm, no Taper
1 x DELTA
2 x DELTA
3 x DELTA
5 Planar
0.02 GW/ 0.89
0.16 GW/ 0.99
1.35 GW/ 1.00
6 Planar
0.13 GW/ 0.90
1.00 GW/ 0.99
3.41 GW/ 1.00
7 Planar
0.60 GW/ 0.90
2.92 GW/ 0.98
4.65 GW/ 0.99
8 Planar
2.69 GW/ 0.83
4.96 GW/ 0.91
4.38 GW/ 0.90

10. Another Method: Reverse Taper
Reverse Taper + Afterburner
Reverse Taper
Regular Taper
Bunching still grows
Schneidmiller 2013
Larger slope means more suppression of power
Rapid increase in power
Power is suppressed

11. Reverse Taper Results 1 nm, no Taper 1 x DELTA 2 x DELTA 3 x DELTA
12 Planar
0.71 GW/ 0.98
2.42 GW/ 0.99
4.37 GW/ 1.00
13 Planar
0.87 GW/ 0.98
2.71 GW/ 0.99
4.64 GW/ 1.00
14 Planar
1.15 GW/ 0.98
3.05 GW/ 0.99
4.72 GW/ 1.00
15 Planar
1.02 GW/ 0.98
2.74 GW/ 0.99
4.56 GW/ 1.00
2 nm, no Taper
1 x DELTA
2 x DELTA
3 x DELTA
10 Planar
1.90 GW/ 0.99
6.02 GW/ 1.00
6.85 GW/ 1.00
11 Planar
2.53 GW/ 0.99
6.38 GW/ 0.99
7.17 GW/ 1.00
12 Planar
3.11 GW/ 0.99
6.69 GW/ 0.99
7.33 GW/ 0.99
13 Planar
3.15 GW/ 0.99
6.92 GW/ 0.99

12. Reverse Taper & Energy Spread (1D Theory)
LCLS (720 eV)
LCLS-II (720 eV)

13. Cost Estimates (H.-D. Nuhn)
Requested in
Transitions to Operations Review:
SLAC Cost per Delta (M$) Labor 0.25 M&S 0.33 Indirects 0.23 Total 0.81 Supports 0.29 Grand Total 1.10
AIP Upgrade Cost (M$)
SXR Delta Undulator Extension (3) 3.30
Total 3.3

14. Questions?

15. Extra

16. Linear from first undulator section (18 uJ)
2 Polarization, 2 Color
Linear Undulator Line
(high energy)
Linear Undulator Line
Delta
Electron Picture
Linear from first undulator section (18 uJ)
Circular Delta (20 uJ)
Discarded Linear

17. Cookie Box

18. Measuring Polarization with e-TOF
e-TOF polarimeter relies upon polarization dependence of of ionized electron trajectories Measures degree of linear polarization, .
Circular (or unpolarized)
Linearly polarized
P2 is the second Legendre poly, ½ * (3 cos^2(theta) - 1)
Beta = -1 for the Ne
Sigma is total cross section

19. Stokes Parameters
Degree of linear polarization = Degree of circular polarization = Light isn’t always completely polarized: Total degree of polarization:
If we assume the total degree of polarization is 1, we can calculate s3/s0 from the degree of linear polarization

20. First Result: Spontaneous Radiation From Delta
Planar
Circular
Planar (theory)
Circular (theory)