LCLS Undulators – Present Status and Future Upgrades

1. LCLS Undulators – Present Status andFuture Upgrades Heinz-Dieter Nuhn – LCLS Undulator Group Leader March 1, 2010

2. Linac Coherent Light Source INJECTOR LINAC BEAM TRANSPORT UNDULATOR HALL

3. Undulator Hall Room for 2nd Undulator Line 33 Undulator Segments Installed

4. Short Break Section BFW Undulator Segment Part of WPM Support RF Cavity BPM Quadrupole and horz/vert Correctors Segment Slider Girder Girder Mover (cam) HLS Sensor

5. Fully Assembled Girder (seen from downstream end) Quadrupole Undulator Segment Vacuum Chamber RF Cavity BPM Girder

6. Girder Precision Alignment on CMM Quadrupole Undulator Segment with mu-Metal Shield Coordinate Measurement Machine Position Sensor RF Cavity BPM

7. LCLS Undulator Components Vacuum Chamber and Support BFW Segment3.400 m Long Break 89.8 cm Quadrupole Cam Shaft Movers WPM BPM Horizontal SlidesNot visible Manual Adjustments Short Break 47.0 cm Sand-Filled, Thermally IsolatedFixed Supports HLS

8. Vacuum Chamber Inserted into Gap Undulator Segment Magnet Block Horizontal Trajectory Shim Holder Vacuum Chamber Pole Piece

9. LCLS Undulator Module Pole Canting Pole canting enables remote K adjustment for fixed gap undulators. • Canting comes from wedged spacers • 4.5 mrad cant angle • Gap can be adjusted by lateral displacement of wedges • 1 mm shift means 4.5 µm in gap, or 8.2 G • Keff can be adjusted to desired value

10. Undulator Roll-Away and K Adjustment Pole Center Line Vacuum Chamber First; K=3.5000; Dx=-4.0 mm Neutral; K=3.4881; Dx= 0.0 mm Neutral; K=3.4881; Dx= 0.0 mm Neutral; K=3.4881; Dx= 0.0 mm Roll-Away; K=0.0000; Dx=+80.0 mm Horizontal Slide

11. LCLS-I Undulator Parameters

12. Taper Design Considerations • Compensation of spontaneous radiation (linear tapering over 132 m) • Compensation of vacuum chamber wakefields (linear tapering over 132 m, for 0.25 nC) • Gain enhancement (linear tapering before saturation) [Z. Huang] • Enhanced energy extraction (quadratic tapering after saturation) [W. Fawley] From Wakefield budget based on S2E Simulations The ratio between changes in E and K to maintain the resonance condition at a given wavelength is

13. K Tapering Requirements K for segment 1 K for segment 33 1.5 Å spont  0.3 % wake gain post sat 15 Å spont  0.3 % gain wake post sat

14. Figure 3: K Tapering Scenarios (Continuous)Avoid Reliance on Good Field Region at 1.5 Å

15. Measured Field Integrals on SN25 y : +200 µm +0 µm -200 µm

16. Beam Based Measurement: 1st Field Integral SN14 Horizontal (I1X) and vertical (I1Y) first field integrals measured by fitting a kick to the difference trajectory as function of undulator displacement SN14 Reference Point Beam Based Measurements Requires 20 nm BPM resolution SN14 MMF Measurement

17. Segmented Undulator Pre-Taper

18. CMM Keff Measurements for U33/SN20 K=3.497 K=3.468

19. Segmented Undulator K Control K ADJUSTMENT RANGE (MEASURED) TEMPERATURE CORRECTED KACT TAPER REQUEST K ADJUSTMENT RANGE (MEASURED)

20. Tolerance Budget Analysis • Analysis based on time dependent SASE simulations with GENESIS • Eight individual error sources considered: • Beta-Function Mismatch, • Launch Position Error, • Segment Detuning, • Segment Offset in x, • Segment Offset in y, • Quadrupole Gradient Error, • Transverse Quadrupole Offset, • Break Length Error. • The ‘observed’ parameter is the average of the FEL power at 90 m (around saturation) and 130 m (undulator exit) • The Results are combined into the Error Budget

21. Segment K Errors Simulation and fit results of Module Detuning analysis. The larger amplitude data occur at the 130-m-point, the smaller amplitude data at the 90-m-point. 130 m 90 m BudgetTolerance

22. Individual Studies (Example K) • Choose a set of DKm/K values to be tested, e.g. { 0.000%, 0.045%, 0.100%, 0.200%} • For each DKm/Kchoose 33 DKs values from a random flat-top distribution with maximum DKm. • Apply these errors, DKs, to the respective segment Ks values and perform a GENESIS FEL simulation. • Evaluate the simulation result to extract power levels at the 90 m and 130 m points, P90,m and P130,m, respectively. • Loop • Plot these results, P90,m and P130,m, versus the rms of the distribution, i.e. • Apply Gaussian fit to obtain rms-dependence.

23. Horizontal Segment Misalignment Simulation and fit results of Horizontal Module Offset analysis. The larger amplitude data occur at the 130-m-point, the smaller amplitude data at the 90-m-point. 130 m 90 m BudgetTolerance

24. Vertical Segment Misalignment Simulation and fit results of Vertical Module Offset analysis. The larger amplitude data occur at the 130-m-point, the smaller amplitude data at the 90-m-point. 130 m 90 m BudgetTolerance

25. Tolerance Budget • Gaussian fit yields functional dependence of power reduction on error amplitude: • Assuming that each error is independent on the others other, i.e. each error source causes a given fraction power reduction independent of the presence of the other sources: tolerance fitted rms fi=qi/si

26. LCLS Tolerance Budget z < 1.10.64<b/b0<1.56

27. 27 Model Detuning Sub-Budget

28. Beam Based Alignment Tolerance Verification Beam Based Measurements Random misalignment with flat distribution of widh ±a => rms distribution a/sqrt(3)

29. Beam Based K Tolerance Verification Beam Based Measurements

30. LCLS Undulator Tolerance Budget BB Verification Tolerance Budget Components 0.06 1200 8.8 770 MEASUREMENTS

31. LCLS-II • An initial rough evaluation of LCLS-II undulator parameters will be presented. • Priority is given to the Soft-Xray line, which is likely to be based on short variable gap undulators. • Shortness is required to enable the low beta-functions needed for optimum FEL performance.

32. full polarization control full polarization control 2-pulse 2-color 6-60 Å adjust. gap EEHG*? 6-60 Å adjust. gap 5 m 3-7-GeV bypass self-seeding option full polarization control self-seeding HXR option (2 bunches) 0.75 Å 0.75-15 Å Phased Enhancement Plan for LCLS-II 4-GeV SXR and 14-GeV HXR simultaneous op’s with bypass line SXR1 (45 m) SXR2 (45 m) 5 m FEE-2 240 nm  6 nm 4-14 GeV Large Gap (0.5-5 Å) Larger Gap Undulator(0.75-7.5 Å) Large Gap (0.5-5 Å) Shortened 74-m Undulator Shortened (1.5-15 Å) SHAB 30 m 5 m Existing 112-m Undulator (1.5-15 Å) FEE-1 Phase-2 Phase-3 Phase-1 Existing Phase-0 No civil construction. Uses existing beam energy and quality. * G. Stupakov, Phys. Rev. Lett. 102, 074801 (2009)

33. LCLS-I U 1 Enhancement Ipk = 3000 A, gexy= 0.6 µm sg = 2.8

34. LCLS-II U 2 FEL Performance Estimate Ipk = 2000 A, gexy= 0.6 µm linear helical <b> = 5 m, sg = 2.8

35. LCLS-II U 2 FEL Performance Estimate Ipk = 2000 A, gexy= 0.6 µm linear helical <b> = 5 m, sg = 2.8

36. Beta-Function at 6 nm • Smallest practical beta function 4-5 m is above optimum. LG~0.69 m for bx,y = 5 m LG~0.65 m for bx,y = 4 m Optimum

37. ‘Optimum’ Beta-Function at 6nm • Optimum beta function would reduce undulator length by more than factor 2 but is not accessible. LG~0.27 m for bx,y ~ 0.1 m

38. Optimum Beta-Function at 0.6 nm • At 0.6 nm beta function of 4-5 m is close to optimum. Considered Value Optimum Value

39. Beta Function and Undulator Length • The smallest average beta-function achievable with a FODO lattice is • The FODO length is determined by segment length and break length • Breaks between segments need to be sufficiently wide to allow space for essential components, such as quadrupole, BPM, Chicane. • Smallest practical quadrupole separation is 2.5 m, corresponding to a FODO length of 5 m . EXAMPLE: Bellows Break0.70 m Undulator: 1.80 m Break0.70 m Half FODO Length: 2.50 m Chicane RF Cavity BPM Quadrupole Minimum <bx,y> = 5 m

40. Example Chicane Dimensions Multi-Segment variable gap undulators require phase shifters between segments to adjust gap dependent inter-segment phase slippage. An example for such achicane is shown here. Field levels have been kept low to reduce in-tunnel powerrelease. L = 9 cm xmax L =4.5 cm L = 4.5 cm 3 cm L = 24 cm

41. Undulator Types A number of different variable field undulator types are under consideration Parallel-Pole Variable Gap Fixed Linear Polarization Hybrid or Pure Permanent Magnet Apple Type Variable Gap Variable Linear/Circular Polarization Hybrid or Pure Permanent Magnet Delta Type Variable Phase Variable Linear/Circular Polarization and Intensity Pure Permanent Magnet Superconducting Helical Variable Excitation current Fixed Circular Polarization [Substantial R&D required] New Designs … Key issues are Precision Hall probe measurements K stability and settability Compact design to mount on movable girders. Gap > 7 mm

42. Summary • The LCLS-I undulators have performed very well during commissioning and first user operation. • Initial parameter development for the LCLS-II undulators has started, giving priority to the new soft x-ray line. • The goal is a compact variable gap design to cover wavelengths between 6 nm and <0.6 nm at electron energies in the range 3-7 GeV. • The low emittance and lower electron energy require beta functions of order 5 m or smaller for best utilization. • Low beta-functions require a short FODO length, i.e., short undulator segments of length 1.8 m and compact break sections. • The total length of each of the 2 soft x-ray undulator lines is expected to be about 50 m.

43. End of Presentation