LCLS Undulators Present Status and Future Upgrades

Transcription

1 LCLS Undulators Present Status and Future Upgrades Heinz-Dieter Nuhn LCLS Undulator Group Leader 1 1 Heinz-Dieter Nuhn

2 Linac Coherent Light Source INJECTOR LINAC BEAM TRANSPORT UNDULATOR HALL 2 2 Heinz-Dieter Nuhn

3 Undulator Hall 33 Undulator Segments Installed 3 3 Heinz-Dieter Nuhn

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

5 Fully Assembled Girder (seen from downstream end) Undulator Segment Quadrupole Vacuum Chamber RF Cavity BPM Girder 5 5 Heinz-Dieter Nuhn

6 Girder Precision Alignment on CMM Quadrupole Undulator Segment with mu-metal Shield Coordinate Measurement Machine Position Sensor RF Cavity BPM 6 6 Heinz-Dieter Nuhn

7 LCLS Undulator Components BFW Vacuum Chamber and Support Segment m Cam Shaft Movers WPM Quadrupole BPM Long Break 89.8 cm Short Break 47.0 cm Manual Adjustments Horizontal Slides Not visible Sand-Filled, Thermally Isolated Fixed Supports HLS 7 7 Heinz-Dieter Nuhn

8 Vacuum Chamber Inserted into Gap Undulator Segment Magnet Block Horizontal Trajectory Shim Holder Vacuum Chamber Pole Piece 8 8 Heinz-Dieter Nuhn

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 K eff can be adjusted to desired value 9 9 Heinz-Dieter Nuhn

10 Undulator Roll-Away and K Adjustment Pole Center Line Vacuum Chamber Neutral; First; K=3.5000; K=3.4881; x= mm Neutral; K=3.4881; x= 0.0 mm Roll-Away; Neutral; K=3.4881; K=0.0000; x= x=+80.0 mm mm Horizontal Slide Heinz-Dieter Nuhn

11 LCLS-I Undulator Parameters units Nominal Undulator Parameter K 3.5 Undulator Period λ u 30 mm Undulator peak Field, B pk B pk T Full Gap Height (fixed) g 6.8 mm Undulator Type Planar Hybrid Permanent Magnet Magnet Material Nd 2 FeB 14 Pole Material Vanadium Permendur Magnet Block Dimensions Pole Dimensions h t w h t w Periods per Segment mm mm 3 Gap Cant Angle α 4.5 mrad Number of Installed Segments Heinz-Dieter Nuhn

12 Taper Design Considerations 1. Compensation of spontaneous radiation (linear tapering over 132 m) ˆ 2 E E/ E = B Nλ T 2 u Vm e 2. Compensation of vacuum chamber wakefields (linear tapering over 132 m, for 0.25 nc) E/ E From Wakefield budget based on S2E Simulations 3. Gain enhancement (linear tapering before saturation) [Z. Huang] E/ E = 2ρ 4. Enhanced energy extraction (quadratic tapering after saturation) [W. Fawley] E/ E 0.25% The ratio between changes in E and K to maintain the resonance condition at a given wavelength is dk dk K 2 = K = de dγ K E γ Heinz-Dieter Nuhn

13 K Tapering Requirements K for segment 1 K for segment Å ± 0.3 % spont wake gain post sat 15 Å spont ± 0.3 % gain post sat wake Heinz-Dieter Nuhn

14 Figure 3: K Tapering Scenarios (Continuous) Avoid Reliance on Good Field Region at 1.5 Å Heinz-Dieter Nuhn

15 Measured Field Integrals on SN25 L 0 B x ( xyz,, ) dz L z 0 0 Bx ( xyz,, ') dz ' dz L 0 B y ( xyz,, ) dz L z 0 0 By ( xyz,, ') dz ' dz y : +200 µm +0 µm -200 µm Heinz-Dieter Nuhn

16 Beam Based Measurement: 1 st 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 Reference Point SN14 Requires 20 nm BPM resolution MMF Measurement Beam Based Measurements SN Heinz-Dieter Nuhn

17 Segmented Undulator Pre-Taper Heinz-Dieter Nuhn

18 CMM K eff Measurements for U33/SN20 K=3.497 K= Heinz-Dieter Nuhn

19 Segmented Undulator K Control TEMPERATURE CORRECTED KACT K ADJUSTMENT RANGE (MEASURED) TAPER REQUEST K ADJUSTMENT RANGE (MEASURED) Heinz-Dieter Nuhn

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 Heinz-Dieter Nuhn

21 Segment K Errors Simulation and fit results of Module Detuning analysis. The larger amplitude data occur at the 130-mpoint, the smaller amplitude data at the 90-m-point. qi = K / K Budget Tolerance 130 m 90 m Module Detuning (Gauss Fit) Location Fit rms Unit 090 m % 130 m % Average % Heinz-Dieter Nuhn

22 Individual Studies (Example K) Choose a set of K m /K values to be tested, e.g. { 0.000%, 0.045%, 0.100%, 0.200%} For each K m /K choose 33 K s values from a random flattop distribution with maximum K m. Apply these errors, K s, to the respective segment K s values and perform a GENESIS FEL simulation. Evaluate the simulation result to extract power levels at the 90 m and 130 m points, P 90,m and P 130,m, respectively. Loop Plot these results, P 90,m and P 130,m, versus the rms of the distribution, i.e. 1 Km K 12 Apply Gaussian fit to obtain rms-dependence. Pi = 0 q 2 Pe σ 2 i 2 i Heinz-Dieter Nuhn

23 Horizontal Segment Misalignment 130 m Simulation and fit results of Horizontal Module Offset analysis. The larger amplitude data occur at the 130-mpoint, the smaller amplitude data at the 90-m-point. 90 m Horizontal Model Offset (Gauss Fit) Location Fit rms Unit 090 m 0782 µm 130 m 1121 µm Average 0952 µm Budget Tolerance Heinz-Dieter Nuhn

24 Vertical Segment Misalignment Simulation and fit results of Vertical Module Offset analysis. The larger amplitude data occur at the 130-mpoint, the smaller amplitude data at the 90-m-point. 130 m 90 m Vertical Model Offset (Gauss Fit) Location Fit rms Unit 090 m 268 µm 130 m 268 µm Average 268 µm Budget Tolerance Heinz-Dieter Nuhn

25 Tolerance Budget Gaussian fit yields functional dependence of power reduction on error amplitude: 2 P i P 0 = e q 2σ 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: i 2 i tolerance fitted rms P P 0 2 i 2 i q 1 1 f 2σ 2 2 e e e = = = 2 2 i fi f i =q i /σ i Heinz-Dieter Nuhn

26 LCLS Tolerance Budget P P 0 = e f i Error Source σ i f i σ i f i 130 m (24.2% red.) Hor/Ver Optics Mismatch (ζ-1) ζ < <β/β 0 <1.56 Hor/Ver Transverse Beam Offset µm Module Detuning K/K % Module Offset in x µm Module Offset in y µm Quadrupole Gradient Error % Transverse Quadrupole Offset µm Break Length Error mm Heinz-Dieter Nuhn

27 Model Detuning Sub-Budget K = K + α T + β x MMF K K ( δk) Parameter p i Typical Value rms dev. δp i Note K MMF ±0.015 % uniform α K C C -1 Thermal Coefficient T 0 C 0.32 C ±0.56 C uniform without compensation β K mm mm -1 Canting Coefficient x 1.5 mm 0.05 mm Horizontal Positioning 2 2 K = δ pi i pi ( ) ( ) ( ) ( ) ( ) MMF K K K K δ K = δ K + Tδα + α δ T + xδβ + β δ x δ K / K = 0.020% LCLS 27 Undulator Status Heinz-Dieter Nuhn

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

29 Beam Based K Tolerance Verification Beam Based Measurements Heinz-Dieter Nuhn

30 LCLS Undulator Tolerance Budget BB Verification P P f i e 2 = Tolerance Budget Components Error Source σ i f i σ i f i 130 m (24.2% red.) Hor/Ver Optics Mismatch (ζ-1) Hor/Ver Transverse Beam Offset µm Module Detuning K/K % Module Offset in x µm Module Offset in y µm Quadrupole Gradient Error % Transverse Quadrupole Offset µm Break Length Error mm Module Offset in z SAT 780 µm MEASUREMENTS 30 Heinz-Dieter Nuhn

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 Heinz-Dieter Nuhn

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

33 LCLS-I U 1 Enhancement σ γ = 2.8 I pk = 3000 A, γε xy = 0.6 µm Heinz-Dieter Nuhn

34 LCLS-II U 2 FEL Performance Estimate helical linear <β> = 5 m, σ γ = 2.8 I pk = 2000 A, γε xy = 0.6 µm Heinz-Dieter Nuhn

35 LCLS-II U 2 FEL Performance Estimate helical linear <β> = 5 m, σ γ = 2.8 I pk = 2000 A, γε xy = 0.6 µm Heinz-Dieter Nuhn

36 Beta-Function at 6 nm L G ~0.69 m for β x,y = 5 m Optimum L G ~0.65 m for β x,y = 4 m Smallest practical beta function 4-5 m is above optimum Heinz-Dieter Nuhn

37 Optimum Beta-Function at 6nm L G ~0.27 m for β x,y ~ 0.1 m Optimum beta function would reduce undulator length by more than factor 2 but is not accessible Heinz-Dieter Nuhn

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

39 Beta Function and Undulator Length β L The smallest average beta-function achievable with a FODO lattice is The FODO length is determined by segment length and break length xy, FODO 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 Break 0.70 m Undulator: 1.80 m Break 0.70 m Half FODO Length: 2.50 m Minimum <β x,y > = 5 m Chicane RF Cavity BPM Quadrupole Heinz-Dieter Nuhn

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 a chicane is shown here. Field levels have been kept low to reduce in-tunnel power release. x max L = 9 cm L = 4.5 cm 3 cm L =4.5 cm L = 24 cm E GeV λ r nm B G x µrad x max µm φ degxray η x µm R nm Heinz-Dieter Nuhn

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 Heinz-Dieter Nuhn

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 Heinz-Dieter Nuhn

43 End of Presentation Heinz-Dieter Nuhn