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LCLS-II Undulator Parameters

LCLS-II Undulator Parameters. Heinz-Dieter Nuhn – LCLS Undulator Group Leader March 12, 2010. 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.

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LCLS-II Undulator Parameters

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  1. LCLS-II Undulator Parameters Heinz-Dieter Nuhn – LCLS Undulator Group Leader March 12, 2010

  2. 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. • Segment shortness is required to enable the low beta-functions needed for increased FEL performance.

  3. 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)

  4. LCLS-I U 1 Enhancement 0.52 Å 130 m 9.6 Å Ipk = 3000 A, gexy= 0.6 µm 0.62 Å 11 Å 1.24 Å 1.5 Å 23 Å 15 Å 15 GeV 3.5 GeV sg = 2.8

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

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

  7. LCLS-II U 2 Small Period Undulator Ipk = 2000 A, gexy= 0.6 µm helical helical <b> = 4 m, sg = 2.8

  8. Optimum beta functions at lu = 4.0 cm helical helical

  9. 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

  10. 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

  11. Beta-Function at 6 nm • Smallest practical beta function 4-5 m is above optimum. Lsat,mag~10.8 m for bx,y = 5 m Lsat,mag~10.0 m for bx,y = 4 m Optimum

  12. ‘Optimum’ Beta-Function at 6nm • Optimum beta function would reduce saturation length by more than factor 2 but is not accessible. Lsat,mag~4.3 m for bx,y ~ 0.1 m

  13. 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

  14. 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

  15. Variable Polarization Undulator Types Adjustable Phase Undulators Two adjustable phase undulators assembled in one device**. APPLE-III* APPLE-II *J. Bahrdt, et al., UNDULATORS FOR THE BESSY SOFTX- RAY FEL, Proccedings of the 2004 FEL Conference, pp. 610-613. **A. Temnykh, Phys. Rev. ST Accel. Beams 11, 120702 (2008). Variable Gap DELTA Fixed Gap Full K range available through row adjustment

  16. Summary • The LCLS-I undulator resonance can be shifted to lower wavelengths with moderate loss in xray energy. • 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.

  17. End of Presentation

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