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Overview of Proposed Parameter Changes Heinz-Dieter Nuhn, SLAC / SSRL October 24, 2003

Overview of Proposed Parameter Changes Heinz-Dieter Nuhn, SLAC / SSRL October 24, 2003. Calculation of On-Axis Undulator Field Undulator Period Maximum Available Linac Energy Undulator Gap Selection New Break Distances Reduction in Focusing Strength. Introduction.

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Overview of Proposed Parameter Changes Heinz-Dieter Nuhn, SLAC / SSRL October 24, 2003

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  1. Overview of Proposed Parameter ChangesHeinz-Dieter Nuhn, SLAC / SSRLOctober 24, 2003 • Calculation of On-Axis Undulator Field • Undulator Period • Maximum Available Linac Energy • Undulator Gap Selection • New Break Distances • Reduction in Focusing Strength Heinz-Dieter Nuhn, SLAC / SSRL

  2. Introduction • Original 6-mm gap height too small • Increase in gap can open spectral range to 1 Å • 50% Power Reduction of at 1.5 Å • Undulator field adjustment comb structure • Power tapering after saturation replenishes power Heinz-Dieter Nuhn, SLAC / SSRL

  3. Workshop Focus • Undulator Period • Reduction of maximum available linac energy • Undulator gap \height increase • Longer break distances • Weaker FODO lattice Heinz-Dieter Nuhn, SLAC / SSRL

  4. Presentations • Charge – M. Reichanadter • Undulator design requirements – S. Milton • Description of new parameters – H.-D. Nuhn • Status of field adjustment comb – J. Noonan • FEL simulation work using new parameters • GENESIS 1.3 – S. Reiche • GINGER – W.M. Fawley • RON – R. Dejus • BBA with new parameters – P. Emma Heinz-Dieter Nuhn, SLAC / SSRL

  5. Expected Workshop Outcome • Signed Document: Workshop Summary • Target Date: Mid November 2003 • Purpose • Implement the new parameters • Document the changes Heinz-Dieter Nuhn, SLAC / SSRL

  6. Adjusting Estimate of On-Axis Undulator Field • Halbach formula for hybrid undulator is used to estimate relation between gap/period and on-axis field • Measured prototype field 5.3% larger than estimated Heinz-Dieter Nuhn, SLAC / SSRL

  7. Undulator Period • Present undulator period length of 3 cm is near optimum for shortest gain length • Change of undulator period length would require more man-power and time than available before next review • Undulator period length will be kept at lu = 3 cm Heinz-Dieter Nuhn, SLAC / SSRL

  8. Maximum Available Linac Energy • 14.35 GeV has been nominal energy to reach 1.5 Å • Loss of available linac energy due to • Removal of linac section • Off-crest acceleration • New maximum energy set to 14.1 GeV to restore operational overhead • Requires change in K value Heinz-Dieter Nuhn, SLAC / SSRL

  9. Undulator Gap Selection • Undulator gap height changes still possible • Present gap height: 6 mm • Gap height corrected for measured field: 6.35 mm • Parameter correction for reduced maximum energy • Larger gap gives access to short wavelength 1.0 Å New Parameters Heinz-Dieter Nuhn, SLAC / SSRL

  10. 1.5 Å at Reduced Electron Beam Energy • With the 8.2 mm gap the 1.5 Å radiation is produced at lower energy (14.35 GeV 11.46 GeV) and smaller undulator parameter (3.711 2.838). • FEL output power reduced by 50 %. • Problem for experiments that need as large a number of photons a possible, such as imaging of bio-molecules. • Solution: New Field Adjustment Comb allows tapering the undulator after the saturation point. • Tapering by about 0.3 % over the last 30 m more than restores the lost energy Heinz-Dieter Nuhn, SLAC / SSRL

  11. New Break Lengths • Separations between undulator modules (breaks) designed to produce slippage by integer number of optical wavelength. • Break increments for adding slippage of 1 optical wavelength is DLB=lu (1+K2/2). DLB=23.7 cm (old); 15.1 cm (new) • Present design uses break pattern 1-1-2 which corresponds to the lengths sequence 18.7 cm – 18.7 cm – 42.1 cm • 18.7 cm gives not enough space for quads, BPMs, etc. 42.1 cm gives not enough space for x-ray diagnostics • New break pattern 3-3-4 (or 3-3-5) corresponding to lengthsequence 44.6 cm – 44.6 cm – 55.7 cm (or 44.6 cm – 44.6 cm – 70.8 cm) Heinz-Dieter Nuhn, SLAC / SSRL

  12. Special Initial Break Lengths • Present design uses special values for the first three break lengths: 28.1 cm – 25.6 cm – 47. 3 cmcompared to the regular values of 18.7 cm – 18.7 cm – 42.1 cm • Introduced by Nikolay Vinokurov to improve the overall FEL gain. • Estimate for new special lengths is 46.6 cm – 45.0 cm – 59.0 cm (74.1 cm) • New numbers will be checked by simulationwith RON and other codes. Heinz-Dieter Nuhn, SLAC / SSRL

  13. Undulator Schematic (Regular Section) 557 446 3410 (708) UNDULATOR 11599 mm (11750 mm) Horizontal Steering Coil Total Length 127184 mm (128845 mm) Vertical Steering Coil Beam Position Monitor X-Ray Diagnostics Quadrupoles Heinz-Dieter Nuhn, SLAC / SSRL

  14. Reduction in Focusing Strength • Present focusing lattice uses 5-cm-long permanent quadrupoles with gradient of 106 T/m (<b> = 18 m at 14.35 GeV) • New undulator parameters require reduced gradient. • Gradient reduced to 60 T/m (<b> = 30 m at 14.04 GeV) • Transverse quadrupole displacement used for steering • Reduced gradients require larger quadrupole displacement for same kick angle. • Beam Based Alignment procedure has been checked Heinz-Dieter Nuhn, SLAC / SSRL

  15. FODO Lattice Energy Limitations 1.5 Å 15 Å 1 Å 1.5 Å 15 Å Heinz-Dieter Nuhn, SLAC / SSRL

  16. LCLS Operating Points for 1 nC Bunch Charge (Old) LCLS Operating Point at 1.5 Å LCLS Operating Point at 15 Å Heinz-Dieter Nuhn, SLAC / SSRL

  17. LCLS Operating Points for 1 nC Bunch Charge (New) Operating Point Operating Point LCLS Operating Point at 1.5 Å Heinz-Dieter Nuhn, SLAC / SSRL

  18. LCLS Operating Points for 1 nC Bunch Charge (New) Operating Point Operating Point Operating Point LCLS Operating Point at 15 Å Heinz-Dieter Nuhn, SLAC / SSRL

  19. LCLS Operating Points for 1 nC Bunch Charge (New) Operating Point Operating Point LCLS Operating Point at 1.0 Å Heinz-Dieter Nuhn, SLAC / SSRL

  20. Summary of Nominal Undulator Design Changes OLD NEW Undulator Type planar hybrid planar hybrid Magnet Material NdFeB NdFeB Wiggle Plane horizontal horizontal Gap 6 8.2 mm Period Length 3.0 3.0 cm Peak On-Axis Field 1.325 1.014 T K 3.71 2.84 Module Length 3.41 3.41 m Number of Modules 33 33 Initial Break Lengths 0.281,0.256,0.473 0.466,0.450,0.590 m Regular Break Lengths 0.187-0.421 0.406-0.557 m Undulator Magnet Length 112.5 112.5 m Undulator Device Length (incl. Breaks) 121.1 127.2 m Undulator Filling Factor 93 88 % Heinz-Dieter Nuhn, SLAC / SSRL

  21. Summary of Nominal Focusing Lattice Changes OLD NEW Lattice Type FODO FODO Magnet Type permanent permanent Nominal Magnet Length 5 5 cm QF Gradient 107 61 T/m QD Gradient -106 -60 T/m Average b Function at 1.5 Å 18.0 24.5 m Lowest Usable Energy 3.17 1.84 GeV Heinz-Dieter Nuhn, SLAC / SSRL

  22. Summary of Electron Beam Parameters At 1.0 Å OLD NEW Electron Beam Energy - 14.04 GeV g - 27483 <b> - 30 m Rms beam radius - 36 mm At 1.5 Å OLD NEW Electron Beam Energy 14.35 11.47 GeV g28082 22439 <b> 18.0 24.4 m Rms beam radius 28 36 mm At 15 Å OLD NEW Electron Beam Energy 4.45 3.64 GeV g8880 7096 <b> 7.3 8.9 m Rms beam radius 35 39 mm Heinz-Dieter Nuhn, SLAC / SSRL

  23. Conclusions • New values have been proposed for • undulator gap, • maximum electron beam energy, • break length pattern, and • quadrupole gradients • Benefits are • more room for vacuum chamber • more space for diagnostics components between undulator modules • increase of accessible wavelength range • Reduction in photon number can be more than compensated by tapering using the new Field Adjuster Comb. Heinz-Dieter Nuhn, SLAC / SSRL

  24. End of Presentation Heinz-Dieter Nuhn, SLAC / SSRL

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