Optimal Undulator Length for LCLS

1. Option – 5m Undulators • What is the optimum length for an LCLS undulator? • XFEL is using 5m undulator segments. • Is this optimum? • What are the advantages and disadvantages of long (or short) undulators. Undulator Alternatives- 5m, M. Rowen, 6-15-11

2. XFEL Undulators • Joachim Pflueger claims 5m devices are more cost effective than short undulators. • A quick and crude calculation for 5m undulator for LCLS-II is a savings on the order of $12M. • Undulator costs based on Pflueger’s reported costs. • Requires 34 vs. 50 segments. • The saving is in the reduced number of inter-space quads and phase shifters. Undulator Alternatives- 5m, M. Rowen, 6-15-11

3. Technical Differences LCLS-II:XFEL • LCLS-II undulators must go to smaller gap: • 7.2mm vs. 10mm. • SXR undulator longer period: • 55mm vs. 48mm. • There is debate at XFEL about their SXR undulator parameters so do not know what there current SASE-3 plans are. • Both lead to larger force at minimum gap. • Recommend more prototyping for 5m device to reduce risk. • This would cost in ~$2M for addition generation of prototype. • Add ~one year on to schedule. Undulator Alternatives- 5m, M. Rowen, 6-15-11

4. Technical Differences (cont.) • The SXR undulator is calculated for 8m b: • Would have to increase b for beam based alignment down to 4.3GeV. • Increased b slightly lower performance • Or limit operations to higher energies • The converse is also true: Setting a higher limit to low energy operation and keeping 3.4m segments could allow slightly improved performance. • Aligning longer devices will take less effort: • Similar layout possible with fewer monuments and fewer set ups => faster process. Undulator Alternatives- 5m, M. Rowen, 6-15-11

5. 5m XFEL Undulator 4 Point Support System - reduces deflection of beam – less rotational stable. • The XFEL undulator is a highly engineered device. • It is operating at near the limits of tolerances. • Might not extrapolate to the higher LCLS-II forces. Rotational stabilizers. Undulator Alternatives- 5m, M. Rowen, 6-15-11

6. Other Potential Costs • The $12M does NOT include Costs of: • Longer vacuum system. • Not calculated, but likely to increase with length. • Larger Magnetic Measurement Facilities. • To expand MMF at SLAC to accommodate 5m segments $+5M, vs. $1-2M to expand for 3.4m devices. (rough estimate) • As LBNL is starting fresh on an MMF the incremental costs would be less. • Both plan to do MMF upgrades off project. • Higher off project costs might not be acceptable. • Hall probe benches ~$1M vs. $700k. • Stiffer beams and large drive systems for larger forces. • Probably could be achieved at some higher cost, say 10%, or ~$1.7M. Undulator Alternatives- 5m, M. Rowen, 6-15-11

7. Summary • Technical: • Risk is higher with long device & due to the larger forces. • Have to modify the b on the SXR undulator line slightly. • Cost: • 5m devices should save on alignment (not calculated). • MMF cost for 5m devices is significantly higher (~$3M). • Not on project, but still an issue. • Increased bench costs ~$900k. • Additional prototyping ~$2M. • Increased cost in undulators ~$1.7M • Delaying the schedule 1 year +$?M. Undulator Alternatives- 5m, M. Rowen, 6-15-11

8. 3 factors indicate that 5m is too long for LCLS-II. • MMF’s for 5m devices would cost significantly more at SLAC. • 5m devices are higher risk. • 5m devices will take longer to develop if risk is to be minimized. Undulator Alternatives- 5m, M. Rowen, 6-15-11

9. Conclusion • $3-8M in savings are not a strong driver to go to 5m undulator segments. • To reduce risk it will take ~1 year longer to develop. • Stick with shorter devices: • It is not clear what the exact optimum length for LCLS-II undulator segments is. • It does not have to be 3.4m. Undulator Alternatives- 5m, M. Rowen, 6-15-11