Fourth-Generation Sources at Third-Generation Facilities

1. Fourth-Generation Sources at Third-Generation Facilities John W. Lewellen Advanced Photon Source Argonne National Laboratory

2. Outline of the Talk • The APS SASE-FEL • System Layout • Recent Activities • Future Plans • Why Did I Just Say All That? • “4” != inc(3) • Peaceful Coexistence • Concluding Thoughts John W. Lewellen

3. The APS SASE-FEL Cartoon Layout pre-compressor linac e meas. & match interleaving dipoles undulator w/ diags BNL-type 1.6-cell RF photoinjector post-compressor linac vertical dogleg bunch compressor John W. Lewellen

4. APS SASE-FEL Layout – In Context Undulator Hall APS Linac PAR End Station Booster Synchrotron Storage Ring John W. Lewellen

5. Recent Activities • User Studies – SPIRIT experiment • Typically, run at ~ 150 nm • Tune +/- 10 nm without lattice change • ~ 50 – 100 mJ pulse energy on target • Starting diagnostics integration for feedback & tuneup • Facilities & FEL Studies • Cross-calibration of VUV with UV-Vis diags • Saturation from 600 nm – 130 nm (195 – 450 MeV) • FROG measurements of pulse characteristics (at 530 nm) • Machine studies for feedback optimization & control John W. Lewellen

6. Limits on Operation • SR Top-Up Mode Operation • ~2 nC delivered to SR every 2 minutes • Charge-per-bunch issues (wakes, CSR, quality) • Drive laser reliability issues • PAR-induced limitations • Constant beam energy • Beam energy ≤ 325 MeV • Personnel & Funding John W. Lewellen

7. Future Plans • Full-time interleaving with top-up • Upgrade drive laser • Upgrade injector area • Timing synchronizer, linac-to-booster • “Multi-Charge” acceleration • ~0.5 nC, bunch compressed, for SASE-FEL • ~3 nC, uncompressed, for booster • Switching “on-demand” between the two • Post-booster energy modulation John W. Lewellen

8. APS “Interleaving Linac” Sketch Energy Modulator Final Matching “Crest Reflection” phase control Beam Metrology (1% of shots) Tunable SASE-FEL Light Energy Controller To Booster Synchrotron – Constant Beam Energy, 10 shots every 2 minutes End Station synchronization pulse New Drive Laser Booster Timing Synchronizer John W. Lewellen

9. Why Did I Tell You This? • The APS SASE-FEL is evolving towards a true user, and usable, facility • CSR, SASE effects seen & lived with every run • Highlights “peaceful coexistence” between two very different types of light sources, with very different performance demands • The basic approach is scalable John W. Lewellen

10. Interlude – Storage Ring Top-Up • Inject charge frequently to maintain ~0.1% beam current stability • constant heat load on beamline optics • always running with max. photons/second • Broadly speaking: • Minimum lifetime set by max. top-up rate • Max. beam current set by max. charge / injection • Both affected by desired charge stability • Allows the use of otherwise inaccessible operating modes (e.g. low-e lattices) John W. Lewellen

11. Interlude – Top-Up Note: Impedance, etc., not included! Cl = desired current stability fb = injection rate Minimum allowable lifetime: Qb = charge injected per bunch Cring= ring circumference tbeam = beam lifetime ≤ tmin Maximum supportable beam current: if tbeam = tmin John W. Lewellen

12. “4” != inc(3) • Yes, I have been spending too much time programming recently! • “3rd-generation SR” sources • Somewhat natural evolution • Not all that different, conceptually, from original SR-based sources • Large, but still incremental, advance • “4th-generation” FEL-based sources • Definitely did not evolve from SR sources • More of a step change than an incremental change • Very different performance characteristics John W. Lewellen

13. Peaceful Coexistence • Moving to top-up operation places stringent demands on the SR injector • no time between fills to fix problems • ~ same up-time requirements as a SASE X-FEL • Top-up is increasingly popular • An X-FEL linac will almost certainly meet SR injector performance requirements for a similar-energy ring • Hmmm… John W. Lewellen

14. APS VUV FEL Storage Ring Booster Synchrotron PAR APS Linac A “LALS” APS John W. Lewellen

15. A “LALS” APS John W. Lewellen

16. Some Numbers … on the SR side Given that C1 = 99.9%: 2 Hz injection  500 s minimum SR beam lifetime 100 Hz injection  10 s minimum SR beam lifetime tbeam = 10 s  Ibeam = 300 mA Given that Qb = 1 nC: tbeam = 500 s  Ibeam = 15 A Nothing says the LALS linac can’t top-up more than one bunch at a time… John W. Lewellen

17. Some Numbers … on the X-FEL side Assume: Undulators have 3.3 cm period, K = 1 – 3.1 John W. Lewellen

18. Other Advantages • Existing pools of local expertise to draw on (accelerator and x-ray science) • Leverage more light sources • convert booster synchrotron to VUV / soft X-ray ring • upgrade the existing linac to SRF, etc. • Low(er) risk • Uses proven (by then) X-FEL and SRF tech. • Avoids trying to make a linac into a ring; but • Recirculation could be kept as a (complicated) option John W. Lewellen

19. Interesting Operational Modes • Once-around-and-dump • Use “flat” short bunches in linac • Bunch compress • Inject into SR: Advantages of short-bunches, without requiring optics retune • Fast bunch pattern change • Fill entire ring with one linac macropulse • Vary SR bunch pattern almost on-the-fly John W. Lewellen

20. Concluding Thoughts • Natural synergies exist between SR-based and linac-based light sources • user science community • similar scale of some “problems” • local accelerator physics expertise • drive to miniaturize • Some SR evolution paths invite symbiotic facilities; others at least tolerate it • Much additional work needed on many issues that aren’t part of “traditional” 3rd- or 4th-generation light source worry space John W. Lewellen