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

2. ICFA S2E Workshop DESY-Zeuthen, 22 August 2003John W. Lewellen2 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

3. ICFA S2E Workshop DESY-Zeuthen, 22 August 2003John W. Lewellen3 The APS SASE-FEL Cartoon Layout BNL-type 1.6-cell RF photoinjector pre-compressor linac bunch compressor  meas. & match post-compressor linac interleaving dipoles vertical dogleg undulator w/ diags

4. ICFA S2E Workshop DESY-Zeuthen, 22 August 2003John W. Lewellen4 APS SASE-FEL Layout – In Context APS Linac PAR Undulator Hall End Station Booster Synchrotron Storage Ring

5. ICFA S2E Workshop DESY-Zeuthen, 22 August 2003John W. Lewellen5 Recent Activities User Studies – SPIRIT experiment Typically, run at ~ 150 nm Tune +/- 10 nm without lattice change ~ 50 – 100  J 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

6. ICFA S2E Workshop DESY-Zeuthen, 22 August 2003John W. Lewellen6 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

7. ICFA S2E Workshop DESY-Zeuthen, 22 August 2003John W. Lewellen7 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

8. ICFA S2E Workshop DESY-Zeuthen, 22 August 2003John W. Lewellen8 APS “Interleaving Linac” Sketch New Drive Laser Energy Controller “Crest Reflection” phase control Beam Metrology (1% of shots) To Booster Synchrotron – Constant Beam Energy, 10 shots every 2 minutes Energy Modulator Booster Timing Synchronizer synchronization pulse End Station Tunable SASE-FEL Light Final Matching

9. ICFA S2E Workshop DESY-Zeuthen, 22 August 2003John W. Lewellen9 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

10. ICFA S2E Workshop DESY-Zeuthen, 22 August 2003John W. Lewellen10 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-  lattices)

11. ICFA S2E Workshop DESY-Zeuthen, 22 August 2003John W. Lewellen11 Interlude – Top-Up Minimum allowable lifetime: C l = desired current stability f b = injection rate Maximum supportable beam current: Q b = charge injected per bunch C ring = ring circumference  beam = beam lifetime ≤  min if  beam =  min Note: Impedance, etc., not included!

12. ICFA S2E Workshop DESY-Zeuthen, 22 August 2003John W. Lewellen12 “4” != inc(3) Yes, I have been spending too much time programming recently! “3 rd -generation SR” sources Somewhat natural evolution Not all that different, conceptually, from original SR-based sources Large, but still incremental, advance “4 th -generation” FEL-based sources Definitely did not evolve from SR sources More of a step change than an incremental change Very different performance characteristics

13. ICFA S2E Workshop DESY-Zeuthen, 22 August 2003John W. Lewellen13 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…

14. ICFA S2E Workshop DESY-Zeuthen, 22 August 2003John W. Lewellen14 A “LALS” APS APS Linac PAR Booster Synchrotron Storage Ring APS VUV FEL

15. ICFA S2E Workshop DESY-Zeuthen, 22 August 2003John W. Lewellen15 A “LALS” APS APS LALS Concept Parameter List Length~ 1 km Beam energy 7 GeV to SR, 4 – 10 GeV at undulator farm Charge / bunch 1 nC Bunches per macropulse 1 – 1000 Macropulse rate 100 Hz Average beam power ~ 1 MW at 1k bunches/macropulse RF structures Superconducting 1.3 GHz TESLA-type Recirculation? Possible; not required for low beam power operation

16. ICFA S2E Workshop DESY-Zeuthen, 22 August 2003John W. Lewellen16 Some Numbers … on the SR side Given that C 1 = 99.9%: 2 Hz injection  500 s minimum SR beam lifetime 100 Hz injection  10 s minimum SR beam lifetime Given that Q b = 1 nC:  beam = 10 s  I beam = 300 mA  beam = 500 s  I beam = 15 A Nothing says the LALS linac can’t top-up more than one bunch at a time…

17. ICFA S2E Workshop DESY-Zeuthen, 22 August 2003John W. Lewellen17 Some Numbers … on the X-FEL side BRANCH LINE BEAM ENERGY [GeV] MINIMUM WAVELENGTH (K=1) [Å] MAXIMUM WAVELENGTH (K=3.1) [Å] 4.0 15.6 5.52.18.3 7.01.35.1 8.50.893.5 10.00.652.5 Assume: Undulators have 3.3 cm period, K = 1 – 3.1

18. ICFA S2E Workshop DESY-Zeuthen, 22 August 2003John W. Lewellen18 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

19. ICFA S2E Workshop DESY-Zeuthen, 22 August 2003John W. Lewellen19 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

20. ICFA S2E Workshop DESY-Zeuthen, 22 August 2003John W. Lewellen20 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” 3 rd - or 4 th - generation light source worry space