1. 1 BROOKHAVEN SCIENCE ASSOCIATES Boris Podobedov boris@bnl.gov LER-2014, Frascati, INFN-LNF September 18, 2014 Touschek Lifetime and IBS at NSLS-II

2. Boris Podobedov, Sept. 18, 2014 Outline Introduction and expectations Results to-date: Touschek lifetime commissioning results Future plans: Probing new lifetime regimes and IBS at NSLS-II

3. Boris Podobedov, Sept. 18, 2014 NSLS-II Storage Ring Parameters Energy 3.0 GeV Circumference 792 m Number of Cells 30 DBA Number of Super-periods 15 Length ID Straights 6.6 & 9.3m Emittance with DW (h/v) 0.9 nm/ 10pm Momentum Compaction.00037 Dipole Bend Radius 25m Energy Loss per Turn (with DW) 0.675MeV Energy Spread (with DW) 0.094% RF Frequency 499.68 MHz Harmonic Number 1320 RF voltage 4.8 MV RF Bucket Height 4.1% RMS Bunch Length 11.5ps Average Current 500mA Current per Bunch ~0.5 mA Touschek Lifetime >3hrs Top-Off Injection Freq 1/min Charge from one injection 7.3nC Stability requirement <10% beam size

4. Boris Podobedov, Sept. 18, 2014 Damping Wiggler 6 (out of 6) units of 1.8 T damping wigglers produced, received, tested, measured and installed in the ring straights 8, 18, and 28. Gap locked open for initial commissioning, will be closed for the first time for commissioning this October.

5. Boris Podobedov, Sept. 18, 2014 Emittance Reduction with Damping Wigglers

6. Boris Podobedov, Sept. 18, 2014 NSLS-II Ring RF Systems ● NSLS-II ring will eventually use two (or more) 500 MHz SC (~CESR-B) cavities manufactured by AES ● PETRA 7-Cell NC cavity from DESY was installed and used for Phase-I commissioning, I up to 25 mA, March 26-May 10. ● In May 7-Cell cavity was replaced by an AES SC cavity used for Phase-II commissioning, I up to 50 mA, June 27-July 13.

7. Boris Podobedov, Sept. 18, 2014 An Episode from NSLS-II Ring Commissioning, Phase-I Ring commissioning started March 26 It progressed fairly quickly, beam accumulation was achieved, BUT Something was drastically wrong with the ring: Not reproducible shift-to-shift, extreme sensitivity to orbit correction, huge jumps in beam lifetime, poor dynamic aperture, etc. Took some detective work to figure out what was wrong Dynamic aperture scans hinted at a physical aperture in cell 10 More systematic studies (with orbit bumps) again confirmed the suspicion about cell 10 and localized the aperture within it. Apr. 16

8. Boris Podobedov, Sept. 18, 2014 The Culprit Was … Chamber was open Apr. 25, and hanging RF contact spring was found after the 1 st dipole of cell10 With the spring removed, commissioning took off, 25 mA reached Apr 29 Lifetime measurement results became much more rational … RF spring hanging in the beam path

9. Boris Podobedov, Sept. 18, 2014 Example of Touschek Lifetime Studies Commissioning with Petra 7-cell cavity, V=1.9 MV Measurements (@ 0.5 mA / bunch):  tous =3.8 hours (+/-10%, gas=34 hours) Expectation (@ 0.5 mA / bunch) :  tous =4.0 hours  x =2.1 nm  =0.32%  acc  =2.5%

10. Boris Podobedov, Sept. 18, 2014 Streak Camera Bunch Length Measurements Weixing Cheng’s single bunch streak camera results Significant bunch-lengthening at low I b => use linear fit for lifetime analysis

11. Boris Podobedov, Sept. 18, 2014 Touschek Lifetime Studies during Phase-II Commissioning Commissioning with superconducting cavity, V=1.2 MV, RF acc. 1.8% Used bunch-by-bunch feedback by DIMTEL as arb. fill pattern generator Few bunch (1-15) fills at various currents, more or less equal intensity:

12. Boris Podobedov, Sept. 18, 2014 Later Example of Touschek Lifetime Results July 13, SC cavity voltage V=1.2 MV, RF acceptance=1.8% 1-15 ~uniform bunch trains fills at various total currents Measurements (@ 0.5 mA / bunch):  tous =2.1 hours (+/-10%, gas> 50 hours) Expectation (@ 0.5 mA / bunch) :  tous =2.1 hours So far no surprises for NSLS-II Touschek lifetime  x =2.1 nm  =0.4%  acc  =1.8%

13. Boris Podobedov, Sept. 18, 2014 Probing New Lifetime Regimes at NSLS-II

14. Boris Podobedov, Sept. 18, 2014 Touschek Lifetime: Historical Remarks C. Bernandini et al., 1963 H. Bruck, 1966 Dispersion effects added, late 1980 ZAP (1986) + many more codes L. le Duff, Single and multiple Touschek effects, in Proc. CAS Berlin 1987, CERN 89-01s lower  x

15. Boris Podobedov, Sept. 18, 2014 Touschek Scaling with Emittance Roughly  x independent, for fixed  y Lower  x (or higher  acc ) gets us over the hill, lifetime starts growing again lower  x Lattice-averaged rates @ 3%  acc  tous  hours  @  x =1. 4nm,  z =3.8 mm  tous  hours  @  x =0.5nm,  z =3.2 mm 15% reduction is due to  z only TBA 630m, center of ID,  x =7.2m,  acc = 3%  @  x =1. 4 nm  @  x =0.5 nm Ignores dispersion Jan 2006  “New Touschek regime”  >0.22

16. Boris Podobedov, Sept. 18, 2014 S. C. Leemann et al., PRST-AB 12, 120701 (2009) Touschek Scaling with Emittance NSLS-II PDR MAX-IV New Touschek lifetime regime is important for present and future light sources but it has not been experimentally verified* * there were some attempts, most notably at ALS by C. Steier & L. Yang

17. Boris Podobedov, Sept. 18, 2014 Will We Reach the New Regime at NSLS-II? Commissioning lattice 0.5 mA/bunch  y =1Å/4  ≈ 8 pm  z =c×18 ps = 5.4 mm  x  analytically for 1.8 Tesla DW Circles show 0, 3, 6,12 DWs Not obvious from this figure …

18. Boris Podobedov, Sept. 18, 2014 How Do We Probe this New Lifetime Regime at NSLS-II? Wait until NSLS-II is fully built up, and (perhaps) more DW installed, plus emittance is reduced due to many other IDs Reduce the ring energy for dedicated lifetime studies Probe this regime at ring locations where it already exists at 3GeV and  x ~1 nm (i.e. long straights) Some other ideas?

19. Boris Podobedov, Sept. 18, 2014 Lowering the Ring Energy to 2.5 GeV Commissioning lattice 0.5 mA/bunch  y =1Å/4  ≈ 8 pm  z =c×18 ps = 5.4 mm  x  analytically for 1.8 Tesla DW Circles show 0, 3, 6,12 DWs New Touschek lifetime regime should be observable at lower energies

20. Boris Podobedov, Sept. 18, 2014  acc = 3% Scatter Rates around the Ring at 3 GeV Local scatter rates drop a lot as  x shrinks! Even at nominal parameters, significant fractions of NSLS-II ring will be in the new Touschek lifetime regime. We are trying to figure out how to convincingly measure this. New regime  >0.22

21. Boris Podobedov, Sept. 18, 2014 Local Scatter Rates with Scrapers and Loss Monitors NSLS-II is well instrumented with scrapers and loss monitors These can measure charge lost at the scraper If an upstream scraper intercepts the Touschek loss around the ring then the losses on a downstream scraper are proportional to the scatter rate between the two, hence the local scatter rate is measured. Other diagnostics needs to be used for beam sizes, energy spread, etc.

22. Boris Podobedov, Sept. 18, 2014 IBS in a Wiggler-Dominated Light Source In a wiggler-dominated light source IBS-induced emittance blow-up is approximately emittance-independent and small Calcs for NSLS-II SR damping time ~ (Loss/turn) -1 IBS growth time ~ (Loss/turn) -1 B. Podobedov, L.Yang PAC’07 Experimental confirmation is needed; we look forward to NSLS-II results

23. Boris Podobedov, Sept. 18, 2014 Talk Summary No surprises during commissioning: measured lifetime well-matches our expectations. Rigorous lifetime monitoring will continue, esp. as we increase the average current, install damping wigglers and small-gap IDs, etc. We believe new Touschek lifetime regime (longer lifetime at lower emittance) should be reachable at NSLS-II, and we are contemplating study plans to probe it. While IBS is not expected to be a problem we have yet to quantify the emittance blow-up effect and compare it with our expectations. Thank you

24. Boris Podobedov, Sept. 18, 2014AcknowledgementsAcknowledgements I acknowledge the contributions of the entire NSLS-II design and commissioning team.

25. Boris Podobedov, Sept. 18, 2014 EXTRA VIEGRAPHS

26. Boris Podobedov, Sept. 18, 2014 Electrons within a bunch collide, rate ~N b 2. Transverse momentum gets transferred to longitudinal and boosted by relativistic  Large angle scattering: electrons with too much or too little momentum get lost (Touschek effect) Small angle scattering (IBS): usually increases in bunch length, energy spread, and emittance. Bad for tiny intense bunches in LS ! Touschek Effect & Intra-Beam Scattering Ultra-Simplified

27. Boris Podobedov, Sept. 18, 2014 Touschek Lifetime Basics For flat and transversely non-relativistic beams (works well for NSLS-II) Decay is non-exponential, but could be assumed linear for frequent topoff Energy spread dependence comes only through beam dimensions Touschek is peak current effect, i.e.  tous_1/2 ~  z /N b Needs averaging over the ring  acc – momentum acceptance (from RF, physical, and dynamic apertures, combined)

28. Boris Podobedov, Sept. 18, 2014 DW Effects on the Ring

29. Boris Podobedov, June 12, 2014 Cool Instability Pictures

30. Boris Podobedov, June 12, 2014 Cool Instability Pictures

31. Boris Podobedov, June 12, 2014 Cool Instability Pictures

32. Boris Podobedov, Sept. 18, 2014 NSLS-II L attice Layout Two rf BPM and two slow correctors (0.8mr) per girder to allow girder by girder orbit correction Three fast correctors (15 μr) per cell Two additional high stability BPMs in each straight section 10 quadrupole magnets per cell, independent power supplies 9 sextupole families, 5 power supplies for one family. Maximum strength: 400 T/m 2 3 chromatic sextupoles are asymmetric about the DBA center F F F c cc c c c HSBPM 3-pole wiggler 3-pole wiggler (1.1T) provide dipole radiation. Most of the drifts are standardized to 17.5 cm

33. Boris Podobedov, Sept. 18, 2014 NSLS-II Commissioning Lattice  x =2.1 nm-rad (DW not included) x,y = (33.216, 16.261)  x,y = (1.946, 1.777) according to PyTracy This will be our day 1 commissioning lattice Deemed adequate for injection and lifetime