Touschek Lifetime and IBS at NSLSII Boris Podobedov

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

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

NSLS-II Storage Ring Parameters Energy 3. 0 Ge. V RF Frequency 499. 68 MHz Circumference 792 m Harmonic Number 1320 Number of Cells 30 DBA RF voltage 4. 8 MV Number of Super-periods 15 RF Bucket Height 4. 1% Length ID Straights 6. 6 & 9. 3 m RMS Bunch Length 11. 5 ps Emittance with DW (h/v) nm/ 10 pm 0. 9 Average Current 500 m. A Momentum Compaction. 00037 Current per Bunch ~0. 5 m. A Dipole Bend Radius Touschek Lifetime 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. Boris Podobedov, Sept. 18, 2014

Emittance Reduction with Damping Wigglers 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 m. A, 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 m. A, June 27 -July 13. 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 Boris Podobedov, Sept. 18, 2014

The Culprit Was … RF spring hanging in the beam path • • Chamber was open Apr. 25, and hanging RF contact spring was found after the 1 st dipole of cell 10 With the spring removed, commissioning took off, 25 m. A reached Apr 29 Boris Podobedov, Sept. 18, 2014

Example of Touschek Lifetime Studies • e =2. 1 nm • Commissioning with Petra 7 -cell cavity, V=1. 9 MV x • k=0. 32% • eacc =2. 5% • Measurements (@ 0. 5 m. A / bunch): ttous=3. 8 hours (+/-10%, gas=34 hours) • Expectation (@ 0. 5 m. A / bunch) : ttous=4. 0 hours Boris Podobedov, Sept. 18, 2014

Streak Camera Bunch Length Measurements • Weixing Cheng’s single bunch streak camera results • Significant bunch-lengthening at low Ib => use linear fit for lifetime analysis 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: 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 • ex=2. 1 nm • k=0. 4% • eacc =1. 8% So far no surprises for NSLS-II Touschek lifetime • Measurements (@ 0. 5 m. A / bunch): gas> 50 hours) ttous=2. 1 hours (+/-10%, Boris Podobedov, Sept. 18, 2014

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

Touschek Lifetime: Historical Remarks lower ex • • 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 -01 s Boris Podobedov, Sept. 18, 2014

Jan 2006 Touschek Scaling with Emittance Roughly ex independent, for fixed ey Ignores dispersion TBA 630 m, center of ID, bx=7. 2 m, eacc = 3% z=0. 13 @ ex=1. 4 nm z=0. 38 @ ex=0. 5 nm Lattice-averaged rates @ 3% eacc “New Touschek regime” x>0. 22 ttous=4 hours @ ex=1. 4 nm, sz=3. 8 x lower ex mm ttous=3. 5 hours @ ex=0. 5 nm, sz=3. 2 mm 15% reduction is due to sz only Lower ex (or higher eacc) gets us over the hill, lifetime starts Boris Podobedov, Sept. 18, 2014 growing again

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

Will We Reach the New Regime at NSLS-II? • Commissioning lattice • 0. 5 m. A/bunch • ey=1Å/4 p ≈ 8 pm • sz=c× 18 ps = 5. 4 mm • d(ex) analytically for 1. 8 Tesla DW • Circles show 0, 3, 6, 12 DWs Not obvious from this figure … 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 3 Ge. V and ex~1 nm (i. e. long straights) • Some other ideas? Boris Podobedov, Sept. 18, 2014

Lowering the Ring Energy to 2. 5 Ge. V • Commissioning lattice • 0. 5 m. A/bunch • ey=1Å/4 p ≈ 8 pm • sz=c× 18 ps = 5. 4 mm • d(ex) analytically for 1. 8 Tesla DW • Circles show 0, 3, 6, 12 DWs New Touschek lifetime regime should be observable at lower energies Boris Podobedov, Sept. 18, 2014

Scatter Rates around the Ring at 3 Ge. V New regime x>0. 22 eacc = 3% • • Local scatter rates drop a lot as ex shrinks! Even at nominal parameters, significant fractions of NSLSII ring will be in the new Touschek lifetime regime. We are trying to figure out how to convincingly measure Boris Podobedov, Sept. 18, 2014 this.

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 Boris Podobedov, Sept. 18, 2014 local scatter rate is measured.

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

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 Boris Podobedov, Sept. 18, 2014

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

EXTRA VIEGRAPHS Boris Podobedov, Sept. 18, 2014

Touschek Effect & Intra-Beam Scattering Ultra-Simplified • Electrons within a bunch collide, rate ~Nb 2. • Transverse momentum gets transferred to longitudinal and boosted by relativistic g • 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 ! Boris Podobedov, Sept. 18, 2014

Touschek Lifetime Basics • For flat and transversely non-relativistic beams (works well for NSLS-II) eacc – momentum acceptance (from RF, physical, and dynamic apertures, combined) Needs averaging over the ring • 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. t ~ s /NBoris Podobedov, Sept. 18, 2014

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

Cool Instability Pictures Boris Podobedov, June 12, 2014

Cool Instability Pictures Boris Podobedov, June 12, 2014

Cool Instability Pictures Boris Podobedov, June 12, 2014

NSLS-II Lattice Layout F c c c F HSBPM 3 -pole wiggler • 3 -pole wiggler (1. 1 T) provide dipole radiation. • Two • Most of the drifts are standardized to 17. 5 cmrf BPM and two slow correctors (0. 8 m per girder to allow girder by girder orbit correction • 10 quadrupole magnets per cell, independent • Three fast correctors (15 μr) per cell power supplies • Two • 9 sextupole families, 5 power supplies for oneadditional high stability BPMs in eac family. Maximum strength: 400 T/m 2 straight section • 3 chromatic sextupoles are asymmetric about the DBA center Boris Podobedov, Sept. 18, 2014

NSLS-II Commissioning Lattice • • • ex=2. 1 nm-rad (DW not included) nx, y= (33. 216, 16. 261) xx, y= (1. 946, 1. 777) according to Py. Tracy This will be our day 1 commissioning lattice Deemed adequate for injection and lifetime Boris Podobedov, Sept. 18, 2014