NSLS-II IR Source

1. NSLS-II IR Source L. Carr, J. Hill, S. Kramer, B. Podobedov, T. Shaftan, J. Rose, G. Wüstefeld NSLS-II Review May 11-12, 2006

2. Outline & Preliminaries • Motivation (why a separate IR ring source) • User requirements + modes of operation • Upgrade path possibilities • Choice of energy and anticipated maximum current • Lifetime scaling from the present VUV ring • CSR mode – what it’s about • CSR mode –implications • RF system • Upgrade or brand-new? • 72 m DBA lattice • Issues to be worked out (beam dynamics only) • Summary and conclusions IR week Apr 3-7, 2006

3. Why a Separate NSLS-II IR Source? • NSLS IR program is the world strongest • We want to preserve & expand IR capabilities • IR Users have very different requirements from X-ray Users • NSLS-II 3 GeV ring falls short of the present VUV ring IR performance (opening angle, ring current, special patterns for timing, etc.) • Shifting IR onto NSLS-II main ring would result in curtailment of existing program. • Dedicated low energy ring resolves this problem. L.Carr 12 mrad @ present

4. Summary of IR User Requirements • Spectral Coverage 1 - 5000 cm-1 (0.12– 600 meV; l=2 mm-10 mm) • Flux about or better than present 4x1012/ph/s/0.1%bw/mrad (I=1A, 0.6eV) • Max Current Drop DI/I = 10% • E-Beam size at the source ~100x100 mm2(can be relaxed to gain stability, lifetime) • Bunch length (timing users ASAP, imagers don’t care) • Min. Injection-to-Injection Interval 15 mins with non-closed bumps, no restriction for closed bumps • Bunch pattern variable and lockable to TiSaph laser L.Carr We expect operations time split between -High-Current mode (1-2 A, 10-30 ps rms) and -CSR mode (10-30 mA, 1 ps rms)

5. VUV-IR Ring Upgrade Scenarios 2) Same as 1), but add SC RF cavity • Same as 1) plus • Shorter bunch (~10 ps) • Coherent mode to ~THz • Gain in flux ~104 • ~ps pulses @ lower I • SCRF experience for NSLS-II, same RF across • $$ for RF, BPMs, chamber (circumf., bellows) upgrade • Same as 1) plus • Coherent performance, chamber & cavity Z(w), PS & RF noise, LCBM fdbk… 3) Same as 1) but run single (or multi)-turn ERL or linac-based source w/o recovery • Inherent top-off, even shorter bunches • Cohrnt. mode to ~10 THz • Sub-ps pulses, lower ex • $$$$ for SC linac, RF, cryo, … • Gun, injector shared with 3GeV ring, kickers (multi-turn), orbit stability, losses & shielding, … 1) Move Present VUV-IR Ring with minimal changes Pros • Operate top-off (x2) • Higher I (injector & Ipick limits, maybe x2) • Cheap, well understood Cons • No new science regimes Acc. Phys. Issues • pick the energy • IBS, instabilities, losses & shielding User’s choice

6. Beam Energy to Meet the Flux Specs Flux from VUV Ring Bend at I=1 A 800 MeV Target spectral range 400 MeV 100 MeV 50 MeV 0.6 Matching Flux at 0.6eV requires E>~100 MeV Ring options will likely end up at E>500 MeV

7. IBS Emittance Blow-up vs. Energy SAD Calcs for present VUV ring Lattice 2.5 % coupling 500 MHz RF @ 1.4 % bucket 70 out of 85 buckets filled IBS suggests E>0.5 GeV We chose E=0.6 GeV e~E2

8. Lifetime Scaling • Present VUV-ring (no HRF) lifetime~3 hours @ 800 MeV, 0.6 A into 7 bunches, st~350 ps rms • Assume lifetime is Touschek dominated, ttous_1/2 ~ st/Nb • For CESR-B 500 MHz RF assume 1 A into 70 bunches, 800 MeV lifetime ~ 1.5 hour @ st~30 ps rms • Approximate scaling with beam energy ttous_1/2 ~ g-4, loose x3 at 0.6 GeV. Harmonic RF, increased coupling, brings it back roughly to the same value. =>Assume 1 hour @ 1.5 A, 600 MeV for injector. With a robust injector lifetime is no problem for high current mode

9. Adding CSR Mode • ISR ~ N, CSR~N 2 => huge gain • Low freq. cutoff due to chamber • Hi freq cutoff due to bunch length • Bunch shape plays a role as well Issues to study (calcs/experiments): • Smallest momentum compaction? √√ • Effects of non-CSR impedance? • Maximum current and lifetime? √ • Optimal RF system? √ How big?

10. Estimate and Scaling of Coherent Gain Stability criterion, Heifets & Stupakov • When do CSR emissions go bursting ? Use Boussard criterion with CSR impedance == “CSR instability” Assumptions: E=800 MeV, CESR-like 500MHz RF @ 2.5 MV, all buckets filled, Gaussian (ignore PWD) bunch with sz=1 or 3 ps rms • Results (compared to 1 A incoherent flux, a0=0.0235, h=21 mm) sz=1 ps: a=a0/100, Nb=107/bunch  Iav=0.7 mA => gain ~ 7000 sz=3 ps: a=a0/10, Nb=3x108/bunch  Iav=24 mA => gain ~ 7x106 • Scaling results from BESSY get similar THz Power/ mrad as BESSY-II @ 3 ps and ~60 mA total current and much higher levels for1 ps bunch.

11. Low-a Optics Impulsabweichung / % G. Wüstefeld • Gode Wüstefeld performed lattice simulations & tracking for present VUV lattice • Qualitatively similar results to MLS source • a value is half BESSY-II user optics => very relaxed, should be easily achievable MLS @ Bessy Present VUV-ring magnets and layout are compatible with operating in coherent THz mode, provided another sextupole family, and an octupole family are added. Initial checks showed sufficient space.

12. RF Considerations 53 MHz VUV-ring RF • Coherent mode <= Short Bunches <= High RF gradient (&low a) • Need to replace 53 MHz RF cavity • SC CESR-B works well in CSR & HC modes • Take 2.5 MV CESR-B & 800 MeV: present (a0=0.0235) =>st=10 ps rms a=a0/100 => 1 ps for CSR mode • Coherent mode imposes strict requirements on RF system noise, these relax some if RF provides high voltage (CESR-B is a good match) • Harmonic RF gains x2-3 in lifetime (high current mode); adds flexibility but not absolutely necessary for coherent mode 500 MHz SC CESR-B CESR-B cryostat fits into existing VUV-ring straight Adds Coherent IR for the Users and jumpstarts NSLS-II SCRF R&D

13. NSLS-II Brand-New Ring Option • Fully optimized for IR(incl. short bunches and CSR mode) • More large aperture IR ports • No dark-time for relocation • Modern components • Better beam stability • $$$$? S. Kramer Present NSLS VUV/IR Ring 2.5 m NSLS-II IR Ring Option

14. DBA-4 ISR Lattice

15. Low Alpha Tuning

16. Accelerator Physics Issues to Study for Ring-like Upgrade Options Option 1 (move as is) • Lifetime, IBS and Instability thresholds vs. Energy (experimental & codes) • LCB Feedback System performance at lower Energy • Identify, characterize & redesign chamber pieces most affected by beam induced resistive heat, i.e. kicker transitions • Closed bump for injection Option 2 (adding HFRF system) • All of the above (experimental is limited due to long bunch now) plus • Compatibility with the present NSLS-1 injector (if install first then move), lifetime, losses and shielding • Circumference adjust, chamber modifications, BPMs • For coherent mode: detailed impedance calculations for bunch shape, short bunch beam dynamics (i.e. onset of bursting CSR emission mode), higher order momentum compaction, detailed RF system requirements, effect of PS and RF noise, …

17. Basic Machine Parameters IN PROGRESS

18. Summary and Conclusions NSLS-II planning must accommodate growing NSLS IR user community. This needs to be done with a dedicated low energy ring source. Options include upgrade of the existing VUV ring, or new NSLS-II IR ring Short bunches (tens of ps for high current mode, ps for CSR) should be achievable in the present ring with CESR-B 500 MHz SC RF cavity Present VUV ring lattice is compatible with CSR mode, provided extra sextupole family and an octupole family are added Brand new ring would provide more flexibility and better performance. We have a straw man lattice design and initial cost estimates Need detailed studies of collective effects, lifetime, CSR, shielding, etc. Start now on SCRF in VUV ring. Will resolve many short bunch issues experimentally, and will add short bunch to the users now.