1 BROOKHAVEN SCIENCE ASSOCIATES

NSLS-II IR Source

NSLS-II ReviewMay 11-12, 2006

L. Carr, J. Hill, S. Kramer, B. Podobedov, T. Shaftan, J. Rose, G. Wüstefeld

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. 1 10 100 1000

10-8

10-7

10-6

1x10-5

1x10-4

10-3

10-2

10-1

100

Brig

htne

ss [

W/c

m-1/(

cm2 -r

ad2 )]

Frequency [cm-1]

IR Ring 1000ma T/O Existing IR 700mA Coh. mode (est. @10ma) NSLS-II 500mA & 20mr

10000 1000 100 10

Wavelength [m]

12 mrad @ presentL.Carr

4

Summary of IR User Requirements

• Spectral Coverage 1 - 5000 cm-1 (0.12– 600 meV; =2 m-10 mm)• Flux about or better than present 4x1012/ph/s/0.1%bw/mrad (I=1A, 0.6eV) • Max Current Drop I/I = 10% • E-Beam size at the source ~100x100 m2 (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

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)

L.Carr

5

VUV-IR Ring Upgrade Scenarios1) 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

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 x

• $$$$ for SC linac, RF, cryo, …

• Gun, injector shared with 3GeV ring, kickers (multi-turn), orbit stability, losses & shielding, …

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(), PS & RF noise, LCBM fdbk…

User’s choice

6

0.001 0.1 10 1000Photon EnergyeV

5. 1011

1. 1012

2. 1012

5. 1012

1. 1013xul

Fhpces1.0%

WBdarm

Beam Energy to Meet the Flux Specs

Matching Flux at 0.6eV requires E>~100 MeVRing options will likely end up at E>500 MeV

Flux from VUV Ring Bend at I=1 A

Target spectral range

100 MeV

400 MeV

800 MeV

0.6

50 MeV

7

IBS Emittance Blow-up vs. Energy

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.80

50

100

150

200

250

300

Energy, GeV

ho

r. e

mitt

an

ce, n

m

0.5 A1.0 A2.0 AIBS OFF

2.5 % coupling500 MHz RF @ 1.4 % bucket70 out of 85 buckets filled

~E2

SAD Calcs for present VUV ring Lattice

IBS suggests E>0.5 GeVWe chose E=0.6 GeV

8

Lifetime Scaling

• Present VUV-ring (no HRF)

lifetime~3 hours @ 800 MeV, 0.6 A into 7 bunches, ~350 ps rms

• Assume lifetime is Touschek dominated, tous_1/2 ~ /Nb

• For CESR-B 500 MHz RF assume 1 A into 70 bunches, 800 MeV

lifetime ~ 1.5 hour @ ~30 ps rms

• Approximate scaling with beam energy tous_1/2 ~ 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 ModeAdding 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

• 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 z=1 or 3 ps rms

• Results (compared to 1 A incoherent flux, 0=0.0235, h=21 mm)zps=0/100, Nb=107/bunch Iav=0.7 mA => gain ~ 7000zps=0/10, 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.

0

20

,4

peZ I

E R

3/ 2

3/ 2 22 ,

3 2k

h

h/Stability criterion, Heifets & Stupakov

11

Low- Optics

• Gode Wüstefeld performed lattice simulations & tracking for present VUV lattice

• Qualitatively similar results to MLS source

• value is half BESSY-II user optics => very relaxed, should be easily achievable

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.

Impulsabweichung / %

G. Wüstefeld

MLS @ Bessy

12

RF Considerations

• Coherent mode <= Short Bunches <= High RF gradient (&low )• 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 (0=0.0235) =>=10 ps rms=0/100 => 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

CESR-B cryostat fits into existing VUV-ring straight

Adds Coherent IR for the Users and jumpstarts NSLS-II SCRF R&D

500 MHz SC CESR-B

53 MHz VUV-ring RF

13

NSLS-II Brand-New Ring OptionNSLS-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

- $$$$?2.5 m

Present NSLS VUV/IR Ring

NSLS-II IR Ring Option

S. Kramer

14

DBA-4 ISR LatticeDBA-4 ISR Lattice

15

Low Alpha Tuning

16

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 injectionOption 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, …

Accelerator Physics Issues to Study for Ring-like Upgrade Options

17

Basic Machine ParametersBasic Machine Parameters

Present NSLS VUV

NSLS VUV Upgrade

NSLS-II 72DBA

Circumference, C [m] 51 51 72Superperiods, Ns

4 4 2 or 4Straight Section Length, Lss [m] 3.3 3.3 6Energy, [MeV] 800 600 600Horizontal Emittance, [nm] 160 90 93@ 600MeVMomentum Compaction, 0.02 0.02 0.0168Dipole Radius, 1.91 1.91 1.91Betatron Tunes, x, y

3.14, 1.26 3.14, 1.26 3.71, 2.37x0, y0 [m] 5.2 , 3.2 5.2 , 3.2 5.2 , 3.2Damping Times, tx,ty,tz [ms] 13, 13, 7 13, 13, 7 45, 47, 24.4Dipole E-Loss Uo [KeV/turn] 20 6 6RF frequency, [MHz] 53 500 500Vrf [MV] 0.080 0.5RF [%] 1.6 1.6Natural Bunch Length, L [ps] 20Natural Energy Spread, E [%] 0.5 0.0 0.036Bunch length with HRF

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.