1 brookhaven science associates nsls ii: accelerator system overview nsls ii advisory committees...

1 BROOKHAVEN SCIENCE ASSOCIATES

NSLS II: Accelerator System Overview

NSLS II Advisory CommitteesOctober 18/19, 2006

Satoshi Ozaki


Introduction

• NSLS II: A highly optimized, third generation, medium energy storage ring for the x-ray synchrotron radiation:

• The CD-0 approval articulated required capabilities as: • ~ 1 nm spatial resolution,• ~ 0.1 meV energy resolution, and• single atom sensitivity (or sufficiently high brightness)

• These and other requirements translate into the target parameters of the storage ring as;• ~3 GeV, 500 mA, top-up injection• Brightness ~ 7x1021 photons/sec/0.1%bw/mm2/mrad2

• Flux ~ 1016 photons/sec/0.1%bw – Ultra low-emittance (x, y): 1 nm horizontal, ~0.01 nm vertical

20 straight sections for insertion devices ( 5 m), • A high level of reliability and stability of operation


Linac

Booster

Storage Ring

Accelerator System Configuration

NSLS II Accelerator System:

• 200 MeV S-band Linac

• 3 GeV 1 Hz Booster

•Top-up injection once per minute

• 3 GeV storage ring: 30 DBA configuration

•15 long (8 m) straight with high -function•15 short (5 m) straight with low -function

Booster

Storage Ring


Rendering of the NSLS II Ring (Rear View)


Injector Linac

• S-band linac system providing 200 MeV electron beams of 7 nC to the Booster in one pulse

• Electron source: thermionic DC gun modulated to match 500 MHz RF of booster and storage ring

• Five accelerating structures with three klystrons operating at 1.3 GHz• The system commercially available in turn-key procurement:

• ACCEL• THALES


Booster Synchrotron

• 200 MeV to 3 GeV booster• Hung below the ceiling of the storage ring tunnel and has the same

circumference of 780 m• The lattice arranged to have no booster components above storage ring

straight sections, except for one 8-m straight for RF cavity• Relatively light weight small magnets; low power and air cooled:

• 60 combined function dipoles: 1.5 m long, 25 mm gap, 0.7 T, ~580 kg• 96 quadrupoles: 0.3 m long, <10T/m, ~45 kg• 15 sextupoles: 0.4 m long, <200T/m2, ~55 kg• 15 sextupoles: 0.2 m long, <200T/m2, ~30 kg• 60 orbit correctors

• Up to 100 bunches per cycle for initial fill• Up to 20 bunches per cycle with the hunt-and-fill bunch pattern• One PETRA-type (commercially available) RF cavity• Very low emittance at the storage injection energy helps smooth low loss

top-up injection.

• Purchase components from industry based on our reference design, and build and commission in-house

• Turn-key procurement of a compact booster in separate tunnel: an option


Booster Lattice and its Relationship with Storage Ring


Storage Ring Lattice Layout

Linac

RF Station


Storage Ring

Storage ring configuration• DBA30 lattice (780m circumference) with 15 super-periods, each ~52m long• Super-period: two identical cells separated by alternating 5m and 8m straights• Short straight: x = 2.7m, y = 0.95m, and dispersion = zero • Long straight: x = 18.2m, y = 3.1m, and dispersion = zero

• This Hi-Lo is suited for variety of ID as well as top-off injection• Weak bends (0.4T) with damping wigglers to achieve ultra-small emittance• Lattice magnet: (designed with 20% head room)

• Dipoles: 60 (50 with 35 mm gap and 10 with 60 mm gap for IR beams)• Quadrupoles: 360• Sextupoles : 390• Correctors and skew quadrupoles: 240 + (4 X ID)

• 500 MHz superconducting RF cavities each operating with 270 kW power level• Harmonic number (No. of buckets): 1300, of which ~ 80% will be filled

• A 2-cell harmonic cavities for bunch lengtheningBasic performances:• 3 GeV, 500 mA, Top-up with current stability of <1%• Bare Lattice: x ~2.1 nm, y ~0.008 nm (Diffraction limited at 12 keV)• Pulse Length (rms): 2.9 mm/~10 psec


Lattice functions of half of an NSLS-II SR super-period (one cell).


Dispersion Section of a Cell

In order to reduce the transmission of ground vibrations beam height is set at 1 m from the SR tunnel floor, instead of standard 1.4 m.

Girder Resonant Frequency > 50 Hz

Alignment tolerance of multipoles on a girder is 30 m, whereas girder-to-girder tolerance is ~100 m


Dynamic Aperture of the Lattice

For on momentum and off momentum cases by 3%


Horizontal Emittance vs. Energy Radiated by DW

Dots represent the cases with 0, 1, 2, 3, 5, 8 damping wigglers, each 7-m long with 1.8 T field


RF Power Up-grade Path

RF Power Requirements for Dipole and Various Insertion Device Configurations.

Covered in baseline proposal

Installed RF Power

(270kW/unit

Power the 3rd cavity with 300kW Transmitter

Add 4th RF station

RF power # P(kW) # P(kW) # P(kW) # P(kW)

Dipoles - 144 - 144 - 144 - 144

Damping Wigglers (9.23 kW/m, 7m each)

3 194 4 259 8 517 8 517

CPMU’s (4.17kW/m, 3m each)

3 38 6 76 6 76 10 127

EPU’s (4.1kW/m, 4m each)

2 33 4 66 4 66 5 83

Additional Devices ? 200

Total

Available Power

409

540

545

540

803

810

1071

1080


Ultimate Configuration and Performances

Ultimate Configuration:• 8 damping wigglers (7 m long, 1.8T peak field)• 4 RF cavities with 1,080 kW of RF power

Expected performances at 3 GeV:• Beam current: 500 mA• Emittance: x ~ 0.5 nm, y ~ 0.008 nm• Flux ~ 1016 photons/sec/0.1%bw • Brightness ~ 7x1021 photons/sec/0.1%bw/mm2/mrad2

• Beam Size (x/ y) at the center of short straights: ~38.5/~3.1 m

• Beam Divergence (x’/y’) ~18.2/~1.8 rad• Pulse Length (rms) with damping wigglers: 4.5 mm/~15 psec• 19 user device (e.g., undulators) straights (15 x 5 m & 4 x 8 m)

• 4 long straights for large gap user insertion devices• 15 short straight for user undulators, some with canting

• 8 user compatible (fixed gap) damping wigglers• Many bending magnets for soft X-ray beam lines (critical energy ~2.4 keV)• Up to 5 bending magnets for IR, far-IR, and THz beamlines


Baseline Configuration & Performances

Proposed baseline (CDR): • 3 damping wigglers (7 m long, 1.8T peak field)• 2 RF cavities with 540 kW of RF power• 5 user beamlines (supported by trust funds)

Expected performances at 3 GeV:• Beam current: step-by-step increase to 500 mA• Emittance: x ~ 1 nm, y ~ 0.008 nm• Flux ~ 1016 photons/sec/0.1%bw ?• Brightness ~ 4x1021 photons/sec/0.1%bw/mm2/mrad2 ?

• Beam Size (x/ y) at the center of short straights: ~54.5/~3.1 m ?• Beam Divergence (x’/y’) ~25.7/~1.8 rad ?• Pulse Length (rms) with damping wigglers: 4.5 mm/~15 psec ?• No. of DW that can be used for light source: 3 • Max number of ID beam lines: ~10 (e.g., 6 CPMU [3 m] and 4 EPU [4 m]) • A number of bending magnets for soft X-ray beam lines (EC ~2.4 keV)• No. of IR beams from wide gap dipoles: 5


Issues for Further Studies

• Development of precision alignment (~30 µm) technology• Development of the optimum orbit correction and feedback scheme

for high level orbit stability: – A factor of ~3 improvement over the submicron stability recently

reported with some recent light sources• Impact and remediation of 5 mm gap undulator with short pitch to the

dynamic aperture and the beam life-time– Because of the vertical focusing effect of undulators with short

pitch, they cannot occupy the part of the ID straight where the vertical -function is large, i.e., areas away from the center of the straight

– This limits the 5 mm gap undulator length to ~3 m• Impact of EPU on dynamics of the beam• Use of canted insertion device • Overall value engineering efforts


Summary

• Made good progress in last nine months in developing CDR for NSLS II• Optimized and define the configuration of the accelerator systems• Undertook conceptual design of accelerator systems, in some case

more detailed• Assembled accelerator parameter tables

• We have a innovative design of a highly optimized synchrotron light source capable of meeting requirements articulated in the CD-0 document with ultra-high performances

• There are a number of issues requiring further study:• Insertion devices and their impact on the dynamic aperture and

beam life-time• Diagnostics and feed-back for the required highly stable beam

operation• General value engineering exercise to control costs


Injector Linac Parameters

Linac

Nominal/maximum linac energy (MeV) 200/270

Frequency (GHz) 2.998

Number of accelerating structures 5

Number of klystrons (no hot spare) 3

Pulse repetition rate (pps) <10

Beam pulse length (ns) 1 - 80 (up to 1µs)

Pulse charge (nC) (overall charge in a macropulse) >7

Energy spread ( %) <0.5

Total number of traveling wave accelerating sections 5


Booster Ring Parameters

Booster RingInjection energy (MeV) 200Nominal top energy (GeV) 3Circumference (m) 780Ramping repetition rate (Hz) 1Acceleration time (s) ~0.4Harmonic number 1300Radio frequency (MHz) 499.46Total number of cells 15Number of combined function bending magnets 60Number of quadrupole 96Dipole nominal aperture (mm) 25Dipole field at injection (T) 0.0533Dipole field at extraction at 3 GeV (T) 0.7Energy loss per turn at 3 GeV (keV) 500Beam current (mA) 2.7Natural emittance at 3 GeV (nm-rad) 11.5Number of bunches from 1 to >100


Storage Ring Parameters

Storage Ring Assembly

Number of DBA cells 30Circumference (m) 780Nominal energy (GeV) 3Circulating current @ 3 GeV, multi-bunch (mA) 500Circulating current @ 3 GeV, single bunch (mA) 0.5Harmonic number 1300No. of filled bunches/harmonic number 80%Nominal bending field @ 3 GeV (T) 0.4Dipole critical energy @ 3 GeV (KeV) 2.4Number of 8 m straights: [βx/βy (m)] 15: [18.15/3.09]Number of 5 m straights: [βx/βy (m)] 15: [2.72/0.945]Number of dipoles 60Number of quadrupoles 360Number of sextupoles 390Number of correctors and scew 240 + (4 X ID)


Storage Ring Parameters (Continue)

Damping Wigglers

Initial number of 7 m damping wigglers 2 Fixed +1 Vari

Final number of 7 m damping wigglers 5 Fixed +3 Vari

Max. peak field (T) 1.8

Radiation energy loss per wiggler (keV) 129.3Initial radiation energy loss with 3 wigglers (keV) 387.9Ultimate radiation energy loss with 8 wigglers (keV) 1,034.4Bending magnet radiation energy loss (keV) 286.4Emittance of bare lattice (nm) 2.1Emittance with 3 wigglers (nm) 1.0Emittance with 8 wigglers (nm) 0.6

Storage Ring RF SystemRadio frequency (MHz) 499.46Number of superconducting cavities 2 +1 spareInstalled RF power for initial configuration (kW) 540Harmonic cavity (2 cells/cavity) 2

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